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MAX8741
(Rev.:2004)

500kHz Multi-Output Power-Supply Controllers with High Impedance in Shutdown

Maxim Integrated 

500kHz Multi-Output Power-Supply Controllers

with High Impedance in Shutdown

PIN

SSOP

TQFN

1

29

2

30

3

31

4

1

5

2

6

3

7

4

8

5

9

7

10

8

11

9

12

10

13

11

14

12

Pin Description

NAME

CSH3

CSL3

FB3

12OUT

(MAX8742)

STEER

(MAX8741)

VDD

(MAX8742)

SECFB

(MAX8741)

SYNC

TIME/ON5

GND

REF

SKIP

RESET

FB5

CSL5

CSH5

FUNCTION

Current-Sense Input for the 3.3V SMPS. Current-limit level is 100mV referred to CSL3.

Current-Sense Input. Also serves as the feedback input in fixed-output mode.

Feedback Input for the 3.3V SMPS. Regulates at FB3 = REF (approximately 2.5V) in

adjustable mode. FB3 is a dual-mode input that also selects the 3.3V fixed output-

voltage setting when connected to GND. Connect FB3 to a resistor-divider for

adjustable-output mode.

12V/120mA Linear-Regulator Output. Input supply comes from VDD. Bypass 12OUT to

GND with 1µF (min).

Logic-Control Input for Secondary Feedback. Selects the PWM that uses a transformer

and secondary feedback signal (SECFB):

STEER = GND: 3.3V SMPS uses transformer

STEER = VL: 5V SMPS uses transformer

Supply Voltage Input for the 12OUT Linear Regulator. Also connects to an internal

resistor-divider for secondary winding feedback and to an 18V overvoltage shunt

regulator clamp.

Secondary Winding Feedback Input. Normally connected to a resistor-divider from an

auxiliary output. SECFB regulates at VSECFB = 2.5V (see the Secondary Feedback

Regulation Loop section). Connect to VL if not used.

Oscillator Synchronization and Frequency Select. Connect to VL for 500kHz operation;

connect to GND for 333kHz operation. Can be driven at 400kHz to 583kHz for external

synchronization.

Dual-Purpose Timing Capacitor Pin and ON/OFF Control Input. See the Power-Up

Sequencing and ON/OFF Controls section.

Low-Noise Analog Ground and Feedback Reference Point

2.5V Reference Voltage Output. Bypass to GND with 1µF (min).

Logic-Control Input that Disables Idle Mode when High. Connect to GND for normal use.

Active-Low Timed Reset Output. RESET swings GND to VL. Goes high after a fixed

32,000 clock-cycle delay following power-up.

Feedback Input for the 5V SMPS. Regulates at FB5 = REF (approximately 2.5V) in

adjustable mode. FB5 is a dual-mode input that also selects the 5V fixed output-

voltage setting when connected to GND. Connect FB5 to a resistor-divider for

adjustable-output mode.

Current-Sense Input for the 5V SMPS. Also serves as the feedback input in fixed-output

mode, and as the bootstrap supply input when the voltage on CSL5/VL is >4.5V.

Current-Sense Input for the 5V SMPS. Current-limit level is 100mV referred to CSL5.

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