19-1174; Rev 0; 12/96
Low-Noise, Dual-Output, Regulated Charge Pump
for GaAsFET, LCD, and VCO Supplies
____________________________Features
o Dual Positive/Negative Regulated Outputs:
±5VOUT from 3VIN
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
______________Ordering Information
PART
Dual Mode is a trademark of Maxim Integrated Products.
__________Typical Operating Circuit
VIN
(3.0V TO 5.5V)
C7
SYNC
POUT
V+
NSHDN
C5
C3
C1+
MAX768
C1
C4
C1-
Positive and Negative LCD Supply
V-
C2+
Cellular Phone
Wireless Handheld Computers
POSITIVE
OUTPUT
+5V
IN
PSHDN
Voltage-Controlled Oscillator (VCO) Supply
Wireless Handsets
Dice*
16 QSOP
Pin Configuration appears at end of data sheet.
GaAsFET Power Amp Bias
PCS and Cordless Phone
PIN-PACKAGE
0°C to +70°C
-40°C to +85°C
*Dice are specified at TA = +25°C, DC parameters only.
________________________Applications
Tuner Diode Power Supply
TEMP. RANGE
MAX768C/D
MAX768EEE
NOUT
C2
C6 NEGATIVE
OUTPUT
-5V
C2RDY
SETN
GND
SETP
OUTPUTREADY
SIGNAL
Wireless PCMCIA Cards
Modems
________________________________________________________________ Maxim Integrated Products
1
For free samples & the latest literature: http://www.maxim-ic.com, or phone 1-800-998-8800
MAX768
_______________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 handsets. 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 combination 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 loading (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 external clock from 20kHz to 240kHz. This flexibility permits
users to optimize their designs based on noise, capacitor 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.
