UCC28720 Constant-Voltage, Constant-Current Controller With Primary-Side Regulation
1 Features
- < 10-mW No-Load Power
- Primary-Side Regulation (PSR) Eliminates Opto-Coupler
- ±5% Voltage and Current Regulation Across Line and Load
- 700-V Start-Up Switch
- 80-kHz Maximum Switching Frequency Enables High-Power Density Charger Designs
- Quasi-Resonant Valley-Switching Operation for Highest Overall Efficiency
- Wide VDD Range Allows Small Bias Capacitor
- Dynamic BJT Drive
- Overvoltage, Low-Line, and Overcurrent Protection Functions
- Programmable Cable Compensation
- SOIC-7 Package
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 UCC28720 flyback power supply controller provides isolated-output Constant-Voltage (CV) and Constant-Current (CC) output regulation without the use of an optical coupler. The devices process information from the primary power switch and an auxiliary flyback winding for precise control of output voltage and current.
An internal 700-V start-up switch, dynamically-controlled operating states and a tailored modulation profile support ultra-low standby power without sacrificing start-up time or output transient response.
Control algorithms in the UCC28720 allow operating efficiencies to meet or exceed applicable standards. The output drive interfaces to a bipolar transistor 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 80 kHz and always maintains control of the peak-primary current in the transformer. Protection features help keep primary and secondary component stresses in check. The UCC28720 allows compensation for voltage drop in the cable to be programmed with an external resistor.
Device Information(1)
| PART NUMBER | PACKAGE | BODY SIZE (NOM) |
|---|---|---|
| UCC28720 | SOIC (7) | 3.91 mm × 4.90 mm |
- For all available packages, see the orderable addendum at the end of the data sheet.
Typical Application
4 Revision History
Changes from A Revision (January 2014) to B Revision
- Added ESD Ratings table, Feature Description section, Device Functional Modes, Application and Implementation section, Power Supply Recommendations section, Layout section, Device and Documentation Support section, and Mechanical, Packaging, and Orderable Information section. Go
Changes from * Revision (May 2014) to A Revision
- Changed CDD equation.Go
5 Pin Configuration and Functions
Pin Functions
| PIN | I/O | DESCRIPTION | |
|---|---|---|---|
| NAME | NO. | ||
| VDD | 1 | I | VDD is the bias supply input pin to the controller. A carefully-placed bypass capacitor to GND is required on this pin. |
| VS | 2 | I | Voltage sense is an input used to provide voltage and timing feedback to the controller. This pin is connected to a voltage divider between an auxiliary winding and GND. The value of the upper resistor of this divider is used to program the AC-mains run and stop thresholds and line compensation at the CS pin. |
| CBC | 3 | I | Cable compensation is a programming pin for compensation of cable voltage drop. Cable compensation is programmed with a resistor to GND. |
| GND | 4 | — | The ground pin is both the reference pin for the controller and the low-side return for the drive output. Special care must be taken to return all AC decoupling capacitors as close as possible to this pin and avoid any common trace length with analog signal return paths. |
| CS | 5 | I | Current sense input connects to a ground-referenced current-sense resistor in series with the power switch. The resulting voltage is used to monitor and control the peak primary current. A series resistor can be added to this pin to compensate the peak switch current levels as the AC-mains input varies. |
| DRV | 6 | O | Drive is an output used to drive the base of an external high voltage NPN transistor. |
| HV | 7 | I | The high-voltage pin connects directly to the rectified bulk voltage and provides charge to the VDD capacitor for start-up of the power supply. |
