MAX744ACPA Fast Delivery |IC PHOENIX CO.,LIMITED

MAX744ACPA ,5V, step-down, current-mode PWM DC-DC converter accept inputs between 65V and 16V and deliver 750mA. 159kHz to 212.5kHz guaranteed oscillator frequency limits.ELECTRICAL CHARACTERISTICS(Circuit of Figure 3, V+ = 9V for the MAX730A, V+ = 12V for the MAX738A/M ..
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MAX744ACPA
5V, step-down, current-mode PWM DC-DC converter accept inputs between 65V and 16V and deliver 750mA. 159kHz to 212.5kHz guaranteed oscillator frequency limits.
__________________General Description
The MAX730A/MAX738A/MAX744A are 5V-output
CMOS, step-down switching regulators. The MAX738A/
MAX744A accept inputs from 6V to 16V and deliver
750mA. The MAX744A guarantees 500mA load capa-
bility for inputs above 6V and has tighter oscillator fre-
quency limits for low-noise (radio) applications. The
MAX730A accepts inputs between 5.2V and 11V and
delivers 450mA for inputs above 6V. Typical efficien-
cies are 85% to 96%. Quiescent supply current is
1.7mA and only 6µA in shutdown.
Pulse-width modulation (PWM) current-mode control
provides precise output regulation and excellent tran-
sient responses. Output voltage accuracy is guaran-
teed to be ±5% over line, load, and temperature varia-
tions. Fixed-frequency switching 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.
The MAX730A/MAX738A/MAX744A also feature cycle-
by-cycle current limiting, overcurrent limiting, undervolt-
age lockout, and programmable soft-start protection.
___________________________Applications
Portable Instruments
Cellular Phones and Radios
Personal Communicators
Distributed Power Systems
Computer Peripherals
________________________________Features750mA Load Currents (MAX738A/MAX744A)High-Frequency, Current-Mode PWM159kHz to 212.5kHz Guaranteed Oscillator
Frequency Limits (MAX744A)85% to 96% Efficiencies1.7mA Quiescent Current6µA Shutdown Supply CurrentSingle Preselected Inductor Value,
No Component Design RequiredOvercurrent, Soft-Start, and Undervoltage
Lockout ProtectionCycle-by-Cycle Current Limiting8-Pin DIP/SO Packages (MAX730A)
_________________Ordering Information
Ordering Information continued at end of data sheet.
*Contact factory for dice specifications.
MAX730A/MAX738A/MAX744A, Step-Down,
Current-Mode PWM DC-DC Converters
_________________Pin Configurations
__________Typical Operating Circuit
19-0165; Rev 2; 1/96
MAX730A/MAX738A/MAX744A, Step-Down,
Current-Mode PWM DC-DC Converters
ABSOLUTE MAXIMUM RATINGS
ELECTRICAL CHARACTERISTICS
(Circuit of Figure 3, V+ = 9V for the MAX730A, V+ = 12V for the MAX738A/MAX744A, ILOAD= 0mA, TA= TMINto TMAX,
unless otherwise noted.)
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.
Pin Voltages
V+ (MAX730A)......................................................+12V, -0.3V
V+ (MAX738A/MAX744A).....................................+18V, -0.3V
LX (MAX730A).................................(V+ - 12V) to (V+ + 0.3V)
LX (MAX738A/MAX744A)................(V+ - 21V) to (V+ + 0.3V)
OUT.................................................................................±25V
SS, CC, SHDN.........................................-0.3V to (V+ + 0.3V)
Peak Switch Current (ILX)........................................................2A
Reference Current (IREF)...................................................2.5mA
Continuous 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:
MAX7_ _AC_ _....................................................0°C to +70°C
MAX7_ _AE_ _.................................................-40°C to +85°C
MAX7_ _AMJA..............................................-55°C to +125°C
Junction Temperatures:
MAX7_ _AC_ _/AE_ _...................................................+150°C
MAX7_ _AMJA.............................................................+175°C
Storage Temperature Range............................-65°C to +160°C
Lead Temperature (soldering, 10sec).............................+300°C
MAX730A/MAX738A/MAX744A, Step-Down,
Current-Mode PWM DC-DC Converters
Note 1: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.
ELECTRICAL CHARACTERISTICS (continued)
(Circuit of Figure 3, V+ = 9V for the MAX730A, V+ = 12V for the MAX738A/MAX744A, ILOAD= 0mA, TA= TMINto TMAX,
unless otherwise noted.)
OUTPUT CURRENT (mA)
EFFICIENCY (%)
MAX730A
EFFICIENCY vs. OUTPUT CURRENT
OUTPUT CURRENT (mA)
EFFICIENCY (%)
MAX738A
EFFICIENCY vs. OUTPUT CURRENT
QUIESCENT SUPPLY CURRENT (mA)
MAX738A/MAX744A
QUIESCENT SUPPLY CURRENT
vs. SUPPLY VOLTAGE
PEAK INDUCTOR CURRENT (mA)
MAX738A/MAX744A
PEAK INDUCTOR CURRENT
vs. OUTPUT CURRENT
MAX730A/MAX738A/MAX744A, Step-Down,
Current-Mode PWM DC-DC Converters
__________________________________________Typical Operating Characteristics
(Circuit of Figure 3, TA = +25°C, unless otherwise noted.)
STANDBY SUPPLY CURRENT (
STANDBY SUPPLY CURRENT
vs. TEMPERATURE
TEMPERATURE (°C)
QUIESCENT SUPPLY CURRENT (mA)
QUIESCENT SUPPLY CURRENT
vs. TEMPERATURE
SUPPLY VOLTAGE (V)
MAXIMUM OUTPUT CURRENT (mA)
MAXIMUM OUTPUT CURRENT vs.
SUPPLY VOLTAGE
SUPPLY VOLTAGE (V)
MAXIMUM OUTPUT CURRENT (mA)
MAXIMUM OUTPUT CURRENT vs.
SUPPLY VOLTAGE, NO R1
200
MAX730A/MAX738A/MAX744A, Step-Down,
Current-Mode PWM DC-DC Converters
____________________________Typical Operating Characteristics (continued)
(Circuit of Figure 3, TA = +25°C, unless otherwise noted.)81014
SUPPLY VOLTAGE (V)
OSCILLATOR FREQUENCY (kHz)
OSCILLATOR FREQUENCY vs.
SUPPLY VOLTAGE16220
TEMPERATURE (°C)
OSCILLATOR FREQUENCY (kHz)
MAX744A
OSCILLATOR FREQUENCY
vs. TEMPERATURE
TEMPERATURE (°C)
SUPPLY CURRENT (mA)
MAX738A
OSCILLATOR FREQUENCY
vs. TEMPERATURE
TEMPERATURE (°C)
OSCILLATOR FREQUENCY (kHz)
MAX730A
OSCILLATOR FREQUENCY
vs. TEMPERATURE
Note 3:Commercial temperature range external component values in Table 3.
Note 4:Wide temperature range external component values in Table 3.
Note 5:Standby and shutdown current includes all external component leakage currents. Capacitor leakage currents dominate at TA> +85°C,
Sanyo OS-CON capacitors were used.
Note 6:Operation beyond the specifications listed in the electrical characteristics may exceed the power dissipation ratings of the device.
MAX730A/MAX738A/MAX744A, Step-Down,
Current-Mode PWM DC-DC Converters
MAX738A/MAX744A
SWITCHING WAVEFORMS,
CONTINUOUS CONDITIONs/div
A: SWITCH VOLTAGE (LX PIN), 5V/div, 0V TO +12V
B: INDUCTOR CURRENT, 200mA/div
C: OUTPUT VOLTAGE RIPPLE, 50mV/div, AC-COUPLED
COUT= 390mF,
V+ = 12V, IOUT= 150mA,
MAX738A/MAX744A
SWITCHING WAVEFORMS,
DISCONTINUOUS CONDITIONs/div
A: SWITCH VOLTAGE (LX PIN), 5V/div, 0V TO +12V
B: INDUCTOR CURRENT, 200mA/div
C: OUTPUT VOLTAGE RIPPLE, 50mV/div, AC-COUPLED
COUT= 390mF,
V+ = 12V, IOUT= 150mA
12V
200mA
0mA
200mA
0mA
MAX730A LINE-TRANSIENT RESPONSE
100ms/div
A: VOUT, 50mV/div, DC-COUPLED
B: V+, 5V/div, 6.0V TO 11.0V
IOUT= 300mA
MAX738A/MAX744A LINE-TRANSIENT RESPONSE
100ms/div
A: VOUT, 50mV/div, DC-COUPLED
B: V+, 5V/div, 10.2V TO 16.0VOUT= 750mA
11V
16V
10.2V
____________________________Typical Operating Characteristics (continued)
(Circuit of Figure 3, TA = +25°C, unless otherwise noted.)
12V
MAX730A/MAX738A/MAX744A, Step-Down,
Current-Mode PWM DC-DC Converters
______________________________________________________________Pin Description
MAX730A
LOAD-TRANSIENT RESPONSE
50ms/div
A: VOUT, 50mV/div, DC-COUPLED
B: IOUT, 200mA/div, 20mA TO 300mA
V+ = 9V
MAX738A/MAX744A
LOAD-TRANSIENT RESPONSE
50ms/div
A: VOUT, 50mV/div, DC-COUPLED
B: IOUT, 500mA/div, 50mA TO 750mA
V+ = 12V
300mA
20mA
____________________________Typical Operating Characteristics (continued)
(Circuit of Figure 3, TA = +25°C, unless otherwise noted.)
750mA
50mA
MAX730A/MAX738A/MAX744A
_________________Detailed Description
The MAX730A/MAX738A/MAX744A switch-mode regu-
lators use a current-mode pulse-width-modulation
(PWM) control system coupled with a simple step-down
(buck) regulator topography. They convert an unregu-
lated DC voltage from 5.2V to 11V for the MAX730A,
and from 6V to 16V for the MAX738A/MAX744A. The
current-mode PWM architecture provides cycle-by-
cycle 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 cur-
rent-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 power transistor 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 con-
nected to the soft-start (SS) pin to ensure an orderly
power-up. Typical values are 0.1µF and 510kΩ. SS con-
trols both the SS 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 cur-
rent-limit threshold. The 510kΩresistor sets the SS
clamp at a value high enough to maintain regulation,
even at currents exceeding 1A. This resistor is not nec-
essary for lower-current loads. Refer to the Maximum
Output Current vs. Supply Voltage graph in the Typical
Operating Characteristics. Table 1 lists timing charac-
teristics for selected capacitor values and circuit condi-
tions.
The overcurrent comparator trips when the load
exceeds approximately 1.5A. An SS cycle begins when
either an undervoltage or overcurrent fault condition
triggers an internal transistor to momentarily discharge
the SS capacitor to ground. An SS cycle also begins at
power-up and when coming out of shutdown mode.
Overcurrent Limiting
The overcurrent comparator triggers when the load cur-
rent 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 SS capacitor must be greater than 0.01µF
for overcurrent protection to function properly. A typical
value is 0.1µF.
Undervoltage Lockout
The MAX738A/MAX744A’s undervoltage-lockout fea-
ture monitors the supply voltage at V+, and allows
operation to start when V+ rises above 5.7V (6V guar-
anteed). When V+ falls, operation continues until the
supply voltage falls below 5.45V (see the
MAX738A/MAX744A Quiescent Supply Current vs.
Supply Voltage graph in the Typical Operating
Characteristics). The MAX730A is similar, starting oper-
ation at V+ > 4.7V and continuing to operate down to
4.45V. When an undervoltage condition is detected,
control logic turns off the output power FET and dis-
charges the SS capacitor to ground. This prevents par-
tial 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 4.7V (MAX730A) or 5.7V (MAX738A/
MAX744A), at which time an SS cycle begins.
Shutdown Mode
The MAX730A/MAX738A/MAX744A are shut down by
keeping SHDNat ground. In shutdown mode, the output
drops to 0V and the output power FET is held in an off
state. The internal reference also turns off, which causes
the SS capacitor to discharge. Typical standby current in
shutdown mode is 6µA. The actual design limit for stand-
by current is much less than the 100µA specified in the
Electrical Characteristics(see Standby Current vs.
Temperature 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 SHDNto V+. Note that
coming out of shutdown mode initiates an SS cycle.
Continuous-/Discontinuous-
Conduction Modes
The input voltage, output voltage, load current, and induc-
tor value determine whether the IC operates in continuous
or discontinuous mode. As the inductor value or load cur-
rent decreases, or the input voltage increases, the
MAX730A/MAX738A/MAX744A tend to operate in discon-
tinuous-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-conduc-
tion mode (CCM), the inductor current never decays to
zero, which is typically more efficient than DCM. CCM
allows the MAX730A/ MAX738A/MAX744A to deliver maxi-
mum load current, and is also slightly less noisy than
DCM, because the peak-to-average inductor current ratio
is reduced., Step-Down,
Current-Mode PWM DC-DC Converters

Partno	Mfg	Dc	Qty	Available	Descript
MAX744ACPA	MAXIM ?	N/a	10	avai	5V, step-down, current-mode PWM DC-DC converter accept inputs between 65V and 16V and deliver 750mA. 159kHz to 212.5kHz guaranteed oscillator frequency limits.