LCS701HG datasheet(5/26 Pages) POWERINT

部品番号	LCS701HG

部品情報	Integrated LLC Controller, High-Voltage Power MOSFETs and Drivers

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メーカー	POWERINT [Power Integrations, Inc.]

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5 / 26 page

Rev. B 062011

5

LCS700-708

www.powerint.com

HiperLCS Basic Operation

The HiperLCS is designed for half-bridge LLC converters, which

are high-efficiency resonant, variable frequency converters. The

HiperLCS is an LLC controller chip with built-in drivers and

half-bridge MOSFETs.

LLC converters require a fixed dead-time between switching

half-cycles. The dead-time, maximum frequency at start-up,

and burst threshold frequencies, are programmed with a resistor

divider on the DT/BF pin from the VREF to the GROUND pins.

The FEEDBACK (FB) pin is the frequency control input for the

feedback loop. Frequency is proportional to FEEDBACK pin

current. The FEEDBACK pin V-I characteristic resembles a

diode to ground.

Burst Mode

If the frequency commanded by the FEEDBACK pin current

exceeds the upper burst threshold frequency (f

STOP, ISTOP)

programmed by the resistor divider on the DT/BF pin, the output

MOSFETs will turn off, and will resume switching when the current

drops below the value which corresponds to the frequency

equal to the lower burst threshold frequency (f

START, ISTART). As a

first approximation, burst mode control resembles a hysteretic

controller where the frequency ramps from f

START to fSTOP, stops

and repeats. An external component network connected from

the VREF pin to the FEEDBACK pin determines the minimum

and start-up FEEDBACK pin currents, and thus the minimum

and start-up switching frequencies. A soft-start capacitor in

this network determines soft-start timing.

The VREF pin provides a nominal 3.4 V as a reference for this

FEEDBACK pin external network and other functions. Maximum

current from this pin must be ≤4 mA.

The Dead-Time/Burst Frequency (DT/BF) pin also has a diode-to-

ground V-I characteristic. A resistor divider from VREF to GROUND

programs dead-time, maximum start-up switching frequency (f

MAX),

and the burst threshold frequencies. The current flowing from the

resistor divider to the DT/BF pin determines f

MAX. The ratio of the

resistors selects from 3 discrete, burst threshold frequency ratios,

which are fixed fractions of f

MAX.

The OV/UV pin senses the high-voltage B+ input through a

resistor divider. It implements brown-in, brown-out, and OV

with hysteresis. The ratios of these voltages are fixed; the user

must select the resistor divider ratio such that the brown-in

voltage is below the minimum nominal bulk (input) voltage

regulation set-point to ensure start-up, and the OV (lower)

restart voltage is above the maximum nominal bulk voltage

set-point, to ensure that the LCS will restart after a voltage swell

event that triggers the OV upper threshold. If different brown-in

to brown-out to OV ratios are required, external circuitry needs

to be added to the resistor divider.

VCC Pin UVLO

The VCC pin has an internal UVLO function with hysteresis. The

HiperLCS will not start until the voltage exceeds the VCC start

threshold V

UVLO(+). HiperLCS will turn off when the VCC drops to

the VCC Shutdown Threshold V

UVLO(-).

VCCH Pin UVLO

The VCCH pin is the supply pin for the high-side driver. It also

has a UVLO function similar to the VCC pin, with a threshold

lower than the VCC pin. This is to allow for a VCCH voltage that

is slightly lower than VCC because the VCCH pin is fed by a

bootstrap diode and series current-limiting resistor from the

VCC supply.

Start-Up and Auto-Restart

Before start-up the FEEDBACK pin is internally pulled up to the

VREF pin to discharge the soft-start capacitor and to keep the

output MOSFETs off. When start-up commences the internal

pull-up transistor turns off, the soft-start capacitor charges, the

outputs begin switching at f

MAX, the FEEDBACK pin current

diminishes, the switching frequency drops, and the PSU output

rises. When the output reaches the voltage set-point, the

optocoupler will conduct, closing the loop and regulating the output.

Whenever the VCC pin is powered up, the DT/BF pin goes into

high impedance mode for 500 ms in order to sense the voltage

divider ratio and select the Burst Threshold. This setting is

stored until the next VCC recycle. The DT/BF pin then goes into

normal mode, resembling a diode to ground, and the sensed

current continuously sets the f

MAX frequency. The burst threshold

frequencies are fixed fractions of f

MAX. The internal oscillator

runs the internal counters at f

MAX whenever the FEEDBACK pin

internal pull-up is on.

When a fault is detected on the IS, OV/UV, or VCC pin (UVLO),

the internal FEEDBACK pin pull-up transistor turns on for

131,072 clock cycles, to discharge the soft-start capacitor

completely, then a restart is attempted. The first power-up after

a VCC recycle only waits 1024 cycles, including the condition

where the OV/UV pin rises above the brown-in voltage for the

first time, after VCC is powered up.

Remote-Off

Remote-off can be invoked by pulling down the OV/UV pin to

ground, or by pulling up the IS pin to >0.9 V. Both will invoke a

131,072 cycle restart cycle. VCC can also be pulled down to

shut the device off, but when it is pulled up, the FEEDBACK pin

is pulled up to the VREF pin to discharge the soft-start capacitor

for only 1024 f

MAX clock cycles. If this scheme is used, the

designer must ensure that the time the VCC is pulled down,

plus 1024 cycles, is sufficient to discharge the soft-start

capacitor, or if not, that the resulting lower starting frequency is

high enough so as not to cause excessive primary currents that

may cause the over-current protection to trip.

Current Sense

The IS pin senses the primary current. It resembles a reverse

diode to the GROUND pin. It is tolerant of negative voltages

provided the negative current is limited to <5 mA. Therefore it

must be connected to the current sense resistor (or primary

capacitive voltage divider + sense resistor) via a series current

limiting resistor of >220 W. Thus it can accept an AC waveform

and does not need a rectifier or peak detector circuit. If the IS

pin senses a nominal positive peak voltage of 0.5 V for 7

consecutive cycles, an auto-restart will be invoked. The IS pin

also has a second, higher threshold at nominally 0.9 V, which

will invoke an auto-restart with a single pulse. The minimum

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