UCC29421, UCC29422, UCC39421, UCC39422

MULTIMODE HIGHFREQUENCY PWM CONTROLLER

SLUS246C − OCTOBER 1999 − REVISED FEBRUARY 2005

5

POST OFFICE BOX 655303

• DALLAS, TEXAS 75265

electrical characteristics over recommended operating free-air temperature range, TA = −40°C to

85

°C for the UCC2942x, 0°C to 70°C for the UCC3942x, RT = 100 kΩ, VVPUMP = 6 V, VVIN = 3 V.

PARAMETER

TEST CONDITIONS

MIN

TYP

MAX

UNITS

Voltage Detection Section (UCC39422 Only)

Threshold voltage

1.18

1.26

1.34

V

Output low voltage

I = 5 mA

0.15

0.3

V

Output leakage

LOWBAT = 8 V

0.05

0.25

µA

PIN DESCRIPTIONS

COMP: This is the output of the transconductance error amplifier. Connect the compensation components from

this pin to ground.

CHRG: This is the gate drive output for the N-channel charge MOSFET. Connect it to the gate directly, or through

a low-value gate resistor.

CP: This is the input for the charge pump. For applications requiring a charge pump, connect this pin to the

charge pump diode and flying capacitor, as shown in the applications diagram of Figure 4. For applications

where no charge pump is required, this pin should be grounded.

FB: The feedback input is the inverting input to the transconductance error amplifier. Connect this pin to a

resistive divider between VOUT and ground. The output voltage is regulated to:

V

OUT +

1.235

(R1

) R2)

R1

where R1 goes to GND and R2 goes to VOUT.

GND: This is the signal ground pin for the device. It should be tied to the local ground plane.

ISENSE: This is the input to the X10 wide bandwidth current-sense amplifier. Connect this pin to the high side

of the current-sense resistor. An internal current is sourced out this pin for slope compensation. For applications

requiring slope compensation (or filtering of the current-sense signal), use a resistor in series with this pin.

LOWBAT: This is the open drain output of the uncommitted comparator. (UCC39422 only). This output is low

when the VDET pin is above 1.25 V.

PFM: This is the programming pin for the PFM (pulse frequency modulation) mode threshold. Connect this pin

to a resistive divider off of the FB pin (or VOUT) to set the PFM threshold. To disable PFM Mode, connect this

pin to ground (below 0.2 V).

PGND: This is the power ground pin for the device. Connect it directly to the ground return of the current-sense

resistor.

RECT: This is the gate drive output for the synchronous rectifier. Connect it to the gate of the P- or N-channel

MOSFET directly, or through a low value gate resistor.

RSEN: This pin is used to sense the voltage across the synchronous rectifier for commutation. In boost

configurations, connect this pin through a 1-k

Ω resistor to the junction of the two MOSFETs and the inductor.

In flyback and SEPIC configurations, connect this pin through a 1-k

Ω resistor to the junction of the drain of the

synchronous rectifier and the secondary side winding of the coupled inductor.

RSADJ: A capacitor from this pin to ground sets the reset delay. (UCC39422 only)

RSEL: This pin programs the device for N- or P-channel synchronous rectifiers by inverting the phase of the

RECT gate drive output. Connect this pin to ground for N-channel MOSFETs, connect it to VIN for P-channel

MOSFETs.