Rainbow Electronics MAX844 - Manual

_______________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
____________________________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 1
( ) ARE FOR MAX843/MAX844
1
2
3
4
8
7
6
5
IN
GND
OUT
FB (CONT) SHDN
NEGOUT
C1-
C1+
MAX840
MAX843
MAX844
SO
TOP VIEW
__________________Pin Configuration
MAX840
FB
OUT
SHDN
NEGOUT
C1-
C1+
IN
GND
V
IN
= 2.5V to 10.0V
(3 CELLS)
0.22 µ F
V OUT = -2.0V
(V GG of GaAsFET)
4.7 µ F
0.22 µ F
0.22 µ F
ON/OFF
__________Typical Operating Circuit
19-0388; Rev 1; 3/96
PART
MAX840 C/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
8 SO
EVALUATION KIT MANUAL
FOLLOWS DATA SHEET
______________Ordering Information
* Dice are specified at T A = +25°C only.
MAX843 C/D 0°C to +70°C Dice*
MAX843ISA -25°C to +85°C 8 SO
MAX843ESA -40°C to +85°C 8 SO
MAX844 C/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