LT3741 datasheet(23/32 Pages) LINER

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LT8390

8390fa

For more information www.linear.com/LT8390

APPLICATIONS INFORMATION

When VCTRL is between 1.15V and 1.35V the current limit

varies with VCTRL, but departs from the equation above

by an increasing amount as VCTRL increases. Ultimately,

when VCTRLislargerthan1.35V,thecurrentlimitnolonger

varies. The typical V(ISP-ISN) threshold vs VCTRL is listed

in Table 2.

Table 2. V(ISP-ISN) Threshold vs VCTRL

VCTRL (V)

V(ISP-ISN) (mV)

1.15

1.20

94.5

1.25

1.30

99.5

1.35

100

When VCTRL is larger than 1.35V, the current threshold

is regulated to:

IIS(MAX) =

100mV

RIS

The CTRL pin should not be left open (tie to VREF if not

used). The CTRL pin can also be used in conjunction with

a thermistor to provide overtemperature protection for

the output load, or with a resistor divider to VIN to reduce

output power and switching current when VIN is low.

The presence of a time varying differential voltage ripple

signal across the ISP and ISN pins at the switching

frequency is expected. If the current sense resistor RIS

is placed between power input and input bulk capacitor

(Figure 13a), or between output bulk capacitor and system

output (Figure 14a), a filter is typically not necessary. If

the RIS is placed between input bulk capacitor and input

decoupling capacitor (Figure 13b), or between output

decoupling capacitor and output bulk capacitor (Figure

14b), a low pass filter formed by RF and CF is recom-

mended to reduce the current ripple and stabilize the

current loop. Since the bias currents of the ISP and ISN

pins are matched, no offset is introduced by RF. If input

or output current limit is not used, the ISP and ISN pins

should be shorted to VIN, VOUT, or ground.

Figure 13. Programming Input Current Limit

Figure 14. Programming Output Current Limit

LT8390

ISP

8390 F13a

ISN

RIS

TO DRAIN OF

SWITCH A

FROM POWER

INPUT

LT8390

ISP

8390 F13b

ISN

RIS

TO DRAIN OF

SWITCH A

FROM POWER

INPUT

(13a)

(13b)

LT8390

ISP

8390 F14a

ISN

RIS

TO SYSTEM

OUTPUT

FROM DRAIN OF

SWITCH D

LT8390

ISP

8390 F14b

ISN

RIS

TO SYSTEM

OUTPUT

FROM DRAIN OF

SWITCH D

(14a)

(14b)

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