Z8E001 AN003501-Z8X0500 Z8E003 Z8ICE000ZEM Z8ICE001ZEM - Datasheet Archive

 

Universal Power and Voltage Control Using the Z8E001 AN003501-Z8X0500 ZILOG WORLDWIDE HEADQUARTERS · 910 E. HAMILTON

 

Application Note Universal Power and Voltage Control Using the Z8E001 Z8E001 AN003501-Z8X0500 AN003501-Z8X0500 ZILOG WORLDWIDE HEADQUARTERS · 910 E. HAMILTON AVENUE · CAMPBELL, CA 95008 TELEPHONE: 408.558.8500 · FAX: 408.558.8300 · WWW.ZILOG.COM Application Note Universal Power and Voltage Control Using the Z8E001 Z8E001 This publication is subject to replacement by a later edition. To determine whether a later edition exists, or to request copies of publications, contact: ZiLOG Worldwide Headquarters 910 E. Hamilton Avenue Campbell, CA 95008 Telephone: 408.558.8500 Fax: 408.558.8300 www.ZiLOG.com Windows is a registered trademark of Microsoft Corporation. Information Integrity The information contained within this document has been verified according to the general principles of electrical and mechanical engineering. Any applicable source code illustrated in the document was either written by an authorized ZiLOG employee or licensed consultant. Permission to use these codes in any form, besides the intended application, must be approved through a license agreement between both parties. ZiLOG will not be responsible for any code(s) used beyond the intended application. Contact the local ZiLOG Sales Office to obtain necessary license agreements. Document Disclaimer © 2000 by ZiLOG, Inc. All rights reserved. Information in this publication concerning the devices, applications, or technology described is intended to suggest possible uses and may be superseded. ZiLOG, INC. DOES NOT ASSUME LIABILITY FOR OR PROVIDE A REPRESENTATION OF ACCURACY OF THE INFORMATION, DEVICES, OR TECHNOLOGY DESCRIBED IN THIS DOCUMENT. ZiLOG ALSO DOES NOT ASSUME LIABILITY FOR INTELLECTUAL PROPERTY INFRINGEMENT RELATED IN ANY MANNER TO USE OF INFORMATION, DEVICES, OR TECHNOLOGY DESCRIBED HEREIN OR OTHERWISE. Except with the express written approval ZiLOG, use of information, devices, or technology as critical components of life support systems is not authorized. No licenses or other rights are conveyed, implicitly or otherwise, by this document under any intellectual property rights. AN003501-Z8X0500 AN003501-Z8X0500 Application Note Universal Power and Voltage Control Using the Z8E001 Z8E001 iii Table of Contents Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 General Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 Theory of Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 Results of Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 Reaffirmation of Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 Technical Support . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 Pin Diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 Flowcharts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 Source Code . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 Assembling/Compiling Code . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 Timing Diagrams and Tables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 Test Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 General Test Setup and Execution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 Test Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 Glossary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 Appendix . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 Acknowledgements Project Lead Engineer Denny Hopp Application and Support Engineers Jon Veres, Mark Shaw, and Randy Rolen System and Code Development Denny Hopp AN003501-Z8X0500 AN003501-Z8X0500 Application Note Universal Power and Voltage Control Using the Z8E001 Z8E001 1 Universal Power and Voltage Control Using the Z8E001 Z8E001 Abstract General Overview The ZiLOG Z8PlusTM Microcontroller family includes many integrated features that greatly simplify power and voltage control system designs. This family of microcontrollers offers the on-chip peripherals that allow power control systems to be designed cost-effectively with as few external components as possible. The Z8E001 Z8E001 used in this design contains many on-board features that provide full functionality in a small microcontroller. These features include three timer/ counters, six internal/external interrupts with selectable edge triggering, 1- s instruction execution time using a 10-MHz crystal, analog comparator, push-pull or open-drain output bit programmability, watch-dog timer, STOP mode recovery, low-power sleep mode, and others. This Application Note describes a design that controls the energy provided to a Xenon gas flashtube. To control the light output to the flashtube, the charge capacitor voltage must be closely controlled and monitored. The Z8E001 Z8E001 precisely handles all aspects of this control. This design also illustrates how the Z8E001 Z8E001 is used to produce output voltages in excess of 200 volts with a supply voltage as low as 14 volts. With an overhead of only two system clock cycles required for interrupt vectoring, this design demonstrates the precise and extremely fast power control realized with the Z8E001 Z8E001. Charge cycles as short as 35 s must be continually modified, and this microcontroller provides this control with ease. In addition to efficiently controlling these short charge pump cycles, the Z8E001 Z8E001 controls additional system timing and input/output functions simultaneously. The potential applications for this type of precise and inexpensive voltage and power control are numerous. This type of control can be used in applications such as motor control, AC/DC and DC/DC converters, circuits requiring high-voltage generation from battery circuits, smart battery chargers for various battery chemistries, power supplies, and any circuit requiring a charge pump for energy storage. The Z8E001 Z8E001 provides the control for these designs, because the overall system design can be completed at a fraction of the cost of other systems using dedicated power and voltage control integrated circuits. Finally, this application demonstrates the superior noise immunity of the Z8Plus microcontrollers. Because the charge pump generates over 200 volts and the trig- AN003501-Z8X0500 AN003501-Z8X0500 Application Note Universal Power and Voltage Control Using the Z8E001 Z8E001 2 ger transformer generates thousands of volts, there is the potential for many noise-induced voltage brownout/reset conditions. Also, note that the microcontroller is switching the FET at frequencies up to 33 kHz. The ZiLOG Z8E001 Z8E001 runs without error in this extremely noisy environment. Discussion Theory of Operation Figure 1 illustrates the overall system operation. Figure 1. Overall System Operation Flash Current Trigger Voltage Flash Current Trigger XFMR Trigger Voltage Dump Trigger Charge Capacitor Strobe SCR Charging Current Flash Control MPU Control of FET Charge Pump ZiLOG Z8E001 Z8E001 MPU FET Resistor Voltage Feedback/Monitor The microprocessor turns on the charge pump and monitors the charge current. When this current reaches the preset level (determined by monitoring the voltage on a feedback resistor), the microprocessor measures the time required to reach the specific charge current value, then determines how long to keep the charge AN003501-Z8X0500 AN003501-Z8X0500 Application Note Universal Power and Voltage Control Using the Z8E001 Z8E001 3 pump off before starting the next charge cycle. When the charge pump is off, the charge pump current flows into the capacitor and builds up the capacitor voltage. This cycle is repeated continually for the entire operation of the circuit. The SCR is turned on once every second, and the capacitor dumps through the trigger transformer and strobe, causing the strobe flash. This transfer of energy from the capacitor to the strobe is caused by the dump trigger signal on the gate of the SCR, causing a high-voltage spike on the external strobe wire. This energy transfer is discussed in detail later. Compare the block diagram in Figure 1 to the circuit schematic diagram in the Appendix. The circuit is comprised of capacitor C1, inductor L1 and FET Q2. When the FET is on, the inductor charges from the supply voltage because the FET allows the current to flow through the inductor. When the FET is turned off after the inductor is charged, the inductor charge is transferred to capacitor C1. Diode D1 allows current to flow only from the inductor and blocks the capacitor charge current from flowing back through the FET when the FET is turned on. This charge pump operation is analogous to blowing up a balloon. Air is blown into a balloon in short bursts, and the balloon neck is pinched off between each burst of air. When the balloon is filled, the final air pressure in the balloon is equal to the sum of the individual air bursts put into the balloon. The charge pump circuit works in the same way. When the inductor is charged to a set point, the FET is turned off, and the inductor energy is transferred to the capacitor. After the inductor transfers its energy to the capacitor, the FET is turned back on to allow the inductor to again build up energy, starting the process over again. The diode acts as the pinch-off mechanism to keep the capacitor charge from flowing back into the FET when the inductor is charging. Because the SCR is held off during these repeated short-charging cycles, the current can only flow into the capacitor when the FET is off. Warning: The capacitor can be charged to voltages in excess of 200 volts. Also, the strobe trigger transformer can generate thousands of volts on the external strobe wire wrapped around the flash tube. Under no circumstances should any of the components be handled during operation. Exercise extreme care to ensure that all components are fully discharged before handling any circuit component. The following statements discuss the importance of controlling each of the charge cycles. V = L di/dt (equ 1.1) Integrate both sides of the equation and the current is: i = 1/L(V dt (equ 1.2) AN003501-Z8X0500 AN003501-Z8X0500 Application Note Universal Power and Voltage Control Using the Z8E001 Z8E001 4 Because P = VI, then: P = Li di/dt (equ 1.3) To evaluate the energy stored in the inductor and transferred to the capacitor, use the fact that power is the time rate of expending energy, which can be expressed as: P = dw/dt = Li di/dt (equ 1.4) Now multiply both sides of equation 1.4 by the time differential, resulting in the equation: dw = Li di (equ 1.5) The integration of both sides of equation 1.5 results in: (dx = L (y dy (equ 1.6) where the left-hand side of the equation is solved for 0 x w, and the righthand side is solved for 0 y i. This integration solution results in: w = Li2 (equ 1.7) Because the current is proportional to the integral of the voltage (equ 1.2), the energy is proportional to the squared integral of the voltage. The rate of energy storage is not a linear function, so the microcontroller must be able to change the charging rate in a non-linear manner for the entire range of the specified operating voltage. For this design, the specified operating voltage is 14V to 24V, so the microcontroller must be able to control the charging current so that capacitor C1 always holds the same amount of energy just prior to flashing the strobe. The software is set up so that the energy storage rate is a linear function over the charging period between strobe flashes. The 8-bit microcontroller performs this complex math easily by using lookup tables. The ZiLOG family of microcontrollers enables lookup tables to be implemented easily and with great flexibility. The software is discussed later, but it is important to note that this easy implementation of lookup tables allows any mathematical equation, no matter how complex, to be approximated (over a defined range) to whatever precision is required for the proper operation of the power control circuit. Look at how the lookup tables are used to control the energy storage rate of the capacitor. When the FET is first turned on, the inductor current graph is almost linear (after a few time constants, the current levels off to its steady-state value). In this design, the inductor charge is stopped before the current becomes non-linear. Even though the inductor current is linear, the energy function is not linear, and this energy storage is of primary interest. As the current increases, the voltage AN003501-Z8X0500 AN003501-Z8X0500 Application Note Universal Power and Voltage Control Using the Z8E001 Z8E001 5 across resistor R5 also increases, because all of the inductor charge current is passing through this resistor. The voltage across this resistor is connected to the microcontroller port B comparator input. When this voltage exceeds the reference voltage supplied on the port B comparator reference input (via voltage divider R9, R10), an interrupt is generated in the microcontroller. The reference voltage is VREF = (5V)(R9 ÷ (R9 + R10) = 0.61V (equ 1.8) Because the feedback resistor R5 is 3.6 Ohms, the microcontroller receives an interrupt when the inductor current reaches I = 0.61V ÷ 3.6 Ohms = 169.44mA (equ 1.9) Figure 2 illustrates the inductor charge cycles. When the FET is turned on, the microcontroller measures the amount of time between the FET turn-on and the reception of the interrupt. When the interrupt is received, a lookup table value is retrieved based on the counter/timer value, and this table value specifies the amount of time that the microcontroller keeps the FET off before turning it back on. This process is repeated for every inductor charge cycle. As an example, look at the first charge cycle. At time 0, the FET is turned on. The FET starts the timer and waits for the interrupt. When the interrupt is received, the Z8 turns the FET off and reads the timer value. In this cycle, the value corresponds to 30 s because the FET was on for 30 s before the interrupt was received. The microcontroller retrieves a lookup table value that corresponds to 10 s (the FET off time). The timer is reloaded to time 10 s (interval between 30 s and 40 s), and when this hold-off period expires, the FET is turned back on and the cycle repeats itself. If the hold-off duration is increased, the FET does not exhibit as many charging cycles per time period. As a result, the energy storage in the capacitor is decreased. If the FET off-time periods are decreased, the capacitor charges to a higher voltage. Figure 2. Inductor Charge Cycles Comparator Voltage 0.9 0.6 0.3 0 0 10 20 30 40 50 60 70 80 90 100 110 120 Time (µsec) AN003501-Z8X0500 AN003501-Z8X0500 Application Note Universal Power and Voltage Control Using the Z8E001 Z8E001 6 The lookup table values are derived either by setting up a spreadsheet to calculate the stored energy based on the area under the sawtooth charge curve or by a trial and error approach. This design uses the trial and error approach. Arbitrary values are assigned in the lookup table, the code is executed, and the capacitor maximum voltage is measured for the voltages in the 14V to 24V range. An oscilloscope measures the sawtooth on-period, and a chart is created to plot the sawtooth period vs. the maximum capacitor C1 voltage for the input voltage (in increments of 2V). If the voltage is too high for a certain charge period, then the lookup table value is increased. If the capacitor voltage is too low, then the offtime value in the lookup table is reduced. Because the efficiencies of capacitors vary greatly, the trial-and-error approach to loading the lookup table is favored. Therefore, the energy calculations must assume a perfect capacitor. Discussion of the remaining circuits follows. The circuit comprised of Q1, R1, R2, and R3 provides the power-on-reset and brownout voltage reset functions. Resistors R1 and R2 provide the voltage divider network to control the transistor. When the transistor is off, the reset line is Low, and the microcontroller remains in the reset state. When the transistor is on, the reset line is connected to VCC through the transistor, and the microcontroller is no longer in the reset state. At power-up, the transistor must be turned on after the microcontroller reaches the minimum operating voltage (3 volts for the Z8E001 Z8E001). To turn transistor Q1 on, the VBE voltage must be approximately 0.7 volts or higher. Because the VBE is exactly the same as VR1 (the two voltages are in parallel), then the supply voltage at the time of Q1 turn-on is: VR1 = (VCC)(R1)/(R1+R2) (equ 1.10) Solving for VCC (knowing that VR1 = 0.7V) VCC = (0.7)(122K) ÷ 22K = 3.88V (equ 1.11) Therefore, the reset signal does not go High until the supply voltage reaches 3.88V. At power-up, the reset line is held Low, well past the minimum operating voltage of the Z8E001 Z8E001, and during voltage brownouts, the reset line goes Low (and reset the micro) long before the voltage drops below the minimum operating voltage. Different resistor values can be used if the reset voltage must be closer to the actual minimum operating voltage of the microcontroller, but for this application, these values work well. A new Z8Plus MCU family member, the Z8E003 Z8E003, eliminates the need for this external reset circuitry, because the voltage brownout and power-on-reset circuits are present on-chip. The last circuit to discuss in this application is the strobe firing circuit. At one-second intervals, the Z8E001 Z8E001 outputs a High signal to the gate of the SCR, causing it to fire and discharge the capacitor energy through the strobe. Here is the sequence of events for the strobe firing: AN003501-Z8X0500 AN003501-Z8X0500 Application Note Universal Power and Voltage Control Using the Z8E001 Z8E001 7 1. Capacitor C1 charges to about 200 volts. 2. Capacitor C5 also charges to about the same voltage as C1 in this same interval. 3. The Z8E001 Z8E001 outputs a High signal to the SCR, causing it to conduct. 4. Capacitor C5 discharges quickly through the SCR, causing a high dv/dt on the primary of the trigger transformer. 5. The fast dv/dt pulse on the transformer primary causes an extremely high voltage on the transformer secondary which is connected to the external wire on the strobe tube, causing a high voltage pulse (3000+ volts) around the outside of the flash tube. 6. The pulse produces an ion path in the Xenon gas, greatly lowering the resistance between the electrodes and the flash tube. 7. When this resistance is lowered, C1 discharges its energy across the tube. 8. The electron flow caused by the capacitor discharge excites the electrons in the Xenon gas molecules. 9. The electrons return to a ground state, releasing the energy in the form of light. Results of Operation Using the Z8E001 Z8E001 program source code listed in the Technical Support section, the circuit (as shown in the schematic in the Appendix) was tested. When power is applied to the circuit, the strobe flashes once every second. The capacitor charges to approximately 190 volts just before the strobe is fired. The source code is written so that performance modifications are made easily. The two main modifications made to the existing design are 1) increase or decrease the flash rate and 2) increase or decrease the flash intensity. The flash rate is easier to modify because only the constant value timer_passes must be changed. With a 10 MHz crystal, the frequency at timer23 is 10 MHz ÷ 8 = 1.25MHz. The timer_passes register is decremented once for each timer interrupt, and when the register reaches zero, the strobe is fired. Therefore, with the current value of 25 in the timer_passes register and 50000 in the timer register, the strobe fires once per second (timer interrupts 1.25MHz ÷ 50KB = 25 interrupts per second, and it takes 25 passes before the timer_passes register decrements to 0, resulting in one fire every second). If the flash rate is changed, the light intensity changes also, because the capacitor charges to a higher voltage for extended flash rates and charge to a lower voltage for shorter flash rates. To maintain the same light output intensity that is set up in the current code, the lookup tables must be modified as described previously. AN003501-Z8X0500 AN003501-Z8X0500 Application Note Universal Power and Voltage Control Using the Z8E001 Z8E001 8 The second modification is to change the light output intensity. For increased light output, the lookup table values must be reduced. Conversely, for decreased light output, the lookup tables must be increased (these values relate to the off-time of the FET). The light intensity is increased or decreased by changing the values of the comparator resistor R5 and/or the values of the voltage resistors R9 and R10. If R10 is increased to increase the reference voltage, then the comparator interrupts on higher voltages on R5, causing a higher charge rate on C1. If comparator resistor R5 is changed, the light intensity is also affected. However, a change in this resistor is not as predictable, because it does not only cause a change in the comparator interrupt voltage, but also a change in the charge rate of the inductor. For example, if R5 is raised, the comparator interrupts at a higher voltage. This change can cause the inductor to charge to a higher voltage, increasing the energy transfer to the capacitor C1, but an increase in this resistance also causes a lower charge current through the inductor, reducing the total energy per charge cycle. Therefore, changing the reference voltage divider produces the most consistent results because the inductor current is not changed. Resistor R5 should be changed only if a different inductor value is chosen to allow an efficient charge current through the inductor. In this circuit, values of R5 between 2 Ohms and 10 Ohms work well, with the lower resistance values providing better results for input voltages up to 40 volts. If higher supply voltages are used, then higher resistance values should be used (higher supply voltages result in higher di/dt values, so the resistor R5 has to be increased to lower the current change rates). Warning: This circuit produces dangerously high voltages on many of the components. Exercise extreme care when operating the circuit or modifying the circuit components. Summary Reaffirmation of Results Although this application of firing a strobe appears simple, the math describing the operation of the circuit (and its operating range) is complex. The supply voltage in this circuit varies from 14 to 24 volts, and the light output intensity of the strobe must remain constant throughout this entire range. The ZiLOG Z8E001 Z8E001 allows power control to be taken to new heights, because it controls the output power without forcing the inductor to store and transfer energy inefficiently. The Z8E001 Z8E001 provides for efficient inductor operation. It allows the inductor to charge naturally during the charge cycle by starting the charge when the inductor is fully discharged and discharging the inductor well before it reaches a steady-state charge (which causes wasted charge time). AN003501-Z8X0500 AN003501-Z8X0500 Application Note Universal Power and Voltage Control Using the Z8E001 Z8E001 9 This design is not possible without the presence of real-time interrupts and a twoclock-cycle interrupt overhead. If the interrupt pin is polled, the charging scheme becomes erratic and unpredictable. The charge cycles can be as low as 30 s. Even if polled within 4 s of every interrupt, the charge rates vary by 13.3% from cycle to cycle. If a power control scheme is only 13% accurate, it is doubtful that any engineer would choose to use it. The accuracy of this scheme is bound only by the accuracy of the comparator offset voltage (10mV for the Z8E001 Z8E001). When using the 0.6V reference in this circuit, the accuracy is better than 1.6%. If the reference voltage is doubled, the accuracy is better than 1%. If the interrupt overhead were too high, a second interrupt might occur before the first interrupt had completed its processing. Interrupts can stack up, resulting in a total loss of output control. With the Z8E001 Z8E001, this situation never occurs, as the interrupt clock cycle overhead is minimal. This power control scheme also depends on efficient implementation of lookup tables. Lookup table values are fetched in one clock cycle with Z8Plus MCUs by use of the load constant (LDC) or load constant and auto-increment (LDCI) instructions. These instructions allow the retrieval of lookup table values without jumping out of normal program code execution. The one clock-cycle lookup table fetch enables the microcontroller to reload the timer quickly to count the FET offtime. The register-to-register architecture also enables data to be transferred quickly without having to first load an accumulator or working register, then load that value to the register for which the data was originally intended. When dealing with only 30 s FET charge cycles, every microsecond counts. The presence of an on-board comparator also allows the Z8E001 Z8E001 to control the charge scheme with few external components. The 16-bit timer allows long timing intervals for the 1-second flash rate, and one of the two remaining 8-bit timers is used to measure the charge cycle period. Even though there are many timing functions occurring in this design, there is still an additional 8-bit timer/counter available if other timing and control functions are required. One important fact that must not be overlooked is that this microcontroller functions without error even though the design poses many potential noise and voltage spike problems. Even with a 30kHz+ FET switching frequency, 200V+ discharge capacitor charge, 200V+ trigger transformer capacitor charge and pulse, and 3000V+ trigger transformer secondary pulse, the Z8E001 Z8E001 continues to accurately monitor and control the charge and flash rates. This same power control algorithm can be used for many other types of power control systems, including DC/DC converters and motor control. It can be adapted to many different types of power and voltage control situations. AN003501-Z8X0500 AN003501-Z8X0500 Application Note Universal Power and Voltage Control Using the Z8E001 Z8E001 10 Technical Support Pin Diagram Figure 3. Z8E001 Z8E001 18-Pin DIP Configuration PB1 PB2 PB3 PB4 RESET PA7 PA6 PA5 PA4 1 2 3 4 5 6 7 8 9 18-Pin DIP 18 17 16 15 14 13 12 11 10 PB0 XTAL1 XTAL2 GND VCC PA0 PA1 PA2 PA3 Table 1. Z8E001 Z8E001 18-Pin Configuration Description Pin Number Symbol Description 1 PB1 2 PB2 3 PB3 Reference 4 PB4 Charge Monitor 5 RESET VBO/POR Circuit 6 PA7 7 PA6 8 PA5 9 PA4 10 PA3 11 PA2 12 PA1 Strobe SCR 13 PA0 Charge FET 14 VCC 5V Bus 15 GND Circuit Ground 16 XTAL2 XTAL Circuit 17 XTAL1 XTAL Circuit 18 PB0 AN003501-Z8X0500 AN003501-Z8X0500 Application Note Universal Power and Voltage Control Using the Z8E001 Z8E001 11 Flowcharts Figure 4. Main Routine Start Main Routine Initialize Control Registers Timer32 interrupt Clear Timer0 and start it to time the first FET charge period Initialize SCR on-time variable Yes Enable Timer32 and Timer0 interrupts Is 25-pass counter 0? Turn on SCR Turn off SCR Decrement SCR on-time counter Reload SCR ontime counter No Initialize look-up total base address Setup Timer32 to interrupt 25 times per second Decrement 25pass counter Program is interrupt-driven- main loop stays idle Stop Timer0 Is SCR ontime counter 0? Yes No Clear Timer0 and restart Turn on FET Reload 25-pass counter Initialize 25-count counter to time 1 second for SCR firing Timer32 interrupt Turn off FET AN003501-Z8X0500 AN003501-Z8X0500 Application Note Universal Power and Voltage Control Using the Z8E001 Z8E001 12 Figure 5. Comparator Interrupt Routine Comparator interrupt Reload Timer0 with off-time value and restart Timer0 Turn off FET Complement Timer0 since it counted down No Load off-time register with 1 No Yes Did Timer0 interrupt occur? Stop Timer0 to clear it Yes Clear Timer0 interrupt Load off-time register with 1 Has Timer0 interrupted? Add table base pointer to Timer0 value to point to lookup table value Clear Timer0 interrupt Load lookup table value into offtime register Reload table pointer with table base value Restart Timer0 Yes Is Timer0 106 or more? No Turn on FET Comparator interrupt return Source Code * * power control2.asm * 8/9/99 * ZiLOG Z8E001 Z8E001 Microcontroller * AN003501-Z8X0500 AN003501-Z8X0500 Application Note Universal Power and Voltage Control Using the Z8E001 Z8E001 13 * * This program controls the charge and flash rates for a strobe * flash. The micro monitors the * charge current of the "kick" inductor, and when the voltage is * high enough, the inductor * control FET is turned off. The on-time is timed by a timer/ * counter, and depending on this * on-time, the off-time is determined by the lookup table. This * inductor controls the charge * rate of the capacitor that is used to fire the strobe. The micro * also controls the timing * between strobe flashes, and is set at 1s. An SCR is fired by the * micro at each timeout * period. The micro maintains the charge capacitor voltage over the * entire 12V to 24V input * voltage * * globals on define regdata,space=rfile space is 0 to 63 define regcontrol,space=rfile space is 192 to 255 define vectordata,space=ROM ;space is 0 to 31 define codedata,space=ROM ;space is 32 to 1023 *NOTE* Above ranges are set up in the ZDS Linker settings segment regdata PASS_COUNTER pass_counter ds equ 1 r0 ;counts timer interrupts for 1s STATUS status ds equ 1 r1 ;bit 0 determines if the ;inductor routine has been ;called or is an interrupt request SCR_ON_COUNTER_HI scr_on_counter_hi ds equ 1 r2 ;length of time to keep the SCR on scr_on_counter equ rr2 SCR_ON_COUNTER_LO scr_on_counter_lo ds equ 1 r3 POINTER_HIGH ds 1 ;location of lookup table value ;needed to control AN003501-Z8X0500 AN003501-Z8X0500 Application Note Universal Power and Voltage Control Using the Z8E001 Z8E001 14 pointer_high equ r4 pointer equ rr4 POINTER_LOW pointer_low ds equ 1 r5 POINTER_HOLD_HIGH pointer_hold_high ds equ 1 r6 POINTER_HOLD_LOW pointer_hold_low ds equ 1 r7 OFF_HOLD off_hold ds equ 1 r8 ;the FET off time ;lookup table base address ;holds the required FET off-time ; Program masks SCR FET inductor_int timer32 T32 start equ equ equ equ 00000010b 00000001b 00010000b 00100000b ;PA1 is scr output ;PA0 is FET output ;irq4 is inductor interrupt ;timer2 interrupt is irq5, and ;bit for the tctllo is also bit 5 ;Program constants scr_on_period that equ timer_load equ timer_passes equ 1000 ;every 1000 counts equals 2ms ;SCR will be held on ;equals 1 sec and is loaded into ;timer32 ;(used in conjunction with ;"timer_passes" ;to count 1 sec) 25 ;number of timer timeouts before ;SCR is fired segment regcontrol 50000 tctllo tctlhi ds ds 1 1 ;C0 ;C1 t0arlo t1arlo t0arhi t1arhi t2ar ds ds ds ds ds ds %C4-%C2 1 1 1 1 1 ;C4 ;C5 ;C6 ;C7 ;C8 AN003501-Z8X0500 AN003501-Z8X0500 Application Note Universal Power and Voltage Control Using the Z8E001 Z8E001 15 t3ar t2val t3val t0val t1val ds ds ds ds ds ds ds ds ds ds ds ds ds ds ptain ptaout ptadir ptbin ptbout ptbdir ptbsfr 1 1 1 1 1 ;C9 ;CA ;CB ;CC ;CD %D0-%CE 1 1 1 1 1 1 1 1 ;D0 ;D1 ;D2 ;D4 ;D5 ;D6 ;D7 segment vectordata jr start ;rollover vector dw start ;irq0 not used dw start ;irq1 not used dw start ;irq2 not used dw start ;irq3 not used dw inductor ;FET interrupt (irq4) dw timer2 ;timer32 interrupt (irq5) segment codedata start: ld tctlhi,#0 start1: di clr tctllo ld ld ld ld ld ld regptr,#0 spl,#%40 ptbout,#0 ptaout,#0 ptbdir,#00000000b ptadir,#00000011b ld ptasfr,#00000000b ld ptbsfr,#00011000b ld imask,#00110000b ;disable WDT ;disable timers (required because ;the micro program jumps back to ;start if a dropout signal is ;received, and timers will be ;running) working register group 0 ;stack is at top of RAM ;clear outputs ;port b all inputs ;port a bits 0,1,4,5,6,7 except ;PB1 are outputs ;all outputs are push/pull ;ptb3 and ptb4 are comparator ;inputs ;(bit 3 is reference, bit 4 is ;input) ;ptb2 enabled as input ;enable IRQ 4, 5 AN003501-Z8X0500 AN003501-Z8X0500 Application Note Universal Power and Voltage Control Using the Z8E001 Z8E001 16 ;initialize program values ld pass_counter,#timer_passes timer counter (25 int's/1s) ;initialize the SCR hold on ;counter ld scr_on_counter_hi,#HIGH(scr_on_period) ld scr_on_counter_lo,#LOW(scr_on_period) clr status clr ireq ld pointer_high,#HIGH(table15) ;load lookup table base ;pointer ld pointer_Low,#LOW(table15) check_done:and ireq,#(~inductor_int) ;clear inductor interrupt ;save the pointer base address in the hold registers for reloading ;into the table pointer ;registers ld pointer_hold_high,pointer_high ld pointer_hold_Low,pointer_Low * * Timer setup * * The oscillator used in this design is 10MHz, so the frequency at * the timer is 10MHz/8=1.25MHz. * The total countdown timeout is 1s, so the timer will countdown * 40ms, and repeat this * count 25 times before the SCR is fired. Therefore, 40ms/ * 0.8us=50000. 25 counts of 50000 * will equal 1s. A separate 25-occurrence countdown counter is * included in the interrupt * routine. * timer_setup:ld t3ar,#HIGH(timer_load) ;load counter for t32 ;countdown ld t2ar,#LOW(timer_load) ld t3val,#HIGH(timer_load) ld t2val,#LOW(timer_load) AN003501-Z8X0500 AN003501-Z8X0500 Application Note Universal Power and Voltage Control Using the Z8E001 Z8E001 17 clr ireq ;clear interrupt request register ld tctllo,#timer32 ;enable t32 fet_timer_setup:clr t0arlo ;0.8uS/count for FET period clr t0val or tctllo,#00000001b;enable t0 to time FET on-time or ptaout,#FET ei main: ;start inductor charge ;enable interrupts jr main * * Timer 32 Interrupt * * This interrupt (IRQ5)is entered every 40ms. To count a full 1s, * this routine is entered * 25 times, so a countdown counter is included and reset in this * routine. After 25 interrupts, * the SCR is fired. The scr-on-counter is decremented to set the * scr on-time, then the SCR is * again turned off. The FET on-time t0 counter is restarted, and * the FET output is turned back * on to restart the cycle (before the SCR is fired, the FET is * turned off, and timer0 is stopped). * * timer2: djnz pass_counter,exit_now ;each decrement is 100s and ptaout,#(~FET) and ireq,#(~inductor_int) ;turn off FET ;cancel any pending ;inductor ints and tctllo,#11111110b and ireq,#11111110b ;stop timer0 ;clear timer0 ireq0 ld pass_counter,#timer_passes ;reload ten occurrence ;counter ;turn on SCR output or ptaout,#SCR scr_wait:decw scr_on_counter jr nz,scr_wait and ptaout,#(~SCR) ;decrement scr_on_counter ;turn off the SCR AN003501-Z8X0500 AN003501-Z8X0500 Application Note Universal Power and Voltage Control Using the Z8E001 Z8E001 18 ;reload the SCR on-time counter ld scr_on_counter_hi,#HIGH(scr_on_period) ld scr_on_counter_lo,#LOW(scr_on_period) fet_timer_setup2:clr t0arlo clr t0val or tctllo,#00000001b or ptaout,#FET ;clear FET interrupt timer ;enable t0 ;turn the FET back on exit_now:iret * * Comparator Interrupt * * This routine is entered each time that the comparator input voltage rises above the reference * voltage. This routine turns the FET output off, stops and complements timer0 (started when the * FET was turned on to measure the on-time), then retrieves the corresponding off-time value from * the lookup table. Timer0 is then reloaded with this value and started again. This routine then * waits for the timer to time-out, then the FET is turned back on. T0 is then reset and restarted * to again time the on-period of the FET signal. * * * inductor: and ptaout,#(~FET) and tctllo,#11111110b com t0val ;turn off FET output to stop ;inductor charging ;stop timer0 ;complement t0 since it has ;counted down ;if timer0 interrupt is set, then the sawtooth period was greater than 256 timer0 counts, or ;204us (frequency at timer is 10MHz/8 = 1.25MHz) tm ireq,#00000001b jr z,highcheck ;timer0 interrupted? ;if not, proceed with the high ;limit check and ireq,#11111110b ;clear the timer0 interrupt AN003501-Z8X0500 AN003501-Z8X0500 Application Note Universal Power and Voltage Control Using the Z8E001 Z8E001 19 ld off_hold,#1 jr proceed3 ;set the off-time to 1 since ;the t0 int occurred ;signifying a long on-period ;skip over lookup table ;retrieval highcheck: cp t0val,#106 ;was the high limit value reached? jr ult,normal ;if not, proceed as normal ld off_hold,#1 ;if so, make off-time as short as possible jr proceed3 ;skip over lookup table ;retrieval normal: location add pointer_Low,t0val ;add location offset to table jr nc,proceed ;if carry flag, add 1 to High byte inc pointer_high proceed: proceed3: ldc off_hold,@pointer ;get the lookup table value ld t0val,off_hold ;load the counter with the off-time value ld t0arlo,off_hold or tctllo,#00000001b ;t0 single pass keep_checking: tm ireq,#00000001b jr z,keep_checking and clr clr and and tctllo,#11111110b t0val t0arlo ireq,#11111110b ireq,#(~inductor_int) ;timer0 timed out? ;if so, off-time wait is ;complete ;stop timer0 ;clear ireq0 ;clear comparator int ;load original lookup table values ld pointer_high,pointer_hold_high ld pointer_Low,pointer_hold_Low or tctllo,#00000001b ;restart timer0 to measure FET ;on-time or ptaout,#FET ;turn on FET iret * * Lookup Table * * The lookup table is loaded with FET off_time values that are used * to control the FET off time. * The larger the number, the longer the off-time. AN003501-Z8X0500 AN003501-Z8X0500 Application Note Universal Power and Voltage Control Using the Z8E001 Z8E001 20 * * table15: db db db db db db db 255 255 255 255 255 255 255 db db db db db db db db db db db db db db db db db db db db db db db db db db db db db db db db db db db db db 255 255 255 255 255 255 255 255 255 255 250 245 240 235 230 225 220 215 210 206 202 199 196 193 190 187 184 181 178 175 172 169 166 163 160 157 154 ;0.8us 1 ;1.6us 2 ;3.2us 3 ;4.0us 4 ;4.8us 5 ;5.6us 6 ;6.4us 7 db 255 ;7.2us 8 ;8.0us 9 ;8.8us 10 ;9.6us 11 ;10.4us 12 ;11.2us 13 ;12.0us 14 ;12.8us 15 ;13.6us 16 ;14.4us 17 ;15.2us 18 ;16.0us 19 ;16.8us 20 ;17.6us 21 ;18.4us 22 ;19.2us 23 ;20.0us 24 ;20.8us 25 ;21.6us 26 ;22.4us 27 ;23.2us 28 ;24.0us 29 ;24.8us 30 ;25.6us 31 ;26.4us 32 ;27.2us 33 ;28.0us 34 ;28.8us 35 ;29.6us 36 ;30.4us 37 ;31.2us 38 ;32.0us 39 ;32.8us 40 ;33.6us 41 ;34.4us 42 ;35.2us 43 ;36.0us 44 ;36.8us 45 AN003501-Z8X0500 AN003501-Z8X0500 Application Note Universal Power and Voltage Control Using the Z8E001 Z8E001 21 db db db db db db db db db db db db db db db db db db db db db db db db db db db db db db db db db db db db db db db db db db db db db db db db 151 148 145 141 138 135 132 129 126 123 120 117 114 112 110 108 106 104 102 100 98 96 94 92 90 88 86 84 82 80 78 76 74 72 70 68 66 64 62 60 58 56 52 40 40 40 40 40 ;37.6us ;38.4us ;39.2us ;40.0us ;40.8us ;41.6us ;42.4us ;43.2us ;44.0us ;44.8us ;45.6us ;46.4us ;47.2us ;48.0us ;48.8us ;49.6us ;50.4us ;51.2us ;52.0us ;52.8us ;53.6us ;54.4us ;55.2us ;56.0us ;56.8us ;57.6us ;58.4us ;59.2us ;60.0us ;60.8us ;61.6us ;62.4us ;63.2us ;64.0us ;64.8us ;65.6us ;66.4us ;67.2us ;68.0us ;68.8us ;69.6us ;70.4us ;71.2us ;72.0us ;72.8us ;73.6us ;74.4us ;75.2us 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 AN003501-Z8X0500 AN003501-Z8X0500 Application Note Universal Power and Voltage Control Using the Z8E001 Z8E001 22 db db db db db db db db db db db db db 40 40 40 40 40 40 40 40 40 40 40 40 40 ;76.0us ;76.8us ;77.6us ;78.4us ;79.2us ;80.0us ;80.8us ;81.6us ;82.4us ;83.2us ;84.0us ;84.8us ;85.6us 94 95 96 97 98 99 100 101 102 103 104 105 106 * Assembling/Compiling Code To assemble and compile the code, the ZiLOG Developer Studio (ZDS) Version 2.11 is used, and the target micro is the Z8E001 Z8E001. The code above is stored as an .asm file and must be included in the project when the project is first created. This source file (used with ZDS) is the only file that required for proper assembling/ compiling of the program. The define assembler directives allow the linker to set the ROM and RAM space boundaries for proper execution of the code. Because the actual code does not specify the ROM and RAM boundaries, these values must be specified within the ZDS linker settings. This setup is accomplished by selecting projectÐsettingsÐ linkerÐranges from the ZDS menu. The define statements containing space = ROM denote code segment space, while the statements containing space = rfile denote register or RAM space. The proper linker range settings are as follows (decimal values): vectordata = 0 to 31 (ROM space) codedata = 32 to 1023 (ROM space) regdata = 0 to 63 (RAM space) regcontrol = 192 to 255 (RAM space) Timing Diagrams and Tables The full lookup table is shown in the Technical Support-Source Code section. As mentioned during the Theory of Operation discussion, this table is used by the program to determine the length of the holdoff or off-time between inductor charging cycles. The db is a ZiLOG assembler directive to assign a byte of ROM to the value that follows the statement. For example, the statement db 111 assigns the value 111 (decimal) to a byte of ROM. It does not matter where in ROM the value AN003501-Z8X0500 AN003501-Z8X0500 Application Note Universal Power and Voltage Control Using the Z8E001 Z8E001 23 is assigned-that is the beauty of the lookup table! To set the start of the look-up table in the source code, two instructions are required, as follows: ld pointer_high,#HIGH(table15) ld pointer_low,#LOW(table15) These instructions take the actual 2-byte ROM address of the start of the lookup table and put the High byte into pointer_high and the Low byte into pointer_low. Now the table is used and the correct off-value is retrieved. The following instructions perform this data retrieval function: normal: add pointer_low,t0val ;add location offset to table location jr nc,proceed ;if carry flag, add 1 to High byte inc pointer_high proceed: ldc off_hold,@pointer ;get the lookup table value proceed3: ld t0val,off_hold ;load the counter with the off-time value ld t0arlo,off_hold or tctllo,#00000001b ;t0 single pass keep_checking: tm ireq,#00000001b;timer0 timed out? jr z,keep_checking ;if so, off-time wait is complete Just before the execution of these instructions, the comparator interrupt occurred, and the length of the FET on-time is held in the t0val register (timer 0 actual value register).The first three instructions load the 2-byte pointer register with the actual look-up table value that is retrieved (the Low byte of the pointer table address is added to the t0val to get the table offset, and if there is a carry, then the High byte is incremented because the table locations requires a full 16-bit address). The ldc instruction then loads the value at the table location pointed to by the 16-bit pointer register pair into the off-hold register (this value is the required off-time that correlates to the FET on-time table offset that was used to obtain the table location). This value is loaded into timer 0, and the timer is restarted. The timer 0 interrupt is then polled, and when it is set, the FET is turned back on, and this process repeats itself when the comparator interrupt is received. The other values in the table are for reference only. The first value after the semicolon shows the on_time FET period that corresponds to the off-time that is loaded into the lookup table. For example, the code: db 14 ;40.8µs 50 indicates that the value of 14 is used as the FET off time when the on-time is measured to be 40.8 s. The 50 value gives the numerical sequence value of the table location. AN003501-Z8X0500 AN003501-Z8X0500 Application Note Universal Power and Voltage Control Using the Z8E001 Z8E001 24 Test Procedure Equipment The equipment used to test and emulate this Application Note is as follows: · · · · ZiLOG Z8ICE000ZEM Z8ICE000ZEM or Z8ICE001ZEM Z8ICE001ZEM emulator Variable DC power supply (14V to 24V range) True RMS voltmeter with maximum value hold Oscilloscope The jumper settings for the emulator are as follows: 1. JP1 is open to isolate emulator power from the target board (target board is powered from the variable DC supply). 2. JP2 is connected. It connects the RESET pin of the ICE chip to pin 5 of the emulated Z8Plus. 3. JP3 is open to isolate the ICE chip oscillator from the target board. 4. JP4 is open to isolate the ICE chip oscillator from the target board. General Test Setup and Execution The test procedures are as follows: 1. Connect the DC adapter to the emulator to power the board. 2. Connect the 18-pin ribbon cable to the target board and emulator. 3. Connect the variable DC power supply to the +/­ wires on the target board. 4. Connect the oscilloscope input lead to the Q2 FET source, and the ground lead to ground (the oscilloscope connection is across resistor R5). 5. Connect the voltmeter across capacitor C1. After the power supply is adjusted for 14 volts, the emulator is started and the strobe begins flashing once every second. The oscilloscope shows the sawtooth FET current that is approximately 68 s in duration. The C1 capacitor voltage is approximately 188 volts (maximum voltage hold setting on the voltmeter). The same tests are taken for successive increments in the DC power supply. Table 2 shows the actual measured values for this circuit in 1-volt supply voltage increments. AN003501-Z8X0500 AN003501-Z8X0500 Application Note Universal Power and Voltage Control Using the Z8E001 Z8E001 25 Warning: This circuit produces dangerously high voltages on many of the components. Exercise extreme care when operating the circuit or modifying the circuit components. Test Results Table 2. Measured Values for Circuit Input Voltage (VDC) Capacitor Voltage (VDC) FET Charge Cycle Period ( s) 14 188 68.0 15 187 62.4 16 186 59.2 17 186 55.2 18 186 48.8 19 187 46.4 20 188 44.0 21 187 41.6 22 190 40.0 23 190 37.6 24 190 36.8 This circuit is set up to maintain a voltage of 187 volts (flash voltage) across the flash capacitor, so the largest voltage regulation error is only 1.6%. The software can maintain an excellent voltage regulation, even though the FET charge resistor tolerance is 1%, and the capacitor has a 5% tolerance. To achieve better regulation, the look-up table values between the data points listed above can be tested and adjusted as required (these points were interpolated in Table 1). The non-linearity of the look-up table is evident from the values shown in the table. At the lower voltages, the FET charge cycle period decreases rapidly with increases in voltage. At the higher voltages, the decrease in the charge cycle is much less for each successive increase in voltage. The look-up table enables the software to simulate a non-linear equation without using complicated mathematics. To obtain higher voltages on the flash capacitor, one of three changes can be made: 1. Change the reference resistors R9 and R10. 2. Change the FET feedback resistor R5. AN003501-Z8X0500 AN003501-Z8X0500 Application Note Universal Power and Voltage Control Using the Z8E001 Z8E001 26 3. Change the values in the look-up table. The most precise results are achieved when a combination of these three methods is used to either raise or lower the output energy. The Theory of Operation section contains a more detailed explanation of these changes. The easiest way to rough-in the look-up table is to determine the table values for a few points in the voltage range. A low, mid, and high voltage value (in the appropriate range) is selected, and the resulting oscilloscope trace is observed. Estimate the hold-off time and entered the estimate into the table. In addition, the intermediate values are interpolated from the actual test values. The voltage is adjusted across its voltage range, and the table values are adjusted again.This process continues until the desired voltage or power control is obtained. References Everything You Always Wanted To Know About Flashtubes, EG&G Optoelectronics (publication date unknown). IES Guide for Calculating the Effective Intensity of Flashing Signal Lights, Aviation Committee of the Illuminating Engineering Society (1964) Glossary Flashtube. A gas discharge tube designed to produce short pulses of light. Xenon is the normal gas used in flashtubes because it most efficiently converts electrical energy into visible photon energy. Flashtube Construction. The flashtube is constructed of a glass or quartz tube, and can be in many different shapes and sizes. The tube is filled with Xenon gas, and an electrode is sealed in at each end AN003501-Z8X0500 AN003501-Z8X0500 Application Note Universal Power and Voltage Control Using the Z8E001 Z8E001 27 Appendix Figure 6. Application Schematic AN003501-Z8X0500 AN003501-Z8X0500