U5 Charge-Pump Regulator Overview
2:17
Here’s a detailed overview of U5 in your design:
Component: U5 – LM27762DSSR charge-pump switching regulator
1. Purpose & Core Function
- Generates both a regulated positive rail (OUT⁺) and negative rail (OUT⁻) from a single input (VIN).
- Ideal when you need small bipolar supplies (e.g. ±2.5 V, ±5 V) but don’t want an inductor-based solution.
- Dual charge-pump architecture with internal 2 MHz oscillator and MOSFET switch array.
- Adjustable outputs via external resistor dividers on FB⁺ and FB⁻ pins.
- Built-in LDO regulators for low-noise, tightly regulated rails.
- Power-Good (PGOOD) flag (open-drain) to indicate when both outputs are in regulation.
- Shutdown pins (EN⁺, EN⁻) enable individual disabling of each pump, reducing quiescent current.
- Capable of up to 250 mA per output.
- Oscillator & Pumping Stage
- A 2 MHz clock drives internal switches that shuttle charge into flying capacitors (C1+, C1–).
- Switch-to-Output Stage
- Pumped voltage is steered through an internal LDO stage to produce regulated OUT⁺ and OUT⁻.
- Feedback & Regulation
- External resistor dividers on FB⁺/FB⁻ set the exact output voltages.
- The chip adjusts switch duty-cycle and LDO gate drive to maintain regulation.
- Monitoring & Control
- PGOOD asserts low when both rails are within regulation bands.
- EN pins allow power-down or sequencing.
- Hi-Fi audio headphone amplifiers (bias rails)
- Op-amp power biasing in precision analog circuits
- Powering data converters (ADC/DAC supply rails)
- Interface supplies for mixed-signal or wireless modules
- Hand-held instrumentation where ± rails are needed without large inductors
- High switching frequency (2 MHz) allows use of small SMD capacitors (0603/0805).
- Low-ESR pump caps yield better efficiency and lower output impedance.
- Exposed pad WSON package for superior thermal performance.
- Wide temperature range (–40 °C to +85 °C).
The LM27762 belongs to TI’s family of high-frequency, dual-output charge-pump regulators.
- Fixed-output variants (e.g. LM27762-5.0) provide factory-set ±5 V with no external divider.
- Adjustable versions (LM27762DSSR) let you pick any ± output within the device’s range (typically ±1.5 V to ±6 V).
- Key differences across the family:
- Output voltage options (fixed vs. adjustable)
- Maximum output current (200–300 mA)
- Package styles (WSON vs. QFN)
- Use-case trade-offs:
- Choose fixed versions for simpler BOM when only one bipolar voltage is needed.
- Choose the adjustable LM27762DSSR for flexibility in mixed-supply or multi-rail systems.
By using U5, your signal generator gains compact, inductor-less ± rails that are essential for driving the op-amps (e.g., U1–U3) and delivering clean, stable waveforms.
Specify output voltages
Add pump caps
Set shutdown behavior
Enable PGOOD pin
Thermal considerations
315 days
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