RT9715CA Datasheet, PDF (9/12 Pages) Richtek Technology Corporation – Reverse Blocking Current

RT9715CA
Thermal Shutdown
Thermal protection limits the power dissipation in
RT9715CA. When the operation junction temperature
exceeds 120°C, the OTP circuit starts the thermal
shutdown function and turns the pass element off. The
pass element turn on again after the junction temperature
cools to 80°C. The RT9715CA lowers its OTP trip level
from 120°C to 100°C when output short circuit occurs
(V_OUT < 1V) as shown in Figure 1.
V_OUT Short to GND
1V
V_OUT
I_OUT
Thermal
Shutdown
OTP
Trip
120 C
Point
100 C
100 C
IC Temperature
80 C
Figure 1. Short Circuit Thermal Folded Back Protection
when Output Short Circuit Occurs (Patent)
Power Dissipation
The junction temperature of the RT9715CA series depend
on several factors such as the load, PCB layout, ambient
temperature and package type. The output pin of the
RT9715CA can deliver the current of up to 1.5A
(RT9715CA) over the full operating junction temperature
range. However, the maximum output current must be
decreased at higher ambient temperature to ensure the
junction temperature does not exceed 100°C. With all
possible conditions, the junction temperature must be
within the range specified under operating conditions.
Power dissipation can be calculated based on the output
current and the R_DS(ON) of the switch as below.
P_D = R_DS(ON) x I_OUT²
Although the device is rated for 1.5A of output current,
but the application may limit the amount of output current
based on the total power dissipation and the ambient
temperature. The final operating junction temperature for
Copyright ©2015 Richtek Technology Corporation. All rights reserved.
DS9715CA-00 April 2015
any set of conditions can be estimated by the following
thermal equation :
P_{D (MAX)} = ( T_{J (MAX)} − T_A ) / θ_JA
Where T_{J (MAX)} is the maximum junction temperature of
the die (100°C) and T_A is the maximum ambient temperature.
The junction to ambient thermal resistance (θ_JA) for
SOT-23-5 package at recommended minimum footprint
are 250°C/W (θ_JA is layout dependent).
Universal Serial Bus (USB) & Power Distribution
The goal of USB is to enable device 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.
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www.richtek.com
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