Low-Noise, Regulated, Negative

Charge-Pump Power Supplies for GaAsFET Bias

6

______________________________________________________________________________________

______________________________________________________________Pin Description

MAX850

MAX851

MAX852

-1.28V

REF

CHARGE

PUMP

IN

N

C1+

C1-

NEGOUT

SHDN (MAX850)

SHDN (MAX851)

OSC (MAX852)

OUT

CONNECT TO

GND TO SET

FB

GND

MAX853

CHARGE

PUMP

IN

N

C1+

C1-

NEGOUT

SHDN

OUT

CONTROL

VOLTAGE

CONT

GND

_______________Detailed Description

The MAX850–MAX853 are low-noise, inverting, regulat-

ed charge-pump power supplies designed for biasing

GaAsFET devices, such as power-amplifier modules in

cellular handsets.

negative voltage at NEGOUT by a capacitive charge

pump. This voltage is then regulated by an internal lin-

ear regulator, and appears at OUT (Figure 1). The mini-

is the inverted positive voltage, plus the 1.0V required

by the post-regulator. The ripple noise induced by the

charge-pump inverter is reduced by the linear regulator

tion, the excellent AC rejection of the linear regulator

attenuates noise on the incoming supply. Up to 5mA is

available at OUT.

Figure 1a. MAX850–MAX852 Block Diagram

Figure 1b. MAX853 Block Diagram

MAX850

1

MAX851

1

MAX853

1

PIN

MAX852

1

NAME

C1+

FUNCTION

Positive terminal for C1

3

–

2

3

3

4

2

3

–

2

4

NEGOUT

SHDN

2

C1-

Active-low TTL logic level Shutdown Input

Negative terminal for C1

–

4

–

–

–

4

–

OSC

–

SHDN

External Clock Input

Active-high TTL logic level Shutdown Input

5

5

–

5

FB

Dual-Mode Feedback Input. When FB is grounded, the output is preset to

-4.1V. To select other output voltages, connect FB to an external resistor

divider. See Figure 2b.

–

5

–

–

CONT

OUT and a positive control voltage between 0V and 10V. See Figure 2c.

7

8

6

7

7

8

6

7

8

6

8

GND

IN

6

OUT

Ground

Positive Power-Supply Input (4.5V to 10V)

Output Voltage