LCS700-708 datasheet(3/26 Pages) POWERINT

3 / 26 page

Rev. B 062011

LCS700-708

www.powerint.com

Pin Functional Description

VCC Pin

IC power pin. In a typical application, VCC is connected to the

12 V system standby supply via a 5 W resistor. This resistor

helps provide filtering and improves noise immunity.

Note: The system standby supply return should be connected to

the B- bus and not to the GROUND pin.

VREF Pin

3.4 VREF pin. An internal voltage reference network used as a

voltage source for FEEDBACK pin and DT/BF pin pull-up

resistor.

GROUND (G) Pin

G is the return node for all analog small signals. All small signal

pin bypass capacitors must be returned to this pin through short

traces, with the exception of the D-S high-voltage bypass

capacitor, and the VCCH bypass capacitor. It is internally

connected to the SOURCE pins to provide a star connection.

Do not connect the GROUND pin to the SOURCE pins,

nor to the B- bus, in the PCB layout.

OV/UV Pin

Overvoltage/Undervoltage pin. B+ is sensed by this pin through

a resistor divider. The OV/UV pin implements brown-in,

brown-out, and overvoltage lockout with hysteresis. Pulling this

pin down to ground will implement a remote-off function.

FEEDBACK (FB) Pin

Current fed into this pin determines LLC switching frequency;

higher current programs higher switching frequency. The pin

V-I characteristic resembles a diode to ground during normal

switching. An RC network between the VREF pin and

FEEDBACK pin determines the minimum operating frequency,

start-up frequency, soft-start time, and delay before start-up.

DEAD-TIME/BURST FREQUENCY (DT/BF) Pin

A resistor divider from VREF to ground programs dead-time,

maximum switching frequency at start-up, and burst-mode

threshold frequencies.

CURRENT-SENSE (IS) Pin

The CURRENT-SENSE pin is used for sensing transformer

primary current, to detect overload and fault conditions, through

a current sense resistor or a capacitive divider plus sense resistor

circuit. It resembles a reverse diode to ground, and does not

require a rectifier circuit for preventing negative pulses from

reaching the pin, provided the reverse current is limited to <5 mA.

Figure 3.

Pin Numbering and Designation.

SOURCE (S1), (S2) Pins

SOURCE pins of internal low-side MOSFET. These should be

connected together on the PCB, and connected to the B- from

the PFC bulk capacitor or input high-voltage DC return.

HB Pin

This is the output of the half-bridge connected MOSFETs

(Source of high-side MOSFET, Drain of low-side MOSFET), to

be connected to the LLC power train (transformer primary and

series resonant capacitor).

VCCH Pin

Floating bootstrap supply pin for the LLC high-side driver. This

pin is referenced to the HB pin, which in turn is internally

connected to the SOURCE pin of the high-side MOSFET. A

bypass/storage capacitor between VCCH and HB pins, and a

boot strap diode with a series resistor from the standby supply,

are required. The storage capacitor is refreshed every time the

lower MOSFET turns on or its body diode conducts.

DRAIN (D) Pin

DRAIN pin of the internal high-side MOSFET. This connects to

the B+ from the PFC bulk capacitor or input high-voltage DC bus.

PI-5636-051311

H Package (eSIP-16C)

1314

910

1 3 4 5 6 7

Exposed Pad

(Backside) Internally

Connected to GROUND

Pin (see eSIP-16C

Package Drawing)

Exposed Metal

(On Package Edge)

Internally

Connected

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