LTC2917/LTC2918
7
29178fb
GND: Device Ground.
MR (LTC2918 only): Manual Reset Input (Active Low). A low
level on the MR input causes the part to issue a reset, which
is released one reset timeout after the input goes high. The pin
has an internal 100k pull-up to V
CC
, and thus may interface
directly to a momentary pushbutton. Leave open if unused.
RST: Open Drain RST Output. Asserts low when VM is
below the threshold selected by SEL1, SEL2 and TOL input
pins. Held low for an adjustable timeout after VM input is
above threshold.
RT: Reset Timeout Control Pin. Attach an external capacitor
(C
RT
) to GND to set a reset timeout of 9ms/nF. Leave RT open
to generate a reset timeout of approximately 400μs. Tie RT to
V
CC
to generate a reset timeout of approximately 200ms.
SEL1, SEL2: Monitor Voltage Select Three-State Input.
SEL1, and SEL2 control the nominal threshold voltage
that VM is set to monitor. Connect to V
CC
, GND or leave
unconnected in open state. (See Table 1).
TOL (LTC2917 only): Three-State Input for Supply Tolerance
Selection (–5%, –10% or –15%). Controls the tolerance
band at which the VM supply is monitored. Connect to V
CC
,
GND, or leave unconnected in open state. (See Table 2)
V
CC
: Power Supply input. Bypass this pin to ground with a
0.1μF ceramic capacitor. A minimum of 1.5V on V
CC
ensures
that the part is out of under voltage lockout and that the
voltage thresholds are accurate. Operates as a direct supply
input for voltages up to 5.5V. Operates as a shunt regulator
for supply voltages greater than 5.7V and should have a
resistor between this pin and the supply to limit V
CC
input
current to no greater than 5mA. When used without a cur-
rent-limiting resistor, pin voltage must not exceed 5.7V.
VM: Voltage Monitor Input to RST comparator. SEL1, SEL2
and TOL inputs select the exact threshold that asserts the
RST output.
WDI: Watchdog Input. This pin must be driven to change
state within a time less than the watchdog upper bound-
ary time, or RST will be asserted low. On the LTC2917-B,
LTC2918-B, the period must also be greater than the
watchdog lower boundary time, and only falling edges
are considered. Tie WT and WDI to GND to disable the
watchdog timer.
WT: Watchdog Timer Control Pin. Attach an external
capacitor (C
WT
) to GND to set a watchdog upper bound-
ary timeout time of 72ms/nF. Tie WT to V
CC
to generate a
timeout of approximately 1.6s. Leave WT open to generate
a timeout of approximately 3.2ms. Tie WT and WDI to GND
to disable the watchdog timer.
Exposed Pad (DFN Only): Exposed Pad may be left open
or connected to device ground.
PIN FUNCTIONS
SUPPLY VOLTAGE, V
CC
(V)
0
0
RST VOLTAGE (V)
1
2
3
4
5
6
1234
29178 G10
5
10k PULL-UP R TO V
CC
SEL1 = SEL2 = TOL = 0V
VM = 0.5V
SUPPLY VOLTAGE, V
CC
(V)
0
0
PULL-DOWN CURRENT, I
RST
(mA)
1
2
3
4
5
6
1234
29178 G11
5
RST AT 150mV
RST AT 50mV
I
RST
(mA)
0
RST VOLTAGE (V)
0.6
0.8
1.0
8
29178 G12
0.4
0.2
0
2
4
6
10
T
A
= 125°C
T
A
= 25°C
T
A
= –40°C
NO PULL-UP R
V
CC
= 2.5V
TYPICAL PERFORMANCE CHARACTERISTICS
RST Output Voltage vs V
CC
RST Pull-Down Current vs V
CC
RST V
OL
vs I
RST
