MAX624C/D MAX624ISE MAX624 MAX624-02 MAX624-01 MAX624-03 MAX624-06 MAX624-05 - Datasheet Archive

 

Dual-Output, 1MHz DC-DC Boost Converter for PCMCIA Applications _Applications _Features o 1MHz Switching Frequency for Small

 

19-0382; Rev 1; 8/95 Dual-Output, 1MHz DC-DC Boost Converter for PCMCIA Applications _Applications _Features o 1MHz Switching Frequency for Small Components o 5V ±4% Boost Converter with Internal Power Switch o Adjustable ±2% Output Boost Converter with External Power Switch o Optional Inrush Surge-Current Limiting o 40µA Shutdown Current o 0.5mA Quiescent Current o 3.0V to 5.5V Input Range o 85% Main 5V SMPS Efficiency o Independent Soft-Start for Each Supply o Reset Output with 2.8V ±3% Threshold and 4ms Timeout _Ordering Information PART PCMCIA Memory Cards TEMP. RANGE PIN-PACKAGE MAX624C/D MAX624C/D 0°C to +70°C Dice* MAX624ISE MAX624ISE -25°C to +85°C 16 Narrow SO * Dice are tested at TA = +25°C. Contact factory for dice specifications. Solid-State Disk Drives Host-Side PCMCIA Adapters LCD Bias Power Supplies _Typical Operating Circuit _Pin Configuration INPUT 3V TO 5.5V 4.7µF 5µH MAIN OUTPUT 5V 200mA 5µH TOP VIEW EXT 1 VIN LX5 DA N CSA 4.7µF 2.2µF 10pF 500k 16 VIN RESET 2 15 LX5 REF 3 GND 4 FB5 SHUTDOWN AUXILIARY OUTPUT 12V 80mA (AS SHOWN) 0.22 14 PGND MAX624 MAX624 13 FB5 SHDN 5 12 DA ONA 6 MAX624 MAX624 SHDN 11 CSA 0.1µF ONA VA SS5 7 10 VA REF AUX. ON/OFF FBA SSA 8 9 EXT GND 3300pF 100k FBA SO _ Maxim Integrated Products Call toll free 1-800-998-8800 for free samples or literature. 1 MAX624 MAX624 _General Description The MAX624 MAX624 is a dual DC-DC converter intended for size-constrained applications, such as power supplies that must fit inside PCMCIA memory cards. At the heart of the MAX624 MAX624 are two boost-topology converters, plus auxiliary functions including a start-up inrush surge-current limiter and a power-on reset output with timer (power-good signal). The MAX624 MAX624 accepts input voltages from 3V to 5.5V and generates two outputs: a fixed 5V ±4% output at 200mA (guaranteed), and an adjustable auxiliary output that is configurable for various loads with an external power transistor. The auxiliary output is typically set to 12V ±2% for flash memory applications, but can be adjusted via a resistor divider from VIN to 30V or more. The MAX624 MAX624's high switching frequency (1MHz) reduces external component sizes. High-frequency switching losses have minimal impact on efficiency, which is 85% for the main 5V supply. Small ceramic filter capacitors, together with the soft-start function, reduce start-up inrush current surges. MAX624 MAX624 Dual-Output, 1MHz DC-DC Boost Converter for PCMCIA Applications ABSOLUTE MAXIMUM RATINGS VIN, FB5, LX5, SHDN, ONA to GND.-0.3V to 7V EXT to GND.-0.3V to 12V RESET, REF to GND.-0.3V to (VIN + 0.3V) PGND to GND.±0.3V SS5, SSA, DA, CSA, FBA to GND.-0.3V to (FB5 + 0.3V) VA to GND .-0.3V to 17V Continuous Power Dissipation (TA = +70°C) SO (derate 8.70mW/°C above +70°C) .696mW Operating Temperature Range MAX624ISE MAX624ISE .-25°C to +85°C Lead Temperature (soldering, 10sec) .+300°C Stresses beyond those listed under "Absolute Maximum Ratings" may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability. ELECTRICAL CHARACTERISTICS (VIN = 3V, GND = PGND = 0V, SHDN = VIN, EXT open, FBA feedback resistors set for 12V, TA = TMIN to TMAX, unless otherwise noted.) PARAMETER CONDITIONS MAX UNITS 3.0 5.5 V 5V Output Voltage 4.80 5.20 V FBA Regulation Point 1.96 2.04 V 60 µA Input Supply Range MIN TYP OUTPUT VOLTAGES SUPPLY CURRENTS VIN Shutdown Current VIN = 5.5V, SHDN = ONA = 0V 40 VIN Quiescent Current Circuit of Figure 1, VIN = 3.3V, ONA = 0V 500 FB5 Quiescent Current FB5 = 5.5V, SHDN = 3V, ONA = 0V 200 400 µA VA Quiescent Current FB5 = 5.5V, VA = 12.5V 30 60 µA FB5 Shutdown Discharge Current FB5 = 5V, VIN = 3V, SHDN = 0V, internal VIN to FB5 discharge switch 100 5000 µA VA Shutdown Discharge Current VA = 12V, VIN = 3V, ONA = 0V, internal VIN to VA discharge switch 5 15 µA FBA Leakage Current VA = 12V, FBA = 2.1V µA 100 nA 0.03 0.2 % 0.33 0.6 10 µA 5V MAIN SMPS Line Regulation 3V < VIN < 5.5V (Note 1) Switch On-Resistance Switch Leakage Current LX5 = 7V Switch Current Limit 0.7 0.9 1.1 A Switch On-Time Constant (K5) 3V < VIN < 5V, tON5 = K5 / VIN 0.8 1.3 1.7 µs-V Switch Off-Time Ratio (SR5) 3V < VIN < 5V, FB5 = 5V (Note 2) 0.2 Efficiency Circuit of Figure 1, ILOAD = 100mA 0.8 85 % AUXILIARY SMPS CONTROLLER Line Regulation 3V < VIN < 5.5V (Note 1) Enable Trip Voltage Level ONA input will be inhibited until FB5 rises above this level 0.03 0.2 4.0 4.5 V 10 3.5 µA 220 mV 15 3.0 µs-V CSA Bias Current CSA Current-Limit Threshold 180 DA On-Resistance FB5 = 5.5V 4 DA Drive Current DA = 2.5V 0.5 Switch On-Time Constant (KA) 3V < VIN < 5V, tONA = KA / VIN 1.5 Switch Off-Time Ratio (SRA) 3V < VIN < 5V, 7V < FBA < 11V (Note 3) 0.2 Efficiency Circuit of Figure 1, ILOAD = 60mA 2 2.2 % A 0.9 75 _ % Dual-Output, 1MHz DC-DC Boost Converter for PCMCIA Applications (VIN = 3V, GND = PGND = 0V, SHDN = VIN, EXT open, FBA feedback resistors set for 12V, TA = TMIN to TMAX, unless otherwise noted.) PARAMETER CONDITIONS MIN TYP MAX UNITS 20 28 k 50 300 0.8 V ±1 µA 0.4 V SOFT-START CONTROL Source Resistance SS5, SSA; SHDN = ONA = 3V Discharge Resistance SS5, SSA; SHDN = ONA = 0V 14 LOGIC INPUTS AND OUTPUTS Input Low Voltage SHDN, ONA Input High Voltage SHDN, ONA Input Leakage SHDN, ONA Output Low Voltage RESET, ISINK = 2mA, VIN = 2.6V Output High Voltage RESET, ISINK = 1mA, VIN = 3V RESET Trip Level Rising VIN edge, typical hysteresis = 1% 2 V VIN - 0.8 V EXT Output Voltage EXT Output Voltage in Reset VIN = 2.9V, ISOURCE = 2µA VIN = 5.5V, ISOURCE = 0µA VIN = 2V, ISINK = 0.1mA 2.9 V 2 RESET Timeout 2.7 10 ms 6.5 11.8 1 V V Note 1: Line Regulation is tested by measuring the reference line regulation, since both converters are supplied from the regulated 5V output. Note 2: Switch off-time ratio guarantees that the inductor will go into continuous conduction. The ratio is tested for two cases for the main SMPS: SR5 = 0.120 x tOFF / tON 1) VIN = 5V, FB5 = 5V 2) VIN = 3V, FB5 = 5V SR5 = 0.867 x tOFF / tON Note that the constants are calculated from: (FB5 + 0.6V - VIN) / VIN Note 3: Switch off-time ratio guarantees that the inductor will go into continuous conduction. The ratio is tested for two cases for the auxiliary SMPS: SRA = 0.520 x tOFF / tON 1) VIN = 5V, VA = 7V 2) VIN = 3V, VA = 11V SRA = 2.867 x tOFF / tON Note that the constants are calculated from: (VA + 0.6V - VIN) / VIN _ 3 MAX624 MAX624 ELECTRICAL CHARACTERISTICS (continued) _Typical Operating Characteristics (Circuit of Figure 1, TA = +25°C, unless otherwise noted.) QUIESCENT INPUT CURRENT vs. TEMPERATURE 4 3 2 1 0 90 MAX624-02 MAX624-02 MAX624-01 MAX624-01 VIN = 3.3V 5 1200 12V AUXILIARY SMPS ONA = HIGH SHDN = HIGH 1000 800 600 5V MAIN SMPS ONA = LOW SHDN = HIGH 400 80 EFFICIENCY (%) RESET DELAY (ms) VIN = 5V 6 1400 QUIESCENT INPUT CURRENT (µA) 8 7 EFFICIENCY vs. LOAD CURRENT (12V AUXILIARY SMPS) -20 20 0 40 60 80 100 VIN = 5V VIN = 3.3V 70 60 50 40 200 30 0 -40 MAX624-03 MAX624-03 RESET DELAY vs. TEMPERATURE 20 -40 -20 20 0 40 60 80 100 0.1m 1m 10m 100m 1 TEMPERATURE (°C) TEMPERATURE (°C) LOAD CURRENT (A) EFFICIENCY vs. LOAD CURRENT (5V MAIN SMPS) QUIESCENT INPUT CURRENT vs. INPUT VOLTAGE (12V AUXILIARY SMPS) QUIESCENT INPUT CURRENT vs. INPUT VOLTAGE (5V MAIN SMPS) 70 VIN = 3.3V 60 50 40 30 20 ONA = LOW 10 ONA = HIGH SHDN = HIGH 1000 800 600 400 200 700 0.1m 1m 10m 100m 0 1 SHDN = HIGH ONA = LOW 600 500 400 300 200 100 0 0 0 MAX624-06 MAX624-06 MAX624-05 MAX624-05 1400 1200 QUIESCENT INPUT CURRENT (µA) VIN = 5V 80 EFFICIENCY (%) MAX624-04 MAX624-04 90 QUIESCENT INPUT CURRENT (µA) 100 1 2 3 4 5 0 6 1 3 2 4 5 6 LOAD CURRENT (A) INPUT VOLTAGE (V) INPUT VOLTAGE (V) SWITCHING FREQUENCY vs. LOAD CURRENT LOAD REGULATION vs. LOAD CURRENT (12V AUXILIARY SMPS) LOAD REGULATION vs. LOAD CURRENT (5V MAIN SMPS) 100 10 5V MAIN SMPS VIN = 3.3V 0.7 0.6 0.5 VIN = 3.3V 0.4 0.3 0.2 10 100 LOAD CURRENT (mA) 1000 MAX624-08 MAX624-08 MAX624-09 MAX624-09 0.8 2.0 VIN = 5V 1.5 1.0 VIN = 3.3V 0.5 0.1 VIN = 5V 0 1 2.5 LOAD REGULATION (%) 0.9 LOAD REGULATION (%) 1000 1 4 1.0 MAX624-07 MAX624-07 10,000 SWITCHING FREQUENCY (kHz) MAX624 MAX624 Dual-Output, 1MHz DC-DC Boost Converter for PCMCIA Applications 0 0 20 40 60 80 100 120 140 160 LOAD CURRENT (mA) 0 200 400 600 LOAD CURRENT (mA) _ 800 1000 Dual-Output, 1MHz DC-DC Boost Converter for PCMCIA Applications SHUTDOWN CURRENT vs. INPUT VOLTAGE 700 TA = -25°C LOAD CURRENT (mA) SHUTDOWN CURRENT (µA) TA = +25°C 40 MAX624-11 MAX624-11 TA = +85°C 45 800 MAX624-10 MAX624-10 50 LOAD CURRENT CAPABILITY vs. INPUT VOLTAGE 35 30 25 20 15 600 5V MAIN SMPS 500 400 300 12V AUXILIARY SMPS 200 10 100 5 0 0 0 1 2 3 4 5 6 3.0 3.2 3.4 3.6 3.8 4.0 4.2 4.4 4.6 4.8 5.0 INPUT VOLTAGE (V) INPUT VOLTAGE (V) START-UP WAVEFORMS (5V MAIN SMPS) START-UP WAVEFORMS (12V AUXILIARY SMPS) (VIN = 3.3V, ILOAD = 0A, ONA = LOW) (VIN = 3.3V, ILOAD = 1.2mA, SHDN = HIGH) A A B B C C D A: ONA (5V/div) B: 12V AUXILIARY SMPS (5V/div) 100µs/div C: IIN (200mA/div) D: VSWITCHED (100mV/div, AC-COUPLED) D 100µs/div A: SHDN (5V/div) C: IIN (200mA/div) B: 5V MAIN SMPS (1V/div) D: VSWITCHED (100mV/div, AC-COUPLED) START-UP INRUSH CURRENT (VIN = 5V) START-UP INRUSH CURRENT (VIN = 3.3V) (ILOAD = 5mA, SHDN = ONA = LOW) (ILOAD = 5mA, SHDN = ONA = LOW) A A B B C C D D 1ms/div 1ms/div A: VIN (5V/div) B: VSWITCHED (5V/div) C: RESET (5V/div) D: IIN (50mA/div) A: VIN (5V/div) B: VSWITCHED (5V/div) C: RESET (5V/div) D: IIN (50mA/div) _ 5 MAX624 MAX624 _Typical Operating Characteristics (continued) (Circuit of Figure 1, TA = +25°C, unless otherwise noted.) MAX624 MAX624 Dual-Output, 1MHz DC-DC Boost Converter for PCMCIA Applications _Typical Operating Characteristics (continued) (Circuit of Figure 1, TA = +25°C, unless otherwise noted.) LOAD-TRANSIENT RESPONSE (12V AUXILIARY SMPS) LOAD-TRANSIENT RESPONSE (5V MAIN SMPS) A A B B 200µs/div A: ILOAD = 0mA to 200mA B: 5V MAIN SMPS (50mV/div, AC-COUPLED) 200µs/div A: ILOAD = 0mA to 80mA B: 12V AUXILIARY SMPS (200mV/div, AC-COUPLED) LINE-TRANSIENT RESPONSE (12V AUXILIARY SMPS) LINE-TRANSIENT RESPONSE (5V MAIN SMPS) A B 100µs/div ILOAD = 20mA A: VIN = 3.3V to 5V B: 12V AUXILIARY OUTPUT (200mV/div, AC-COUPLED) 6 A B 100µs/div ILOAD = 40mA A: VIN = 3.3V to 5V B: 5V MAIN OUTPUT (50mV/div, AC-COUPLED) _ Dual-Output, 1MHz DC-DC Boost Converter for PCMCIA Applications PIN NAME FUNCTION 1 EXT Gate-Drive Output. Drives inrush surge-current limiting MOSFET. EXT is fed by an internal charge-pump tripler that swings from GND to VIN x 3. 2 RESET Power-On Reset Output. Low when VIN < 2.8V and for 4ms after VIN > 2.8V. EXT is low when RESET is low. Swings from GND to VIN. 3 REF 2V Reference Output. Bypass to GND with 0.1µF. No external load current is allowed. 4 GND Quiet Analog Ground and Low-Side Current-Sense Input for Auxiliary SMPS 5 SHDN Shutdown. Disables both SMPSs when low. In shutdown, the surge-protection input MOSFET is kept on. 6 ONA On/Off Control Input for Auxiliary SMPS, low = off 7 SS5 Soft-Start Input for 5V Main SMPS. An external soft-start capacitor varies the 5V start-up time. Ramp time to full current limit is approximately 50µs per nF of soft-start capacitance. 8 SSA Soft-Start Input for Auxiliary SMPS. An external soft-start capacitor varies the auxiliary SMPS start-up time. Ramp time to full current limit is approximately 50µs per nF of soft-start capacitance. 9 FBA Feedback Input for Auxiliary SMPS. Regulates around REF (2V nominal). FBA is a high-impedance CMOS input. 10 VA Output Voltage Sense Input for Auxiliary SMPS. The only purpose of this pin is to set the SMPS timing algorithm. Internally, VA connects to the top of a 250k ±30% resistor that connects to VIN. 11 CSA 12 DA Gate-Drive Output for Auxiliary SMPS. Swings 0V to FB5. 13 FB5 Feedback Input for 5V Main SMPS. FB5 also serves as the supply voltage rail for much of the internal circuitry for both SMPSs (bootstrap supply input). 14 PGND 15 LX5 Drain Connection for 5V Main SMPS Power MOSFET 16 VIN Input Supply Voltage from the External Supply. Normal operating range is 3V to 5.5V. Current-Sense Input for Auxiliary SMPS. Current-limit threshold is 200mV nominal with respect to GND. Power Ground, source connection for the main 5V SMPS power MOSFET _ 7 MAX624 MAX624 _Pin Description MAX624 MAX624 Dual-Output, 1MHz DC-DC Boost Converter for PCMCIA Applications _Standard Application Circuit In the standard application circuit (Figure 1), the MAX624 MAX624 generates 5V at 200mA (guaranteed) and 12V at 80mA from a 3.3V or 5V input, and includes soft-start and inrush surge-current limiting features. Successful use of the circuit does not require calculations; use the values given in Figure 1. For more detailed applications information, see the Design Procedure for Main and Auxiliary SMPS. _Detailed Description The MAX624 MAX624 is a dual-output DC-DC boost converter. The device accepts input voltages from 3V to 5.5V and generates two outputs: a 5V output at 200mA, and an adjustable output (i.e. 12V or 30V). The main 5V output has an internal MOSFET switch and currentsense resistor (0.15), which senses the output current and triggers the current-limit comparator. The auxiliary SMPS's current-limit resistor and MOSFET switch are external to the device. The current-limit voltage of the auxiliary SMPS is 200mV. Both the main and auxiliary SMPS have a soft-start feature that varies the start-up time of the outputs. The SS output source impedance of the two outputs is 20k to charge the external SS capacitor to 150mV (5V output) or 200mV (auxiliary output). The impedance of the SS pin when the device is in reset (5V) and when ONA = low (auxiliary) is 50 to GND. Full current limit is reached at a 50µs/nF rate. To prevent surge currents when the card is plugged into a live socket, this device is capable of driving an external high-side N-channel MOSFET in series with the main VCC supply to the card. The EXT pin drives the gate of the external MOSFET and is fed by an internal chargepump tripler that delivers three-times VIN, even in shutdown mode. The output source impedance of EXT is approximately 100k, and has an active pull-down. The SS capacitor and the external inrush-limiting MOSFET are optional components, not necessary unless inrush current is a concern. However, do not remove C9. When the MAX624 MAX624 is in reset, the FB5 and VA outputs are discharged to VIN via two internal switches (Figure 2). Discharging the output capacitors to a low voltage level protects against false programming of flash memory chips. 5V Main SMPS The main output is powered from the FB5 pin (i.e., bootstrapped) for higher speed and lower on-resistance of the power MOSFET. This SMPS consists of an error comparator, an output undervoltage-lockout comparator (set at 4V output), a timing generator for tON 8 C9 3300pF 1/2 7101 VSWITCHED VIN C1 4.7µF R2 10 C5 4.7µF +5V MAIN OUTPUT 200mA D1* L2 5µH L1 5µH 16 VIN 15 DA CSA 13 7 C7 0.1µF SHUTDOWN ON/OFF 6 12 11 Q1 1/2 7101 R1 0.22 FB5 C3 2.2µF R5 500k C4 10pF SS5 MAX624 MAX624 5 D2* 1 EXT LX5 C2 4.7µF AUXILIARY OUTPUT +12V 80mA VA SHDN ONA FBA SSA REF RESET GND 4 10 9 8 3 C6 0.1µF 2 C8 0.01µF R6 100k TO MICROCONTROLLER PGND 14 *D1, D2: MOTOROLA MBR0520L MBR0520L C5 CAN BE REDUCED IN VALUE (0.1µF) IF THE INPUT LEAD INDUCTANCE IS LOW. NOTE: BOLD LINES DESIGNATE HIGH-CURRENT PATHS AND SHOULD BE KEPT TO MINIMAL LENGTHS. Figure 1. Standard Application Circuit and tOFF, a current-limit comparator, a MOSFET driver, and the power switch (Figure 2). The error comparator's noninverting input voltage is internally set to VREF. FB5's voltage is scaled internally, so that when it exceeds 5V the comparator output trips and shuts down the PFM. Leaving only the error comparator on when the switch is off keeps the quiescent current low. The current comparator is powered up after the switch is turned on. This provides leading-edge blanking on the current comparator, in order to filter noise spikes caused by switch gate capacitance so they don't trip the overcurrent comparator and turn off the switch. The main PFM has an undervoltage-lockout circuit that trips at 4V (preset internal threshold). Until the 4V threshold is reached, the timing generator is disabled and a 100kHz start-up oscillator is used to generate the output. _ Dual-Output, 1MHz DC-DC Boost Converter for PCMCIA Applications MAX624 MAX624 Table 1. Recommended Components for 12V/80mA Auxiliary SMPS and 5V Main SMPS DESIGNATION QTY DESCRIPTION SOURCE/TYPE Q1 1 Dual, N-channel MOSFET IRF7101 IRF7101 or Si9956DY Si9956DY L1, L2 2 5µH inductors Sumida CLS-62B CLS-62B, drawing #94T-217 94T-217 C1, C2 2 4.7µF ceramic capacitors Marcon THCR40E1E475ZT THCR40E1E475ZT or THCS40E1E475ZT THCS40E1E475ZT C3 1 2.2µF ceramic capacitor Marcon THCR30E1E225ZT THCR30E1E225ZT or THCS30E1E225ZT THCS30E1E225ZT C4 1 10pF capacitor C5, C6, C7 3 0.1µF capacitors C8 1 10nF capacitor Murata-Erie GRM42-6X7R104K025V GRM42-6X7R104K025V C9 1 3300pF capacitor D1, D2 2 IF = 1A, VR = 20V Schottky rectifier Motorola MBR0520L MBR0520L R1 1 0.22 ±10% resistor Ohmtek 1205LR220LBT 1205LR220LBT or IMS RC-I-1206 RC-I-1206 R2 1 10 resistor Table 2. Component Suppliers PHONE FAX IMS SUPPLIER (401) 683-9700 (401) 683-5571 International Rectifier (310) 241-7876 (310) 640-6515 Motorola (602) 244-3576 (602) 244-4015 Murata-Erie (800) 831-9172 (814) 238-0490 Ohmtek (716) 283-4025 (716) 283-5932 Siliconix (408) 988-8000 (408) 970-3950 Sumida USA (708) 956-0666 (708) 956-0702 Sumida Japan (03) 607-5111 (03) 607-5144 Toshiba Marcon (708) 913-9980 (708) 913-1150 Table 3. Operating States VIN SHDN ONA VMAIN VAUX* EXT I (VIN) Reset STATE 2.8V LO X OFF OFF ON 40µA Main On >2.8V HI LO 5.0V OFF ON 0.52mA Both On >2.8V HI HI 5.0V 12V* ON 1.2mA * When off, VAUX = VIN. * VAUX is set to 12V in this example. _ 9 MAX624 MAX624 Dual-Output, 1MHz DC-DC Boost Converter for PCMCIA Applications FB5 11V P EXT VOLTAGE TRIPLER CHARGE PUMP VIN IC POWER OUT 150k ENBL S 100k 2V Q R 2.0V REFERENCE REF LX PFM LOGIC D N 0.2 Q tON = K5/VIN K5 tOFF = ­­­­­­­­­­­­­ 2(VFB5 + 0.6V - VIN) ENBL CURRENT LIMIT 0.15 250k PGND 2V 2.8V VIN RESET 20k SS5 Q 5ms DELAY D MAX624 MAX624 N R P VA SHDN FBA S 2V PFM LOGIC Q R D FB5 tON = KA/VIN KA tOFF = ­­­­­­­­­­­­ 2(VA + 0.6V - VIN) ENBL DA PGND CURRENT LIMIT CSA 180k FB5 N 20k 2V 4V ONA GND Figure 2. Functional Block Diagram 10 _ SSA Dual-Output, 1MHz DC-DC Boost Converter for PCMCIA Applications Surge Prevention Surge prevention is accomplished by slowly high-side driving an N-channel switch. The gate is driven by an on-chip charge pump that triples the input voltage. This charge pump is powered from the input voltage and runs continuously. The reset trip voltage is set to 2.8V to guarantee that the surge-prevention MOSFET can be turned on under worst-case low input voltage conditions. Otherwise, the card would go out of reset even though the supply voltage is unavailable. Voltage Reference The MAX624 MAX624's internal 2.00V reference is powered from the VIN input. The reference is kept alive in all modes (needed for reset function) and must be bypassed with a 0.1µF capacitor to GND for low-noise operation. No external load current is allowed. Pulse-Frequency-Modulation Control Scheme A unique pulse-frequency-modulation (PFM) control scheme, with adjustable on-time/off-time circuitry and current limit, is a key feature of both the main SMPS regulator and the auxiliary SMPS converter. The PFM scheme combines the advantages of pulse-width modulation (high output power and efficiency) with those of a traditional pulse-skipper (ultra-low quiescent currents). The on-time is calculated from the input voltage, and the offtime is calculated from VOUT - VIN. The off-time is divided by two so that the inductor current can ramp into continuous conduction. Switch on-times are adjusted down at high input voltages in order to minimize output ripple. Use the following formulas to calculate tON and tOFF: tON = K / VIN tOFF = 0.5 x K / (VOUT + 0.6V - VIN) Nominally, K = 1.3µs-V for the main SMPS, and K = 2.2µs-V for the auxiliary SMPS. The K (design constant) scale factor that sets the switching frequency also sets the peak inductor current to control no-load output ripple at low input-to-output differentials (e.g., VIN = 5V, VOUT = 5V). The PFM's high switching frequency (1MHz) helps reduce external component size. When the peak current limit is reached, the MOSFET switch turns off for at least the off-time set by the one-shot. When the comparator monitoring the output voltage is less than the desired value, it starts another cycle by turning the switch on. Design Procedure for _Main and Auxiliary SMPS Output Filter Capacitor Selection The output filter capacitor should have the minimum possible ESR for low ripple, and the minimum possible value for smallest physical size (i.e., ceramic). Larger sizes can be used for lower cost (i.e., tantalum). The output ripple is the sum of two components, due to CF and ESR. To select the filter capacitor value, follow the steps below: 1) Select the maximum ripple you can tolerate (e.g., 80mV). 2) Calculate the value of CF, using the formula below: 2 x K x ILOAD CF (in F) > - VRIPPLEC (VOUT + 0.5V - VIN) where K is a design constant. Use the worst-case value from the Electrical Characteristics. 3) Calculate the output capacitor's required ESR, using the formula below. VRIPPLEESR x VIN ESR (in ) < - 4 x ILOAD (VOUT + 0.5V - VIN) For example: For the 5V main SMPS with K = 1.7µs-V, ILOAD = 200mA, VOUT = 5V, VIN = 3.3V, and maximum tolerable ripple = 80mVp-p, assume VRIPPLEC = 60mV and VRIPPLEESR = 20mV. Calculate CF > 5µF with ESR < 37m. Inductor Selection Select the inductor value to optimize one of the following: · High Load Currents: Higher inductor values give higher load currents, since the inductor operates in deep continuous conduction. · Small Physical Size: Lower inductor values result in lower energy storage requirements, hence smaller physical size. The filter capacitor can also be smaller, since the inductor current can ramp up faster when the load is suddenly increased. _ 11 MAX624 MAX624 Adjustable Auxiliary SMPS The auxiliary output is adjustable from 5V to 15V; two external resistors set the output voltage. The auxiliary SMPS is similar to the main SMPS, but it does not have an undervoltage-lockout comparator, and requires an external power MOSFET (see Typical Operating Circuit and Design Procedure for Main and Auxiliary SMPS). The 5V SMPS undervoltage-lockout circuit overrides the ONA input until the 5V main SMPS (VMAIN) output reaches about 4V. This feature ensures that the external auxiliary SMPS MOSFET has sufficient gate-drive voltage. The adjustable output voltage can be increased to 30V or higher (Figure 9). However, such high output voltages cause the inductor current to become discontinuous, consequently reducing the load-current capability. MAX624 MAX624 Dual-Output, 1MHz DC-DC Boost Converter for PCMCIA Applications To select the inductor value for the main SMPS, take the following steps: 1) Select the input voltage. 2) Select ILIMIT and ILOAD. 3) Use the specified data sheet values and the following formula: SR5 x K5 (VIN - A) L (in H) = - 2 x ILIMIT (VIN + A) - 2 x ILOAD x B A = ILIMIT x RON B = VOUT + VDIODE where: inductor current = I LIMIT (min) = 0.7A, ILOAD(min) = 200mA, SR5 (the switch off-time ratio) = 0.8, K5(max) = 1.7µs-V, RON(max) = 0.6, VOUT = 5V, VDIODE = 0.5V, VIN(min) = 3.0V, and L = 5µH (for best performance, use a Sumida 5µH (CLS-62B CLS-62B). Input Filter Capacitor Selection The input filter capacitor is required to reduce reflected current ripple to the input source, and to improve efficiency by providing a low-impedance path for the ripple current. For memory card applications, the input filter capacitor is absolutely necessary due to possible contact resistance in the edge connector. To limit surge currents, use smaller values. Ceramic capacitors are the best choice. Output Voltage and Component Selection for the Auxiliary SMPS To select the output voltage and component values for the auxiliary SMPS, take the following steps: 1) Select the desired output voltage between 5V and 15V (e.g., 12V). 2) Select the minimum input voltage (VIN). 3) Select R6 and R5. Choose R6 in the 10k to 200k range (e.g., 100k). Choose R5 = R6 (VOUT / VREF 1). For example, if VOUT = 12V, then R6 = 100k and R5 = 500k. 4) Select the desired output current (IOUT). Calculate the minimum inductor current (ILIMIT) using the following formula: ILIMIT (in Amps) = [(VOUT + 0.5V) / (VIN(min) - 0.3V)] x ILOAD x 2 For example: VOUT = 12V, VIN(min) = 3V,ILOAD = 80mA, and ILIMIT = 0.7A. 5) To calculate the minimum required inductor value, use the following formula: SRA x KA (VIN - A) L (in H) = - 2 x ILIMIT (VIN - A) - 2 x ILOAD x B 12 A = ILIMIT x RON B = VOUT + VDIODE For example: ILOAD = 80mA, ILIMIT = 0.7A (calculated using the above formula), SRA (switch off-time ratio) = 0.9, KA (switch on-time) = 3.0µs-V, RON(max) = 0.2, VOUT = 12V, VDIODE = 0.5V, and L(min) = 3.8µH. 6) R (in ) = 180mV / ILIMIT = 0.25 for ILIMIT = 0.7A. 7) To select the output capacitor value, take the following steps: A) Select the maximum ripple you can tolerate. B) Calculate CF using the formula below. 2 x KA x ILOAD CF (in F) = - VRIPPLEC x (VOUT + 0.5 - VIN) C) Calculate the output capacitor's required ESR using the formula below. VRIPPLEESR x VIN ESR (in ) = - 4 x ILOAD x (VOUT + 0.5V - VIN) _PC Board Layout and Grounding Because of the MAX624 MAX624's high-frequency operation, careful PC board layout is necessary to minimize ground bounce and noise. PC board layout instructions should be explicit, and the layout artist should work from a pencil sketch that shows the placement of power switching components and high-current routing. Use Figures 3­8 (the component placement guide and PC board layouts for the MAX624 MAX624 evaluation board) as a rough guide for component placement and ground connections. A ground plane is essential for optimum performance. In most applications, the circuit will be located on a multilayer board, and full use of the four or more copper layers is recommended. Use the following step-by-step guide. 1) Place the high-power components (C1, C2, C3, D1, D2, L1, L2, Q1, and R1) first. Priority 1: Minimize current-sense resistor trace lengths. Priority 2: Minimize ground trace lengths in the highcurrent paths (the bold lines in the application circuits). Priority 3: Minimize other trace lengths in the high-current paths. Use traces more than 5mm wide. Ideally, surface-mount power components are butted up against one another with their ground terminals almost touching. These high-current grounds _ Dual-Output, 1MHz DC-DC Boost Converter for PCMCIA Applications 2) Place the IC and signal components. Keep the main switching node traces (LX node) short and away from sensitive analog components (current-sense traces and REF and SS capacitors). Important: the IC must be no farther than 5mm from the currentsense resistor. Keep the gate-drive trace shorter than 10mm and route it away from REF and SS. Figure 3. MAX624 MAX624 PC Board Component Placement Guide Figure 5. MAX624 MAX624 PC Board Layout-Component Side Figure 4. MAX624 MAX624 PC Board Drill and Mechanical Guide Figure 6. MAX624 MAX624 PC Board Layout-VSWITCHED Plane _ 13 MAX624 MAX624 (C1, C2, C3, R1, and PGND) are then connected with a wide filled zone of top-layer copper, so they don't go through vias. The resulting top-layer "subground plane" is connected to the normal inner-layer ground plane at the ground output terminals (at the ground of C2). Other high-current paths should also be minimized, but focusing on short ground and current-sense connections eliminates about 90% of all PC board layout problems. See Figures 3­8 for examples. MAX624 MAX624 Dual-Output, 1MHz DC-DC Boost Converter for PCMCIA Applications Figure 7. MAX624 MAX624 PC Board Layout-Ground Plane _Application Circuits Positive 30V Auxiliary Output Circuits The MAX624 MAX624 can be used to generate a 30V output at 25mA (Figures 9 and 10). Note that the 12V zener clamp shown in Figure 10 must be used for 5V input applications. A 30V output at 25mA can be generated by tying the VA pin to the main SMPS output, but this circuit does not make optimal use of the inductor (the off-time is about 0.5µs). An alternative approach is to clamp the VA output to 12V using a zener. The off-time is optimized (reduced), which in turn makes better use of the inductor and produces a higher output current of about 35mA (Figure 10). Note that the 12V zener clamp shown in Figure 10 must be used for 5V input applications. Figure 8. MAX624 MAX624 PC Board Layout-Solder Side VIN 3.3V ONLY 4.7µF L2 L1 +5V MAIN OUTPUT D1 200mA VIN 15 LX5 DA C2 CSA 10 13 1 The MAX624 MAX624 can be used to generate a negative 30V output to power-up LCD supplies (Figure 11). This circuit is part switching regulator and part charge pump. The switching regulator boosts the input to a high positive voltage (30V), while the actual negative voltage is generated using a charge-pump tap on the switching node. The negative 30V output has a 5% load-regulation error from 1mA to 20mA. The ratio of R5 and R6 resistors can be used to adjust the LCD contrast. C7 R1 0.22 6 10pF EXT SS5 3 C8 PGND 14 NOTE: USE FOR VIN = 3.3V ONLY NOTE: BOLD LINES DESIGNATE HIGH-CURRENT PATHS AND SHOULD BE KEPT TO MINIMAL LENGTHS. L2: 2.2µH, MURATA-ERIE LQH3C2R2MO400 LQH3C2R2MO400 C3: 4.7µF, MARCON THCR30E1H474ZT THCR30E1H474ZT D2: MOTOROLA MBR0540 MBR0540 Figure 9. Positive 30V (25mA) Auxiliary Output Application Circuit 14 R6 36k C6 ONA GND 4 9 8 SSA REF ON/OFF R5 500k 11 FB5 MAX624 MAX624 FBA 7 C3 0.47µF 12 VA 3300pF Negative Output Application Circuit AUXILIARY OUTPUT +30V 25mA D2 16 _ Dual-Output, 1MHz DC-DC Boost Converter for PCMCIA Applications C14 0.1µF VIN 4.7µF +5V MAIN OUTPUT D1 200mA D2 16 AUXILIARY OUTPUT +30V 35mA 15 LX5 DA CSA 13 1 FB5 C3 12 3300pF 100k C7 FBA ONA 1 FB5 11 R1 0.22 EXT 100k 7 C7 FBA GND REF PGND 4 3 C8 R6 36k 14 ON/OFF 6 ONA L2: 2.2µH, MURATA-ERIE LQH3C2R2MO400 LQH3C2R2MO400 C3: 0.47µF, MARCON THCR30E1H474ZT THCR30E1H474ZT D2: MOTOROLA MBR0540 MBR0540 NOTE: BOLD LINES DESIGNATE HIGH-CURRENT PATHS AND SHOULD BE KEPT TO MINIMAL LENGTHS. Figure 10. Positive 30V (35mA) Auxiliary Output Application Circuit 9 8 SSA GND REF PGND 4 C6 10 12V 9 8 SSA VA SS5 R5 50k 10pF MAX624 MAX624 10 12V 6 13 R5 500k +30V C3 0.1µF 12 3300pF VA SS5 DA CSA 10pF MAX624 MAX624 7 LX5 C2 11 R1 0.22 EXT D2 16 VIN 15 C15 0.47µF D3 L2 L1 +5V MAIN OUTPUT D1 200mA VIN C2 ON/OFF 4.7µF L2 L1 AUXILIARY OUTPUT -30V D4 25mA 3 C8 R6 3.6k 14 L2: C14, C15: D2: D3, D4: C6 2.2µH, MURATA-ERIE LQH3C2R2MO400 LQH3C2R2MO400 CERAMIC (50V) 1N4148 1N4148 MOTOROLA MBR0540 MBR0540 NOTE: BOLD LINES DESIGNATE HIGH-CURRENT PATHS AND SHOULD BE KEPT TO MINIMAL LENGTHS. Figure 11. Negative 30V Auxiliary Output Application Circuit _ 15 MAX624 MAX624 VIN MAX624 MAX624 Dual-Output, 1MHz DC-DC Boost Converter for PCMCIA Applications _Chip Topography RESET EXT VIN LX5 PGND REF FB5 GND 0.149" (3.785mm) DA SHDN CSA ONA SS5 SSA FBA VA 0.085" (2.159mm) TRANSISTOR COUNT: 926 SUBSTRATE CONNECTED TO GND Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are implied. Maxim reserves the right to change the circuitry and specifications without notice at any time. 16 _Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 (408) 737-7600 © 1995 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.