Document Number: 72660

S11-0598-Rev. E, 25-Apr-11

www.vishay.com

7

Vishay Siliconix

SiP2800, SiP2801, SiP2802, SiP2803, SiP2804, SiP2805

This datasheet is subject to change without notice.

The SiP280X family incorporates internal leading-edge

blanking on the CS pin, to keep any spurious voltages on the

CS pin from reaching the comparator inputs during the

100 ns interval immediately following the rising edge on OUT

(for example, voltages due to capacitive charging currents).

Because of this internal leading-edge blanking, many

applications require no external RC filter on the CS input.

Compared to circuits requiring the use of an external RC filter

circuit, leading-edge blanking provides a shorter effective CS

to OUT propagation delay.

FB

FB is the inverting input of the VEA. Internally compared

To avoid stability problems, keep lead lengths to FB as short

as possible, and use good layout practices to minimize the

stray capacitances of components connected to this pin.

GND

The GND pin is both the reference ground and the power

ground for this part.

OUT

OUT is the output of a high-current driver capable of peak

currents in excess of ± 750 mA. OUT is therefore well suited

to driving the gates of power MOSFETs. This pin is

threshold, to ensure a predictable system turn-on. Since the

OUT pin is internally connected to a low impedance CMOS

buffer, it is capable of rapid rail-to-rail transitions. This output

topology also mitigates the effects of undershoot and

overshoot. For this reason, external Schottky clamp diodes

are generally not required on this pin.

RC

from RC to GND. Due to the high impedances encountered

in low power control circuits, this connection must be a short

and quiet return to GND (preferably by means of a dedicated

signal trace, separated from all other circuit functions).

The oscillator frequency for the SiP280X family of parts is

approximated by the following formulas:

For the SiP2800, SiP2801, SiP2802, and SiP2804:

For the SiP2803 and SiP2805:

For the SiP2800, SiP2801, SiP2802 and SiP2804:

For the SiP2803 and SiP2805:

on-chip 130

 resistor, unless the circuit is configured with

an inherent internal comparator delay time of 100 ns. The

capacitance associated with the RC pin is approximately

Note that the SiP2801, SiP2804, and SiP2805 have an

internal toggle flip-flop at the output of the oscillator, to

ensure that the output duty cycle never exceeds 50 %. This

divides the frequency appearing at the OUT pin to one-half

of the oscillator frequency for these three parts.

values will prevent the oscillator from properly discharging

REF

The reference generator block of the Si280X provides an

accurate and stable 4.0 V or 5.0 V (depending upon part

number), which is available at this pin of the IC. This voltage

is also used internally for other functions on the IC. One of

these uses is as the logic power supply for high speed

switching logic on the IC; this, and stability concerns, make it

ceramic capacitor, as close to the part as possible. An

electrolytic or tantalum capacitor may be used in addition to

threshold, REF is pulled to ground through a 5 k

 resistor.

Hence, REF can also be used as an output to indicate the

controller IC, and should be the most positive terminal on the

limiting resistor. The required start-up supply current will

UVLO voltage of the SiP280X, and can remain at or below

500 µA total supply current once the part starts switching.

To prevent the IC from being damaged by overvoltage

conditions, each of the SiP2800 family of parts has an

internal clamp (effectively a 13.5 V Zener diode) between

its rated voltage, nor will the device as a whole exceed its

rated power dissipation. This does require knowing what the

operating current of the IC will be, so that the value of the

dropping resistor can be calculated. A good estimate of the

three components:

(a)

(b)

The operating current required by the IC itself, and

(c)

power switch.