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HIP6004ACB

Buck and Synchronous-Rectifier (PWM) Controller and Output Voltage Monitor

Intersil 

HIP6004A

Functional Description

Initialization

The HIP6004A 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

10µA 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.

PGOOD

(2V/DIV.)

0V

SOFT-START

(1V/DIV.)

OUTPUT

VOLTAGE

(1V/DIV.)

0V

0V

t1

t2

t3

TIME (5ms/DIV.)

FIGURE 3. SOFT START INTERVAL

6

Over-Current Protection

The over-current function protects the converter from a

shorted output by using the upper MOSFET’s on-resistance,

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

converter’s efficiency and reduces cost by eliminating a

current sensing resistor.

4V

2V

0V

15A

10A

5A

0A

TIME (20ms/DIV.)

FIGURE 4. OVER-CURRENT OPERATION

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 200µA 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 converter dissipates very

little power with this method. The measured input power for the

conditions of Figure 4 is 2.5W.

The over-current function will trip at a peak inductor current

(IPEAK) determined by:

IPEAK = I--O-----C----S----rE--D--T--S---•-(--O-R----NO----)-C----S----E----T--

where IOCSET is the internal OCSET current source (200µA

typical). The OC trip point varies mainly due to the

MOSFET’s rDS(ON) variations. To avoid over-current

tripping in the normal operating load range, find the ROCSET

resistor from the equation above with:

1. The maximum rDS(ON) at the highest junction

temperature.

2. The minimum IOCSET from the specification table.

3. Determine IPEAK for IPEAK > IOUT(MAX) + (∆I) ⁄ 2 ,

where ∆I is the output inductor ripple current.

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