LTC2923IDE datasheet(12/20 Pages) LINER

12 / 20 page

LTC2923

2923fa

In this example, all supplies remain low while the ON pin

is held below 1.23V. When the ON pin rises above 1.23V,

10µA pulls up CGATE and the gate of the FET at 1000V/s. As

the gate of the FET rises, the source follows and pulls up

the output to 3.3V at 1000V/s. This output serves as the

master signal and is buffered from the RAMP pin to the

RAMPBUF pin. As this output and the RAMPBUF pin rise,

the current from the TRACK pins is reduced. Conse-

quently, the voltage at the slave supply’s outputs in-

creases, and the slave supplies track the master supply.

When the ON pin is again pulled below 1.23V, 10µA will

pull down CGATE and the gate of the FET at 1000V/s. If the

loads on the outputs are sufficient, all outputs will track

down coincidently at 1000V/s.

APPLICATIO S I FOR ATIO

Coincident Tracking Example

1ms/DIV

2923 F10b

1V/DIV

1ms/DIV

2923 F10a

1V/DIV

Figure 10. Coincident Tracking (from Figure 11)

MASTER

SLAVE2

SLAVE1

Figure 11. Coincident Tracking Example

A typical three supply application is shown in Figure 11. The

master signal is a 3.3V module. The slave 1 supply is a 1.8V

switching power supply and the slave 2 supply is a 2.5V

switching power supply. Both slave supplies track coinci-

dently with the 3.3V supply that is controlled with an ex-

ternal FET. The ramp rate of the supplies is 1000V/s. The

3-step design procedure detailed previously can be used

to determine component values. Only the slave 1 supply is

considered here as the procedure is the same for the slave 2

supply.

Set the ramp rate of the master signal.

From Equation 1:

GATE =

1000

Solve for the pair of resistors that provide the desired

slave supply behavior, assuming no delay.

From Equation 2:

TB =

Ω

16 5

1000

16 5

.•

From Equation 3:

TA′ =

Ω

ΩΩ

≈Ω

1 235

16 5

1 235

35 7

16 5

–

Choose RTA to obtain the desired delay.

Since no delay is desired, RTA = RTA′

CGATE

10nF

VCC

RONB

138k

3.3V

RTB1

16.5k

RTB2

887k

RFA1

35.7k

1.8V

SLAVE1

3.3V

MASTER

RFB1 16.5k

RTA2

412k

RTA1

13k

RONA

100k

FB1

GATE

LTC2923

GND

2923 F11

RAMP

RFA2

412k

2.5V

SLAVE2

RFB2

887k

RAMPBUF

TRACK1

TRACK2

FB2

DC/DC

3.3V

FB = 1.235V OUT

DC/DC

FB = 0.8V

OUT

0.1µF

10Ω

LTC2923IDE датащи(PDF) 12 Page - Linear Technology

LTC2923IDE датащи(HTML) 12 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

датащи скачать

ссылки URL