An internal micropower charge pump generates a high-

side supply that drives the gate of an internal 75m

Ω

NMOS switch.

On/Off Control and Undervoltage

Lockout (UVLO)

SEL sets the active polarity of the logic input of the

MAX1946. Connect ON to the same voltage as SEL to

enable OUT. Connect ON to the opposite voltage as

SEL to disable OUT (see Table 1). The output enters a

high-impedance state when disabled.

The MAX1946 includes a UVLO circuit to prevent erro-

neous switch operation when the input voltage goes

low during startup and brownout conditions. Input volt-

ages less than 2.5V inhibit operation of the device.

FAULT asserts low during a UVLO condition.

Output Fault Protection and Autoreset

The MAX1946 senses the switch output voltage and

operates in a continuous current-limit mode that limits

device operates in short-circuit current-limit mode,

sourcing 1.2A pulses to the load. When either fault con-

dition persists for 20ms, the output turns off and the

fault flag asserts. The output automatically restarts

20ms after the short or overload is removed.

The MAX1946 detects short-circuit removal by sourcing

25mA from the output and monitoring the output volt-

age. When the voltage at the output exceeds 0.5V for

20ms, the fault flag resets, the output turns back on,

and the 25mA current source turns off.

Thermal Shutdown

When the MAX1946 die temperature exceeds +160°C

the switch turns off and FAULT goes low. Thermal shut-

down does not utilize the 20ms fault-blanking timeout

period. When the junction temperature cools by 15°C

the switch turns on again and FAULT returns high.The

switch cycles on and off if the overload condition per-

sists, resulting in a pulsed output that reduces the aver-

age system load.

Single USB Switch with Autoreset and

Fault Blanking in Tiny TDFN

_______________________________________________________________________________________

9

Figure 1. Functional Diagram

IN

OUT

25mA

THERMAL

SHUTDOWN

FAULT LOGIC

20ms TIMERS

GND

ON

SEL

UVLO

OSC

25kHz

IN

ILIM

CHARGE

PUMP

REF

BIAS

FAULT

MAX1946

Table 1. On/Off Control

SEL

ON

OUT BEHAVIOR

GND

ON

GND

OFF

GND

OFF

ON