LT3790 datasheet(24/32 Pages) LINER

24 / 32 page

LT8390

8390fa

For more information www.linear.com/LT8390

APPLICATIONS INFORMATION

ISMON Current Monitor

The ISMON pin provides a buffered monitor output of the

currentflowingthroughtheISP/ISNcurrentsenseresistor,

RIS. The VISMON voltage is calculated as V(ISP-ISN) • 10 +

0.25V. Since the ISMON pin has the same 0.25V offset

as the CTRL pin, the master LT8390 ISMON pin can be

directly tied to the slave LT8390 CTRL pin for equal current

sharing in parallel applications.

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 LT8390 power output from the

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

LT8390 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

LT8390applicationsrequiringloadswitchcontrol.Thehigh

sidePMOSloadswitchistypicallyselectedfordrain-source

voltage VDS, gate-source threshold voltage VGS(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 LT8390 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 •

+R4

In addition, the FB pin also sets output overvoltage

threshold, PGOOD upper and lower thresholds, and out-

put short threshold. For an application with small output

capacitors, the output voltage may overshoot a lot during

load transient event. Once the FB pin hits its overvoltage

threshold 1.1V, the LT8390 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 •

+R4

To provide the output short-circuit detection and protec-

tion, the output short threshold can be set as:

VOUT(SHORT) = 0.25V •

+R4

Power GOOD (PGOOD) Pin

The LT8390 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.

Soft-Start and Short-Circuit Protection

As shown in Figure 8 and explained in the Operation sec-

tion, the SS pin can be used to program the output voltage

soft-start by connecting an external capacitor from the SS

pin to ground. The internal 12.5µA pull-up current charges

up the capacitor, creating a voltage ramp on the SS pin.

As the SS pin voltage rises linearly from 0.25V to 1V (and

beyond), the output voltage rises smoothly into its final

voltageregulation.Thesoft-starttimecanbecalculatedas:

tSS = 1V •

CSS

12.5µA

LT8390

VOUT

8390 F15

Figure 15. Feedback Resistor Connection

LT3790 数据表(PDF) 24 Page - Linear Technology

LT3790 数据表(HTML) 24 Page - Linear Technology

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32

数据表下载