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19-0195; Rev 0; 10/93
Adjustable, Step-Down, Current-Mode PWM Regulators
_______________General Description
The MAX750A/MAX758A are adjustable-output, CMOS, step-down, DC-DC switching regulators. The MAX758A accepts inputs from 4V to 16V and delivers 750mA, while the MAX750A accepts inputs from 4V to 11V and delivers 450mA. Typical efficiencies are 85% to 90%. Typical quiescent current is 1.7mA, or only 6A in shutdown mode. The output does not exhibit any ripple at subharmonics of the switching frequency over its specified range. Pulse-width-modulation (PWM) current-mode control provides precise output regulation and excellent transient responses. Output voltage accuracy is guaranteed to be 4.5% plus feedback-resistor tolerance over line, load, and temperature variations. Fixed-frequency switching and absence of subharmonic ripple allows easy filtering of output ripple and noise, as well as the use of small external components. These regulators require only a single inductor value to work in most applications, so no inductor design is necessary.
____________________________Features
o o o o o o o o o o Up to 750mA Load Currents 160kHz High-Frequency, Current-Mode PWM 85% to 96% Efficiencies 33H or 100H Pre-Selected Inductor Value, No Component Design Required 1.7mA Quiescent Supply Current 6A Shutdown Supply Current Adjustable Output Voltage Overcurrent, Soft-Start, and Undervoltage Lockout Protection Cycle-by-Cycle Current Limiting 8-Pin DIP/SO Packages (MAX750A)
MAX750A/MAX758A
______________Ordering Information
PART MAX750ACPA MAX750ACSA MAX750AC/D MAX750AEPA MAX750AESA MAX750AMJA TEMP. RANGE 0C to +70C 0C to +70C 0C to +70C -40C to +85C -40C to +85C -55C to +125C PIN-PACKAGE 8 Plastic DIP 8 SO Dice* 8 Plastic DIP 8 SO 8 CERDIP**
________________________Applications
Cellular Phones & Radios Portable Communications Equipment Portable Instruments Computer Peripherals
Ordering Information continued on last page. * Contact factory for dice specifications. **Contact factory for availability and processing to MIL-STD-883.
_________________Pin Configurations
TOP VIEW
SHDN REF 1 2 8 7 V+ LX GND I.C.
__________Typical Operating Circuit
INPUT 4V TO 16V OUTPUT ADJ. FROM VREF TO V+
SS 3 CC 4
MAX750A MAX758A
V+ LX
33H
6 5
DIP
ON/OFF
SHDN REF 1 2 8 7 V+ LX GND I.C.
MAX750A MAX758A
SHDN CC
SS 3 CC 4
MAX750A
REF SS GND
6 5
SO
Pin Configurations continued on last page.
________________________________________________________________ Maxim Integrated Products 1
Call toll free 1-800-998-8800 for free samples or literature.
Adjustable, Step-Down, Current-Mode PWM Regulators MAX750A/MAX758A
ABSOLUTE MAXIMUM RATINGS
Pin Voltages V+ (MAX750A).........................................................+12V, -0.3V V+ (MAX758A).........................................................+18V, -0.3V LX (MAX750A) ....................................(V+ - 12V) to (V+ + 0.3V) LX (MAX758A) ....................................(V+ - 21V) to (V+ + 0.3V) SS, CC, SHDN.............................................-0.3V to (V+ + 0.3V) Peak Switch Current (ILX).........................................................2A Reference Current (IREF) ...................................................2.5mA Power Dissipation (TA = +70C) 8-Pin Plastic DIP (derate 9.09mW/C above +70C) .....727mW 8-Pin SO (derate 5.88mW/C above +70C)..................471mW 16-Pin Wide SO (derate 9.52mW/C above +70C) ......762mW 8-Pin CERDIP (derate 8.00mW/C above +70C)..........640mW Operating Temperature Ranges: MAX75_AC_ _ .......................................................0C to +70C MAX75_AE_ _ ....................................................-40C to +85C MAX75_AMJA ..................................................-55C to +125C Junction Temperatures: MAX75_AC_ _/AE_ _ ......................................................+150C MAX75_AMJA ................................................................+175C Storage Temperature Range .............................-65C to +160C Lead Temperature (soldering, 10sec) .............................+300C
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
(Circuit of Figure 3, V+ = 9V for the MAX750A, V+ = 12V for the MAX758A, VOUT = 5V, R2 = 40.20k, R3 = 13.0k, ILOAD = 0mA, TA = TMIN to TMAX, unless otherwise noted.) PARAMETER CONDITIONS V+ = 6.0V to 11.0V; 0mA < ILOAD < 450mA for MAX750AC, 0mA < ILOAD < 450mA for MAX750AE, 0mA < ILOAD < 300mA for MAX750AM Output Voltage (Note 1) V+ = 6.0V to 16.0V; 0mA < ILOAD < 450mA for MAX758AC/AE, 0mA < ILOAD < 350mA for MAX758AM V+ = 10.2V to 16.0V, 0mA < ILOAD < 750mA Input Voltage Range Line Regulation Load Regulation Efficiency Supply Current Shutdown Supply Current (Note 2) Shutdown Input Threshold Shutdown Input Leakage Current Short-Circuit Current 1.5 SHDN = 0V VIH VIL 2.0 0.25 1.0 1.5 V+ = 4.0V to 11.0V V+ = 4.0V to 16.0V ILOAD = 0mA to 450mA ILOAD = 0mA to 750mA V+ = 9.0V, ILOAD = 300mA V+ = 12V, ILOAD = 750mA 1.7 6.0 3.0 100.0 2.0 0.25 1.0 92 0.0005 0.0005 90 87 1.7 6.0 3.0 100.0 4.0 0.15 0.15 11.0 MIN 4.75 MAX750A TYP 5.00 MAX 5.25 MIN MAX758A TYP MAX UNITS
4.75
5.00
5.25
V
4.75 4.0
5.00
5.25 16.0 V %/V %/mA % mA A V A A
2
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Adjustable, Step-Down, Current-Mode PWM Regulators
ELECTRICAL CHARACTERISTICS (continued)
(Circuit of Figure 3, V+ = 9V for the MAX750A, V+ = 12V for the MAX758A, VOUT = 5V, R2 = 40.20k, R3 = 13.0k, ILOAD = 0mA, TA = TMIN to TMAX, unless otherwise noted.) PARAMETER Undervoltage Lockout LX On Resistance LX Leakage Current Reference Voltage Reference Drift Oscillator Frequency Compensation Pin Impedance 130 TA = +25C 1.15 V+ rising V+ falling ILX = 500mA CONDITIONS MIN MAX750A TYP 3.75 3.5 0.5 1.0 1.22 50 170 7500 210 130 1.30 1.15 MAX 4.00 MIN MAX758A TYP 3.75 3.5 0.5 1.0 1.22 50 160 7500 190 1.30 MAX 4.00 UNITS V A V ppm/C kHz
MAX750A/MAX758A
Note 1: Output voltage tolerance over temperature is 4.5% plus the tolerances of R3 and R4 in Figure 3. Note 2: The standby current typically settles to 25A (over temperature) within 2 seconds; however, to decrease test time, the part is guaranteed at a 100A maximum value.
__________________________________________Typical Operating Characteristics
(Circuit of Figure 3, VOUT = 5V, TA = +25C, unless otherwise noted.)
MAX750A EFFICIENCY vs. OUTPUT CURRENT
MAX750A/58A-1
MAX758A EFFICIENCY vs. OUTPUT CURRENT
(NOTES 3, 6) 90 EFFICIENCY (%)
MAX750A/58A-2
100 (NOTES 3, 6) 90 EFFICIENCY (%)
100
80
V+ = 5.5V V+ = 7V V+ = 9V
80
V+ = 6V V+ = 8V V+ = 12V V+ = 16V
70
V+ = 11V
70
60 0 200 400 600 800 1000 OUTPUT CURRENT (mA)
60 0 200 400 600 800 1000 OUTPUT CURRENT (mA)
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Adjustable, Step-Down, Current-Mode PWM Regulators MAX750A/MAX758A
_____________________________Typical Operating Characteristics (continued)
(Circuit of Figure 3, VOUT = 5V, TA = +25C, unless otherwise noted.)
MAX758A PEAK INDUCTOR CURRENT vs. OUTPUT CURRENT
MAX1750A/58A-4
MAX758A PEAK INDUCTOR CURRENT vs. OUTPUT CURRENT
600 500 400 300 200 100 0 V+ = 10.2V V+ = 8.0V V+ = 6.6V V+ = 6.0V 0 50 100 150 200 250 300 L1 = 18H C4 = 1000F
MAX1750A/58A-5
OSCILLATOR FREQUENCY vs. SUPPLY VOLTAGE
(NOTE 3) OSCILLATOR FREQUENCY (kHz) 210 200 190 MAX750A 180 170 MAX758A 160 150 4 6 8 10 12 14 16
MAX1750A/58A-6
1000 PEAK INDUCTOR CURRENT (mA) L1 = 100H C4 = 300F 800
700 PEAK INDUCTOR CURRENT (mA)
220
600 V+ 8.0V TO 16.0V 400 V+ = 6.6V
200
0 0 100 200 300 400 500 600 700 800 OUTPUT CURRENT (mA)
OUTPUT CURRENT (mA)
SUPPLY VOLTAGE (V)
MAX758A NO-LOAD SUPPLY CURRENT vs. SUPPLY VOLTAGE
MAX1750A/58A-7
NO-LOAD SUPPLY CURRENT vs. TEMPERATURE
MAX750A/58A-8
SHUTDOWN SUPPLY CURRENT vs. TEMPERATURE
SHUTDOWN SUPPLY CURRENT (A) 18 16 14 12 10 8 6 4 2 0 -60 -40 -20 0 20 40 60 80 100 120 140 TEMPERATURE (C)
MAX758A ONLY, V+ = 16V MAX758A ONLY, V+ = 12V V+ = 9V V+ = 6V
NO-LOAD SUPPLY CURRENT (mA)
NO-LOAD SUPPLY CURRENT (mA)
(NOTES 3, 5) 2.5 2.0 1.5 1.0 0.5 0 0 2 4 6 8 10 12 14 UNDERVOLTAGE LOCKOUT V+ RISING (OPERATION BEGINS)
(NOTES 4, 5) 2.5 2.0 1.5 1.0 0.5 MAX750A, V+ = 9.0V MAX758A, V+ = 12.0V
(NOTES 4, 5)
UNDERVOLTAGE LOCKOUT V+ FALLING (OPERATION ENDS)
16
0 -60 -40 -20 0 20 40 60 80 100 120 140 TEMPERATURE (C)
SUPPLY VOLTAGE (V)
MAX750A OSCILLATOR FREQUENCY vs. TEMPERATURE
240 OSCILLATOR FREQUENCY (kHz) 220 200 180 160 140 V+ = 7.0V V+ = 9.0V V+ = 11.0V (NOTE 4)
MAX758A OSCILLATOR FREQUENCY vs. TEMPERATURE
200 (NOTE 4) 190 180 170 160 150 140 130 V+ = 12.0V V+ = 9.0V V+ = 16.0V V+ = 6.0V
OSCILLATOR FREQUENCY (kHz)
V+ = 5.5V
0 -60 -40 -20
0
20 40 60 80 100 120 140 TEMPERATURE (C)
120 -60 -40 -20
0
20 40 60 80 100 120 140 TEMPERATURE (C)
4
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MAX750A/58A-9
3.0
2.0
20
Adjustable, Step-Down, Current-Mode PWM Regulators
_____________________________Typical Operating Characteristics (continued)
(Circuit of Figure 3, VOUT = 5V, TA = +25C, unless otherwise noted.)
MAXIMUM OUTPUT CURRENT vs. SUPPLY VOLTAGE, R1 OMITTED
MAX750A/58A-10
MAX750A/MAX758A
MAXIMUM OUTPUT CURRENT vs. SUPPLY VOLTAGE
1400 MAXIMUM OUTPUT CURRENT (mA) (NOTES 3, 6) MAXIMUM OUTPUT CURRENT (mA)
(NOTES 3, 6) 1200
MAX758A
1200
MAX758A
1000 800 600
MAX750A
1000
MAX750A
400 200
800 4 6 8 10 12 14 16 SUPPLY VOLTAGE (V)
4
6
8
10
12
14
16
SUPPLY VOLTAGE (V)
MAX758A SWITCHING WAVEFORMS CONTINUOUS CONDUCTION
MAX758A SWITCHING WAVEFORMS DISCONTINUOUS CONDUCTION
MAX750A/58A-11
1400
12V A 0V 200mA 0mA 5V C 2s/div A: SWITCH VOLTAGE (LX PIN), 5V/div, 0V TO +12V B: INDUCTOR CURRENT, 100mA/div C: OUTPUT VOLTAGE RIPPLE, 50mV/div COUT = 390F, V+ = 12V, IOUT = 20mA B
12V A 0V 100mA 0mA 5V B
C
2s/div A: SWITCH VOLTAGE (LX PIN), 5V/div, 0V TO +12V B: INDUCTOR CURRENT, 200mA/div C: OUTPUT VOLTAGE RIPPLE, 50mV/div COUT = 390F, V+ = 12V, IOUT = 150mA
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Adjustable, Step-Down, Current-Mode PWM Regulators MAX750A/MAX758A
_____________________________Typical Operating Characteristics (continued)
(Circuit of Figure 3, VOUT = 5V, TA = +25C, unless otherwise noted.) MAX750A LINE-TRANSIENT RESPONSE MAX758A LINE-TRANSIENT RESPONSE
A A 16V 11V 6V 0V B 10.2V 0V B
100ms/div A: VOUT, 50mV/div, AC-COUPLED B: V+, 5V/div, 6.0V TO 11.0V IOUT = 300mA
100ms/div A: VOUT, 50mV/div, AC-COUPLED B: V+, 5V/div, 10.2V TO 16.0V IOUT = 750mA
MAX750A LOAD-TRANSIENT RESPONSE
MAX758A LOAD-TRANSIENT RESPONSE
A
A
300mA B 20mA
750mA B 50mA
50ms/div A: VOUT, 50mV/div, AC-COUPLED B: IOUT, 200mA/div, 20mA TO 300mA V+ = 9V
50ms/div A: VOUT, 50mV/div, AC-COUPLED B: IOUT, 500mA/div, 50mA TO 750mA V+ = 12V
Note 3: Commercial temperature range external component values in Table 2. Note 4: Wide temperature range external component values in Table 2. Note 5: Supply current includes all external component leakage currents. External capacitor leakage currents dominate at T > +85C. A C3 and C4 = Sanyo Oscon through-hole capacitors. Note 6: Operation beyond the specifications listed in the Electrical Characteristics may exceed the power dissipation ratings of the device. 6 _______________________________________________________________________________________
Adjustable, Step-Down, Current-Mode PWM Regulators
______________________________________________________________Pin Description
PIN 8-PIN DIP/SO 16-PIN WIDE SO NAME FUNCTION
MAX750A/MAX758A
1
2
2
3
SHDN
Shutdown--active low. Ground to power-down chip, tie to V+ for normal operation. Output voltage falls to 0V when SHDN is low. Reference Voltage Output (+1.22V) supplies up to 100A for external loads. Bypass to GND with a capacitor that does not exceed 0.047F. Soft-Start. Capacitor between SS and GND provides soft-start and short-circuit protection. 510k resistor from SS to SHDN provides current boost. External voltage divider feedback point. When an external voltage divider is connected from the output voltage to CC and GND, this pin becomes the feedback input for adjusting the output voltage. Connect a 330pF compensation capacitor between the output and CC. Internal Connection. Make no external connection to this pin. Ground* Drain of internal P-channel power MOSFET* Supply Voltage Input. Bypass to GND with 1.0F ceramic and large-value electrolytic capacitors in parallel. The 1F capacitor must be as close to the V+ and GND pins are possible.* No Connect--not internally connected.
REF
3
7
SS
4 5 6 7 8 -
8 9 10, 11 12, 13, 14 1, 15, 16 4, 5, 6
CC I.C. GND LX V+ N.C.
*16-Pin Wide SO: All pins with the same name must be connected together externally.
_______________Detailed Description
The MAX750A/MAX758A switch-mode regulators use a current-mode pulse-width-modulation (PWM) control system coupled with a simple step-down (buck) regulator topography. Input voltages range from 4V to 11V for the MAX750A, and from 4V to 16V for the MAX758A. The current-mode PWM architecture provides cycle-bycycle current limiting, improved load transient response characteristics, and simpler outer-loop design. The controller consists of two feedback loops: an inner (current) loop that monitors the switch current via the current-sense resistor and amplifier, and an outer (voltage) loop that monitors the output voltage through the error amplifier (Figure 1). The inner loop performs cycle-by-cycle current limiting, truncating the powertransistor on-time when the switch current reaches a predetermined threshold. This threshold is determined by the outer loop. For example, a sagging output voltage produces an error signal that raises the threshold, allowing the circuit to store and transfer more energy during each cycle.
Programmable Soft-Start
Figures 1 and 2 show a capacitor and a resistor connected to the soft-start (SS) pin to ensure an orderly powerup. Typical values are 0.1F and 510k. SS controls both the soft-start timing and the maximum output current that can be delivered while maintaining regulation. The charging capacitor slowly raises the clamp on the error-amplifier output voltage, limiting surge currents at power-up by slowly increasing the cycle-by-cycle currentlimit threshold. The 510k resistor sets the soft-start clamp at a value high enough to maintain regulation, even at currents exceeding 1A. This resistor is not necessary for lower current loads. Refer to the Maximum Output Current vs. Supply Voltage, No. R1 graph in the Typical Operating Characteristics. Table 1 lists timing characteristics for selected capacitor values and circuit conditions. The overcurrent comparator trips if the load exceeds approximately 1.5A. A soft-start cycle begins when either an undervoltage or overcurrent fault condition triggers an internal transistor to discharge the softstart capacitor to ground. A soft-start cycle also begins at power-up and when coming out of the shutdown mode.
7
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Adjustable, Step-Down, Current-Mode PWM Regulators MAX750A/MAX758A
V IN
SHDN OVERCURRENT COMPARATOR BIAS GEN SLOPE COMPENSATION
V+
C2 1F
C3*
C5 330pF R2 CC R1 510K R3
MAX750A MAX758A
ERROR AMP
RAMP GEN RSENSE CURRENT SENSE AMP F/F R Q S LX L1 VOUT C4*
1.23V BANDGAP
PWM COMPARATOR
REF C6 0.01F SS C1 0.1F SS CLAMP 1M 35%
OSC
D1 1N5817
UNDERVOLTAGE LOCKOUT
VUVLO
GND
* SEE TABLE 3 FOR COMPONENT VALUES AND SUPPLIERS.
Figure 1. Detailed Block Diagram with External Components
Overcurrent Limiting
The overcurrent comparator triggers when the load current exceeds approximately 1.5A. On each clock cycle, the output FET turns on and attempts to deliver current until cycle-by-cycle or overcurrent limits are exceeded. Note that the soft-start capacitor must be greater than 0.01F for overcurrent protection to function properly. A typical value is 0.1F. A soft-start cycle is initiated when the overcurrent comparator is triggered.
undervoltage condition is detected, control logic turns off the output power FET and discharges the soft-start capacitor to ground. This prevents partial turn-on of the power MOSFET and avoids excessive power dissipation. The control logic holds the output power FET off until the supply voltage rises above approximately 3.75V, at which time a soft-start cycle begins.
Shutdown Mode
The MAX750A/MAX758A are shut down by keeping SHDN at ground. In shutdown mode, the output power FET is held off and the output drops to 0V. The internal reference also turns off, which causes the soft-start capacitor to discharge. The 6A typical standby current includes external-component leakage currents. As temperature increases past +85C, the external capaci-
Undervoltage Lockout
The undervoltage lockout feature monitors the supply voltage at V+ and allows operation to start when V+ rises above 3.75V. When V+ falls, operation continues until the supply voltage falls below 3.50V. When an
8
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Adjustable, Step-Down, Current-Mode PWM Regulators
Oscillator
FROM SHDN
MAX750A/MAX758A
The internal oscillator of the MAX750A typically operates at 170kHz (160kHz for the MAX758A). The Typical Operating Characteristics indicate stability of the oscillator frequency over temperature and supply voltage.
MAX750A MAX758A
SS CLAMP
__________Applications Information
Figure 3 shows the MAX750A/MAX758A configured for a standard 5V step-down application. Table 2 lists the components for the desired operating temperature range. These circuits are useful in systems that require high current at high efficiency and are powered by an unregulated supply, such as a battery or wall-plug AC-DC transformer. They will operate over the entire line, load, and temperature ranges using the single set of component values shown in Figure 3 and listed in Table 2.
R1 510k
SS 1M 35% C1 1.23V
Inductor Selection
The MAX750A/MAX758A require no inductor design because they are tested in-circuit, and are guaranteed to deliver the power specified in the Electrical Characteristics with high efficiency using a single 100H (MAX75_AC) or 33H (MAX75_AE/AM) inductor The inductor's incremental saturation-current rating should be greater than 1A, and its DC resistance should be less than 0.8. Table 2 lists inductor types and suppliers for various applications. The surfacemount inductors and the larger-size through-hole inductors have nearly equivalent efficiencies.
Figure 2. Block Diagram of Soft-Start Circuitry
tors' leakage currents rises sharply. The actual design limit for standby current is much less than the 100A specified in the Electrical Characteristics (see the Standby Current vs. Temperature graph in the Typical Operating Characteristics). However, testing to tighter limits is prohibitive because the current takes several seconds to settle to a final value. For normal operation, connect SHDN to V+. Coming out of shutdown mode initiates a soft-start cycle.
Adjusting the Output Voltage
The MAX750A/MAX758A have outputs adjustable from 1.25V to the input voltage. To set the output voltage, connect a voltage divider to the feedback input pin (CC) as shown in Figure 3. The output voltage is set by R2 and R3 as follows: Let R3 be any resistance in the 10k to 20k range (typically 10k), then R2 = R3 [((VOUT/1.22V) - 1)] Output tolerance over temperature is 4.5% plus external resistor tolerances.
Continuous-/DiscontinuousConduction Modes
The input voltage, output voltage, load current, and inductor value determine whether the IC operates in continuous or discontinuous mode. As the inductor value or load current decreases, or the input voltage increases, the MAX750A/MAX758A tend to operate in discontinuous-conduction mode (DCM). In DCM, the inductor-current slope is steep enough so it decays to zero before the end of the transistor off-time. In continuous-conduction mode (CCM), the inductor current never decays to zero, which is typically more efficient than DCM. CCM allows the MAX750A/MAX758A to deliver maximum load current, and is also slightly less noisy than DCM because the ripple current in the output capacitor is smaller.
Output Filter Capacitor Selection
The primary criterion for selecting the output filter capacitor is low equivalent series resistance (ESR). The product of the inductor-current variation and the ESR of the output capacitor determines the amplitude of the sawtooth ripple seen on the output voltage. In addition, the ESR of the output filter capacitor should be minimized to maintain AC stability. The ESR of the capacitor should be less than 0.25 to keep the output ripple less than 50mVp-p over the entire current range (using a 100H inductor). Capacitor ESR ususally rises
9
Internal Reference
The +1.23V bandgap reference supplies up to 100A at REF. Connect a 0.01F bypass capacitor from REF to GND.
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Adjustable, Step-Down, Current-Mode PWM Regulators MAX750A/MAX758A
Table 1. Typical Soft-Start Times
MAX750A CIRCUIT CONDITIONS R1 (k) 510 510 510 510 510 510 510 None None None None None None V+ (V) 6 9 11 9 9 9 9 6 9 11 9 9 9 IOUT (mA) 0 0 0 150 300 150 150 0 0 0 150 150 150 C4 (F) 100 100 100 100 100 390 680 100 100 100 100 390 680 C1 = 0.01 2 1 1 1 1 3 4 16 10 8 34 39 40 SOFT-START TIME (ms) vs. C1 (F) C1 = 0.047 6 4 2 4 5 6 6 34 22 18 134 147 152 C1 = 0.1 11 6 4 8 9 9 9 51 34 28 270 280 285 C1 = 0.47 28 15 11 21 27 23 24 125 82 66 1263 1275 1280
MAX750A CIRCUIT CONDITIONS R1 (k) 510 510 510 510 510 None None None None V+ (V) 7 12 16 12 12 7 12 16 12 IOUT (mA) 0 0 0 300 750 0 0 0 300 C4 (F) 100 100 100 100 100 100 100 100 100 C1 = 0.01 1 1 1 1 1 12 7 6 27
SOFT-START TIME (ms) vs. C1 (F) C1 = 0.047 4 2 1 3 5 27 16 13 112 C1 = 0.1 6 3 2 5 8 40 25 20 215 C1 = 0.47 18 8 6 3 21 100 54 68 1114
as the temperature falls, and excessive ESR is the most likely cause of trouble at temperatures below 0C. Sanyo OS-CON series through-hole and surface-mount tantalum capacitors exhibit low ESR at temperatures below 0C. Refer to Table 2 for recommended capacitor values and suggested capacitor suppliers.
provides the widest input voltage range and best transient characteristics. For low-current applications, the 510k resistor may be omitted (see the Maximum Output Current vs. Supply Voltage, R1 Removed graph in the Typical Operating Characteristics).
Printed Circuit Layouts
A good layout is essential for clean, stable operation. The layouts and component placement diagrams given in Figures 4-7 have been successfully tested over a wide range of operating conditions. The 1F bypass capacitor (C2) must be positioned as close to the V+
Other Components
The catch diode should be a Schottky or high-speed silicon rectifier with a peak current rating of about 1A for full-load (750mA) operation. The 1N5817 is a good choice. The 330pF outer-loop compensation capacitor
10
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Adjustable, Step-Down, Current-Mode PWM Regulators MAX750A/MAX758A
MAX750A: 4.0V TO 11.0V MAX758A: 4.0V TO 16.0V
C2 1F C3* 8 1 V+ SHDN LX 7 D1 IN5817 L1* R1 510k OUTPUT OPTIONAL LOWPASS OUTPUT FILTER L2 25F C7 2.2F FILTER OUTPUT
MAX750A MAX758A
I.C.
5 C5 330pF R2 40.2k
OUTPUT 5V C4*
3
SS GND REF 2
CC
4
C1 0.1F
6
C6 0.01F
R3 13.0k
PART MAX750A MAX758A
INPUT SUPPLY RANGE (V) 6.0 to 11.0 6.0 to 16.0 10.2 to 16.0
GUARANTEED OUTPUT CURRENT AT 5V OUTPUT (mA) 450 450 750
NOTE: PIN NUMBERS REFER TO 8-PIN PACKAGES.
* SEE TABLE 2 FOR EXTERNAL COMPONENT SUPPLIERS.
Figure 3. Standard Step-Down Circuit
and GND pins as possible. Also, place the output capacitor as close to the inductor and the GND pin as possible. The traces connecting the input and output filter capacitors and the catch diode must be short to minimize inductance and capacitance. For this reason, avoid using sockets, and solder the IC directly to the PC board. Use an uninterrupted ground plane if possible; otherwise, use a star ground connection.
Output-Ripple Filtering
A simple lowpass pi-filter (Figure 3) can be added to the output to reduce output ripple to about 5mVp-p. The cutoff frequency with the values shown is 21kHz. Since the filter inductor is in series with the circuit output, its resistance should be kept to a minimum so the voltage drop across it is not excessive.
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11
Adjustable, Step-Down, Current-Mode PWM Regulators MAX750A/MAX758A
Table 2. Component Values and Suppliers
ASSEMBLY METHOD MAX750AC/MAX758AC COMMERCIAL TEMPERATURE RANGE INDUCTORS L1 = 33H to 100H Sumida (708) 956-0666 CD54-101KC (MAX750AC) CD105-101KC (MAX758AC) Coiltronics (305) 781-8900 CTX100 series CAPACITORS C3 = 68F, 16V C4 = 100F, 6.3V Matsuo (714) 969-2491 267 series Sprague (603) 224-1961 595D/293D series MAX750AE/M, MAX758AE/M WIDE TEMPERATURE RANGE INDUCTORS L1 = 33H Sumida (708) 956-0666 CD54-33ON (MAX750AC) CD105-33ON (MAX758AE/M) Coiltronics (305) 781-8900 CTX50 series CAPACITORS C3 = 68F, 16V C4 = 100F, 6.3V Matsuo (714) 969-2491 267 series Sprague (603) 224-1961 595D/295D series C3 = 150F, 16V C4 = 220F, 10V C3 = 150F, 16V C4 = 150F, 16V or 390F, 6.3V Nichicon (708) 843-7500 PL series Low-ESR electrolytics Sanyo (619) 661-6322 OS-CON series Low-ESR organic semiconductor (Rated from -55C to +105C) Mallory (317) 273-0090 THF series C3 = 100F, 20V C4 = 220F, 10V (Rated from -55C to +125C)
Surface Mount
L1 = 33H to 100H Miniature ThroughHole Sumida (708) 956-0666 RCH654-101K (MAX750A) RCH895-101K (MAX758A)
L1 = 33H Sumida (708) 956-0666 RCH654-330M (MAX750A) RCH895-330M (MAX758A)
L1 = 100H Low-Cost ThroughHole Maxim MAXL001 100H iron-powder toroid Renco (516) 586-5566 RL1284-100
C3 = 150F, 16V C4 = 390F, 6.3V Maxim MAXC001 150F, low-ESR electrolytic United Chemicon (708) 843-7500
12
______________________________________________________________________________________
Adjustable, Step-Down, Current-Mode PWM Regulators MAX750A/MAX758A
Figure 4. DIP PC Layout, Through-Hole Component Placement Diagram (1x Scale)
Figure 5. DIP PC Layout, Component Side (1x Scale)
Figure 6. DIP PC Layout, Solder Side (1x Scale)
Figure 7. DIP PC Layout, Drill Guide (1x Scale)
______________________________________________________________________________________
13
Adjustable, Step-Down, Current-Mode PWM Regulators MAX750A/MAX758A
____Pin Configurations (continued)
TOP VIEW
V+ 1 SHDN 2 REF 3 N.C. 4 N.C. 5 N.C. 6 SS 7 CC 8
__Ordering Information (continued)
PART MAX758ACPA MAX758ACWE MAX758AC/D MAX758AEPA MAX758AEWE MAX758AMJA TEMP. RANGE 0C to +70C 0C to +70C 0C to +70C -40C to +85C -40C to +85C -55C to +125C PIN-PACKAGE 8 Plastic DIP 16 Wide SO Dice* 8 Plastic DIP 16 Wide SO 8 CERDIP**
16 V+ 15 V+ 14 LX
MAX758A
13 LX 12 LX 11 GND 10 GND 9 I.C.
* Contact factory for dice specifications. **Contact factory for availability and processing to MIL-STD-883.
Wide SO
___________________________________________________________Chip Topographies
MAX750A
SHDN V+
MAX758A
SHDN V+
REF
REF
LX 0.116" (2.946mm)
LX 0.131" (3.327mm)
SS GND
SS
CC 0.072" (1.828mm)
GND
CC 0.116" (2.946mm)
TRANSISTOR COUNT: 274 (MAX750A) 286 (MAX758A); SUBSTRATE CONNECTED TO V+.
14
______________________________________________________________________________________
Adjustable, Step-Down, Current-Mode PWM Regulators
________________________________________________________Package Information
D1
DIM A A1 A2 A3 B B1 C D D1 E E1 e eA eB L INCHES MAX MIN 0.200 - - 0.015 0.175 0.125 0.080 0.055 0.022 0.016 0.065 0.050 0.012 0.008 0.390 0.348 0.035 0.005 0.325 0.300 0.280 0.240 0.100 BSC 0.300 BSC 0.400 - 0.150 0.115 15 0 MILLIMETERS MIN MAX - 5.08 0.38 - 3.18 4.45 1.40 2.03 0.41 0.56 1.27 1.65 0.20 0.30 8.84 9.91 0.13 0.89 7.62 8.26 6.10 7.11 2.54 BSC 7.62 BSC - 10.16 2.92 3.81 0 15
21-324A
MAX750A/MAX758A
E D A3 A A2 E1
L
A1 e B
C B1 eA eB
8-PIN PLASTIC DUAL-IN-LINE PACKAGE
DIM A A1 B C D E e H h L
E
H
INCHES MAX MIN 0.069 0.053 0.010 0.004 0.019 0.014 0.010 0.007 0.197 0.189 0.157 0.150 0.050 BSC 0.244 0.228 0.020 0.010 0.050 0.016 8 0
MILLIMETERS MIN MAX 1.35 1.75 0.10 0.25 0.35 0.49 0.19 0.25 4.80 5.00 3.80 4.00 1.27 BSC 5.80 6.20 0.25 0.50 0.40 1.27 0 8
21-325A
D A e B
0.127mm 0.004in.
h x 45
A1
C
L
8-PIN PLASTIC SMALL-OUTLINE PACKAGE
______________________________________________________________________________________
15
Adjustable, Step-Down, Current-Mode PWM Regulators MAX750A/MAX758A
___________________________________________Package Information (continued)
DIM A A1 B C D E e H h L INCHES MAX MIN 0.104 0.093 0.012 0.004 0.019 0.014 0.013 0.009 0.413 0.398 0.299 0.291 0.050 BSC 0.419 0.394 0.030 0.010 0.050 0.016 8 0 MILLIMETERS MIN MAX 2.35 2.65 0.10 0.30 0.35 0.49 0.23 0.32 10.10 10.50 7.40 7.60 1.27 BSC 10.00 10.65 0.25 0.75 0.40 1.27 0 8
21-589B
E
H
D A e B
0.127mm 0.004in.
h x 45
A1
C
L
16-PIN PLASTIC SMALL-OUTLINE (WIDE) PACKAGE
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 (c) 1993 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.

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