xDSL/Cable Modem Triple/Quintuple Output

Power Supplies

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9

Pin Description

PIN

MAX1864

MAX1865

NAME

FUNCTION

1

1

POK

Open-Drain Power-Good Output. POK is low when the output voltage is more than

10% below the regulation point. POK is high impedance when the output is in

regulation. Connect a resistor between POK and VL for logic-level voltages.

2

2

COMP

Compensation Pin. Connect a series RC to GND to compensate the control loop.

Typical values are 47k

Ω and 8.2nF.

3

3

OUT

Regulated Output Voltage High-Impedance Sense Input. Internally connected to a

resistive-divider and negative gain block (MAX1865).

44

FB

Dual-Mode Switching-Regulator Feedback Input. Connect to GND for the preset 3.3V

output. Connect to a resistive-divider from output to FB to GND to adjust the output

voltage between 1.236V and 0.8

55

B2

Open-Drain Output PNP Transistor Driver (Regulator #2). Internally connected to the

drain of a DMOS. B2 connects to the base of an external PNP pass transistor to form a

positive linear regulator.

6

6

FB2

Analog Gain-Block Feedback Input (Regulator #2). Connect to a resistive-divider

between the positive linear regulator’s output and GND to adjust the output voltage.

The feedback set point is 1.24V.

77

B3

Open-Drain Output PNP Transistor Driver (Regulator #3). Internally connected to the

drain of a DMOS. B3 connects to the base of an external PNP pass transistor to form a

positive linear regulator.

8

8

FB3

Analog Gain-Block Feedback Input (Regulator #3). Connect to a resistive-divider

between the positive linear regulator’s output and GND to adjust the output voltage.

The feedback set point is 1.24V.

—

9B4

Open-Drain Output PNP Transistor Driver (Regulator #4). Internally connected to the

drain of a DMOS. B4 connects to the base of an external PNP pass transistor to form a

positive linear regulator.

—

10

FB4

Analog Gain-Block Feedback Input (Regulator #4). Connect to a resistive-divider

between the positive linear regulator’s output and GND to adjust the output voltage.

The feedback set point is 1.24V.

—

11

B5

Open-Drain Output NPN Transistor Driver (Regulator #5). Internally connected to the

drain of a P-channel MOSFET. B5 connects to the base of an external NPN pass

transistor to form a negative linear regulator.

—

12

FB5

Analog Gain-Block Feedback Input (Regulator #5). Connect to a resistive-divider

between the negative linear regulator’s output and a positive reference voltage,

typically one of the positive linear regulator outputs, to adjust the output voltage. The

feedback set point is at GND.