LTC2906/LTC2907
8
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APPLICATIO S I FOR ATIO
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Supply Monitoring
The LTC2906/LTC2907 are low power, high accuracy dual
supply monitoring circuits with an adjustable input and
another input with selectable threshold. Reset delay is set
to a nominal of 200ms for LTC2906 and is adjustable using
an external capacitor for LTC2907.
The three-state input pin (S1) selects one of three possible
threshold voltage levels for V1. Another three-state input
pin sets the supply tolerance (5%, 7.5% or 10%). Both
input voltages (V1 and V
ADJ
) must be above predeter-
mined thresholds for the reset not to be invoked. The
LTC2906/LTC2907 assert the reset outputs during power-
up, power-down and brownout conditions on any one of
the voltage inputs.
Power-Up
The greater of V1, V
CC
is the internal supply voltage
(V
MAX
). V
MAX
powers the drive circuits for the RST pin.
Therefore, as soon as V1 or V
CC
reaches 1V during power
up, the RST output asserts low.
V
MAX
also powers the drive circuits for the RST pin in the
LTC2906. Therefore, RST weakly pulls high when either
V1 or V
CC
reaches at least 1V.
Threshold programming is complete, when V1 reaches at
least 2.17V. After programming, if any one of the Vx inputs
TI I G DIAGRA
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V
X
RST
RST
t
UV
t
RST
1V
1V
V
RTX
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Vx Monitor Timing
falls below its programmed threshold, RST asserts low
(RST weakly pulls high) as long as V
MAX
is at least 1V.
Once both V1 and V
ADJ
inputs rise above their thresholds,
an internal timer is started. After the programmed delay
time, RST weakly pulls high (RST asserts low).
Power-Down
On power-down, once either V1 or V
ADJ
drops below its
threshold, RST asserts logic low and RST weakly pulls
high. V
MAX
of at least 1V guarantees a logic low of 0.4V
at RST.
Auxiliary Power
If an auxiliary power is available it can be connected to the
V
CC
pin. Since the internal supply voltage (V
MAX
) is the
greater of V1, V
CC
; a V
CC
of at least 1V guarantees logic low
of 0.4V at RST for voltage inputs (V1 and/or V
ADJ
) down
to 0V.
Programming Pins
The two three-state input pins, S1 and TOL, should be
connected to GND, V1 or left unconnected during normal
operation. Note that when left unconnected, the maximum
leakage current allowable from the pin to either GND or V1
is 10µA.
