1 Features

1• Less than 10-mW No-Load Power Capability

• Optocoupled Feedback for CV, and

Primary-Side Regulation (PSR) for CC

• Enables ±1% Voltage Regulation and ±5%

Current Regulation Across Line and Load

• 700-V Startup Switch

• 100-kHz Maximum Switching Frequency Enables

High-Power-Density Charger Designs

• Resonant-Ring Valley-Switching Operation for

Highest Overall Efficiency

• Frequency Dithering to Ease EMI Compliance

• Clamped Gate-Drive Output for MOSFET

• Overvoltage, Low-Line, and Overcurrent

Protection Functions

• SOIC-7 Package

• Create a Custom Design Using the UCC28740

With the WEBENCH® Power Designer

2 Applications

• USB-Compliant Adapters and Chargers for

Consumer Electronics

– Smart Phones

– Tablet Computers

– Cameras

• Standby Supply for TV and Desktop

• White Goods

3 Description

The UCC28740 isolated-flyback power-supply

controller provides Constant-Voltage (CV) using an

optical coupler to improve transient response to largeload

steps. Constant-Current (CC) regulation is

accomplished through Primary-Side Regulation (PSR)

techniques. This device processes information from

opto-coupled feedback and an auxiliary flyback

winding for precise high-performance control of

output voltage and current.

An internal 700-V startup switch, dynamically

controlled operating states, and a tailored modulation

profile support ultra-low standby power without

sacrificing startup time or output transient response.

Control algorithms in the UCC28740 allow operating

efficiencies to meet or exceed applicable standards.

The drive output interfaces to a MOSFET power

switch. Discontinuous conduction mode (DCM) with

valley-switching reduces switching losses. Modulation

of switching frequency and primary current-peak

amplitude (FM and AM) keeps the conversion

efficiency high across the entire load and line ranges.

The controller has a maximum switching frequency of

100 kHz and always maintains control of the peakprimary

current in the transformer. Protection features

keep primary and secondary component stresses in

check. A minimum switching frequency of 170 Hz

facilitates the achievement of less than 10-mW noload

power.