Datasheet

LTC2904/LTC2905
9
29045fd
APPLICATIONS INFORMATION
V
X
RST
RST
t
UV
t
RST
1V
1V
V
RTX
29045 TD
V
X
Monitor Timing
TIMING DIAGRAM
Supply Monitoring
The LTC2904/LTC2905 are low power, high accuracy dual
supply monitors with a common reset output and selectable
thresholds. Reset delay is set to a nominal of 200ms for
the LTC2904 and is adjustable using an external capacitor
for the LTC2905.
The two 3-state input pins (S1 and S2) select one of nine
possible threshold voltage combinations. Another three-
state input pin sets the supply tolerance (5%, 7.5% or
10%). Both input voltages (V1 and V2) must be above
predetermined thresholds for the reset not to be invoked.
The LTC2904/LTC2905 assert the reset outputs during
power-up, power-down and brownout conditions on either
of the voltage inputs.
Power-Up
The greater of V1, V2 is the internal supply voltage (V
CC
).
V
CC
powers the drive circuits for the RST pin. Therefore as
soon as V1 or V2 reaches 1V during power-up, the RST
output asserts low.
V
CC
also powers the drive circuits for the RST pin in the
LTC2904. Therefore, RST weakly pulls high when V1 or
V2 reaches at least 1V.
Threshold programming is complete when V1 reaches
at least 2.17V. After programming, if either V1 or V2 falls
below its programmed threshold, RST asserts low (RST
weakly pulls high) as long as V
CC
is at least 1V.
Once V1 and V2 rise above their thresholds, an internal
timer is started. After the programmed delay time, RST
weakly pulls high (RST asserts low).