Maxim MAX750ACPA Adjustable, step-down, current-mode pwm regulator Datasheet

19-0195; Rev 0; 10/93
Adjustable, Step-Down,
Current-Mode PWM Regulators
________________________Applications
Cellular Phones & Radios
Portable Communications Equipment
Portable Instruments
____________________________Features
♦
♦
♦
♦
♦
♦
♦
♦
♦
♦
Up to 750mA Load Currents
160kHz High-Frequency, Current-Mode PWM
85% to 96% Efficiencies
33µH or 100µH Pre-Selected Inductor Value,
No Component Design Required
1.7mA Quiescent Supply Current
6µA Shutdown Supply Current
Adjustable Output Voltage
Overcurrent, Soft-Start, and Undervoltage
Lockout Protection
Cycle-by-Cycle Current Limiting
8-Pin DIP/SO Packages (MAX750A)
______________Ordering Information
PART
TEMP. RANGE
MAX750ACPA
0°C to +70°C
8 Plastic DIP
PIN-PACKAGE
MAX750ACSA
MAX750AC/D
MAX750AEPA
MAX750AESA
0°C to +70°C
0°C to +70°C
-40°C to +85°C
-40°C to +85°C
8 SO
Dice*
8 Plastic DIP
8 SO
MAX750AMJA
-55°C to +125°C
8 CERDIP**
Ordering Information continued on last page.
* Contact factory for dice specifications.
**Contact factory for availability and processing to MIL-STD-883.
Computer Peripherals
_________________Pin Configurations
__________Typical Operating Circuit
INPUT
4V TO 16V
TOP VIEW
SHDN
1
8
V+
REF
2
7
LX
6
GND
5
I.C.
SS 3
MAX750A
MAX758A
CC 4
V+
LX
MAX750A
MAX758A
DIP
ON/OFF
SHDN
1
REF
2
SS 3
MAX750A
CC 4
33µH
OUTPUT ADJ.
FROM
VREF TO V+
8
V+
7
LX
6
GND
5
I.C.
SHDN
CC
REF
SS
GND
SO
Pin Configurations continued on last page.
________________________________________________________________ Maxim Integrated Products
Call toll free 1-800-998-8800 for free samples or literature.
1
MAX750A/MAX758A
_______________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
6µA 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.
MAX750A/MAX758A
Adjustable, Step-Down,
Current-Mode PWM Regulators
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 = +70°C)
8-Pin Plastic DIP (derate 9.09mW/°C above +70°C) .....727mW
8-Pin SO (derate 5.88mW/°C above +70°C)..................471mW
16-Pin Wide SO (derate 9.52mW/°C above +70°C) ......762mW
8-Pin CERDIP (derate 8.00mW/°C above +70°C)..........640mW
Operating Temperature Ranges:
MAX75_AC_ _ .......................................................0°C to +70°C
MAX75_AE_ _ ....................................................-40°C to +85°C
MAX75_AMJA ..................................................-55°C to +125°C
Junction Temperatures:
MAX75_AC_ _/AE_ _ ......................................................+150°C
MAX75_AMJA ................................................................+175°C
Storage Temperature Range .............................-65°C to +160°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
(Circuit of Figure 3, V+ = 9V for the MAX750A, V+ = 12V for the MAX758A, VOUT = 5V, R2 = 40.20kΩ, R3 = 13.0kΩ, ILOAD = 0mA,
TA = TMIN to TMAX, unless otherwise noted.)
MIN
MAX758A
TYP
MAX
V+ = 6.0V to 16.0V;
0mA < ILOAD < 450mA for MAX758AC/AE,
0mA < ILOAD < 350mA for MAX758AM
4.75
5.00
5.25
V+ = 10.2V to 16.0V,
0mA < ILOAD < 750mA
4.75
5.00
5.25
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)
Input Voltage Range
Line Regulation
Load Regulation
Efficiency
MIN
MAX750A
TYP
MAX
4.75
5.00
5.25
4.0
V+ = 4.0V to 11.0V
Shutdown Input
Threshold
ILOAD = 0mA to 450mA
92
2
90
V+ = 12V, ILOAD = 750mA
%
87
SHDN = 0V
1.7
3.0
6.0
100.0
2.0
1.7
3.0
mA
6.0
100.0
µA
2.0
VIL
0.25
0.25
1.0
1.5
V
%/mA
0.0005
V+ = 9.0V, ILOAD = 300mA
V
%/V
0.0005
ILOAD = 0mA to 750mA
VIH
16.0
0.15
Shutdown Input
Leakage Current
Short-Circuit Current
4.0
V+ = 4.0V to 16.0V
Supply Current
Shutdown Supply
Current (Note 2)
11.0
0.15
UNITS
1.0
1.5
_______________________________________________________________________________________
V
µA
A
Adjustable, Step-Down,
Current-Mode PWM Regulators
(Circuit of Figure 3, V+ = 9V for the MAX750A, V+ = 12V for the MAX758A, VOUT = 5V, R2 = 40.20kΩ, R3 = 13.0kΩ, ILOAD = 0mA,
TA = TMIN to TMAX, unless otherwise noted.)
CONDITIONS
PARAMETER
MIN
MAX750A
TYP
MAX
4.00
MIN
MAX758A
TYP
MAX
3.75
4.00
UNITS
Undervoltage
Lockout
V+ rising
3.75
V+ falling
3.5
3.5
LX On Resistance
ILX = 500mA
0.5
0.5
Ω
1.0
1.0
µA
LX Leakage Current
Reference Voltage
TA = +25°C
1.15
1.22
Reference Drift
1.30
1.15
50
Oscillator Frequency
130
Compensation Pin
Impedance
1.22
1.30
50
170
210
130
7500
V
V
ppm/°C
160
190
kHz
Ω
7500
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 25µA (over temperature) within 2 seconds; however, to decrease test time, the part
is guaranteed at a 100µA maximum value.
__________________________________________Typical Operating Characteristics
(Circuit of Figure 3, VOUT = 5V, TA = +25°C, unless otherwise noted.)
(NOTES 3, 6)
100
MAX750A/58A-1
100
MAX758A
EFFICIENCY vs. OUTPUT CURRENT
(NOTES 3, 6)
90
EFFICIENCY (%)
EFFICIENCY (%)
90
MAX750A/58A-2
MAX750A
EFFICIENCY vs. OUTPUT CURRENT
V+ = 5.5V
80
V+ = 7V
V+ = 9V
70
80
V+ = 6V
V+ = 8V
V+ = 12V
70
V+ = 11V
V+ = 16V
60
60
0
200
400
600
800
OUTPUT CURRENT (mA)
1000
0
200
400
600
800
1000
OUTPUT CURRENT (mA)
_______________________________________________________________________________________
3
MAX750A/MAX758A
ELECTRICAL CHARACTERISTICS (continued)
_____________________________Typical Operating Characteristics (continued)
(Circuit of Figure 3, VOUT = 5V, TA = +25°C, unless otherwise noted.)
MAX758A
PEAK INDUCTOR CURRENT
vs. OUTPUT CURRENT
600
V+ 8.0V TO 16.0V
400
V+ = 6.6V
200
600
500
400
300
V+ = 10.2V
V+ = 8.0V
V+ = 6.6V
V+ = 6.0V
200
100
220
(NOTE 3)
0
100 200 300 400 500 600 700 800
2.5
UNDERVOLTAGE
LOCKOUT V+ FALLING
(OPERATION ENDS)
1.0
UNDERVOLTAGE
LOCKOUT V+ RISING
(OPERATION BEGINS)
2
4
6
8
12
10
150
200
250
14
16
2.5
2.0
1.5
1.0
0.5
10
12
20
18
(NOTES 4, 5)
16
14
12
10
MAX758A ONLY, V+ = 16V
MAX758A ONLY, V+ = 12V
V+ = 9V
V+ = 6V
8
6
4
2
MAX758A
OSCILLATOR FREQUENCY vs. TEMPERATURE
200
(NOTE 4)
160
V+ = 7.0V
V+ = 9.0V
(NOTE 4)
190
V+ = 6.0V
180
V+ = 16.0V
170
160
150
V+ = 12.0V
140
V+ = 9.0V
130
0
20 40 60 80 100 120 140
TEMPERATURE (°C)
4
16
TEMPERATURE (°C)
V+ = 5.5V
0
-60 -40 -20
14
TEMPERATURE (°C)
OSCILLATOR FREQUENCY (kHz)
OSCILLATOR FREQUENCY (kHz)
8
0
-60 -40 -20 0 20 40 60 80 100 120 140
180
140
6
0
-60 -40 -20 0 20 40 60 80 100 120 140
240
200
4
300
MAX750A, V+ = 9.0V
MAX758A, V+ = 12.0V
MAX750A
OSCILLATOR FREQUENCY vs. TEMPERATURE
220
MAX758A
160
SHUTDOWN SUPPLY CURRENT
vs. TEMPERATURE
(NOTES 4, 5)
SUPPLY VOLTAGE (V)
V+ = 11.0V
170
SUPPLY VOLTAGE (V)
2.0
0
0
MAX750A
180
SHUTDOWN SUPPLY CURRENT (µA)
(NOTES 3, 5)
NO-LOAD SUPPLY CURRENT (mA)
MAX1750A/58A-7
3.0
0.5
190
NO-LOAD SUPPLY CURRENT
vs. TEMPERATURE
MAX758A
NO-LOAD SUPPLY CURRENT vs. SUPPLY VOLTAGE
1.5
200
OUTPUT CURRENT (mA)
OUTPUT CURRENT (mA)
2.0
100
50
MAX750A/58A-8
0
210
150
0
0
MAX1750A/58A-6
L1 = 18µH
C4 = 1000µF
MAX750A/58A-9
800
700
MAX1750A/58A-5
L1 = 100µH
C4 = 300µF
PEAK INDUCTOR CURRENT (mA)
MAX1750A/58A-4
PEAK INDUCTOR CURRENT (mA)
1000
OSCILLATOR FREQUENCY
vs. SUPPLY VOLTAGE
OSCILLATOR FREQUENCY (kHz)
MAX758A
PEAK INDUCTOR CURRENT
vs. OUTPUT CURRENT
NO-LOAD SUPPLY CURRENT (mA)
MAX750A/MAX758A
Adjustable, Step-Down,
Current-Mode PWM Regulators
120
-60 -40 -20
0
20 40 60 80 100 120 140
TEMPERATURE (°C)
_______________________________________________________________________________________
Adjustable, Step-Down,
Current-Mode PWM Regulators
MAXIMUM OUTPUT CURRENT
vs. SUPPLY VOLTAGE, R1 OMITTED
MAXIMUM OUTPUT CURRENT
vs. SUPPLY VOLTAGE
MAX758A
1200
MAX750A
1000
MAX750A/58A-11
MAX750A/58A-10
MAXIMUM OUTPUT CURRENT (mA)
(NOTES 3, 6)
MAXIMUM OUTPUT CURRENT (mA)
1400
1400
(NOTES 3, 6)
1200
MAX758A
1000
800
600
MAX750A
400
200
800
4
6
8
10
12
14
16
4
6
8
10
12
14
16
SUPPLY VOLTAGE (V)
SUPPLY VOLTAGE (V)
MAX758A
SWITCHING WAVEFORMS
DISCONTINUOUS CONDUCTION
MAX758A
SWITCHING WAVEFORMS
CONTINUOUS CONDUCTION
12V
12V
A
A
0V
0V
200mA
100mA
B
0mA
0mA
5V
2µs/div
5V
C
B
C
2µs/div
A: SWITCH VOLTAGE (LX PIN), 5V/div, 0V TO +12V
B: INDUCTOR CURRENT, 200mA/div
C: OUTPUT VOLTAGE RIPPLE, 50mV/div
A: SWITCH VOLTAGE (LX PIN), 5V/div, 0V TO +12V
B: INDUCTOR CURRENT, 100mA/div
C: OUTPUT VOLTAGE RIPPLE, 50mV/div
COUT = 390µF, V+ = 12V, IOUT = 150mA
COUT = 390µF, V+ = 12V, IOUT = 20mA
_______________________________________________________________________________________
5
MAX750A/MAX758A
_____________________________Typical Operating Characteristics (continued)
(Circuit of Figure 3, VOUT = 5V, TA = +25°C, unless otherwise noted.)
MAX750A/MAX758A
Adjustable, Step-Down,
Current-Mode PWM Regulators
_____________________________Typical Operating Characteristics (continued)
(Circuit of Figure 3, VOUT = 5V, TA = +25°C, unless otherwise noted.)
MAX750A
LINE-TRANSIENT RESPONSE
MAX758A
LINE-TRANSIENT RESPONSE
A
A
16V
10.2V
11V
6V
B
0V
B
0V
100ms/div
100ms/div
A: VOUT, 50mV/div, AC-COUPLED
B: V+, 5V/div, 6.0V TO 11.0V
A: VOUT, 50mV/div, AC-COUPLED
B: V+, 5V/div, 10.2V TO 16.0V
IOUT = 300mA
IOUT = 750mA
MAX750A
LOAD-TRANSIENT RESPONSE
MAX758A
LOAD-TRANSIENT RESPONSE
A
A
750mA
300mA
B
B
50mA
20mA
50ms/div
50ms/div
A: VOUT, 50mV/div, AC-COUPLED
B: IOUT, 200mA/div, 20mA TO 300mA
A: VOUT, 50mV/div, AC-COUPLED
B: IOUT, 500mA/div, 50mA TO 750mA
V+ = 9V
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 TA > +85°C.
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
8-PIN
DIP/SO
16-PIN
WIDE SO
NAME
1
2
SHDN
2
3
REF
Reference Voltage Output (+1.22V) supplies up to 100µA for external loads. Bypass to
GND with a capacitor that does not exceed 0.047µF.
3
7
SS
Soft-Start. Capacitor between SS and GND provides soft-start and short-circuit protection. 510kΩ resistor from SS to SHDN provides current boost.
4
8
CC
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.
FUNCTION
Shutdown—active low. Ground to power-down chip, tie to V+ for normal operation.
Output voltage falls to 0V when SHDN is low.
5
9
I.C.
6
10, 11
GND
7
12, 13, 14
LX
Drain of internal P-channel power MOSFET*
8
1, 15, 16
V+
Supply Voltage Input. Bypass to GND with 1.0µF ceramic and large-value electrolytic capacitors in parallel. The 1µF capacitor must be as close to the V+ and GND pins are possible.*
–
4, 5, 6
N.C.
Ground*
No Connect—not internally connected.
*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 0.1µF and 510kΩ. 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 510kΩ 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
MAX750A/MAX758A
______________________________________________________________Pin Description
MAX750A/MAX758A
Adjustable, Step-Down,
Current-Mode PWM Regulators
V IN
V+
SHDN
C2
1µF
C3*
OVERCURRENT COMPARATOR
BIAS
GEN
SLOPE COMPENSATION
Σ
MAX750A
MAX758A
C5
330pF
RAMP
GEN
RSENSE
CURRENT
SENSE AMP
R2
ERROR
AMP
CC
R1
510K
R3
F/F
R
PWM
COMPARATOR
1.23V
BANDGAP
REF
C6
0.01µF
LX
L1
D1
1N5817
OSC
VOUT
C4*
1M
±35%
SS
C1
0.1µF
Q
S
UNDERVOLTAGE
LOCKOUT
SS CLAMP
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 0.01µF for overcurrent protection to function properly. A typical value is 0.1µF. A soft-start
cycle is initiated when the overcurrent comparator is
triggered.
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
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 6µA typical standby current includes external-component leakage currents. As
temperature increases past +85°C, the external capaci-
_______________________________________________________________________________________
Adjustable, Step-Down,
Current-Mode PWM Regulators
FROM SHDN
MAX750A
MAX758A
R1
510k
SS CLAMP
SS
1M
±35%
C1
1.23V
__________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.
Inductor Selection
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 100µA
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.
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.
Internal Reference
The +1.23V bandgap reference supplies up to 100µA
at REF. Connect a 0.01µF bypass capacitor from REF
to GND.
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
100µH (MAX75_AC) or 33µH (MAX75_AE/AM) inductor
The inductor’s incremental saturation-current rating
should be greater than 1A, and its DC resistance
should be less than 0.8Ω. Table 2 lists inductor types
and suppliers for various applications. The surfacemount inductors and the larger-size through-hole
inductors have nearly equivalent efficiencies.
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 10kΩ to 20kΩ range
(typically 10kΩ), then
R2 = R3 [((VOUT/1.22V) - 1)]
Output tolerance over temperature is ±4.5% plus external resistor tolerances.
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 0.25Ω to keep the output
ripple less than 50mVp-p over the entire current range
(using a 100µH inductor). Capacitor ESR ususally rises
_______________________________________________________________________________________
9
MAX750A/MAX758A
Oscillator
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
Adjustable, Step-Down,
Current-Mode PWM Regulators
Table 1. Typical Soft-Start Times
MAX750A CIRCUIT CONDITIONS
SOFT-START TIME (ms) vs. C1 (µF)
R1 (kΩ)
V+ (V)
IOUT (mA)
C4 (µF)
C1 = 0.01
C1 = 0.047
C1 = 0.1
C1 = 0.47
510
6
0
100
2
6
11
28
510
9
0
100
1
4
6
15
510
11
0
100
1
2
4
11
510
9
150
100
1
4
8
21
510
9
300
100
1
5
9
27
510
9
150
390
3
6
9
23
510
9
150
680
4
6
9
24
None
6
0
100
16
34
51
125
None
9
0
100
10
22
34
82
None
11
0
100
8
18
28
66
None
9
150
100
34
134
270
1263
None
9
150
390
39
147
280
1275
None
9
150
680
40
152
285
1280
MAX750A CIRCUIT CONDITIONS
SOFT-START TIME (ms) vs. C1 (µF)
R1 (kΩ)
V+ (V)
IOUT (mA)
C4 (µF)
C1 = 0.01
C1 = 0.047
C1 = 0.1
C1 = 0.47
510
7
0
100
1
4
6
18
510
12
0
100
1
2
3
8
510
16
0
100
1
1
2
6
510
12
300
100
1
3
5
3
510
12
750
100
1
5
8
21
None
7
0
100
12
27
40
100
None
12
0
100
7
16
25
54
None
16
0
100
6
13
20
68
None
12
300
100
27
112
215
1114
as the temperature falls, and excessive ESR is the most
likely cause of trouble at temperatures below 0°C.
Sanyo OS-CON series through-hole and surface-mount
tantalum capacitors exhibit low ESR at temperatures
below 0°C. 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
510kΩ resistor may be omitted (see the Maximum
Output Current vs. Supply Voltage, R1 Removed graph
in the Typical Operating Characteristics).
Other Components
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 1µF bypass
capacitor (C2) must be positioned as close to the V+
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
Printed Circuit Layouts
______________________________________________________________________________________
Adjustable, Step-Down,
Current-Mode PWM Regulators
MAX750A/MAX758A
MAX750A: 4.0V TO 11.0V
MAX758A: 4.0V TO 16.0V
C2
1µF
C3*
OPTIONAL LOWPASS OUTPUT FILTER
8
1
V+
SHDN
LX
7
OUTPUT
D1
IN5817
L1*
MAX750A
MAX758A
R1
510k
3
C1
0.1µF
I.C.
5
CC
GND
REF
6
2
FILTER
OUTPUT
C7
2.2µF
OUTPUT
5V
C5
330pF
SS
L2
25µF
R2
40.2k
C4*
4
R3
13.0k
C6
0.01µF
PART
INPUT SUPPLY RANGE
(V)
GUARANTEED OUTPUT CURRENT AT 5V OUTPUT
(mA)
MAX750A
6.0 to 11.0
450
6.0 to 16.0
450
10.2 to 16.0
750
MAX758A
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.
______________________________________________________________________________________
11
MAX750A/MAX758A
Adjustable, Step-Down,
Current-Mode PWM Regulators
Table 2. Component Values and Suppliers
ASSEMBLY
METHOD
MAX750AC/MAX758AC
COMMERCIAL TEMPERATURE RANGE
INDUCTORS
L1 = 33µH to 100µH
Surface
Mount
Sumida (708) 956-0666
CD54-101KC (MAX750AC)
CD105-101KC
(MAX758AC)
Coiltronics (305) 781-8900
CTX100 series
CAPACITORS
C3 = 68µF, 16V
C4 = 100µF, 6.3V
Matsuo (714) 969-2491
267 series
Sprague (603) 224-1961
595D/293D series
MAX750AE/M, MAX758AE/M
WIDE TEMPERATURE RANGE
INDUCTORS
L1 = 33µH
Sumida (708) 956-0666
CD54-33ON (MAX750AC)
CD105-33ON
(MAX758AE/M)
Coiltronics (305) 781-8900
CTX50 series
CAPACITORS
C3 = 68µF, 16V
C4 = 100µF, 6.3V
Matsuo (714) 969-2491
267 series
Sprague (603) 224-1961
595D/295D series
C3 = 150µF, 16V
C4 = 220µF, 10V
L1 = 33µH to 100µH
Miniature
ThroughHole
Sumida (708) 956-0666
RCH654-101K (MAX750A)
RCH895-101K (MAX758A)
L1 = 100µH
Low-Cost
ThroughHole
Maxim
MAXL001
100µH iron-powder toroid
Renco (516) 586-5566
RL1284-100
12
C3 = 150µF, 16V
C4 = 150µF, 16V or
390µF, 6.3V
Nichicon (708) 843-7500
PL series
Low-ESR electrolytics
L1 = 33µH
Sumida (708) 956-0666
RCH654-330M (MAX750A)
RCH895-330M (MAX758A)
Sanyo (619) 661-6322
OS-CON series
Low-ESR organic
semiconductor
(Rated from -55°C to +105°C)
Mallory (317) 273-0090
THF series
C3 = 100µF, 20V
C4 = 220µF, 10V
(Rated from -55°C to +125°C)
C3 = 150µF, 16V
C4 = 390µF, 6.3V
Maxim
MAXC001
150µF, low-ESR
electrolytic
United Chemicon
(708) 843-7500
______________________________________________________________________________________
Adjustable, Step-Down,
Current-Mode PWM Regulators
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)
______________________________________________________________________________________
MAX750A/MAX758A
Figure 4. DIP PC Layout, Through-Hole Component Placement
Diagram (1x Scale)
13
MAX750A/MAX758A
Adjustable, Step-Down,
Current-Mode PWM Regulators
____Pin Configurations (continued)
__Ordering Information (continued)
TOP VIEW
V+ 1
16 V+
SHDN 2
15 V+
REF 3
N.C. 4
14 LX
MAX758A
13 LX
N.C. 5
12 LX
N.C. 6
11 GND
SS 7
10 GND
CC 8
9
PART
TEMP. RANGE
MAX758ACPA
0°C to +70°C
8 Plastic DIP
PIN-PACKAGE
MAX758ACWE
MAX758AC/D
MAX758AEPA
MAX758AEWE
0°C to +70°C
0°C to +70°C
-40°C to +85°C
-40°C to +85°C
16 Wide SO
Dice*
8 Plastic DIP
16 Wide SO
MAX758AMJA
-55°C to +125°C
8 CERDIP**
* Contact factory for dice specifications.
**Contact factory for availability and processing to MIL-STD-883.
I.C.
Wide SO
___________________________________________________________Chip Topographies
MAX758A
MAX750A
SHDN
SHDN
V+
V+
REF
REF
LX
LX
0.116"
(2.946mm)
0.131"
(3.327mm)
SS
GND
GND
SS
CC
0.072"
(1.828mm)
CC
0.116"
(2.946mm)
TRANSISTOR COUNT: 274 (MAX750A)
286 (MAX758A);
SUBSTRATE CONNECTED TO V+.
14
______________________________________________________________________________________
Adjustable, Step-Down,
Current-Mode PWM Regulators
DIM
D1
A
A1
A2
A3
B
B1
C
D
D1
E
E1
e
eA
eB
L
α
E
E1
D
A3
A
A2
L
A1
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
α
8-PIN PLASTIC
DUAL-IN-LINE
PACKAGE
C
e
B1
eA
B
eB
DIM
E
A
A1
B
C
D
E
e
H
h
L
α
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
h x 45˚
D
α
A
0.127mm
0.004in.
e
A1
C
L
8-PIN PLASTIC
SMALL-OUTLINE
PACKAGE
B
______________________________________________________________________________________
15
MAX750A/MAX758A
________________________________________________________Package Information
MAX750A/MAX758A
Adjustable, Step-Down,
Current-Mode PWM Regulators
___________________________________________Package Information (continued)
DIM
E
A
A1
B
C
D
E
e
H
h
L
α
H
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
h x 45˚
D
α
A
0.127mm
0.004in.
e
B
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
© 1993 Maxim Integrated Products
Printed USA
is a registered trademark of Maxim Integrated Products.