rt9706 Richtek Technology Corporation, rt9706 Datasheet - Page 10

• Manufacturer Part Number: rt9706
• Description: 500ma High-side Power Switch With Flag
• Manufacturer: Richtek Technology Corporation

RT9706
Chip Enable Input
The switch will be disabled when the EN pin is in a logic
high condition. During this condition, the internal circuitry
and MOSFET are turned off, reducing the supply current
to 0.1μA typical. The maximum guaranteed voltage for a
logic low at the EN pin is 0.8V. A minimum guaranteed
voltage of 2V at the EN pin will turn the RT9706 off. Floating
the input may cause unpredictable operation. EN should
not be allowed to go negative with respect to GND.
www.richtek.com
10
Applications Information
The RT9706 is a single N-Channel MOSFET high-side
power switch with active-low enable input, optimized for
self-powered and bus-powered Universal Serial Bus (USB)
applications. The RT9706 equipped with a charge pump
circuitry to drive the internal NMOS switch; the switch's
low R
and a flag output is available to indicate fault conditions
to the local USB controller.
Input and Output
V
circuitry and the drain of the MOSFET. V
the source of the MOSFET. In a typical application, current
flows through the switch from V
If V
V
Unlike a normal MOSFET, there is no a parasitic body
diode between drain and source of the MOSFET, the
RT9706 prevents reverse current flow if V
externally forced to a higher voltage than V
output disabled (V
D
IN
IN
OUT
(input) is the power source connection to the internal
since the MOSFET is bidirectional when on.
Normal MOSFET
DS(ON)
is greater than V
, 80mΩ, meets USB voltage drop requirements;
G
EN
> 2V).
Figure 1
IN
S
, current will flow from V
D
IN
to V
OUT
RT9706
toward the load.
OUT
G
IN
(output) is
OUT
when the
OUT
being
to
S
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 RT9706 provides a FLG signal pin which is an
N-Channel open drain MOSFET output. This open drain
output goes low when V
the die temperature exceeds 130°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
upon valid over-current conditions and that erroneous error
reporting is eliminated. The FLG response delay time t
is typically 12ms.
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.
Under-Voltage Lockout
Under-voltage lockout (UVLO) prevents the MOSFET
switch from turning on until input voltage exceeds
approximately 1.7V. If input voltage drops below
approximately 1.3V, UVLO turns off the MOSFET switch,
FLG will be asserted accordingly. 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 800mA
through the switch of RT9706. 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.
D
, has elapsed. This ensures that FLG is asserted only
OUT
< V
DS9706-02 March 2007
IN
−
1V, current limit or
D