LT3790 datasheet(23/30 Pages) LINER

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LT8390A

8390afa

For more information www.linear.com/LT8390A

Figure 14. Programming Output Current Limit

LT8390A

ISP

8390a F14a

ISN

RIS

TO SYSTEM

OUTPUT

FROM DRAIN OF

SWITCH D

LT8390A

ISP

8390a F14b

ISN

RIS

TO SYSTEM

OUTPUT

FROM DRAIN OF

SWITCH D

(14a)

(14b)

APPLICATIONS INFORMATION

Load Switch Control

The LOADEN and LOADTG pins provide high side PMOS

load switch control. The LOADEN pin accepts a logic level

ON/OFF signal and then drives the LOADTG pin to turn on

or off the high side PMOS load switch, thereby connect-

ing or disconnecting the LT8390A power output from the

system output. When the LOADEN pin is forced low, the

LT8390A turns off TG1 and TG2, turns on BG1 and BG2,

disconnects the VC pin from all internal loads, and turns

off LOADTG. The LOADEN pin should not be left open (tie

to INTVCC or VREF if not used).

High Side PMOS Load Switch Selection

A high side PMOS load switch is recommended in some

LT8390A applications requiring load switch control. The

high side PMOS load switch is typically selected for drain-

sourcevoltageVDS,gate-sourcethresholdvoltageVGS(TH),

and continuous drain current ID. For proper operations,

VDS rating should exceed the output regulation voltage

set by the FB pin, the absolute value of VGS(TH) should

be less than 3V, and ID rating should be above IOUT(MAX).

Programming Output Voltage and Thresholds

The LT8390A has a voltage feedback pin FB that can be

used to program a constant-voltage output. The output

voltage can be set by selecting the values of R3 and R4

(Figure 15) according to the following equation:

VOUT = 1V •

R3+R4

In addition, the FB pin also sets output overvoltage

threshold, output power good thresholds, and output

short threshold. For an application with small output

capacitors, the output voltage may overshoot a lot during

LT8390A

VOUT

8390a F15

Figure 15. Feedback Resistor Connection

load transient event. Once the FB pin hits its overvoltage

threshold 1.1V, the LT8390A stops switching by turning

off TG1, BG1, TG2, and BG2, and also turns off LOADTG

to disconnect the output load for protection. The output

overvoltage threshold can be set as:

VOUT(OVP) = 1.1V •

R3+R4

Toprovidetheoutputshort-circuitdetectionandprotection,

the output short falling threshold can be set as:

VOUT(SHORT) = 0.25V •

R3+R4

Power GOOD (PGOOD) Pin

The LT8390A provides an open-drain status pin, PGOOD,

which is pulled low when VFB is within ±10% of the 1.00V

regulation voltage. The PGOOD pin is allowed to be pulled

up by an external resistor to INTVCC or an external voltage

source of up to 6V.

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