Datasheet
7
LTC1536
1536fa
TI I G DIAGRA S
W
W
U
V
CC
Monitor Timing Pushbutton Reset Function Timing
t < t
PB
t
PB
t
RST
t
DB
t
SRST
1536 TD02
PBR
RST
SRST
t
RST
1536 TD01
V
RTX
V
CCX
RST
t
FAIL
Fast Undervoltage Detect
t
FAIL
500mV
1536 TD03
V
CC3 OR
V
CC5
V
RTX
SLEW RATE ≤0.1V/µs
RST
t
PF
300mV
1536 TD04
V
CC5
FALL TIME ≤ 10ns, V
CC3
= 3.3V
RST
3.3V
Power-Fail Detect
APPLICATIONS INFORMATION
WUU
U
Operation
The LTC1536 is a low power, high accuracy triple supply
monitoring circuit. This reset generator has two basic
functions: generation of a reset when power supplies are
out of range, and generation of a reset or “soft” reset when
the reset button is pushed. The LTC1536 has the added
feature that when the reset supplies are grossly undervolt-
age there is a very short delay from undervoltage detect to
assertion of RST.
Supply Monitoring
All three V
CC
inputs must be above predetermined thresh-
olds for 200ms before the reset output is released. The
LTC1536 will assert reset during power-up, power-down
and brownout conditions on any one or more of the V
CC
inputs.
On power-up, either the V
CC5
or V
CC3
pin can power the
drive circuits for the RST pin. This ensures that RST will
be low when either V
CC5
or V
CC3
reaches 1V. As long as
any one of the V
CC
inputs is below its predetermined
threshold, RST will stay a logic low. Once all of the V
CC
inputs rise above their thresholds, an internal timer is
started and RST is released after 200ms. RST outputs the
inverted state of what is seen on RST.
RST is reasserted whenever any one of the V
CC
inputs
drops below its predetermined threshold and remains
asserted until 200ms after all of the V
CC
inputs are above
their thresholds.
On power-down, once any of the V
CC
inputs drops below
its threshold, RST is held at a logic low. A logic low of 0.4V
is guaranteed until V
CC3
and V
CC5
drops below 1V.
Pushbutton Reset
The LTC1536 provides a pushbutton reset input pin. The
PBR input has an internal pull-up current source to V
CC3
.
If the PBR pin is not used it can be left floating.