TPS25810_16 Datasheet, PDF (24/38 Pages) Texas Instruments – USB Type-C DFP Controller and Power Switch with Load Detection

TPS25810
SLVSCR1B – SEPTEMBER 2015 – REVISED MAY 2016
www.ti.com
Typical Applications (continued)
8.2.1.1 Design Requirements
8.2.1.1.1 Input and Output Capacitance
Input and output capacitance improves the performance of the device. The actual capacitance should be
optimized for the particular application. For all applications, a 0.1-μF or greater ceramic bypass capacitor
between IN and GND is recommended as close to the device as possible for local noise de-coupling.
All protection circuits such as the TPS25810 have the potential for input voltage overshoots and output voltage
undershoots. Input voltage overshoots can be caused by either of two effects. The first cause is an abrupt
application of input voltage in conjunction with input power bus inductance and input capacitance when the IN
terminal is high impedance (before turn on). Theoretically, the peak voltage is 2 times the applied. The second
cause is due to the abrupt reduction of output short circuit current when the TPS25810 turns off and energy
stored in the input inductance drives the input voltage high. Input voltage droops may also occur with large load
steps and as the TPS25810 output is shorted. Applications with large input inductance (for instance connecting
the evaluation board to the bench power-supply through long cables) may require large input capacitance to
reduce the voltage overshoot from exceeding the absolute maximum voltage of the device.
The fast current-limit speed of the TPS25810 to hard output short circuits isolate the input bus form faults.
However, ceramic input capacitance in the range of 1 μF to 22 μF adjacent to the TPS25810 input aids in both
response time and limiting the transient seen on the input power bus. Momentary input transients to 6.5 V are
permitted. Output voltage undershoot is caused by the inductance of the output power bus just after a short has
occurred and the TPS25810 has abruptly reduced OUT current. Energy stored in the inductance drives the OUT
voltage down and potentially negative as it discharges. An application with large output inductance (such as from
a cable) benefits from use of a high-value output capacitor to control voltage undershoot.
When implementing a USB standard application, 120 μF minimum output capacitance is required. Typically a
150-μF electrolytic capacitor is used, which is sufficient to control voltage undershoots. Since in Type-C DFP is a
cold socket when no UFP is attached, the output capacitance should be placed at the IN pin versus OUT as is
used in USB Type A ports. It is also recommended to put a 10-μF ceramic capacitor on the OUT pin for better
voltage bypass.
8.2.1.2 Detailed Design Procedure
The TPS25810 device supports three different input voltages based on the application. In the simplest
implementation all input supplies are tied to a single voltage source as shown in Figure 20 which is set to 5 V.
However, it is recommended to set a slightly higher (100 mV to 200 mV) input voltage, when possible, to
compensate for IR drop from the source to the Type C connector.
Other design considerations are listed below:
• Place at least 120 µF of bypass capacitance close to the IN pins versus OUT as Type C is a cold socket
connector.
• A 10-µF bypass capacitor is recommended placed near a Type-C receptacle V_BUS pin to handle load
transients.
• Depending on the max current level advertisement supported by the Type-C port in the system, set CHG and
CHG_HI levels accordingly. 3 A advertisement is shown in Figure 20.
• EN, CHG, and CHG_HI pins can be tied directly to GND or VAUX without a pull-up resistor.
– CHG and CHG_HI can also be dynamically controlled by a µC to change the current advertisement level
to the UFP.
• When an open drain output of the TPS25810 is not used, it can be left as NC or tied to GND.
• Use a 1% 100-kΩ resistor to connect between the REF and REF_RTN pins placing it close to the device pin
and isolated from switching noise on the board.
24
Submit Documentation Feedback
Product Folder Links: TPS25810
Copyright © 2015–2016, Texas Instruments Incorporated