LM7705
June 10, 2009
Low Noise Negative Bias Generator
General Description
The LM7705 is a switched capacitor voltage inverter with a
low noise, −0.23V fixed negative voltage regulator. This de-
vice is designed to be used with low voltage amplifiers to
enable the amplifiers output to swing to zero volts. The −0.23
volts is used to supply the negative supply pin of an amplifier
while maintaining less then 5.5 volts across the amplifier. Rail-
to-Rail output amplifiers cannot output zero volts when oper-
ating from a single supply voltage and can result in error
accumulation due to amplifier output saturation voltage being
amplified by following gain stages. A small negative supply
voltage will prevent the amplifiers output from saturating at
zero volts and will help maintain an accurate zero through a
signal processing chain. Additionally, when an amplifier is
used to drive an ADC’s input, it can output a zero voltage sig-
nal and the full input range of an ADC can be used. The
LM7705 has a shutdown pin to minimize standby power con-
sumption
Features
■
Regulated output voltage
−0.232V
■
Output voltage tolerance
5%
■
Output voltage ripple
4 mV
PP
■
Max output current
26 mA
■
Supply voltage
3V to 5.25V
■
Conversion efficiency
up to 98%
■
Quiescent current
78 µA
■
Shutdown current
20 nA
■
Turn on time
500 µs
■
Operating temperature range
−40°C to 125°C
■
8-Pin MSOP Package
Applications
■
True zero amplifier output
■
Portable instrumentation
■
Low voltage split power supplies
Typical Application
20173001
© 2009 National Semiconductor Corporation
201730
www.national.com
LM7705 Low Noise Negative Bias Generator
