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UCC2897RTJT Datasheet(PDF) 7 Page - Texas Instruments |
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UCC2897RTJT Datasheet(HTML) 7 Page - Texas Instruments |
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7 / 40 page  UCC2897 SLUS591G − NOVEMBER 2003 − REVISED DECEMBER 2008 7 www.ti.com TERMINAL FUNCTIONS TERMINAL I/O DESCRIPTION NAME UCC2897 I/O DESCRIPTION AUX 14 O This output drives the auxiliary clamp P−channel MOSFET which is turned on when the main PWM switching device is turned off. The AUX pin can directly drive the auxiliary switch with 2-A source turn- on current and 2-A sink turn-off current. CS 9 I This pin is used to sense the peak current utilized for current mode control and for current limiting func- tions. The peak signal which can be applied to this pin before pulse-by-pulse current limiting activates is approximately 0.50 V for the UCC2897. FB 11 I This pin is used to bring 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 is used to pull 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 − This pin serves as the fundamental analog ground for the PWM control circuitry. This pin should be connected to PGND directly at the device. LINEOV 19 I Provides the LINE overvoltage function. LINEUV 18 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, then 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 O This output pin drives the main PWM switching element MOSFET in an active clamp controller. It can directly drive an N-channel device with 2-A source turn-on current and 2-A sink turn-off current. PGND 13 − 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 I This is the supply pin for the power devices in the IC. It is separated internally from the VDD pin. RSLOPE 10 I A resistor connected from this pin to GND programs an internal current source that sets the slope com- pensation ramp for the current mode control circuitry. RTDEL 3 I A resistor from this pin to GND programs the turn-on delay of the two gate drive outputs to accommo- date the resonant transitions of the active clamp power converter. RTOFF 5 I A resistor connected from this pin to GND programs an internal current source that discharges the in- ternal timing capacitor. RTON 4 I A resistor connected from this pin to GND programs an internal current source that charges the internal timing capacitor. SS/SD 12 I A capacitor from SS/SD to ground is charged by an internal current source of IRTON to program the soft-start interval for the controller. During a fault condition this capacitor is discharged by a current source equal to IRTON. SYNC 7 I The SYNC pin serves as a bidirectional synchronization input/output for the internal oscillator. The syn- chronization function is implemented such that the user programmable maximum duty cycle (set by RTON and RTOFF) remains accurate during synchronized operation. VDD 17 I This is the power supply for the device. There should be a minimum 0.1- µF capacitor directly from VDD to PGND. VIN 1 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 avail- able. VREF 6 O This is the 5-V reference voltage that can be utilized for an external load of up to 5 mA. Since this refer- ence provides the supply rail for internal logic, it should be bypassed to AGND as close as possible to the device. |
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