hip6004a Intersil Corporation, hip6004a Datasheet - Page 6

• Manufacturer Part Number: hip6004a
• Description: Buck And Synchronous-rectifier Pwm Controller And Output Voltage Monitor
• Manufacturer: Intersil Corporation

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 (V
the OCSET pin. The level on OCSET is equal to V
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, V
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 (C
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
C
pin) controls the converter’s output voltage. At t
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 t
output voltage, the clamp on the reference input controls the
output voltage. This is the interval between t
At t
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.
SS
0V
0V
0V
3
= 0.1µF. Initially the clamp on the error amplifier (COMP
the SS voltage exceeds the DACOUT voltage and the
SOFT-START
(1V/DIV.)
FIGURE 3. SOFT START INTERVAL
t
1
TIME (5ms/DIV.)
(2V/DIV.)
PGOOD
IN
t
2
6
and VCC are equivalent and
t
3
2
and t
2
1
. With sufficient
in Figure 3,
OUTPUT
VOLTAGE
(1V/DIV.)
3
in Figure 3.
IN
SS
IN
less a
) on
) on
HIP6004A
Over-Current Protection
The over-current function protects the converter from a
shorted output by using the upper MOSFET’s on-resistance,
r
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 (R
programs the over-current trip level. An internal 200µA current
sink develops a voltage across R
V
referenced to V
over-current function initiates a soft-start sequence. The soft-
start function discharges C
inhibits PWM operation. The soft-start function recharges C
and PWM operation resumes with the error amplifier clamped
to the SS voltage. Should an overload occur while recharging
C
charging C
operation with an overload condition. Note that the inductor
current increases to over 15A during the C
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
(I
where I
typical). The OC trip point varies mainly due to the
MOSFET’s r
tripping in the normal operating load range, find the R
resistor from the equation above with:
I
DS(ON)
1. The maximum r
2. The minimum I
3. Determine I
PEAK
PEAK)
IN
SS
. When the voltage across the upper MOSFET (also
temperature.
where ∆I is the output inductor ripple current.
15A
10A
, the soft start function inhibits PWM operation while fully
5A
0A
4V
2V
0V
=
OCSET
determined by:
to monitor the current. This method enhances the
I
-------------------------------------------------- -
OCSET
FIGURE 4. OVER-CURRENT OPERATION
SS
DS(ON)
to 4V to complete its cycle. Figure 4 shows this
r
IN
DS ON
is the internal OCSET current source (200µA
PEAK
) exceeds the voltage across R
•
(
R
OCSET
DS(ON)
OCSET
variations. To avoid over-current
)
for
TIME (20ms/DIV.)
I
SS
PEAK
from the specification table.
at the highest junction
with a 10µA current sink and
OCSET
>
I
OUT MAX
(
that is referenced to
SS
)
charging interval
+
(
OCSET
∆I
) 2 ⁄
OCSET
,
OCSET
, the
SS
)
,