LTC1727 datasheet(7/16 Pages) LINER

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LTC2917/LTC2918

29178f

GND: Device Ground.

⎯M⎯R (LTC2918 only): Manual Reset Input (Active Low). A

low level on the ⎯M⎯R input causes the part to issue a reset,

which is released one reset timeout after the input goes

high. The pin has an internal 100k pull-up to VCC, and

thus may interface directly to a momentary pushbutton.

Leave open if unused.

⎯R⎯S⎯T: Open Drain ⎯R⎯S⎯T Output. Asserts low when VM is

below the threshold selected by SEL1, SEL2 and TOL input

pins. Held low for an adjustable timeout after VM input is

above threshold.

RT: Reset Timeout Control Pin. Attach an external capaci-

tor (CRT) to GND to set a reset timeout of 9ms/nF. Leave

RT open to generate a reset timeout of approximately

400μs. Tie RT to VCC to generate a reset timeout of ap-

proximately 200ms.

SEL1, SEL2: Monitor Voltage Select Three-State Input.

SEL1, and SEL2 control the nominal threshold voltage

that VM is set to monitor. Connect to VCC, GND or leave

unconnected in open state. (See Table 1).

TOL (LTC2917 only): Three-State Input for Supply Tol-

erance Selection (–5%, –10% or –15%). Controls the

tolerance band at which the VM supply is monitored.

Connect to VCC, GND, or leave unconnected in open state.

(See Table 2)

VCC: Power Supply input. Bypass this pin to ground with

a 0.1μF ceramic capacitor. A minimum of 1.5V on VCC

ensures that the part is out of under voltage lockout and

that the voltage thresholds are accurate. Operates as a

direct supply input for voltages up to 5.5V. Operates as a

shunt regulator for supply voltages greater than 5.7V and

should have a resistor between this pin and the supply

to limit VCC input current to no greater than 5mA. When

used without a current-limiting resistor, pin voltage must

not exceed 5.7V.

VM: Voltage Monitor Input to ⎯R⎯S⎯T comparator. SEL1, SEL2

and TOL inputs select the exact threshold that asserts the

⎯R⎯S⎯T output.

WDI: Watchdog Input. This pin must be driven to change

state within a time less than the watchdog upper bound-

ary time, or ⎯R⎯S⎯T will be asserted low. On the LTC2917-B,

LTC2918-B, the period must also be greater than the

watchdog lower boundary time, and only falling edges

are considered. Tie WT and WDI to GND to disable the

watchdog timer.

WT: Watchdog Timer Control Pin. Attach an external

capacitor (CWT) to GND to set a watchdog upper bound-

ary timeout time of 72ms/nF. Tie WT to VCC to generate a

timeout of approximately 1.6s. Leave WT open to generate

a timeout of approximately 3.2ms. Tie WT and WDI to

GND to disable the watchdog timer.

Exposed Pad (DFN Only): Exposed pad may be left open

or connected to device ground.

PIN FUNCTIONS

SUPPLY VOLTAGE, VCC (V)

1234

29178 G10

10k PULL-UP R TO VCC

SEL1 = SEL2 = TOL = 0V

VM = 0.5V

SUPPLY VOLTAGE, VCC (V)

123

29178 G11

RST AT 150mV

RST AT 50mV

IRST (mA)

0.6

0.8

1.0

29178 G12

0.4

0.2

TA = 125°C

TA = 25°C

TA = –40°C

NO PULL-UP R

VCC = 2.5V

TYPICAL PERFORMANCE CHARACTERISTICS

⎯R⎯S⎯T Output Voltage vs VCC

⎯R⎯S⎯T Pull-Down Current vs VCC

⎯R⎯S⎯T VOL vs IRST

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