LTM4607 datasheet(15/28 Pages) LINER

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LTC3780

3780fe

OPERATION

FOLDBACK CURRENT

Foldback current limiting is activated when the output

voltage falls below 70% of its nominal level, reducing

power waste. During start-up, foldback current limiting

is disabled.

INPUT UNDERVOLTAGE RESET

The SS capacitor will be reset if the input voltage is al-

lowed to fall below approximately 4V. The SS capacitor

will attempt to charge through a normal soft-start ramp

after the input voltage rises above 4V.

OUTPUT OVERVOLTAGE PROTECTION

An overvoltage comparator guards against transient over-

shoots (>7.5%) as well as other more serious conditions

that may overvoltage the output. In this case, synchronous

switch B and synchronous switch D are turned on until the

overvoltage condition is cleared or the maximum negative

current limit is reached. When inductor current is lower

than the maximum negative current limit, synchronous

switch B and synchronous switch D are turned off, and

switch A and switch C are turned on until the inductor

current reaches another negative current limit. If the

comparator still detects an overvoltage condition, switch

A and switch C are turned off, and synchronous switch B

and synchronous switch D are turned on again.

SHORT-CIRCUIT PROTECTION AND CURRENT LIMIT

Switch A on-time is limited by output voltage. When output

voltage is reduced and is lower than its nominal level,

switch A on-time will be reduced.

In every boost mode cycle, current is limited by a voltage

reference, which is proportional to the ITH pin voltage. The

maximum sensed current is limited to 160mV. In every

buck mode cycle, the maximum sensed current is limited

to 130mV.

STANDBY MODE PIN

The STBYMD pin is a three-state input that controls circuitry

within the IC as follows: When the STBYMD pin is held at

ground, the SS pin is pulled to ground. When the pin is

left open, the internal SS current source charges the SS

capacitor, allowing turn-on of the controller and activat-

ing necessary internal biasing. When the STBYMD pin is

taken above 2V, the internal linear regulator is turned on

independent of the state on the RUN and SS pins, providing

an output power source for “wake-up” circuitry. Bypass

the pin with a small capacitor (0.1μF) to ground if the pin

is not connected to a DC potential.

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