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.