LTC3118 datasheet(20/40 Pages) LINER

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LTC3118

3118fa

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RUN1 and RUN2 Pin Comparators

Forcing both RUN1 and RUN2 to a logic low places the

LTC3118 in a low current shutdown state. When the volt-

age on either pin is brought above a 0.65V logic threshold,

certain IC functions are enabled as shown in Figure 4a.

The RUN1 and RUN2 pins also include accurate internal

comparators that allow them to be used to set custom

rising and falling ON/OFF thresholds for VIN1 and VIN2,

respectively,withtheadditionofexternalresistordividers.

IfeitherRUNpinvoltageisincreasedtoexceeditsaccurate

comparatorthreshold(1.22Vnominal),allfunctionsofthe

buck-boost converter will be enabled and switching will

commence, assuming the respective VIN and VCC UVLO

circuits are cleared (see Figure 2).

If both RUN1 and RUN2 are brought below the accurate

comparatorthreshold,thebuck-boostconverterwillinhibit

switching, but the VCC regulator and control circuitry will

remain powered unless both RUN pins are brought below

the logic threshold. Therefore, in order to completely

shut down the IC and reduce the VIN currents to < 2µA

(typical), it is necessary to ensure that both RUN pins are

brought below the worst-case low logic threshold of 0.2V.

RUN1 and RUN2 are high voltage capable inputs but must

be connected to their respective VIN1 and VIN2 supplies

throughahighvalueresistorgreaterthan200ktoprevent

a potential latch condition at the pin. The RUN pins can

be driven above VIN or VOUT within their specified voltage

ratings. If either RUN pin is forced above 5V, it will sink a

small current, as given by the following equation:

IRUN ≈

VRUN − 5V

Ω

With the addition of optional resistor divider(s), as shown

in Figure 4a, the RUN pin(s) can be used to establish a

user-programmable turn-on and turn-off threshold.

The buck-boost converter is enabled when the voltage

on either RUN pin reaches 1.22V. Therefore, the turn-on

voltage threshold on VIN is given by:

VTURNON = 1.22V 1+













Figure 4. (a) Accurate RUN1 or RUN2 Pin Comparators, (b) Manual VIN Select with Overlap Timing, (c) Active VIN Indicators

operaTion

1.22V

VIN

LTC3118

3118 F04a

RUN1 OR

RUN2

ENABLE

SWITCHING

LOGIC

THRESHOLD

ACCURATE

THRESHOLD

ENABLE LDO AND

CONTROL CIRCUITS

–

0.65V

–

(a)

(b)

(c)

3118 F04b

LOGIC

SIGNAL

LOGIC

SIGNAL

100pF

RUN1

100pF

RUN2

VIN1

VIN2

VIN1

VIN2

3118 F04c

100pF

VIN1 ACTIVE

VIN2 ACTIVE

CN1

100pF

CN2

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