LTC2906_15 Datasheet, PDF (8/16 Pages) Linear Technology – Precision Dual Supply Monitors with One Pin-Selectable Threshold and One Adjustable Input

LTC2906/LTC2907
WU
W
TI I G DIAGRA
V_RTX
V_X
Vx Monitor Timing
t_UV
t_RST
RST
1V
RST
1V
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APPLICATIO S I FOR ATIO
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
8
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.
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