參數(shù)資料
型號: LTC3856EUH#PBF
廠商: LINEAR TECHNOLOGY CORP
元件分類: 穩(wěn)壓器
英文描述: SWITCHING CONTROLLER, PQCC38
封裝: 5 X 5 MM, LEAD FREE, PLASTIC, MO-220WHHD-X, QFN-32
文件頁數(shù): 22/40頁
文件大?。?/td> 2222K
代理商: LTC3856EUH#PBF
LTC3856
3856f
Figure 14. Setting Output Voltage without the DIFFAMP
LTC3856
VFB
VOUT/DIFFOUT
RB
CFF
RA
3856 F14
applicaTions inForMaTion
Setting Output Voltage
If the DIFFAMP is not used, the LTC3856 output voltage
is set by an external feedback resistive divider carefully
placed across the output, as shown in Figure 14. The
regulated output voltage is determined by:
V
R
OUT
B
A
=
+
0 6
1
.
To improve the frequency response, a feedforward ca-
pacitor, CFF, may be used. Great care should be taken to
route the VFB line away from noise sources, such as the
inductor or the SW line.
If the diffamp is used, then VFB should be connected to the
output of the diffamp, DIFFOUT, as shown in the Typical
Application on the first page.
Fault Conditions: Current Limit and Current Foldback
The LTC3856 includes current foldback to help limit load
current when the output is shorted to ground. If the out-
put falls below 50% of its nominal output level, then the
maximum sense voltage is progressively lowered from its
maximumprogrammedvaluetoone-thirdofthemaximum
value. Foldback current limiting is disabled during the
soft-start or tracking up. Under short-circuit conditions
with very low duty cycles, the LTC3856 will begin cycle
skipping in order to limit the short-circuit current. In this
situation the bottom MOSFET will be dissipating most of
the power but less than in normal operation. The short
circuit ripple current is determined by the minimum on-
time tON(MIN) of the LTC3856 (≈ 90ns), the input voltage
and inductor value:
I
t
V
L
L SC
ON MIN
IN
( )
(
)
=
The resulting short-circuit current is:
I
V
R
I
SC
SENSE MAX
SENSE
L SC
=
1 3
1
2
/
(
)
( )
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