參數(shù)資料
型號: LTC4365HDDB#TRPBF
廠商: LINEAR TECHNOLOGY CORP
元件分類: 電源管理
英文描述: 1-CHANNEL POWER SUPPLY SUPPORT CKT, PDSO8
封裝: 3 X 2 MM, LEAD FREE, PLASTIC, M0-229WECD-1, DFN-8
文件頁數(shù): 16/16頁
文件大?。?/td> 369K
代理商: LTC4365HDDB#TRPBF
LTC4365
9
4365f
Overvoltage and Undervoltage Protection
The LTC4365 provides two accurate comparators to moni-
tor for overvoltage (OV) and undervoltage (UV) conditions
at VIN. If the input supply rises above the user adjustable
OV threshold, the gate of the external MOSFET is quickly
turned off, thus disconnecting the load from the input.
Similarly, if the input supply falls below the user adjust-
able UV threshold, the gate of the external MOSFET also
is quickly turned off. Figure 3 shows a UV/OV application
for an input supply of 12V.
Figure 2. Gate Drive (GATE – VOUT) vs VOUT
APPLICATIONS INFORMATION
Figure 2 highlights the dependence of the gate drive on VIN
and VOUT. When system power is first turned on (SHDN
low to high, VOUT = 0V), gate drive is at a maximum for all
values of VIN. This helps prevent start-up problems into
heavy loads by ensuring that there is enough gate drive
to support the load.
As VOUT ramps up from 0V, the absolute value of the GATE
voltage remains fixed until VOUT is greater than the lower
of (VIN –1V) or 6V. Once VOUT crosses this threshold,
gate drive begins to increase up to a maximum of 9.8V
(for VIN ≥ 12V). The curves of Figure 2 were taken with
a GATE load of –1μA. If there were no load on GATE, the
gate drive for each VIN would be slightly higher.
Note that when VIN is at the lower end of the operating
range, the external N-channel MOSFET must be selected
with a corresponding lower threshold voltage.
VIN
12V
UVTH = 3.5V
OVTH = 18V
4365 F03
DISCHARGE GATE
WITH 50mA SINK
LTC4365
OV
COMPARATOR
UV
COMPARATOR
R3
1820k
UV
0.5V
OV
R2
243k
R1
59k
+
25mV
+
25mV
Figure 3. UV, OV Comparators Monitor 12V Supply
The external resistive divider allows the user to select
an input supply range that is compatible with the load at
VOUT. Furthermore, the UV and OV inputs have very low
leakage currents (typically < 1nA at 100°C), allowing for
large values in the external resistive divider. In the applica-
tion of Figure 3, the load is connected to the supply only if
VIN lies between 3.5V and 18V. In the event that VIN goes
above 18V or below 3.5V, the gate of the external N-channel
MOSFET is immediately discharged with a 50mA current
sink, thus isolating the load from the supply.
Table 1 lists some external MOSFETs compatible with
different VIN supply voltages.
Table 1. Dual MOSFETs for Various Supply Ranges
VIN
MOSFET
VTH(MAX)
VGS(MAX)
VDS(MAX)
2.5V
SiB914
0.8V
5V
8V
3.3V
Si5920
1.0V
5V
8V
5V
Si7940
1.5V
8V
12V
≤30V
Si4230
3.0V
20V
30V
≤60V
Si9945
3.0V
20V
60V
VOUT (V)
0
ΔV
GATE
(V)
2
4
6
10
8
12
9
15
4365 F02
36
12
VIN = 30V
VIN = 12V
VIN = 5V
VIN = 3.3V
VIN = 2.5V
T = 25°C
IGATE = –1μA
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