参数资料
型号: LTC3785IUF
厂商: LINEAR TECHNOLOGY CORP
元件分类: 稳压器
英文描述: 3 A SWITCHING CONTROLLER, 1000 kHz SWITCHING FREQ-MAX, PQCC24
封装: 4 X 4 MM, PLASTIC, MO-220WGGD, QFN-24
文件页数: 3/20页
文件大小: 275K
代理商: LTC3785IUF
LTC3785
3785fc
operaTion
To have the power converter latch off on a fault, a pull-up
current between 4A and 7A on the RUN/SS pin will allow
the RUN/SS capacitor to discharge during an extended
fault,butwillpreventcyclingofthefaultwhichwillcausethe
converter to stay off. One method to implement this is by
placingadiode(anodetiedtoVOUT)andaresistorfromVOUT
totheRUN/SSpin.ThecurrentsourcedintoRUN/SSwillbe
VOUT – 0.7 divided by the resistor value. To ignore all faults
sourcegreaterthan40AintotheRUN/SSpin(At1.225Von
theRUN/SSpin).Sincethemaximumfaultcurrentislimited,
this will prevent any discharging of the RUN/SS capacitor,
the soft-start capacitor will need to be sized accordingly to
accommodatetheextrachargingcurrentatstart-up.
During an output short-circuit or if VOUT is less than 1.8V,
the current limit folds back to 50% of the programmed
level.
REVERSE CURRENT LIMIT
The LTC3785 can be programmed to provide full class D
operation or allowed to source and sink current equal to
the current limit set value. This is achieved by asserting a
high level on the CCM pin. To minimize the reverse output
current, the CCM pin should be driven low or strapped to
ground. During this mode only, –15mV typical is allowed
across output switch D and is sensed with the ISVOUT and
ISSW2pins.
Figure 3. Block Diagram of Current Limit Fault Circuitry
+
+
+
+
+
+
gm
gm = 1/20k
ILIMIT COMP
IMAX COMP
TURN
SWITCHES
B AND D ON
V = 60k/RILSET
(15k/RILSET WHEN VOUT < 1.8V)
X10
V = 90k/RILSET
0.7V
2A
2.2V
CSS
1/3 ILIM(OUT)
10A MAX
ILIM(OUT)
30A MAX
1A
RUN/SS
VOUT
FB
R1
R2
ILIM COMP
IMAX COMP
VC
CP1
1.225V
THERMAL SD
RUN
FAULT
LOGIC
ILIMIT
SET
SAMPLED
REVERSE
CURRENT LIMIT
CCM = HIGH = 6k/RILSET
CCM = LOW = 15mV
ISVIN
VIN
VOUT
COUT
L1
TG1
SW1
SW2
A
B
D
C
ISSW2
ISSW1
CCM
ISVOUT
+
TG2
3785 F03
SWITCH D
OFF
1.225V
ERROR AMP
+
ILSET
RILSET
BG1
BG2
S
1
4
3
2
5
15
14
13
12
10
6
17
18
19
20
22
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