Features: · PFC With Isolation, VO < VIN
· Single Power Stage
· Zero Current Switched IGBT
· Programmable ZCS Time
· Corrects PF to >0.99
· Fixed Frequency, Average Current Control
· Improved RMS Feedforward
· Soft Start
· 9V to 18V Supply V Range
· 20-Pin DW, N, J, and L PackagesPinout
SpecificationsInput Supply Voltage (VIN, VD) . . . . . . . . . . . . . . . . . . . 18V
General Analog/Logic Inputs
(CRMS, MOUT, CA, VA, CT, RT, PKLMT)
(Maximum Forced Voltage). . . . . . . . . . . . . . . . 0.3V to 5V
IAC (Maximum Forced Current) . . . . . . . . . . . . . . . . . 300A
Reference Output Current . . . . . . . . . . . . Internally Limited
Output Current (MOSDRV, IGDRV1, IGDRV2)
Pulsed. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1A
Continuous . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 200mA
Storage Temperature . . . . . . . . . . . . . .. .-65°C to +150°C
Junction Temperature. . . . . . . . . . . . . . . -55°C to +150°C
Lead Temperature (Soldering, 10 Sec.). . . . . . . . . +300°C
Unless otherwise indicated, voltages are reference to ground and currents are positive into, negative out of the specified terminal. Pulsedis defined as a less than 10% duty cycle with a maximum duration of 500 s. Consult Packaging Section of Databook for thermal limitations and considerations of packages.DescriptionThe UCC3857 provides all of the control functions necessary for an Isolated oost PFC Converter. These converters have the advantage of transformer solation between primary and secondary, as well as an output bus oltage that is lower than the input voltage. By providing both power factor orrection and down conversion in a single power processing stage, the CC3857 is ideal for applications which require high efficiency, integration, nd performance.
The UCC3857 brings together the control functions and drivers necessary o generate overlapping drive signals for external IGBT switches, and provides separate output to drive an external power MOSFET which provides ero current switching (ZCS) for both the IGBTs. Full programmability s provided for the MOSFET driver delay time with an external RC network. CS for the IGBT switches alleviates the undesirable turn off losses typically ssociated with these devices. This allows for higher switching frequencies, maller magnetic components and higher efficiency. The power actor correction (PFC) portion of the UCC3857 employs the familiar average urrent control scheme used in previous Unitrode controllers. Internal ircuitry changes, however, have simplified the design of the PFC section nd improved performance.
UCC3857 Controller improvements include an internal 6 bit A-D onverter for RMS input line voltage detection, a zero oad power circuit, and significantly lower quiescent operating urrent. The A-D converter eliminates an external pole low pass filter for RMS detection.
This simplifies UCC3857 the converter design, eliminates 2nd harmonic ipple from the feedforward component, and provides n approximate 6 times improvement in input line ransient response. The zero load power comparator revents energy transfer during open load conditions ithout compromising power factor at light loads. Low tartup and operating currents which are achieved hrough the use of Unitrode's BCDMOS process simplify he auxiliary bootstrap supply design.
Additional features of UCC3857 include: under voltage lockout for reliable ff-line startup, a programmable over current shutdown,an auxiliary shutdown port, a precision 7.5V eference, a high amplitude oscillator ramp for improved oise immunity, softstart, and a low offset analog square,multiple and divide circuit. Like previous Unitrode PFC ontrollers, worldwide operation without range switches s easily implemented.
UCC2875 Data Sheet
