RT9712 Datasheet, PDF (9/14 Pages) Richtek Technology Corporation – 90mΩ, 1A/1.5A High-Side Dual Power Switches with Flag

Applications Information
The RT9712A/B/C/D are dual N-MOSFET high-side power
switch with enable input, optimized for self-powered and
bus-powered Universal Serial Bus (USB) applications. The
RT9712 series are equipped with a charge pump circuitry
to drive the internal N-MOSFET switch; the switch's low
R_DS(ON), 90mΩ, meets USB voltage drop requirements;
and a flag output is available to indicate fault conditions
to the local USB controller.
Input and Output
V_IN (input) is the power source connection to the internal
circuitry and the drain of the MOSFET. V_OUT (output) is
the source of the MOSFET. In a typical application, current
flows through the switch from V_IN to V_OUT toward the load.
If V_OUT is greater than V_IN, current will flow from V_OUT to
V_IN since the MOSFET is bidirectional when on.
Unlike a normal MOSFET, there is no parasitic body diode
between drain and source of the MOSFET, the RT9712A/
B/C/D prevents reverse current flow if V_OUT is externally
forced to a higher voltage than V_IN when the chip is disabled
(V_EN < 0.8V or V_EN > 2V).
D
SD
S
G
Normal MOSFET
G
RT9712A/B/C/D
Chip Enable Input
The switch will be disabled when the EN/EN pin is in a
logic low/high condition. During this condition, the internal
circuitry and MOSFET will be turned off, reducing the
supply current to 0.1μA typical. Floating the EN/EN may
cause unpredictable operation. EN should not be allowed
to go negative with respect to GND. The EN/EN pin may
be directly tied to V_IN (GND) to keep the part on.
RT9712
Soft Start for Hot Plug-In Applications
In order to eliminate the upstream voltage droop caused
by the large inrush current during hot-plug events, the
“soft-start” feature effectively isolates the power source
from extremely large capacitive loads, satisfying the USB
voltage droop requirements.
Fault Flag
The RT9712 series provides a FLG signal pin which is an
N-Channel open drain MOSFET output. This open drain
output goes low when current limit or the die temperature
exceeds 120°C approximately. The FLG output is capable
of sinking a 10mA load to typically 200mV above ground.
The FLG pin requires a pull-up resistor, this resistor should
be large in value to reduce energy drain. A 100kΩ pull-up
resistor works well for most applications. In the case of
an over-current condition, FLG will be asserted only after
the flag response delay time, t_D, has elapsed. This ensures
that FLG is asserted only upon valid over-current conditions
and that erroneous error reporting is eliminated.
For example, false over-current conditions may occur
during hot-plug events when extremely large capacitive
loads are connected and causes a high transient inrush
current that exceeds the current limit threshold. The FLG
response delay time t_D is typically 12ms.
Under-Voltage Lockout
Under-voltage lockout (UVLO) prevents the MOSFET
switch from turning on until the input voltage exceeds
approximately 1.7V. If input voltage drops below
approximately 1.3V, UVLO turns off the MOSFET switch.
Under-voltage detection functions only when the switch
is enabled.
Current Limit and Short-Circuit Protection
The current limit circuitry prevents damage to the MOSFET
switch and the hub downstream port. Besides, in order to
prevent the miss-trigger because of USB plug in and other
inrush current, the device allows load current greater than
current limit threshold (typically 1.5A for RT9712A/B and
1A for RT9712C/D) at a short time as shown in Figure 1.
Copyright ©2012 Richtek Technology Corporation. All rights reserved.
DS9712-04 November 2012
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
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