TJ2205 Datasheet, PDF (12/13 Pages) HTC Korea TAEJIN Technology Co. – Dual-Channel Power Distribution Switch

Dual-Channel Power Distribution Switch
TJ2205
Function Description
Supply Filtering
A 0.1uF to 1uF bypass capacitor from IN pin to GND pin is recommended to control power supply
transients. Without this bypass capacitor, an output short can cause ringing from supply lead inductance
on the input and damage the internal control circuitry.
Input or output transients must never exceed the absolute maximum supply voltage (VINmax = 6V)
Power Dissipation
The device’s junction temperature depends on several factors such as the load, PCB layout, ambient
temperature, and package type. Equations that can be used to calculate power dissipation of each
channel and junction temperature are found below:
P_D=R_DS(ON) x I_OUT2
Total power dissipation of the device will be the summation of P_D for both channels. To relate this to
junction temperature, the following equation can be used:
T_J=P_D x θ_JA +T_A
Where:
T_J = Junction temperature
T_A = Ambient temperature
θ_JA= Thermal resistance of the package
Enable/Shutdown
The EN1 and EN2 control pins must be driven to a logic high or logic low for a clearly defined signal input.
Floating these control lines may cause unpredictable operation.
Fault Flag
The FLG signal is open-drained output of N-channel MOSFET, the FLG output is pulled low to signal the
following fault conditions: input under voltage, output to GND short, and thermal shutdown.
Soft-Start Condition
The TJ2205 has high impedance when off, which gradually shifts to low impedance as the chip turns on.
This prevents an inrush current from causing voltage drops that result from charging a capacitive load and
can pull the USB voltage bus below specified levels. This satisfies the USB voltage droop requirements
for bus-powered applications.
The TJ2205 can provide inrush current limiting for applications with large load capacitances where C_L
>10uF.
Current Sense
A sense MOSFET monitors the current supplied to the load. The sense MOSFET measures current more
efficiently than conventional resistance methods. When an overload or short circuit is encountered, the
current-sense circuitry sends a control signal to the driver. The driver in turn reduces the gate-source
voltage and drives the power MOSFET into its saturation region, which switches the output into a
constant-current mode and holds the current constant while varying the voltage on the load.
Over-Current and Short-Circuit Protection
The TJ2205 features an over-current protection circuitry to protect the device against overload conditions.
The current limit threshold is preset internally. It protects the output MOSFET switches from damage due
to undesirable short circuit conditions of excess inrush current often encountered during hot plug-in. The
low limit of the current limit threshold of the TJ2205 allows a minimum current of 0.5A through the
Oct. 2011 – R1.1
- 12 -
HTC