Datasheet

LTC2953
18
2953f
TYPICAL APPLICATIONS
Dual Supply Monitor with μP Reset
The circuit of Figure 22 monitors two supplies and provides
a μP reset. When either the
⎯
P
⎯
F
⎯
I or the VM input voltage
falls below its threshold (0.5V), the
⎯
R
⎯
S
⎯
T output is asserted
low.
⎯
R
⎯
S
⎯
T remains low for 200ms after both inputs rise
above 0.5V. The low leakage
⎯
P
⎯
F
⎯
O output allows for large
valued external resistors.
Reverse Battery Protection
To protect the LTC2953 from a reverse battery connec-
tion, place a 1k resistor (R8) in series with the V
IN
pin.
See Figure 23.
2953 F22
LTC2953
–
+
–
+
0.5V
0.5V
RST
RST
PFI
VM
PFO
μP
V2
V1
V
IN
V
OUT
ON/OFF
ENV
IN
LTC2953-1
LT1761
SHDN
8.4V
R5
910k
2953 F23
PB
+
R8
1k
Figure 22. Dual Supply Monitor with μP Reset
Figure 23. Reverse Battery Protection Using R8
Operation with Supply Transients over 40V
The application circuit of Figure 24 operates from a 24V
nominal supply, but can withstand supply transients as
high as 40V.
The high voltage
⎯
E
⎯
N output of the LTC2953-2 has an ab-
solute maximum rating of 50V, which makes it suitable for
driving the gate of the external power PFET. The external
30V Zener diode (Z1) and the 10k current limiting resistor
(RZ) protect the V
IN
supply pin of the LTC2953-2. Note
that under normal 24V operation, the external Zener diode
does not conduct any current. The voltage drop across
RZ should be kept below 1V. Z2 should have a breakdown
voltage smaller than the PFET’s gate-to-source breakdown
voltage.
ON/OFF
ENV
IN
LTC2953-2
2953 F24
PB
R5
100k
RZ
10k
R9
100k
24V NOMINAL,
40V TRANSIENTS
FDS4685
Si2319DS
NDS9407
10V
Z2
BZX84C10
30V
Z1
BZX84C30
50V
ABS MAX
1μF
50V
Figure 24. Operation with 40V Supply Transients
Power Path Controller with Low Battery Detect
The application in Figure 25 uses the push button to
completely disconnect the load from the battery. If the
battery voltage falls below the user specifi ed threshold, the
push button is prevented from turning on system power
(asserting the enable output).