A Charge Pump is an inductor-less DC-DC topology that transfers electric charge solely through the charging and discharging of capacitors.
Take the TPS60403 as an example. Shown below is the core equivalent model of an inverting switched-capacitor charge pump, which matches the internal circuitry of the TPS60400 IC.
(Images sourced from Texas Instruments, TI)
Core Component: Flying Capacitor (Cfly)
This capacitor acts as the energy transfer medium. The IC alternately charges the flying capacitor and discharges it in reverse polarity over two operating phases, thereby generating negative voltage at the output. No power inductor or Schottky freewheeling diode is required throughout the operation.
The TPS60400 is a switched-capacitor negative charge pump from TI. Inductor-free, it transfers charge via capacitors to deliver an equal-magnitude negative output from a positive input. It is designed to supply negative rails for low-current analog loads such as op-amps, DACs and voltage references.
(Images sourced from Texas Instruments, TI)
Functions of the Three Critical Capacitors
All three shall be low-ESR X7R ceramic capacitors.
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Input Capacitor CI (IN to GND, 1 µF)
It filters high-frequency input spikes generated by internal switching of the chip and stabilizes the upstream power supply. Mandatory for designs with long input cables.
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Flying Capacitor Cfly (Pin 5 ↔ Pin 3, 1 µF)
The core component for charge transfer. It completes charge transportation across two switching phases and serves as the only energy storage element for generating negative voltage.
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Output Capacitor CO (OUT to GND, 1 µF)
It smooths negative output ripple and stores charge to power the load. Larger capacitance yields lower output ripple.
Core Circuit Advantages
- Inductor-free design: No magnetic components, resulting in extremely low EMI radiation. Ideal for RF circuits and high-precision analog front ends.
- Minimal peripheral components: Only three surface-mount ceramic capacitors, requiring a tiny PCB footprint.
Related Documents
Related Part
TPS60403: Unregulated charge pump negative voltage inverter
Input voltage range: 1.6 V to 5.5 V; maximum negative output current: 60 mA.
Requires merely three external capacitors, featuring compact size. Suitable for low-current bias power supply of op-amps and LCD panels.
Further Reading on Negative Voltage Fundamentals
- Negative Voltage Basics: What Is Negative Voltage?
- Negative Voltage Basics: Voltages in Communication Circuits
- Negative Voltage Basics: Why Op-Amp & Audio Analog Circuits Require Positive/Negative Power Supplies
- Negative Voltage Basics: Charge Pump Implementations
- Negative Voltage Basics: Positive and Negative Voltage Design for Buck Circuits
- Negative Voltage Basics: Negative Rail Supply for Precision Op-Amp AC Signal Amplification