Datasheet

An internal micropower charge pump generates a high-
side supply that drives the gate of an internal 75mΩ
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
selects continuous current limiting for V
OUT
greater
than 1V or short-circuit current limiting for V
OUT
less
than 1V. When V
OUT
is greater than 1V, the device
operates in a continuous current-limit mode that limits
output current to 1.1A. When V
OUT
is less than 1V, the
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.
MAX1946
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
V
IN
OFF
GND OFF
V
IN
V
IN
ON