AN9670 HIP5020 HIP5020EVAL2 41C/W MBR0540 4K/20K TPSE227M010S0100 - Datasheet Archive

 

No. AN9670 Harris Intelligent Power January 1997 HIP5020 Circuit 2 - Evaluation Board (HIP5020EVAL2) Author: Mike Walters

 

Harris Semiconductor No. AN9670 AN9670 Harris Intelligent Power January 1997 HIP5020 HIP5020 Circuit 2 - Evaluation Board (HIP5020EVAL2 HIP5020EVAL2) Author: Mike Walters Introduction The thermal cooling path for the HIP5020 HIP5020 includes these pins, the eight vias linking both sides of the printed circuit board, and approximately one square inch of total copper trace area. The thermal resistance from junction-to-ambient of HIP5020 HIP5020 mounted on this board is approximately 41C/W 41C/W. The HIP5020EVAL2 HIP5020EVAL2 is a DC-to-DC converter evaluation tool for the HIP5020 HIP5020. The converter is designed for portable power systems and is optimized for small size. For detailed information on the HIP5020 HIP5020, please refer to the HIP5020 HIP5020 data sheet [1]. The data sheet shows three example application circuits. Each circuit is optimized for a specific goal: Circuit 1 is optimized for high efficiency, Circuit 2 is optimized for small size, and Circuit 3 is optimized for low cost. The HIP5020EVAL2 HIP5020EVAL2 is Circuit 2. Table 1 shows the parts listing for the HIP5020EVAL2 HIP5020EVAL2 board. See the data sheet for supplier phone numbers. Design Considerations for Small Size This application note should be treated as a supplement to the data sheet. In addition to the data sheet, design and simulation software [2] is available for the HIP5020 HIP5020. This software can be useful for modifying the evaluation circuit for specific needs. Information provided by this note is specific to the HIP5020EVAL2 HIP5020EVAL2 converter. Included in this note is the detailed schematic, part listing and circuit board traces of the HIP5020EVAL2 HIP5020EVAL2. Additionally this application note describes techniques for designing small size converters with the HIP5020 HIP5020 and methods for measuring light load efficiency. Small size power conversion is achieved by increasing the switching frequency. This reduces the output filter energy storage requirements and enables smaller size filter components. This section describes the techniques used to achieve a small size DC-DC converter with the HIP5020 HIP5020. The inductor selection is critical for a small size converter. They are available in many different styles according to the shape of their magnetic core. Styles include open core inductors which are usually bobbin, rod, or stick shaped cores and closed core inductors which use pot, toroid, or E-core shapes. Open core inductors are a tempting choice for small size converters because the energy storage (inductance and saturation current) is very high for the apparent volume. However, the magnetic flux is not confined within the inductor's volume and can interfere (EMI) with nearby circuits. The magnetic flux flows from one end of the rod or bobbin through the air to the other end. The flux induces a voltage into any conductive material within the inductor's magnetic field. This may cause unstable operation, reduced efficiency, or interference with other circuits. If any of these problems is observed with an open core inductor, try re-arranging the printed circuit board layout or use a closed core inductor. Description The HIP5020EVAL2 HIP5020EVAL2 converter is designed to operate from a lithium-Ion (Li-Ion) battery with a series stack of 2 cells. Fully charged, this battery provides 8.4V to the DC-to-DC converter. As the battery discharges the input terminal voltage decreases to approximately 5.4V. The highest input voltage occurs when the portable system operates from the battery charger with the battery removed. Under this condition, the converter accepts up to 12V. The converter limits the maximum load current to less than 3.3A. The converter switches from normal current mode to hysteretic mode when the load drops below approximately 0.7A. The switching frequency is set for a nominal 625kHz. The inductor in the HIP5020EVAL2 HIP5020EVAL2 converter uses closed core which is a toroidal shape in a surface-mount assembly. This assembly is only 0.35 inches square and less than 0.24 inches tall. The inductor has two windings and four terminals. We parallel both windings for a rating of 3ADC with a no-load inductance of 5.0µH. The inductance swings to 3.1µH at 3ADC. The ripple current with a 3A load and 7.4V input is 1.34A peak-to-peak. Figure 1 shows the HIP5020EVAL2 HIP5020EVAL2 converter schematic. The converter includes numerous test points for OVERLOAD, ENABLE, PHASE, VCC, HMI and SLOPE indications. An additional testpoint (TP7) provides a signal connection to circuit ground. Figure 2 shows the component layout and printed circuit board traces of the HIP5020EVAL2 HIP5020EVAL2. Notice the ground plane connection to pins 6, 7, 8, 9, 21, 22, and 23 of the HIP5020 HIP5020. Copyright © Harris Corporation 1997 1 Application Note 9670 TP1 OVERLOAD TP3 PHASE L1 OUT U1 5µH HIP5020 HIP5020 1 VIN PHASE 27 3 VIN C14 100µF PHASE 28 2 VIN IN SD 26 4 PHASE C10 PGND 21 GND 20 10 GND SPARE C7 390pF HMI TP6 C8 43nF TP4 VCC C5 1µF BOOT 16 14 SLOPE TP5 R2 GND VCC 17 13 HMI 24.9K TP8 PGND CP+ 18 12 VINF R4 R6 10K CP- 19 11 FB 1µF C11 220µF PGND 22 9 PGND R5 2K C1 220µF PGND 23 8 PGND GND 0.1µF OVLD 24 7 PGND C12 0.1µF C3 SOFT 25 5 PHASE 6 PGND C2 100µF C13 220µF TP7 GND D1 MBR0540 MBR0540 TP2 CT 15 CLK C6 150pF C4 0.27µF SLOPE C9 R6 SPARE R1 SPARE SPARE R12, 12.4K/20K 4K/20K FIGURE 1. HIP5020EVAL2 HIP5020EVAL2 SCHEMATIC C12 R5 C8 R7 R2 C10 R6 R12 R1 C9 C3 C5 R4 C7 C6 D1 FIGURE 2A. SILK SCREEN - TOP FIGURE 2B. SILK SCREEN - BOTTOM (TOP SIDE VIEW) FIGURE 2C. CIRCUIT TRACES - TOP FIGURE 2D. CIRCUIT TRACES - BOTTOM (TOP SIDE VIEW) FIGURE 2. HIP5020EVAL2 HIP5020EVAL2 BOARD LAYOUT 2 Application Note 9670 TABLE 1. HIP5020EVAL2 HIP5020EVAL2 PARTS LISTING ITEM # QUANTITY REFERENCE DESCRIPTION MANUFACTURE PART NUMBER 1 3 C1, C11, C13 220µF AVX TPSE227M010S0100 TPSE227M010S0100 2 2 C2, C14 100µF AVX TPSE107M016S0100 TPSE107M016S0100 3 2 C3, C10, C12 0.1µF Various 1206 Case 4 2 C5, C4 0.22µF Various 1206 Case 5 1 C6 150pF Various 0805 Case 6 1 C7 390pF Various 0805 Case 7 1 C8 0.033µF Various 1206 Case 8 2 D1 0.5A, 40V Schottky Motorola MBR0540 MBR0540 9 1 L1 5µH CoilTronics CTX5-2 10 1 R4 37.4K Various 0805 Case 11 1 R5 2K Various 0805 Case 12 1 R7 10K Various 0805 Case 13 1 R12 12.4K/20K 4K/20K CMD PAC27A01T PAC27A01T 14 4 Terminal Posts Keystone 1613-2 15 7 TP1 - TP7 Test Points Jolo SPCJ-123-01 SPCJ-123-01 16 1 U1 HIP5020 HIP5020 Harris HIP5020 HIP5020 R1, R2 Spare Resistors 0805 Case C9 Spare Capacitor 0805 Case (ESL). Capacitors are generally useful as output capacitors for switching frequencies up to the ESL zero ( ESR / 2 · · ESL ). The tantalum output capacitors in Table 1 have a small (1nH to 2nH) ESL. If different output capacitors are used with the compensation method above, be sure that the ESL zero frequency is well above the unity gain frequency. In addition, measure the loop gain and phase for stable operation. Adjust R1 if required for the proper compensation gain and confirm the selection with closed-loop measurements. The control loop design uses the minimum number of components for compensation. HIP5020 HIP5020 utilizes peak current mode control with the entire current loop integrated within the HIP5020 HIP5020. Additionally, the HIP5020 HIP5020 includes a 12pF integration capacitor across the error amplifier. This evaluation board only needs the resister R1 for a stable design. Key to this realization is the high switching frequency and the output capacitor characteristics. The objective for stable operation with minimum compensation is to pick the unity gain frequency of the control loop above the ESR zero frequency (fESR) and below 1/2 of the switching frequency. The ESR zero is the corner frequency of the output capacitor ( 1 / ( 2 · · C1 · ESR ) ) and for the surface-mount tantalum capacitor (C1, C11, or C13) shown in Table 1 is approximately 12kHz. The the compensation transfer function, 1 / ( s · R 1 · 12 · 10 ­ 12 ) includes the internal 12pF integration capacitor and increases the loop gain at DC for good regulation characteristics. R1 sets the loop gain for the desired unity gain frequency. The unity gain frequency of the HIP5020EVAL2 HIP5020EVAL2 converter is approximately 35kHz, which is well below half of the 625kHz switching frequency. Notice that the resistor R2 does not affect stability. R2 only sets the output voltage level. First stabilize the control loop by selecting R1 and then determine R2 for the desired output voltage level. Both of these resistors are included in the resistor network, R12 in the evaluation board. This device contains a matched resistor divider in a SOT-23 package. The ratio of the resistors is within 0.5% over the temperature range. The printed circuit board includes placeholders for R1 and R2. The input and output capacitors are both low ESR, surfacemount, tantalum capacitors. These capacitors have excellent high frequency characteristics. Three capacitors are required on the output to lower the output ripple voltage below 30mV at 3ADC. Two capacitors are required to pro- All capacitors become inductive at high frequency and a useful lumped parameter is the equivalent series inductance 3 Application Note 9670 an operational amplifier (op amp) integrator. The op amp integrator uses the circuit shown in Figure 3 to supply power to the device under test. The circuit works as follows: In hysteretic mode, the converter draws its current in discrete "bursts". The integrator "servos" the converter's input voltage so that it is equal to the input source voltage, but it cannot respond to the short current bursts. The burst current is supplied by the 1000µF capacitor and the current through the 100 resistor is the DC average of the current supplied to the HIP5020EVAL2 HIP5020EVAL2 converter. Measure the voltage across the 100 resistor and divide by 100 to get the average current. The operational amplifier must be capable of supplying the entire load current, but since the technique is for light loads only this should not be a drawback. It is necessary to start the circuit by shorting the input power source to the IN terminal on the HIP5020EVAL2 HIP5020EVAL2 board until the converter has started and reached steady state. cess the input ripple current. The HIP5020EVAL2 HIP5020EVAL2 uses a Schottky diode for the bootstrap diode (D1). Compared with a silicon junction diode a Schottky bootstrap diode is faster and exhibits a lower forward drop to maximize the bootstrap voltage. The circuit board layout and design are extremely important for small size designs. Provide wide copper traces for all the high current paths. Especially important is the ground copper trace for pins 6, 7, 8, 9, 21, 22, and 23. These pins not only provide a high current return path, but also provide the cooling path for the HIP5020 HIP5020. Increased copper area lowers the thermal resistance and junction temperature. Both top and bottom copper planes of the circuit board can be linked together with vias and used for cooling. See Figure 2 for an example of a good ground trace design with vias linking both top and bottom planes. Measuring Hysteretic Mode Efficiency In hysteretic mode, the HIP5020 HIP5020 converter draws current from the input source in short, discrete intervals. Not all laboratory meters accurately report the average value of this pulsating current wave shape. This complicates the process for measuring the efficiency of the converter at light loads. Any method for determining the light load efficiency must first accurately measure the average input current and compute the efficiency from the average input voltage, input current, output voltage and output current. We have successfully used three methods to accurately measure the average input current and light load efficiency. 1µF MEASURE AVERAGE INPUT CURRENT ACROSS THIS RESISTOR IIN = V/100 1M +18V IN + TP3 100 1000µF INPUT POWER SOURCE GND CLOSE TO START We have used a storage scope with waveform math to measure the average input current. A digital signal oscilloscope (DSO) like the Tektronix 11402/11403 series or DSA 602 series can measure the input current directly, store the waveform, and find the average input current using the scope's built-in math features. Make sure that a few `run' cycles are displayed and analyzed. Additionally, check that a sufficient number of data points have accurately captured the current wave shape. Check the accuracy of reported input current against another method given below to verify the instrumentation. OUT HIP5020 HIP5020 - GND HIP5020EVAL2 HIP5020EVAL2 LIGHT LOAD RESISTOR R > 20 FIGURE 3. MEASURE LIGHT LOAD INPUT CURRENT WITH AN INTEGRATING OP AMP Performance Figure 4 shows the typical efficiency of the HIP5020EVAL2 HIP5020EVAL2 over the load range and with an input voltage of 5.4VDC and 12VDC 12VDC. The converter operates in hysteretic mode for load currents below approximately 0.7ADC. The simplest method for measuring the pulsating input current is with a true RMS meter. Be careful to choose the proper true RMS meter. Not all meters claiming to be true RMS accurately measure the RMS or average of the pulsating input current. Some true RMS ac current meters such as the HP34401A HP34401A can give very good results. The key specification of the meter is the accuracy at very low frequency. The HP34401A HP34401A specifies a measurement accuracy of 1% at 3Hz. Any meter claiming to be true RMS should be checked (at least once) against another method in order to verify that the RMS circuitry reacts correctly to the input current drawn at light loads. 100 VO = 3.3VDC EFFICIENCY (%) 95 VIN = 5.4V 90 VIN = 12V 85 80 75 Another technique for measuring light load efficiency inserts a low pass filter between the input source and the HIP5020 HIP5020 converter. The average input current can be read directly before the filter. The low pass filter can be either an inductor-capacitor filter (we use 3mH and 1500µF) or even 70 0.001 0.01 0.1 LOAD CURRENT (A) 1 FIGURE 4. EFFICIENCY vs LOAD CURRENT 4 10 Application Note 9670 Conclusions Figure 5 shows the output voltage and inductor current during a load transient The inductor current was measured with a current probe around one of the leads of an leaded inductor (the leaded inductor is equivalent to the surface mount inductor shown in the parts listing. This application note described the HIP5020EVAL2 HIP5020EVAL2 as an evaluation tool for the HIP5020 HIP5020. The circuit design emphasizes small size and is suitable as a reference design for portable computer applications. Two other example application designs are shown in the datasheet that emphasizes size and cost. These three example applications illustrate the trade-off of efficiency, size and cost with the choice of components for a HIP5020 HIP5020 converter. OUTPUT VOLTAGE (V) 3.32 3.31 3.30 3.29 References 3.28 [1] HIP5020 HIP5020 data sheet Harris web page http://www.semi.harris.com/ , Harris AnswerFAX (407-724-7800) document #4243. 3.27 INDUCTOR CURRENT (A) 4 3 [2] HIP5020 HIP5020 design and simulation software. Harris web page http://www.semi.harris.com/ 2 1 0 0.000 0.040 0.080 0.120 TIME (ms) 0.160 0.200 FIGURE 5. HYSTERETIC MODE OPERATION 50% TO FULL LOAD TRANSIENT (1A/µs) All Harris Semiconductor products are manufactured, assembled and tested under ISO9000 ISO9000 quality systems certification. Harris Semiconductor products are sold by description only. Harris Semiconductor reserves the right to make changes in circuit design and/or specifications at any time without notice. Accordingly, the reader is cautioned to verify that data sheets are current before placing orders. Information furnished by Harris is believed to be accurate and reliable. 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