Application Examples

p-Channel/n-Channel High-Side Load

Switch with Controlled Turn-On

In load-switching applications, when a controlled volt-

age ramp or inrush current limiting is required, add a

series resistor to slow the switch turn-on and turn-off

times. The external MOSFET gate has a typical capaci-

tance of 150pF to 2000pF, but an optional external

capacitance can be added to further slow the switching

time (Figure 6). If a slow turn-on time is required, use

an n-channel MOSFET with a high-value pullup resistor

and no series resistor. Similarly, if a fast turn-on and a

slow turn-off are desired, use a p-channel MOSFET with

a high-value pullup resistor and no series resistor.

Battery Switch with

Back-to-Back MOSFETs

Many battery-operated applications use back-to-back

MOSFETs to prevent reverse currents from the load to

the supply (Figure 7). This protects the battery from

potential damage and isolates the load from the power

source.

LED Driver

The MAX1608/MAX1609 can be used as programma-

ble LED drivers (Figure 8). With their low quiescent cur-

rent, these devices are ideal for use as indicator light

drivers on the front panel of a notebook computer.

Octal SMBus-to-Parallel I/O Expanders

______________________________________________________________________________________

13

IO0

IO2

IO1

ADD0

IO7

ADD1

IO0

IO2

IO1

ADD0

IO7

ADD1

MAX1609

TO/FROM

HOST

+5V

V+

GND

LOAD1

LOAD2

LOAD3

ALERT

0.1

μF

0.01

μF*

0.01

μF*

0.01

μF*

0.01

μF*

0.01

μF*

0.01

μF*

IRF7406

IRF7413

IRF7406

IRF7413

IRF7406

IRF7413

+12V

10k

Ω

10k

Ω

10k

Ω

SMBCLK

SMBDATA

SMBSUS

MAX1608

TO/FROM

HOST

+5V

V+

GND

LOAD1

LOAD2

LOAD3

ALERT

0.1

μF

10k

Ω

10k

Ω

10k

Ω

10k

Ω

10k

Ω

10k

Ω

10k

Ω

10k

Ω

10k

Ω

200k

Ω

200k

Ω

200k

Ω

200k

Ω

200k

Ω

200k

Ω

SMBCLK

SMBDATA

SMBSUS

*OPTIONAL

Figure 6. Load Switch with Controlled Turn-On