HIP6003 datasheet(5/12 Pages) INTERSIL

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RT/OVP (Pin 15)

This pin is multiplexed, providing two functions. The ﬁrst

function is oscillator switching frequency adjustment. By

placing a resistor (RT) from this pin to GND, the nominal

200KHz switching frequency is increased according to the

following equation:

Conversely, connecting a pull-up resistor (RT) from this pin

to VCC reduces the switching frequency according to the

following equation:

The second function for this pin is to drive an external SCR

in the event of an overvoltage condition.

VSEN (Pin 16)

This pin is connected to the converters output voltage. The

PGOOD and OVP comparator circuits use this signal to

report output voltage status and for overvoltage protection.

Functional Description

Initialization

The HIP6003 automatically initializes upon receipt of power.

Special sequencing of the input supplies is not necessary.

The Power-On Reset (POR) function continually monitors

the input supply voltages. The POR monitors the bias

voltage at the VCC pin and the input voltage (VIN) on the

OCSET pin. The level on OCSET is equal to VIN less a ﬁxed

voltage drop (see over-current protection). The POR function

initiates soft start operation after both input supply voltages

exceed their POR thresholds. For operation with a single

+12V power source, VIN and VCC are equivalent and the

+12V power source must exceed the rising VCC threshold

before POR initiates operation.

Soft Start

The POR function initiates the soft start sequence. An

internal 10

µA current source charges an external capacitor

(CSS) on the SS pin to 4V. Soft start clamps the error

ampliﬁer output (COMP pin) and reference input (+ terminal

of error amp) to the SS pin voltage. Figure 3 shows the soft

start interval with CSS = 0.1µF. Initially the clamp on the error

ampliﬁer (COMP pin) controls the converter’s output voltage.

At t1 in Figure 3, the SS voltage reaches the valley of the

oscillator’s triangle wave. The oscillator’s triangular

waveform is compared to the ramping error ampliﬁer voltage.

This generates PHASE pulses of increasing width that

charge the output capacitor(s). This interval of increasing

pulse width continues to t2. With sufﬁcient output voltage,

the clamp on the reference input controls the output voltage.

This is the interval between t2 and t3 in Figure 3. At t3 the

SS voltage exceeds the DACOUT voltage and the output

voltage is in regulation. This method provides a rapid and

controlled output voltage rise. The PGOOD signal toggles

‘high’ when the output voltage (VSEN pin) is within

±5% of

DACOUT. The 2% hysteresis built into the power good

comparators prevents PGOOD oscillation due to nominal

output voltage ripple.

Over-Current Protection

The over-current function protects the converter from a

shorted output by using the upper MOSFETs on-resistance,

rDS(ON) to monitor the current. This method enhances the

converter’s efﬁciency and reduces cost by eliminating a

current sensing resistor.

The over-current function cycles the soft-start function in a

hiccup mode to provide fault protection. A resistor (ROCSET)

programs the over-current trip level. An internal 200

µA current

sink develops a voltage across ROCSET that is referenced to

VIN. When the voltage across the upper MOSFET (also

referenced to VIN) exceeds the voltage across ROCSET, the

over-current function initiates a soft-start sequence. The soft-

start function discharges CSS with a 10µA current sink and

inhibits PWM operation. The soft-start function recharges

CSS, and PWM operation resumes with the error amplifier

clamped to the SS voltage. Should an overload occur while

recharging CSS, the soft start function inhibits PWM operation

while fully charging CSS to 4V to complete its cycle. Figure 4

shows this operation with an overload condition. Note that the

inductor current increases to over 15A during the CSS

charging interval and causes an over-current trip. The

200kHz

≈

510

•

T kΩ

()

---------------------

T to GND

()

200kHz

≈

410

•

T kΩ

()

---------------------

T to 12V

()

FIGURE 3. SOFT START INTERVAL

TIME (5ms/DIV)

SOFT-START

(1V/DIV)

OUTPUT

(1V/DIV)

VOLTAGE

PGOOD

(2V/DIV)

HIP6003

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