Low-Noise / Dual-Output / Regulated Charge Pump for GaAsFET / LCD / and VCO Supplies
|Total Page||12 Pages|
|Features||Datasheet pdf 19-1174; Rev 0; 12/96 Low-Noise, Dual-O utput, Regulated Charge Pump for GaAsFE T, LCD, and VCO Supplies ______________ _General Description The MAX768 low-noi se, dual-output, regulated charge pump provides a negative output for biasing GaAsFET power amplifiers, and a positiv e output for powering voltage-controlle d oscillators (VCOs) in wireless handse ts. The outputs can also be used to pow er LCDs. Output ripple is less than 2mV p-p. The MAX768 is intended for use in low-voltage systems where a simple char ge-pump inverter is inadequate, or wher e the VCO needs more range to improve i ts signal-to-noise ratio. The input ran ge is 2.5V to 5.5V, enabling direct pow er from 1Li+ and 3-cell NiMH/NiCd ba.|
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19-1174; Rev 0; 12/96
Low-Noise, Dual-Output, Regulated Charge Pump
for GaAsFET, LCD, and VCO Supplies
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
GaAsFET Power Amp Bias
Voltage-Controlled Oscillator (VCO) Supply
Tuner Diode Power Supply
Positive and Negative LCD Supply
PCS and Cordless Phone
Wireless Handheld Computers
Wireless PCMCIA Cards
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
0°C to +70°C
-40°C to +85°C
*Dice are specified at TA = +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
(3.0V TO 5.5V)
SETN GND SETP
________________________________________________________________ Maxim Integrated Products 1
For free samples & the latest literature: http://www.maxim-ic.com, or phone 1-800-998-8800