SLUS829G August   2008  – February 2020 UCC2897A


  1. Features
  2. Applications
  3. Description
    1.     Device Images
      1.      Typical Application Diagram
  4. Revision History
  5. Device Options
  6. Pin Configuration and Functions
    1.     Pin Functions
  7. Specifications
    1. 7.1 Absolute Maximum Ratings
    2. 7.2 ESD Ratings
    3. 7.3 Recommended Operating Conditions
    4. 7.4 Thermal Information
    5. 7.5 Electrical Characteristics
    6. 7.6 Timing Requirements
    7. 7.7 Typical Characteristics
  8. Detailed Description
    1. 8.1 Overview
    2. 8.2 Functional Block Diagram
    3. 8.3 Feature Description
      1. 8.3.1 Detailed Pin Descriptions
        1.  RDEL
        2.  RON
        3.  ROFF
        4.  VREF
        5.  SYNC
        6.  GND
        7.  CS
        8.  RSLOPE
        9.  FB
        10. SS/SD
        11. PGND
        12. AUX
        13. OUT
        14. VDD
        15. LINEUV
        16. VIN
        17. LINEOV
      2. 8.3.2 JFET Control and UVLO
      3. 8.3.3 Line Undervoltage Protection
      4. 8.3.4 Line Overvoltage Protection
      5. 8.3.5 Pulse Skipping
      6. 8.3.6 Synchronization
      7. 8.3.7 Gate Drive Connection
      8. 8.3.8 Bootstrap Biasing
    4. 8.4 Device Functional Modes
  9. Application and Implementation
    1. 9.1 Application Information
    2. 9.2 Typical Application
      1. 9.2.1 Design Requirements
      2. 9.2.2 Detailed Design Procedure
        1. Oscillator
        2. Soft Start
        3. VDD Bypass Requirements
        4. Delay Programming
        5. Input Voltage Monitoring
        6. Current Sense and Slope Compensation
      3. 9.2.3 Application Curves
  10. 10Power Supply Recommendations
  11. 11Layout
    1. 11.1 Layout Guidelines
    2. 11.2 Layout Example
  12. 12Device and Documentation Support
    1. 12.1 Documentation Support
      1. 12.1.1 Related Documentation
    2. 12.2 Receiving Notification of Documentation Updates
    3. 12.3 Community Resources
    4. 12.4 Trademarks
    5. 12.5 Electrostatic Discharge Caution
    6. 12.6 Glossary
  13. 13Mechanical, Packaging, and Orderable Information

Package Options

Mechanical Data (Package|Pins)
Thermal pad, mechanical data (Package|Pins)
Orderable Information

Pin Configuration and Functions

PW Package
20-Pin TSSOP
Top View
UCC2897A pin_assign_top_view_SLUS829.gif
RGP Package
20-Pin VQFN
Bottom View
UCC2897A pin_assign_bot_view_SLUS829.gif

Pin Functions

AUX 14 11 O This output drives the auxiliary-clamp MOSFET which turns on when the main PWM-switching device turns off. The AUX pin directly drives the auxiliary switch with a 2-A source turn-on current and a 2-A sink turn-off current.
CS 9 6 I This pin senses the peak current utilized for current-mode control and for current-limiting functions. The peak signal is applied to this pin before pulse-by-pulse current limiting activates and is approximately 0.5 V.
FB 11 8 I This pin brings the error signal from an external optocoupler or error amplifier into the PWM-control circuitry. Often, there is a resistor tied from FB to VREF, and an optocoupler pulls the control pin closer to GND to reduce the pulse width of the OUT output driving the main-power switch of the converter.
GND 8 5 This pin serves as the fundamental-analog ground for the PWM-control circuitry. This pin is connected to PGND directly at the device.
LINEOV 19 16 I The LINEOV pin is an input pin of voltage comparator with programmable hysteresis and 1.27-V threshold, providing LINE overvoltage or other functions.
LINEUV 18 15 I This pin provides a means to accurately enable/disable the power converter stage by monitoring the bulk input voltage or another parameter. When the circuit initially starts (or restarts from a disabled condition), a rising input on LINEUV enables the outputs when the threshold of 1.27 V is crossed. After the circuit is enabled, a falling LINEUV signal disables the outputs when the same threshold is reached. The hysteresis between the two levels is programmed using an internal current source.
OUT 15 12 O This output pin drives the main PWM switching element MOSFET in an active-clamp controller. The OUT pin directly drives an N-channel device with a 2-A source turnon-current and a 2-A sink turnoff-current. TI recommends connecting a 10-kΩ resistor from this pin to PGND pin.
PGND 13 10 The PGND should serve as the current return for the high-current output drivers OUT and AUX. Ideally, the current path from the outputs to the switching devices, and back would be as short as possible, and enclose a minimal-loop area.
PVDD 16 13 I The PVDD pin is the supply pin for the power devices. It is separated internally from the VDD pin.
RSLOPE 10 7 I A resistor connected from this pin to GND programs an internal current source that sets the slope-compensation ramp for the current-mode control-circuitry.
RTDEL 3 20 I A resistor from this pin to GND programs the turn-on delay of the two gate-drive outputs to accommodate the resonant transitions of the active-clamp power converter.
ROFF 5 2 I A resistor connected from this pin to GND programs an internal-current source that discharges the internal timing-capacitor.
RON 4 1 I A resistor connected from this pin to GND programs an internal-current source that charges the internal timing-capacitor.
SS/SD 12 9 I A capacitor from SS/SD to ground is charged by an internal-current source of IRON to program the soft-start interval for the controller. During a fault condition this capacitor is discharged by a current source equal to IRON.
SYNC 7 4 I The SYNC pin serves as a bidirectional-synchronization input for the internal oscillator. The synchronization function is implemented such that the user-programmable maximum duty-cycle (set by RON and ROFF) remains accurate during synchronized operation. This pin is left open when not in use. The external capacitance is minimized. No capacitors are connected to this pin.
VDD 17 14 I The VDD pin is the power supply for the device. There should be a 1-μF capacitor directly from VDD to PGND. The capacitor value should be at least 10-times larger than that on VREF. PGND and GND are connected externally and directly from PGND pin to GND pin. (To make a full design of capacitance on VDD pin, please refer to, Application Note: Understanding and Designing an Active Clamp Current Mode Controlled Converter (SLUA535), section 7.3)
VIN 1 18 I This pin is connected to the input-power rail directly. Inside the device, a high-voltage start-up device is utilized to provide the start-up current for the controller until a bootstrap-type bias rail becomes available.
VREF 6 3 O The VREF pin is the 5-V reference voltage that is used for an external load of up to 5 mA. Since this reference provides the supply rail for internal logic, VREF is bypassed to AGND as close as possible to the device. The VREF bias profile is not always monotonic before VDD reaches 5 V.