Detailed Description

The MAX1940 triple current-limited USB power switch

provides three independent switches, each with its own

enable-control input and fault indicator (see Figure 1).

A logic input sets the active polarity of the enable con-

trol inputs. The fault indicators notify the system when

the current-limit, short-circuit, undervoltage lockout, or

thermal-shutdown threshold is exceeded.

The MAX1940 operates from a 4V to 5.5V input supply

and supplies a minimum output current of 700mA per

channel. A built-in current limit of 0.9A (typ) limits the

output current in the event of an overload condition.

Built-in short-circuit detection pulses the output current if

the output voltage falls below 1V, resulting in lower RMS

output current and reduced power dissipation in the

device. Independent thermal shutdown allows normal

operation to continue if one channel experiences a pro-

longed overload or short-circuit condition.

vide three switches in the space-saving 16-pin QSOP

package. An internal micropower charge pump gener-

ates the high-side supply needed for driving the gates

of these high-side switches. Separate current-limiting

and thermal-shutdown circuitry permits each switch to

operate independently, improving system robustness.

Triple USB Switch with Autoreset and

Fault Blanking

8

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FAULT LOGIC

20ms TIMERS

THERMAL

SHUTDOWN

CHARGE

PUMP

SWITCH B

(SEE SWITCH A)

SWITCH C

(SEE SWITCH A)

BIAS

REF

UVLO

OSC

25kHz

25mA

ILIM

SWITCH A

(EXPANDED)

IN2

IN_

FAULTA

FAULTB

FAULTC

OUTC

OUTA

IN2 IN3

IN4

IN5

GND

ONC

ONB

SEL

IN1

ONA

OUTB

MAX1940

Figure 1. Functional Diagram