9

LTC1623

To avoid turning on the external power MOSFETs too

quickly, an internal 10k resistor has been placed in series

with each of the output gate drive pins (see Functional

Block Diagram). Therefore, it only needs an external 0.1

µF

capacitor to create enough RC delay (10k • 0.1

µF = 1ms)

to slow down the ramp rate of the output gate drive. In

other words, it will take a minimum of 1ms to charge up

the external MOSFET. An additional external 1k resistor

between the 0.1

µF capacitor and the gate of the MOSFET

(Figure 3) is required to eliminate possible MOSFET self

oscillations.

GA

GB

LTC1623

GND

3.5V TO 5.5V

0.1

µF

1k

13

8

680

Ω

56

3.3k

3.3V

10k

10

µF

CLK

DATA

(PROGRAMMABLE)

(FROM SMBus)

AD0

AD1

510pF

LOAD

Si3442DV

Si3442DV

LT1431

1623 F04

470

µF

6V

+

Figure 4. 3.3V/3A Extremely Low Voltage Drop

Regulator and Load Switch

Figure 3. Dual Load Switch with Q2 On upon Power-Up

2.7V TO 5.5V

10

µF

(PROGRAMMABLE)

FAN

DISPLAY

1623 F03

(FROM

SMBus)

LTC1623

GND

AD0

AD1

CLK

DATA

GA

GB

0.1

µF

Q1

Si3442DV

Q2

Si6433DQ

0.1

µF

1k

1k

Figure 6. Switching Regulator with Low-Battery

Detect Using 22

µA Standby Current

2.7V TO 4.5V

0.1

µF

100

µF

1k

3

8

4

2

499k

5

7

LBO

22

µH*

*SUMIDA CD54-220

604k

10

µF

(PROGRAMMABLE)

(FROM

SMBus)

1N5817

LOAD

SHDN

Si3442DV

Si3442DV

LT1304-5

1623 F05

+

2200

µF

5V

200mA

100k

+

GA

GB

LTC1623

GND

CLK

DATA

AD0

AD1

GA

GB

LTC1623

GND

3.5V TO 5.5V

13

8

680

Ω

56

3.3k

3.3V

SWITCHED

3.3V

10k

10

µF

CLK

DATA

(PROGRAMMABLE)

(FROM SMBus)

AD0

AD1

510pF

0.1

µF

Si3442DV

LT1431

1623 TA03

1k

470

µF

6V

Si3442DV

+

Figure 5. SMBus Controlled Low Dropout Regulator

For active-low applications in which the load needs to be

on upon power-up, an external P-channel switch can be

used (Figure 3). This load can be switched off later after the

proper protocol has been sent.

Used with the LT

extremely low voltage drop regulator (Figures 4 and 5). In

this application, the other output channel can be used to

drive a separate load, or it can also be used to control the

output of the LDO so that the user has total control over the

switching in and switching out of the LDO (Figure 5). Also,

with the help of the LT1304-5, the LTC1623 can be used

to make a boost switching regulator with a low standby

current of 22

µA (Figure 6).