19-0388; Rev 1; 3/96
UAL
IT MAN
TION K
A
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EVALU
DATA S
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Low-Noise, Regulated, -2V GaAsFET Bias
_______________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
IN
> 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.
____________________________Features
o
Fixed -2V or Adjustable -0.5V to -9.4V Output
at 4mA (MAX840)
o
2.5V to 10V Input Voltage Range
o
Operate with Small Capacitors (as low as 0.22µF)
o
1mVp-p Output Voltage Ripple
o
Charge-Pump Switching Frequency:
100kHz in Normal Operation
20kHz in Shutdown Mode (MAX844)
o
1µA Max Logic-Level Shutdown Over Temp.
(MAX840/MAX843)
o
Small 8-Pin SO Package
MAX840/MAX843/MAX844
______________Ordering Information
PART
MAX840C/D
MAX840ISA
MAX840ESA
MAX843C/D
MAX843ISA
MAX843ESA
MAX844C/D
MAX844ISA
MAX844ESA
TEMP. RANGE
0°C to +70°C
-25°C to +85°C
-40°C to +85°C
0°C to +70°C
-25°C to +85°C
-40°C to +85°C
0°C to +70°C
-25°C to +85°C
-40°C to +85°C
PIN-PACKAGE
Dice*
8 SO
8 SO
Dice*
8 SO
8 SO
Dice*
8 SO
8 SO
________________________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
__________Typical Operating Circuit
V
IN
= 2.5V to 10.0V
(3 CELLS)
* Dice are specified at T
A
= +25°C only.
0.22µF
IN
C1+
0.22µF
C1-
V
OUT
= -2.0V
(V
GG
of GaAsFET)
OUT
4.7µF
NEGOUT
0.22µF
__________________Pin Configuration
TOP VIEW
MAX840
C1+ 1
C1- 2
NEGOUT 3
SHDN 4
8
IN
GND
OUT
FB (CONT)
MAX840
MAX843
MAX844
7
6
5
ON/OFF
SHDN
GND
FB
SO
( ) ARE FOR MAX843/MAX844
________________________________________________________________
Maxim Integrated Products
1
For free samples & the latest literature: http://www.maxim-ic.com, or phone 1-800-998-8800
MAXIM [ MAXIM INTEGRATED PRODUCTS ]
