AN1660 datasheet(4/13 Pages) STMICROELECTRONICS

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AN1660 APPLICATION NOTE

4/13

L6598 DEVICE DESCRIPTION

The L6598 is an integrated circuit realised in BCD OFF-LINE technology. Able to drive POWER MOS or

IGBT, in half bridge topology, the L6598 is provided with all the features (such as VCO, SOFT-START,

OP-AMP and ENABLES) needed to implement and control properly a resonant SMPS with a minimum

components count. Even though the device is able to withstand high voltage (up to 600V), it can operate

at low voltage starting from its operative supply.

Table 1. Device Pins Description

Pin N°

Name

Function

1CSS

Soft Start Timing Capacitor. The capacitor CSS sets the soft start time, according to the rela-

tions: TSS = kSSCSS (typ. kSS = 0.15 s/µF). During tSS the capacitor is charged by means of a

current which depends on Rfstart value (i.e. on the difference between fstart and fmin). In this

way TSS is always set at kSSCSS (i.e. TSS depends only by CSS). In steady state the voltage at

pin 1 is 5V.

2Rfstart

Maximum Oscillation Frequency Setting. The 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, and so Rfstart set the Ifstart current equal to VREF/Rfstart. The mini-

mum Rfstart value which can be connected to this pin is 25 kOhm.

3Cf

Oscillator Frequency Setting. The capacitor CF, along with to Rfstart and Rfmin, sets fstart and

fmin. In normal operation this pin shows a triangular wave.

4Rfmin

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

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

rent equal to VREF/Rfmin. The minimum Rfmin value which can be connected to this pin is 25

kOhm.

5OPout

Out of the operational amplifier. To implement a feedback control loop this pin can be connected

to the Rfmin pin by means an appropriate circuitry.

6OPon-

Inverting Input of the operational amplifier.

7OPon+

Non Inverting Input of the operational amplifier.

EN1

Enable 1. This pin (active high), forces the device in a latched shutdown state (like in the under

voltage conditions). There are two ways to resume normal operation.

The first is to reduce the supply voltage below the undervoltage 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).

EN2

Enable 2. EN2 input (active high) restarts the start-up procedure (soft-start sequence).

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, connected to the supply filter capacitor, is internally clamped (15.6V

typical).

N.C.

Not Connected. It ensures the insulation between the high voltage section and the low voltage

one.

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. Between this pin and VS must be connected the bootstrap capac-

itor. A patented integrated circuitry replaces the high voltage external diode. This features is

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

FET.

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