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參數(shù)資料
| 型號(hào)： | ISL6406 |
| 廠商： | Intersil Corporation |
| 英文描述： | Single Synchronous Buck Pulse-Width Modulation (PWM) Controller(單同步降壓PWM控制器) |
| 中文描述： | 單同步降壓脈寬調(diào)制（PWM）控制器（單同步降壓的PWM控制器） |
| 文件頁(yè)數(shù)： | 9/18頁(yè) |
| 文件大?。?/td> | 380K |
| 代理商： | ISL6406 |
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9
FN9073.7
January 16, 2007
.
Frequency Synchronization and Enable
The external frequency synchronization and enable
functions are combined in SYNC/EN pin. This pin is TTL
compatible for VCC = 3.3V or 5V. The device is disabled if
the input to this pin is TTL LOW for more than 40
μ
s (typ.); it
is enabled if the input is TTL HIGH without delay. When
disabling the IC, the charge pump is turned off and the
BOOT pin is left charged at ~5V. In some cases this charge
will inadvertant leak through the upper gate driver and can
possibly turn on the upper FET. To avoid this, it is
recommended that a 1M
Ω
‘bleed’ resistor be connected from
the BOOT pin to GND. This resistor is shown in the typical
application schematic in page 4 as R
BOOT
.
The SYNC/EN pin is monitored by the internal timer. The
timer allows SYNC pulses (TTL LOW level) to pass through,
as long as the pulses are shorter than 22
μ
s. The minimum
SYNC pulse width is 40ns (typ.).
The oscillator can SYNC to an external frequency of
between 1.1 times and 2.0 times the free-running frequency.
Loop acquisition time is about 200 clock cycles. The timing
resistor (RT) is always required, regardless of whether
SYNC pulses are being used or not.
For instance, if RT is selected such that the switching
frequency is 100kHz then the ISL6406 can be synchronized
to a switching frequency from 110kHz to 200kHz.
Overcurrent Protection
The overcurrent function protects the converter from a
shorted output by using the upper MOSFET 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 (see Typical Application diagrams). An internal
20μA (typical) current sink develops a voltage across
R
OCSET
that is referenced to V
IN
. When the voltage across
the upper MOSFET (also referenced to V
IN
) exceeds the
voltage across R
OCSET
, the over current function initiates a
soft-start sequence.
Figure 5 illustrates the protection feature responding to an
overcurrent event. At time t0, an overcurrent condition is
sensed across the upper MOSFET. As a result, the regulator
is quickly shutdown and the internal soft-start function begins
producing soft-start ramps. The delay interval seen by the
output is equivalent to three soft-start cycles. The fourth
internal soft-start cycle initiates a normal soft-start ramp of the
output, at time t1. The output is brought back into regulation
by time t2, as long as the overcurrent event has cleared. Had
the cause of the over current still been present after the delay
interval, the over current condition would be sensed and the
regulator would be shut down again for another delay interval
of three soft-start cycles. The resulting hiccup mode style of
protection would continue to repeat indefinitely.
The overcurrent function will trip at a peak inductor current
(I
peak
) determined by Equation 3:
where I
OCSET
is the internal OCSET current source (20μA
typical). The OC trip point varies mainly due to the MOSFET
r
DS(ON)
variations. To avoid overcurrent tripping in the
FIGURE 4. OUTPUT VOLTAGE SELECTION
+
R1
C3
C
OUT
+3.3V
V
OUT
R4
L
OUT
ISL6406,
C4
Q1
FB
UGATE
VCC
BOOT
COMP
D1
R2
C2
C1
R3
PHASE
LGATE
Q2
CPVOUT
VIN
FIGURE 5. OVERCURRENT PROTECTION RESPONSE
0V
TIME
V
OUT
(2.5V)
t1
t0
t2
INTERNAL SOFT-START FUNCTION
DELAY INTERVAL
I
PEAK
I
-----------------r
(
)
R
DS ON
(
)
)
=
(EQ. 3)
ISL6406
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相關(guān)代理商/技術(shù)參數(shù) |
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|---|---|
| ISL6406CB | 制造商:Rochester Electronics LLC 功能描述:HI EFFICIENCY, LO VOLTAGE, SINGLE PWM W/ADJ. OUTPUT - Bulk |
| ISL6406CB-T | 制造商:Rochester Electronics LLC 功能描述:- Tape and Reel |
| ISL6406CR | 制造商:Rochester Electronics LLC 功能描述:- Bulk 制造商:Intersil Corporation 功能描述: |
| ISL6406CRZ | 制造商:Intersil Corporation 功能描述: |
| ISL6406CV | 制造商:Rochester Electronics LLC 功能描述:- Bulk |
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