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LTC2906/LTC2907

29067f

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 VADJ) 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, VCC is the internal supply voltage

(VMAX). VMAX powers the drive circuits for the RST pin.

Therefore, as soon as V1 or VCC reaches 1V during power

up, the RST output asserts low.

VMAX also powers the drive circuits for the RST pin in the

LTC2906. Therefore, RST weakly pulls high when either

V1 or VCC 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

RST

tUV

tRST

VRTX

29067 TD

Vx Monitor Timing

falls below its programmed threshold, RST asserts low

(RST weakly pulls high) as long as VMAX is at least 1V.

Once both V1 and VADJ 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 VADJ drops below its

threshold, RST asserts logic low and RST weakly pulls

high. VMAX 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

VCC pin. Since the internal supply voltage (VMAX) is the

greater of V1, VCC; a VCC of at least 1V guarantees logic low

of 0.4V at RST for voltage inputs (V1 and/or VADJ) 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 10

µA.

LTC2906 Datasheet(PDF) 8 Page - Linear Technology

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