LTC2913 datasheet(16/24 Pages) LINER

16 / 24 page

LT4363

4363fa

APPLICATIONS INFORMATION

Shutdown

The LT4363 can be shut down to a low current mode when

the voltage at the SHDN pin is pulled below the shutdown

threshold of 0.4V. The quiescent current drops down to

7µA with internal circuitry turned off.

The SHDN pin can be pulled up to 100V or below GND by

up to 60V without damage. Leaving the pin open allows

an internal current source to pull it up and turn on the part

while clamping the pin to 2.2V. The leakage current at the

pin should be limited to no more than 1µA if no pull up

device is used to help turn it on.

Supply Transient Protection

The LT4363 is tested to operate to 80V and guaranteed to

be safe from damage up to 100V. Nevertheless, voltage

transients above 100V may cause permanent damage.

During a short-circuit condition, the large change in cur-

rent flowing through power supply traces and associated

wiring can cause inductive voltage transients which could

exceed100V.Tominimizethevoltagetransients,thepower

trace parasitic inductance should be minimized by using

wide traces. A small RC filter, in Figure 8, at the VCC pin

will clamp the voltage spikes.

Another way to limit transients above 100V at the VCC

pin is to use a Zener diode and a resistor, D1 and R7 in

Figure 8. The Zener diode limits the voltage at the pin

while the resistor limits the current through the diode to

a safe level during the surge. However, D1 can be omitted

if the filtered voltage, due to R7 and C1, at the VCC pin

is below 100V. The inclusion of R7 in series with the VCC

pin will increase the minimum required voltage at VIN due

to the extra voltage drop across it. This voltage drop is

due to the supply current of the LT4363 and the leakage

current of D1.

A total bulk capacitance of at least 22µF low ESR electro-

lytic is required close to the source pin of MOSFET Q1. In

addition, the bulk capacitance should be at least 10 times

larger than the total ceramic bypassing capacitor on the

input of the DC/DC converter.

Layout Considerations

To achieve accurate current sensing, Kelvin connection

to the current sense resistor (RSNS in Figure 8) is recom-

mended. The minimum trace width for 1 oz copper foil is

0.02" per amp to ensure the trace stays at a reasonable

temperature. 0.03" per amp or wider is recommended.

Note that 1oz copper exhibits a sheet resistance of about

530µΩ/square.Smallresistancescancauselargeerrorsin

Figure 8. Overvoltage Regulator with Input Voltage Detection

CTMR

47nF

RSNS

10m

FDB33N25

VIN

VOUT

4363 F08

LT4363DE-2

GND TMR

OUT

SNS

0.1µF

D1*

SMAJ58A

4.99k

100k

GATE

VCC

*DIODES INC.

**SANYO 25CE22GA

SHDN

DC/DC

CONVERTER

GND

SHDN

VCC

FLT

ENOUT

CL**

22µF

FAULT

90.9k

10k

374k

47nF

CTMR

0.1µF

RSNS

10m

IRLR2908

SI7461DP

VIN

12V

VOUT

12V, 3A

CLAMPED

AT 16V

4363 F07

LT4363DE-2

GND

TMR

OUT

SNS

VCC

D1*

SMAJ58CA

4.99k

57.6k

GATE

10k

1N5245

15V

*DIODES INC.

SHDN

FLT

ENOUT

47nF

Figure 7. Overvoltage Regulator with P-channel MOSFET

Reverse Input Protection

LTC2913 датащи(PDF) 16 Page - Linear Technology

LTC2913 датащи(HTML) 16 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

датащи скачать

ссылки URL