RT9715 Просмотр технического описания (PDF) - Richtek Technology
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RT9715 Datasheet PDF : 15 Pages
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RT9715
Applications Information
The RT9715 is a single N-MOSFET high-side power
switches with enable input, optimized for self-powered and
bus-powered Universal Serial Bus (USB) applications. The
RT9715 is equipped with a charge pump circuitry to drive
the internal N-MOSFET switch; the switch's low RDS(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
VIN (input) is the power source connection to the internal
circuitry and the drain of the MOSFET. VOUT (output) is
the source of the MOSFET. In a typical application, current
flows through the switch from VIN to VOUT toward the load.
If VOUT is greater than VIN, current will flow from VOUT to
VIN 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 RT9715
prevents reverse current flow if VOUT is externally forced to
a higher voltage than VIN when the chip is disabled (VEN <
0.8V or VEN > 2V).
D
S
D
S
G
Normal MOSFET
G
RT9715
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 0.1uA 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 VIN (GND) to keep the part on.
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.
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Fault Flag
The RT9715 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, tD, 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 tD is typically 12ms.
Under-Voltage Lockout
Under-voltage lockout (UVLO) prevents the MOSFET switch
from turning on until input the 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 Limiting and Short-Circuit Protection
The current limit circuitry prevents damage to the MOSFET
switch and the hub downstream port but can deliver load
current up to the current limit threshold of typically 2A
through the switch of the RT9715A/B, 1.5A for
RT9715C/D, 1.1A for RT9715E/F and 0.7A for
RT9715G/H respectively. When a heavy load or short circuit
is applied to an enabled switch, a large transient current
may flow until the current limit circuitry responds. Once
this current limit threshold is exceeded, the device enters
constant current mode until the thermal shutdown occurs
or the fault is removed.
Thermal Shutdown
Thermal protection limits the power dissipation in RT9715.
When the operation junction temperature exceeds 120°C,
the OTP circuit starts the thermal shutdown function and
DS9715-03 April 2011
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