UCC2800/2801/2802/2803/2804/2805Q1

LOW POWER BICMOS CURRENT MODE PWM

SGLS121B − JULY 2002 − REVISED 2004

6

POST OFFICE BOX 655303

detailed terminal descriptions

COMP

COMP is the output of the error amplifier and the input of the PWM comparator.

Unlike other devices, the error amplifier in the UCC2800 family is a true, low output-impedance, 2-MHz

operational amplifier. As such, the COMP terminal can both source and sink current. However, the error

amplifier is internally current limited, so that one can command zero duty cycle by externally forcing COMP to

GND.

The UCC2800 family features built-in full cycle soft start. Soft start is implemented as a clamp on the maximum

COMP voltage.

CS

CS is the input to the current sense comparators. The UCC2800 family has two different current sense

comparators: the PWM comparator and an over-current comparator.

The UCC2800 family contains digital current sense filtering, which disconnects the CS terminal from the current

sense comparator during the 100 ns interval immediately following the rising edge of the OUT pin. This digital

filtering, also called leading-edge blanking, means that in most applications, no analog filtering (RC filter) is

required on CS. Compared to an external RC filter technique, the leading-edge blanking provides a smaller

effective CS to OUT propagation delay. Note, however, that the minimum non-zero on-time of the OUT signal

is directly affected by the leading-edge-blanking and the CS to OUT propagation delay.

The over-current comparator is only intended for fault sensing, and exceeding the over-current threshold

causes a soft start cycle.

FB

FB is the inverting input of the error amplifier. For best stability, keep the FB lead length as short as possible

and the FB stray capacitance as small as possible.

ground (GND)

GND is reference ground and power ground for all functions on this part.

OUT

OUT is the output of a high-current power driver capable of driving the gate of a power MOSFET with peak

currents exceeding

The high-current power driver consists of FET output devices, which can switch all of the way to GND and all

that in many cases, external Schottky clamp diodes are not required.