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_______________General Description

The MAX840/MAX843/MAX844 low-noise, inverting

charge-pump power supplies are ideal for biasing

GaAsFETs in cellular telephone transmitter amplifiers.

They operate with inputs down to 2.5V.

The MAX840 offers both a -2V preset output and a -0.5V

to -9.4V adjustable output. The MAX843/MAX844 use

an external positive control voltage to set the negative

output voltage. Input voltage range for all the devices is

2.5V to 10V, and output current is 4mA with V

> 2.7V.

These circuits can operate with small capacitors, as low

as 0.22µF.

An internal linear regulator reduces the MAX840’s out-

put voltage ripple to 1mVp-p. With a well-filtered control

voltage (V

CTRL

), the MAX843/MAX844 also achieve less

than 1mVp-p typical output ripple. Supply current is

750µA, and reduces to less than 1µA in shutdown

(MAX840/MAX843). The MAX844’s unregulated output

is active in shutdown, with the charge pump switching at

20kHz. It provides a low-power LCD supply.

________________________Applications

Cellular Phones

GaAsFET Power Amplifier Modules

Personal Communicators, PDAs

Wireless Data Loggers

Continuously Adjustable GaAsFET Bias

LCD-Bias Contrast Control

Regulated Negative Power Supplies

____________________________Features

♦ Fixed -2V or Adjustable -0.5V to -9.4V Output

at 4mA (MAX840)

♦ 2.5V to 10V Input Voltage Range

♦ Operate with Small Capacitors (as low as 0.22µF)

♦ 1mVp-p Output Voltage Ripple

♦ Charge-Pump Switching Frequency:

100kHz in Normal Operation

20kHz in Shutdown Mode (MAX844)

♦ 1µA Max Logic-Level Shutdown Over Temp.

(MAX840/MAX843)

♦ Small 8-Pin SO Package

MAX840/MAX843/MAX844

Low-Noise, Regulated, -2V GaAsFET Bias

________________________________________________________________

Maxim Integrated Products

( ) ARE FOR MAX843/MAX844

GND

OUT

FB (CONT)

SHDN

NEGOUT

C1-

C1+

MAX840

MAX843

MAX844

TOP VIEW

__________________Pin Configuration

MAX840

OUT

SHDN



NEGOUT

C1-

C1+

GND

= 2.5V to 10.0V

(3 CELLS)

0.22µF

OUT

= -2.0V

of GaAsFET)

4.7µF

0.22µF

ON/OFF

__________Typical Operating Circuit

19-0388; Rev 1; 3/96

PART

MAX840C/D

MAX840ISA

MAX840ESA -40°C to +85°C

-25°C to +85°C

0°C to +70°C

TEMP. RANGE PIN-PACKAGE

Dice*

8 SO

EVALUATION KIT MANUAL

FOLLOWS DATA SHEET

______________Ordering Information

* Dice are specified at T

= +25°C only.

MAX843C/D

0°C to +70°C Dice*

MAX843ISA -25°C to +85°C 8 SO

MAX843ESA -40°C to +85°C 8 SO

MAX844C/D

0°C to +70°C Dice*

MAX844ISA -25°C to +85°C 8 SO

MAX844ESA -40°C to +85°C 8 SO

For free samples & the latest literature: http://www.maxim-ic.com, or phone 1-800-998-8800

Summary of content (10 pages)

PAGE 1
9-0388; Rev 1; 3/96 UAL IT MAN TION K A ET U E L H A S EV TA WS DA FOLLO Low-Noise, Regulated, -2V GaAsFET Bias The MAX840/MAX843/MAX844 low-noise, inverting charge-pump power supplies are ideal for biasing GaAsFETs in cellular telephone transmitter amplifiers. They operate with inputs down to 2.5V. The MAX840 offers both a -2V preset output and a -0.5V to -9.4V adjustable output. The MAX843/MAX844 use an external positive control voltage to set the negative output voltage.
PAGE 2
MAX840/MAX843/MAX844 Low-Noise, Regulated, -2V GaAsFET Bias ABSOLUTE MAXIMUM RATINGS Operating Temperature Ranges Supply Voltage, VIN to GND ..................................-0.3V to 10.5V VNEGOUT to GND ...................................................-10.5V to 0.3V MAX84_I_ _A ...................................................-25°C to +85°C VIN to VNEGOUT.........................................................-0.3V to 21V MAX84_E_ _A ..................................................
PAGE 3
Low-Noise, Regulated, -2V GaAsFET Bias OUTPUT VOLTAGE vs. OUTPUT CURRENT OUTPUT VOLTAGE vs. INPUT VOLTAGE OVER TEMPERATURE MAX840-02 -2.065 MAX840-01 -2.070 OUTPUT VOLTAGE (V) -2.050 -2.055 TA = +85°C -2.050 TA = +25°C TA = -40°C -2.045 -2.040 -2.040 0 1 2 3 4 5 6 8 7 9 10 2 3 4 OUTPUT CURRENT (mA) MAXIMUM OUTPUT CURRENT vs. INPUT VOLTAGE NEGOUT CURRENT (mA) High-current operation not recommended for extended periods of time.
PAGE 4
____________________________Typical Operating Characteristics (continued) (Circuit of Figure 2a, VIN = 3.6V, TA = +25°C, unless otherwise noted.) OSCILLATOR FREQUENCY vs. SUPPLY VOLTAGE MAX844 OSCILLATOR FREQUENCY vs.
PAGE 5
Low-Noise, Regulated, -2V GaAsFET Bias MAX840 NOISE SPECTRUM (C1 = C2 = C3 = 1µF, C4 = 10µF) 40 VIN = 3.6V, IOUT = 4mA NOISE (dBµV) 30 20 10 0 -10 0.1 10 1 100 1000 100 1000 100 1000 FREQUENCY (kHz) MAX840 NOISE SPECTRUM (C1 = C2 = C3 = 0.22µF, C4 = 4.7µF) 50 VIN = 3.6V, IOUT = 4mA NOISE (dBµV) 40 30 20 10 0 0.1 1 10 FREQUENCY (kHz) MAX843/MAX844 NOISE SPECTRUM (C1 = C2 = C3 = 1µF, C4 = 10µF) 40 VIN = 3.
PAGE 6
____________________________Typical Operating Characteristics (continued) (Circuit of Figure 2a, VIN = 3.6V, TA = +25°C, unless otherwise noted.) MAX843/MAX844 NOISE SPECTRUM (C1 = C2 = C3 = 0.22µF, C4 = 4.7µF) 50 VIN = 3.6V, IOUT = 4mA 40 NOISE (dBµV) MAX840/MAX843/MAX844 Low-Noise, Regulated, -2V GaAsFET Bias 30 20 10 0 VOUT NOTE: dBµV = 20 LOG ______ 1µV 0.1 10 1 100 1000 FREQUENCY (kHz) START-UP FROM SHUTDOWN 0V VOUT 1V/div VSHDN 2V/div 0V 500µs/div VIN = 3.
PAGE 7
Low-Noise, Regulated, -2V GaAsFET Bias PIN NAME FUNCTION MAX840 MAX843 MAX844 1 1 C1+ Positive Terminal for C1 2 2 C1- Negative Terminal for C1 3 3 NEGOUT 4 4 SHDN 5 — FB — 5 CONT 6 6 OUT Regulated Negative Output Voltage 7 7 GND Ground 8 8 IN Negative Output Voltage (unregulated) Active-Low, TTL Logic-Level Shutdown Input Dual Mode™ Feedback Input. When FB is grounded, the output is preset to -2V.
PAGE 8
MAX840/MAX843/MAX844 Low-Noise, Regulated, -2V GaAsFET Bias _______________Detailed Description The MAX840/MAX843/MAX844 are low-noise, inverting, regulated charge-pump power supplies designed for biasing GaAsFET devices, such as power-amplifier modules in cellular handsets. The applied input voltage (VIN) is first inverted to a negative voltage at NEGOUT by a capacitive charge pump. This voltage is then regulated by an internal low-noise linear regulator, and appears at OUT (Figure 1).
PAGE 9
Low-Noise, Regulated, -2V GaAsFET Bias VIN 8 1 C1 1µF 2 3 C2 1µF 4 ON/OFF 8 C3 1µF IN C1+ MAX840 C1- OUT 6 VOUT = -2V (VGG of GaAsFET) 1 C1 1µF C4 10µF NEGOUT C1+ 2 C1- 3 FB 5 ON/OFF MAX840 4 FB 8 3 C2 1µF MAX843 MAX844 OUT 6 NEGOUT R2 100k CONT SHDN GND 7 8 C3 1µF VOUT = -0.5V to -9.4V @ 4mA 4 ON/OFF R1 100k VIN IN C1- 5 Figure 2b. MAX840 Adjustable Configuration VIN 2 ) R2 100k GND 7 Figure 2a.
PAGE 10
MAX840/MAX843/MAX844 Low-Noise, Regulated, -2V GaAsFET Bias ___________________Chip Topography IN C1+ GND GND C1- 0.145" (3.683mm) NEGOUT NEGOUT OUT SHDN FB (CONT) 0.085" (2.