MAX840 Datasheet, PDF (1/10 Pages) Maxim Integrated Products – Low-Noise, Regulated, -2V GaAsFET Bias

19-0388; Rev 1; 3/96
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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.
________________________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)
0.22µF
0.22µF
IN
C1+
C1- ^{MAX840 OUT}
NEGOUT
0.22µF
V_OUT = -2.0V
(V_GG of GaAsFET)
4.7µF
ON/OFF
SHDN
FB
GND
____________________________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
______________Ordering Information
PART
TEMP. RANGE
MAX840C/D
0°C to +70°C
MAX840ISA
-25°C to +85°C
MAX840ESA
MAX843C/D
MAX843ISA
MAX843ESA
MAX844C/D
MAX844ISA
MAX844ESA
-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
* Dice are specified at T_A = +25°C only.
PIN-PACKAGE
Dice*
8 SO
8 SO
Dice*
8 SO
8 SO
Dice*
8 SO
8 SO
__________________Pin Configuration
TOP VIEW
C1+ 1
C1- 2
NEGOUT 3
SHDN 4
MAX840
MAX843
MAX844
SO
( ) ARE FOR MAX843/MAX844
8 IN
7 GND
6 OUT
5 FB (CONT)
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