AN1673 datasheet(2/24 Pages) STMICROELECTRONICS

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AN1673 APPLICATION NOTE

2/24

DEVICE PINS FUNCTION

Pin #

Name

Description

1CSS

Soft Start Timing Capacitor. The device is provided with Soft Start features. The capacitor CSS

sets the soft start time, according to the relations: TSS = kSS · CSS (typ. kSS = 0.15 s/µF). In

steady state the voltage at pin1 is 5V. During TSS a current Iss, function of Ifstart, charges the

capacitor. Anyway TSS, set at kSS · CSS depends only on CSS value. See pin-2 and timing

description in the data-sheet.

2Rfstart

Maximum Oscillation Frequency Setting. A resistance connected between this pin and ground

sets the fstart value, fixing the difference between fstart and fmin (fstart > fmin). The voltage at this

pin is fixed at VREF = 2V, so Rfstart programs the Ifstart current = VREF/Rfstart. The Rfstart value is

recommended to be not less than 18 - 20 kOhm.

3Cf

Oscillator Frequency Setting. The CF capacitor, with Rfstart and Rfmin, sets fstart and fmin. In

normal operation this pin shows a triangular wave. See timing and oscillator section in the data-

sheet.

4Rfmin

Minimum Oscillation Frequency Setting. A resistance connected between this pin and ground

sets the fmin value. The voltage at this pin is fixed at VREF =2V, so Rfmin sets the Ifmin current

equal to VREF/Rfmin. To set precise frequency, the Rfmin value is recommended not to be less

than 20 kOhm.

5OPout

Out of the operational amplifier. Characterized with 1M-gain bandwidth product, this Op Amp is a

free feature for any need. To implement a feedback control loop this pin can be connected to the

Remind pin by means of an appropriate circuitry.

6OPIN-

Inverting Input of the operational amplifier.

7OPIN+

Non Inverting Input of the operational amplifier.

EN1

Enable 1. This pin forces the device in latched shutdown state (The same as in under voltage

conditions). Active high, the typical threshold level is 0.6V. There are two ways to resume normal

operation. The first is to reduce the supply voltage below the under voltage threshold and then

increase it again until the valid supply is recognized. The second is activating EN2 input. The

enable-1 is especially designed for strong fault (e.g. in case of short circuit or open load).

EN2

Enable 2. Enable input (active high at 1.2V threshold level). When activated, this function forces

the soft-start sequence to be executed. The EN2 is prevalent on EN1 and so; it is possible to

cancel the latched enable (EN1).

GND

Ground

LVG

Low Side Driver Output. This pin must be connected to the low side power MOSFET gate of the

half bridge. A resistor connected between this pin and the power MOS gate can be used to

reduce the peak current.

Supply Voltage. This pin will be connected to the supply filter capacitor. An internal clamp (15.6V

typical) limits the supply voltage.

N.C.

Not Connected. This pin is not internally connected thus increasing the distance between the

high voltage and low voltage circuitry. The increased distance gives benefit for insulation.

OUT

High Side Driver Floating Reference. This pin must be connected close to the source of the high

side power MOS or IGBT.

HVG

High Side Driver Output. This pin must be connected to the high side power MOSFET gate of the

half bridge. A resistor connected between this pin and the power MOS gate can be used to

reduce the peak current.

Vboot

Bootstrapped Supply Voltage. The bootstrap capacitor must be connected between this pin and

VS. A patented integrated circuitry replaces the high voltage external diode. This feature is

achieved by means of a high voltage DMOS, synchronously driven with the low side power

MOSFET. See Bootstrap section in the data-sheet for details.

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