lm2781tpx National Semiconductor Corporation, lm2781tpx Datasheet

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lm2781tpx

Manufacturer Part Number
lm2781tpx
Description
Ultra-low Ripple Switched Capacitor Voltage Inverter
Manufacturer
National Semiconductor Corporation
Datasheet
© 2003 National Semiconductor Corporation
LM2781
Ultra-Low Ripple Switched Capacitor Voltage Inverter
General Description
The LM2781 is a charge pump that inverts an input voltage
in the range of 1.8V to 5.5V to the corresponding output
voltage of -1.8V to -5.5V. With use of three or four low-cost
external ceramic capacitors, the LM2781 can provide up to
50mA of output current.
The LM2781 operates at a 210kHz typical switching fre-
quency to minimize supply current (0.7mA typ.). Two charge
pumps operate 180˚ out of phase to significantly reduce the
output voltage ripple compared to that of traditional single-
phase charge pump circuits. If larger output ripple can be
tolerated, optional capacitor C2 may be omitted to reduce
the cost and size of the solution. The LM2781 is available in
an 8-pin Micro SMD chip-scale package.
See also: LM2780, a slow clock (12kHz typ) version of this
topology with extremely low supply current.
Typical Application Circuit
DS200447
Features
n Inverts Input Voltage
n Ultra-Low Voltage Ripple and 8Ω Typical Output
n Output Resistance of 18Ω Using One Flying Capacitor
n 210kHz (typ.) Switching Frequency
n 8-pin micro SMD Package (1.4mm x 1.4mm x 0.5mm)
Applications
n Cellular Phones
n Pagers
n PDAs
n Op-Amp Power Supplies
n Interface Power Supplies
n Handheld Instruments
Resistance with Two Flying Capacitors
20044701
www.national.com
March 2003

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lm2781tpx Summary of contents

Page 1

... Micro SMD chip-scale package. See also: LM2780, a slow clock (12kHz typ) version of this topology with extremely low supply current. Typical Application Circuit © 2003 National Semiconductor Corporation Features n Inverts Input Voltage n Ultra-Low Voltage Ripple and 8Ω Typical Output Resistance with Two Flying Capacitors n Output Resistance of 18Ω ...

Page 2

... A3 C2 OUT C3 C1- Ordering Information Order Number LM2781TP LM2781TPX www.national.com 8-Bump Thin Micro SMD Package NS Package Number TPA08 Description Secondary flying-capacitor connection Input voltage. Input range: 1.8V to 5.5V Primary flying-capacitor connection Shutdown pin logic input. Low = on, High = shutdown Ground Secondary flying-capacitor connection Output voltage ...

Page 3

Absolute Maximum Ratings 2) If Military/Aerospace specified devices are required, please contact the National Semiconductor Sales Office/ Distributors for availability and specifications. V pin: Voltage to GND IN SD pin: Voltage to GND Output Short-to-GND Duration (Note 3) Maximum Junction ...

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Typical Performance Characteristics Unless otherwise specified 25˚ Output Voltage vs. Load Current Output Resistance vs. Temperature (I Switching Frequency vs. Temperature www.national.com = 1µF. IN OUT Power Efficiency vs. Load ...

Page 5

Block Diagram Operation Description The LM2781 is a switched capacitor voltage inverter that produces a negative output voltage from a positive input voltage. To minimize output voltage ripple, the LM2781 con- tains two charge pump inverters that operate 180˚ out ...

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Operation Description OUTPUT RESISTANCE Output resistance (R ) models the internal non-idealities OUT of a charge pump that result in droop in the output voltage. The effect of output resistance on output voltage is ex- pressed in the following equation: ...

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... NATIONAL’S PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORT DEVICES OR SYSTEMS WITHOUT THE EXPRESS WRITTEN APPROVAL OF THE PRESIDENT AND GENERAL COUNSEL OF NATIONAL SEMICONDUCTOR CORPORATION. As used herein: 1. Life support devices or systems are devices or systems which, (a) are intended for surgical implant ...

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