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MAX748ACPAMAXIMN/a228avai3.3V, Step-Down, Current-Mode PWM DC-DC Converters
MAX748ACPAMAXIM ?N/a123avai3.3V, Step-Down, Current-Mode PWM DC-DC Converters
MAX748ACWEMAXN/a6avai3.3V, Step-Down, Current-Mode PWM DC-DC Converters
MAX748AEPAMAXIM ?N/a8avai3.3V, Step-Down, Current-Mode PWM DC-DC Converters
MAX748AEWEMAXIMN/a4avai3.3V, Step-Down, Current-Mode PWM DC-DC Converters


MAX748ACPA ,3.3V, Step-Down, Current-Mode PWM DC-DC ConvertersGeneral Description ____________
MAX748ACPA ,3.3V, Step-Down, Current-Mode PWM DC-DC ConvertersFeaturesThe MAX748A/MAX763A are 3.3V-output CMOS, step- ' Up to 500mA Load Currentsdown switching r ..
MAX748ACPA+ ,3.3V, Step-Down, Current-Mode PWM DC-DC ConvertersFeaturesThe MAX748A/MAX763A are 3.3V-output CMOS, step- ♦ Up to 500mA Load Currentsdown switching r ..
MAX748ACWE ,3.3V, Step-Down, Current-Mode PWM DC-DC ConvertersMAX748A/MAX763A19-0190; Rev 0; 9/933.3V, Step-Down,Current-Mode PWM DC-DC Converters_______________ ..
MAX748AEPA ,3.3V, Step-Down, Current-Mode PWM DC-DC ConvertersELECTRICAL CHARACTERISTICS(Circuit of Figure 3, V+ = 5V, I = 0mA, T = T to T , unless otherwise not ..
MAX748AEWE ,3.3V, Step-Down, Current-Mode PWM DC-DC ConvertersApplicationsMAX748AC/D 0°C to +70°C Dice*5V-to-3.3V ConvertersMAX748AEPA -40°C to +85°C 8 Plastic D ..
MB6M ,MINIATURE GLASS PASSIVATED SINGLE-PHASE BRIDGE RECTIFIERThermal Characteristics (TA = 25°C unless otherwise noted)Parameter Symbol MB2M MB4M MB6M UnitDevic ..
MB6S ,Bridge RectifiersThermal Characteristics (T = 25°C unless otherwise noted)AParameter Symbol MB2S MB4S MB6S UnitDevic ..
MB7117E , Schottky TTL 2048-Bit Bipolar Programmable Read-Only Memory
MB71A38-25 , PROGRAMMABLE SCHOTTKY 16384-BIT READ ONLY MEMORY


MAX748ACPA-MAX748ACWE-MAX748AEPA-MAX748AEWE
3.3V, Step-Down, Current-Mode PWM DC-DC Converters
__________________General Description
The MAX748A/MAX763A are 3.3V-output CMOS, step-
down switching regulators. The MAX748A accepts
inputs from 3.3V to 16V and delivers up to 500mA. The
MAX763A accepts inputs between 3.3V and 11V and
delivers up to 500mA. Typical efficiencies are 85% to
90%. Quiescent supply current is 1.4mA (MAX763A),
and only 0.2µA in shutdown.
Pulse-width-modulation (PWM) current-mode control pro-
vides precise output regulation and excellent transient
responses. Output voltage accuracy is guaranteed to be
±5% over line, load, and temperature variations.
Fixed-frequency switching allows easy filtering of output
ripple and noise, as well as the use of small external
components. A 22µH inductor works in most applica-
tions, so no magnetics design is necessary.
The MAX748A/MAX763A also feature cycle-by-cycle cur-
rent limiting, overcurrent limiting, undervoltage lockout,
and programmable soft-start protection. The MAX748A
is available in 8-pin DIP and 16-pin wide SO packages;
the MAX763A comes in 8-pin DIP and SO packages.
___________________________Applications

5V-to-3.3V Converters
Cellular Phones
Portable Instruments
Hand-Held Computers
Computer Peripherals
________________________________Features
Up to 500mA Load CurrentsGuaranteed 159kHz to 219.5kHz Current-Mode
PWM
85% to 90% Efficiencies1.7mA Quiescent Current (MAX748A)
1.4mA Quiescent Current (MAX763A)
0.2µA Shutdown Supply Current22µH Preselected Inductor Value;
No Component Design Required
Overcurrent, Soft-Start, and Undervoltage
Lockout Protection
Cycle-by-Cycle Current Limiting8-Pin DIP/SO Packages (MAX763A)
_________________Ordering Information
MAX748A/MAX763A
3.3V, Step-Down,
Current-Mode PWM DC-DC Converters
_______________________________________________________________________Maxim Integrated Products1
Call toll free 1-800-998-8800 for free samples or literature.

19-0190; Rev 0; 9/93
Ordering Information continued on last page.

* Contact factory for dice specifications.
____________________Pin Configurations
____________Typical Operating Circuit
MAX748A/MAX763A
3.3V, Step-Down,
Current-Mode PWM DC-DC Converters________________________________________________________________________________________________

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+ = 5V, ILOAD= 0mA, TA= TMINto TMAX, unless otherwise noted.)
ABSOLUTE MAXIMUM RATINGS

Pin Voltages:
V+ (MAX748A)......................................................+17V, -0.3V
V+ (MAX763A)......................................................+12V, -0.3V
LX (MAX748A).................................(V+ - 21V) to (V+ + 0.3V)
LX (MAX763A).................................(V+ - 12V) to (V+ + 0.3V)
OUT.................................................................................±25V
SS, CC, SHDN..........................................-0.3V to (V+ + 0.3V)
Peak Switch Current (ILX).....................................................2.0A
Reference Current (IREF)...................................................2.5mA
Continuous Power Dissipation (TA= +70°C)
8-Pin Plastic DIP (derate 6.90mW/°C above +70°C)...552mW
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/E..............................................................+150°C
MAX7__AM.................................................................+175°C
Storage Temperature Range............................-65°C to +160°C
Lead Temperature (soldering, 10sec)............................+300°C
MAX748A/MAX763A
3.3V, Step-Down,
Current-Mode PWM DC-DC Converters
_________________________________________________________________________________________________3
Note 1:
The standby current typically settles to 10µA (over temperature) within 2 seconds; however, to decrease test time, the part
is guaranteed at a 100µA maximum value.
MAXIMUM OUTPUT CURRENT
vs. SUPPLY VOLTAGE

MAXIMUM OUTPUT CURRENT (mA)
SUPPLY VOLTAGE (V)
MAX763A
EFFICIENCY vs. OUTPUT CURRENT

EFFICIENCY (%)
OUTPUT CURRENT (mA)
MAX748A
EFFICIENCY vs. OUTPUT CURRENT

EFFICIENCY (%)
OUTPUT CURRENT (mA)
________________________________________________Typical Operating Characteristics
(Circuit of Figure 3, TA = +25°C, VOUT= 3.3V, unless otherwise noted.)
MAX748A/MAX763A
3.3V, Step-Down,
Current-Mode PWM DC-DC Converters_______________________________________________________________________________________
____________________________Typical Operating Characteristics (continued)

(Circuit of Figure 3, TA = +25°C, VOUT= 3.3V, unless otherwise noted.)
MAX763A
QUIESCENT SUPPLY CURRENT
vs. SUPPLY VOLTAGE

SUPPLY VOLTAGE (V)
QUIESCENT SUPPLY CURRENT (mA)
MAX748A
QUIESCENT SUPPLY CURRENT
vs. SUPPLY VOLTAGE
QUIESCENT SUPPLY CURRENT (mA)
SUPPLY VOLTAGE (V)246810121416
PEAK INDUCTOR CURRENT
vs. OUTPUT CURRENT

PEAK INDUCTOR CURRENT (mA)
OUTPUT CURRENT (mA)
OSCILLATOR FREQUENCY
vs. SUPPLY VOLTAGE

OSCILLATOR FREQUENCY (kHz)
SUPPLY VOLTAGE (V)
OUTPUT VOLTAGE
vs. OUTPUT CURRENT

OUTPUT VOLTAGE (V)
OUTPUT CURRENT (mA)
SHUTDOWN CURRENT
vs. TEMPERATURE

TEMPERATURE (°C)
SHUTDOWN CURRENT (
OUTPUT VOLTAGE
vs. SUPPLY VOLTAGE
OUTPUT VOLTAGE (V)
SUPPLY VOLTAGE (V)
OSCILLATOR FREQUENCY
vs. TEMPERATURE

OSCILATOR FREQUENCY (kHz)
TEMPERATURE (°C)
MAX748A/MAX763A
3.3V, Step-Down,
Current-Mode PWM DC-DC Converters
_______________________________________________________________________________________5
_________________________________Typical Operating Characteristics (continued)

(Circuit of Figure 3, TA = +25°C, VOUT= 3.3V, unless otherwise noted.)
SWITCHING WAVEFORMS,
CONTINUOUS CONDUCTION
s/div
A: SWITCH VOLTAGE (LX PIN), 5V/div, 0V TO +6V
B: INDUCTOR CURRENT, 200mA/div
C: OUTPUT VOLTAGE RIPPLE, 50mV/div
V+ = 6V, IOUT= 250mA
400mA
0mAB
SWITCHING WAVEFORMS,
DISCONTINUOUS CONDUCTION
s/div
A: SWITCH VOLTAGE (LX PIN), 5V/div, 0V TO +6V
B: INDUCTOR CURRENT, 100mA/div
C: OUTPUT VOLTAGE RIPPLE, 50mV/div
V+ = 6V, IOUT= 75mA
200mA
0mA
LINE-TRANSIENT RESPONSE

5ms/div
A: VOUT, 50mV/div
B: V+, 5V/div, 7.0V TO 10.0V
IOUT= 350mA
10V
LOAD-TRANSIENT RESPONSE

5ms/div
A: VOUT, 50mV/div
B: IOUT, 200mA/div, 0mA TO 500mA
V+ = 6V
500mA
0mA
Note 2:
Operation beyond the specifications listed in the Electrical Characteristicsmay exceed the power dissipation ratings of
the device.
Note 3:
Wide temperature range circuit of Figure 5 using Sprague surface-mount capacitors.
Note 4:
Standby current includes all external component leakage currents. Capacitor leakage currents dominate at TA= +85°C.
_________________Detailed Description
The MAX748A/MAX763A switch-mode regulators use a
current-mode pulse-width-modulation (PWM) control
system in a step-down (buck) regulator topography.
They convert an unregulated DC input voltage from 4V
to 11V (MAX763A) or from 4V to 16V (MAX748A) to a
regulated 3.3V output at 300mA. For loads less than
300mA, V+ may be less than 4.0V (see the Output
Voltage vs. Supply Voltage graph in the Typical
Operating Characteristics). The current-mode
PWM architecture provides cycle-by-cycle current limit-
ing, improved load-transient response, and simpler
outerloop 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 (volt-
age) 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 volt-
age produces an error signal that raises the threshold,
allowing the circuit to store and transfer more energy
during each cycle.
Programmable Soft-Start

Figure 2 shows a capacitor connected to the soft-start
(SS) pin to ensure orderly power-up. A typical value is
0.047µF. SS controls both the SS timing and the maxi-
mum output current that can be delivered while main-
taining 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
current-limit threshold. Table 1 lists timing characteris-
tics for selected capacitor values and circuit conditions.
The overcurrent comparator trips when the load exceeds
approximately 1.2A. When either an undervoltage or over-
current fault condition is detected, an SS cycle is actively
initiated, which triggers an internal transistor to discharge
the SS capacitor to ground. An SS cycle is also enabled
at power-up and when coming out of shutdown mode.
Overcurrent Limiting

The overcurrent comparator triggers when the load
current exceeds approximately 1.2A. 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 prop-
erly. A typical value is 0.047µF.
MAX748A/MAX763A
3.3V, Step-Down,
Current-Mode PWM DC-DC Converters_______________________________________________________________________________________
_______________________________________________________________________Pin Description

*16-pin wide SO package: All pins sharing the same name must be connected together externally.
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