RT9721A RICHTEK [Richtek Technology Corporation], RT9721A Datasheet - Page 10

• Manufacturer Part Number: RT9721A
• Description: 80m?, 500mA High-Side Power Switches with Flag
• Manufacturer: RICHTEK [Richtek Technology Corporation]

RT9721A/B
Thermal Shutdown
Thermal shutdown is employed to protect the device from
damage if the die temperature exceeds approximately
150°C. The power switch will auto-recover when the IC is
cooling down. The thermal hysteresis temperature is about
25°C.
Universal Serial Bus (USB) & Power Distribution
The goal of USB is to enable devices from different vendors
to interoperate in an open architecture. USB features
include ease of use for the end user, a wide range of
workloads and applications, robustness, synergy with the
PC industry, and low-cost implementation. Benefits include
self-identifying peripherals, dynamically attachable and
reconfigurable peripherals, multiple connections (support
for concurrent operation of many devices), support for as
many as 127 physical devices, and compatibility with PC
Plug-and-Play architecture.
The Universal Serial Bus connects USB devices with a
USB host: each USB system has one USB host. USB
devices are classified either as hubs, which provide
additional attachment points to the USB, or as functions,
which provide capabilities to the system (for example, a
digital joystick). Hub devices are then classified as either
Bus-Power Hubs or Self-Powered Hubs.
A Bus-Powered Hub draws all of the power to any internal
functions and downstream ports from the USB connector
power pins. The hub may draw up to 500mA from the
upstream device. External ports in a Bus-Powered Hub
can supply up to 100mA per port, with a maximum of four
external ports.
Self-Powered Hub power for the internal functions and
downstream ports does not come from the USB, although
the USB interface may draw up to 100mA from its upstream
connect, to allow the interface to function when the
remainder of the hub is powered down. The hub must be
able to supply up to 500mA on all of its external
downstream ports. Please refer to Universal Serial
Specification Revision 2.0 for more details on designing
compliant USB hub and host systems.
www.richtek.com
10
Over-Current protection devices such as fuses and PTC
resistors (also called polyfuse or polyswitch) have slow
trip times, high on-resistance, and lack the necessary
circuitry for USB-required fault reporting.
The faster trip time of the RT9721A/B power distribution
allow designers to design hubs that can operate through
faults. The RT9721A/B have low on-resistance and internal
fault-reporting circuitry that help the designer to meet
voltage regulation and fault notification requirements.
Because the devices are also power switches, the designer
of self-powered hubs has the flexibility to turn off power to
output ports. Unlike a normal MOSFET, the devices have
controlled rise and fall times to provide the needed inrush
current limiting required for the bus-powered hub power
switch.
Supply Filter/Bypass Capacitor
A 1uF low-ESR ceramic capacitor from VIN to GND, located
at the device is strongly recommended to prevent the input
voltage drooping during hot-plug events. However, higher
capacitor values will further reduce the voltage droop on
the input. Furthermore, without the bypass capacitor, an
output short may cause sufficient ringing on the input (from
source lead inductance) to destroy the internal control
circuitry. The input transient must not exceed 6.5V of the
absolute maximum supply voltage even for a short duration.
Output Filter Capacitor
A low-ESR 150uF aluminum electrolytic or tantalum
between VOUT and GND is strongly recommended to meet
the 330mV maximum droop requirement in the hub VBUS
(Per USB 2.0, output ports must have a minimum 120uF
of low-ESR bulk capacitance per hub). Standard bypass
methods should be used to minimize inductance and
resistance between the bypass capacitor and the
downstream connector to reduce EMI and decouple voltage
droop caused when downstream cables are hot-insertion
transients. Ferrite beads in series with VBUS, the ground
line and the 0.1μF bypass capacitors at the power
connector pins are recommended for EMI and ESD
protection. The bypass capacitor itself should have a low
dissipation factor to allow decoupling at higher frequencies.
DS9721A/B-02 April 2011