Detailed Description

The MAX1838 is a dual, current-limited switch with

auxiliary inputs designed for USB applications. It has

two independent channels, each with its own fault-

blanking and autoreset function. Each channel has an

error flag output to notify the USB controller when the

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

mal shutdown threshold is reached. A single input

enables both channels. The MAX1838 supplies the out-

puts from one of two inputs, IN or AUX, selected by

SEL (Table 1).

The MAX1838 operates from 4V to 5.5V input voltage

range and guarantees a 500mA (min) output current. A

0.9A built-in current limit limits the current in the event

of a heavy overload condition. When powering the

switches from the auxiliary input, each channel has an

adjustable current limit. The MAX1838 has independent

thermal shutdown for each channel in the event of a

prolonged overload or short-circuit condition. The

autoreset function monitors the overload and automati-

cally turns the switch on when the overload is removed.

MAX1838 to provide four switches in the small 16-pin

QSOP package. Internal micropower charge pumps

generate the gate drive of these high-side switches.

Separate current limiting and thermal shutdown circuits

permit each switch to operate independently, improv-

ing system robustness.

Input Voltage Requirements and

Undervoltage Lockout

The MAX1838 operates in one of three modes (Table 1).

The device receives its supply current from the AUX

lockout voltage, the MAX1838 shuts down to prevent

erroneous switch operation.

Dual USB Switch with Fault Blanking

and Autoreset

8

_______________________________________________________________________________________

CHANNEL B CONTROL

CIRCUITRY

AUX

IN

OUTB1

FAULT LOGIC

THERMAL

SHUTDOWN A

20ms

BLANKING

FAULT LOGIC

ON

SEL

IC POWER

FAULTB

N

N

ADJB

ADJA

OUTB2

CHANNEL A CONTROL

CIRCUITRY

OUTA1

OUTA2

20ms

BLANKING

THERMAL

SHUTDOWN B

FAULTA

Figure 1. Simplified Functional Diagram

Pin Description (continued)

PIN

NAME

FUNCTION

15

ADJA

Current-Limit Adjust for Channel A. When operating from auxiliary input, adjust the current limit by

connecting a resistor from ADJA to GND as shown in Programmable Current Limit.

16

FAULTA

Fault Indicator Output for Channel A. This open-drain output goes low when channel A is in

thermal shutdown or undervoltage lockout or in a sustained (>20ms) current-limit or short-circuit

condition.

Power from IN

(SEL high)

Both A and B outputs receive

current from IN. The IC is powered

from AUX.

Power from AUX

(SEL low)

Both A and B outputs receive

current from AUX. The IC is

to zero in this mode.

Full Shutdown

(ON high)

Both A and B outputs are open and

Table 1. MAX1838 Operation Modes