19-1174; Rev 0; 12/96
Low-Noise, Dual-Output, Regulated Charge Pump
for GaAsFET, LCD, and VCO Supplies
_______________General Description
The MAX768 low-noise, dual-output, regulated charge
pump provides a negative output for biasing GaAsFET
power amplifiers, and a positive output for powering
voltage-controlled oscillators (VCOs) in wireless hand-
sets. The outputs can also be used to power LCDs.
Output ripple is less than 2mVp-p. The MAX768 is
intended for use in low-voltage systems where a simple
charge-pump inverter is inadequate, or where the VCO
needs more range to improve its signal-to-noise ratio.
The input range is 2.5V to 5.5V, enabling direct power
from 1Li+ and 3-cell NiMH/NiCd batteries.
The MAX768 includes a voltage-doubler charge pump,
followed by an inverting charge pump. This combina-
tion produces unregulated outputs that are ±2x the
input. Two internal low-dropout linear regulators provide
the low-noise, regulated positive and negative outputs.
Output current is guaranteed to be at least 5mA per
output. The linear regulators use CMOS devices, so the
quiescent current remains independent of output load-
ing (even in dropout), and the dropout voltage
approaches zero with no load current.
The MAX768 has two preset switching frequencies
(25kHz or 100kHz), or can be synchronized by an exter-
nal clock from 20kHz to 240kHz. This flexibility permits
users to optimize their designs based on noise, capaci-
tor size, and quiescent-supply-current criteria.
The device features Dual Mode™ operation: the output
voltage is preset to +5V and -5V, or can be adjusted by
adding external resistor dividers. Other features include
independent shutdowns and a logic output that signals
when the negative voltage has risen to within 10% of its
regulation setpoint (to protect the power amplifier
GaAsFET). The MAX768 is available in a space-saving,
16-pin QSOP, which is the same size as a standard
8-pin SO.
____________________________Features
o
Dual Positive/Negative Regulated Outputs:
±5V
OUT
from 3V
IN
o
Output-Ready Indicator to Protect GaAsFET PAs
o
2.5V to 5.5V Input Voltage Range
o
Low-Noise Output Ripple: < 2mVp-p
o
Synchronizable Switching Frequency
o
Uses Only Small, Low-Cost Capacitors
o
0.1µA Independent Shutdown Controls
o
Adjustable Output Voltages
o
Small 16-Pin QSOP Package
MAX768
______________Ordering Information
PART
MAX768C/D
MAX768EEE
TEMP. RANGE
0°C to +70°C
-40°C to +85°C
PIN-PACKAGE
Dice*
16 QSOP
*Dice
are specified at T
A
= +25°C, DC parameters only.
Pin Configuration appears at end of data sheet.
Dual Mode is a trademark of Maxim Integrated Products.
__________Typical Operating Circuit
V
IN
(3.0V TO 5.5V)
C7
IN
POUT
V+
C3
C5
POSITIVE
OUTPUT
+5V
SYNC
PSHDN
NSHDN
C1+
C1
C1-
C2+
C2
C2-
________________________Applications
GaAsFET Power Amp Bias
Voltage-Controlled Oscillator (VCO) Supply
Tuner Diode Power Supply
Positive and Negative LCD Supply
Cellular Phone
PCS and Cordless Phone
Wireless Handsets
Wireless Handheld Computers
Wireless PCMCIA Cards
Modems
MAX768
V-
NOUT
RDY
SETN
GND
SETP
C4
C6 NEGATIVE
OUTPUT
-5V
OUTPUT-
READY
SIGNAL
________________________________________________________________
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 ]
