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HIP6004A_02 Datasheet(数据表) 6 Page - Intersil Corporation

部件型号  HIP6004A
说明  Buck and Synchronous-Rectifier (PWM) Controller and Output Voltage Monitor
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制造商  INTERSIL [Intersil Corporation]
网页  http://www.intersil.com/cda/home
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HIP6004A Datasheet(HTML) 6 Page - Intersil Corporation

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6
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
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 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.
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 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:
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
,
where
∆I is the output inductor ripple current.
0V
0V
0V
TIME (5ms/DIV.)
SOFT-START
(1V/DIV.)
OUTPUT
(1V/DIV.)
VOLTAGE
t2
t3
PGOOD
(2V/DIV.)
t1
FIGURE 3. SOFT START INTERVAL
0A
0V
TIME (20ms/DIV.)
5A
10A
15A
2V
4V
FIGURE 4. OVER-CURRENT OPERATION
I
PEAK
I
OCSET
R
OCSET
r
DS ON
()
---------------------------------------------------
=
I
PEAK
I
OUT MAX
()
∆I
() 2
+
>
HIP6004A




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