參數(shù)資料
型號: LTM4600IVPBF
廠商: Linear Technology Corporation
英文描述: 10A High Effi ciency DC/DC レModule
中文描述: 10A條高艾菲布缺陷直流/直流レ模塊
文件頁數(shù): 12/24頁
文件大?。?/td> 370K
代理商: LTM4600IVPBF
LTM4600
12
4600fa
APPLICATIU
After the controller has been started and given adequate
time to charge up the output capacitor, CSS is used as a
short-circuit timer. After the RUN/SS pin charges above 4V,
if the output voltage falls below 75% of its regulated value,
then a short-circuit fault is assumed. A 1.8μA current then
begins discharging CSS. If the fault condition persists until
the RUN/SS pin drops to 3.5V, then the controller turns
off both power MOSFETs, shuting down the converter
permanently. The RUN/SS pin must be actively pulled
down to ground in order to restart operation.
The over-current protection timer requires the soft-start
timing capacitor CSS be made large enough to guarantee
that the output is in regulation by the time CSS has reached
the 4V threshold. In general, this will depends upon the
size of the output capacitance, output voltage and load
current characteristic. A minimum external soft-start
capacitor can be estimated from:
W
U
U
Generally 0.1μF is more than sufficient.
Since the load current is already limited by the current
mode control and current foldback circuitry during a
shortcircuit, over-current latchoff operation is NOT always
needed or desired, especially the output has large amount
of capacitance or the load draw huge current during start
up. The latchoff feature can be overridden by a pull-up
current greater than 5μA but less than 80μA to the RUN/SS
pin. The additional current prevents the discharge of CSS
during a fault and also shortens the soft-start period. Us-
ing a resistor from RUN/SS pin to V
IN
is a simple solution
C
pF
C
V
F V
SS EXT
_
OUT
OUT
S
(
])
+
>
1000
10
3
V
IN
V
IN
500k
RUN/SS
PGND
4600 F04
LTM4600
SGND
Figure 4. Defeat Short-Circuit Latchoff with a Pull-Up
Resistor to V
IN
Figure 3. RUN/SS Pin Voltage During Startup and
Short-Circuit Protection
V
RUN/SS
3.5V
t
t
75%V
O
SWITCHING
STARTS
SOFT-START
CLAMPING
OF I
L
RELEASED
SHORT-CIRCUIT
LATCHOFF
OUTPUT
OVERLOAD
HAPPENS
SHORT-CIRCUIT
LATCH ARMED
4V
3V
1.5V
4600 F03
V
O
to defeat latchoff. Any pull-up network must be able to
maintain RUN/SS above 4V maximum latchoff threshold
and overcome the 4μA maximum discharge current. Figure
3 shows a conceptual drawing of V
RUN
during startup and
short circuit.
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