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參數(shù)資料
| 型號(hào)： | HIP6011 |
| 廠商： | HARRIS SEMICONDUCTOR |
| 元件分類： | 穩(wěn)壓器 |
| 英文描述： | Buck Pulse-Width Modulator (PWM) Controller and Output Voltage Monitor |
| 中文描述： | SWITCHING CONTROLLER, 1000 kHz SWITCHING FREQ-MAX, PDSO14 |
| 文件頁(yè)數(shù)： | 5/9頁(yè) |
| 文件大?。?/td> | 89K |
| 代理商： | HIP6011 |
5
Functional Description
Initialization
The HIP6011 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 and the enable (EN) pin. The POR
monitors the bias voltage at the VCC pin and the input volt-
age (V
IN
) on the OCSET pin. The level on OCSET is equal
to V
IN
less a fixed voltage drop (see over-current protection).
With the EN pin held to VCC, 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
IN
and VCC are equivalent and the +12V power
source must exceed the rising VCC threshold before POR
initiates operation.
The Power-On Reset (POR) function inhibits operation with
the chip disabled (EN pin low). With both input supplies
above their POR thresholds, transitioning the EN pin high ini-
tiates a soft start interval.
Soft Start
The POR function initiates the soft start sequence. An
internal 10
μ
A current source charges an external capacitor
(C
SS
) on the SS pin to 4V. Soft start clamps the error ampli-
fier output (COMP pin) and reference input (+ terminal of
error amp) to the SS pin voltage. Figure 3 shows the soft
start interval with C
SS
= 0.1
μ
F. 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 wave-
form 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 out-
put voltage rise.
Over-Current Protection
The over-current function protects the converter from a
shorted output by using the upper MOSFET’s on-resistance,
r
DS(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 (R
OCSET
)
programs the over-current trip level. An internal 200
μ
A (typi-
cal) current sink develops a voltage across R
OCSET
that is
reference to V
IN
. When the voltage across the upper MOS-
FET (also referenced to V
IN
) exceeds the voltage across
R
OCSET
, the over-current function initiates a soft-start
sequence. The soft-start function discharges C
SS
with a
10
μ
A current sink and inhibits PWM operation. The soft-start
function recharges C
SS
, and PWM operation resumes with
the error amplifier clamped to the SS voltage. Should an
overload occur while recharging C
SS
, the soft start function
inhibits PWM operation while fully charging C
SS
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 C
SS
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.
(I
PEAK)
determined by:
where I
OCSET
is the internal OCSET current source
(200
μ
A - typical). The OC trip point varies mainly due to the
MOSFET’s r
DS(ON)
variations. To avoid over-current tripping
in the normal operating load range, find the R
OCSET
resistor
from the equation above with:
1) The maximum r
DS(ON)
at the highest junction
temperature.
TIME (5ms/DIV)
SOFT-START
(1V/DIV)
0V
0V
t1
t2
t3
OUTPUT
VOLTAGE
(1V/DIV)
FIGURE 3. SOFT START INTERVAL
O
S
0A
0V
TIME (20ms/DIV)
5A
10A
15A
2V
4V
FIGURE 4. OVER-CURRENT OPERATION
I
PEAK
I
---------------------------------------------------
R
DS ON
)
=
HIP6011
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