SLVSES4D September 2019 – June 2024 TPS54J060
PRODUCTION DATA
The TPS54J060 implements a circuit to allow both internal fixed soft start and external adjustable soft start. The internal soft-start time is typically 1.5 ms and has a 1-ms minimum value. The internal soft-start time can be increased by adding a SS capacitor between SS/REFIN and AGND. The SS capacitor value can be determined by Equation 2. Note, any CSS calculation that uses a soft-start time of less than 1.5 ms will be ignored by the internal soft-start time circuit. Therefore, selecting a capacitor less than or equal to 15 nF will result in the internal default 1.5 ms soft-start time (See Section 7.2.2.7).
The SS/REFIN pin can also be used as an analog input to accept an external reference. When an external voltage signal is applied to SS/REFIN pin, it acts as the reference voltage, thus the FB voltage follows this external voltage signal. Apply the external reference to the SS/REFIN pin before soft start. The external reference voltage must be equal to or higher than the internal reference level to ensure correct Power Good thresholds during soft start. With an external reference applied, the internal fixed soft start controls output voltage ramp during start-up.
After soft start, the external reference voltage signal can be in a range of 0.5 V to 1.2 V.
When driving the SS/REFIN pin with an external resistor divider, the resistance must be low enough so that the external voltage source can overdrive the internal current source. Note that the internal current source remains active.
When the TPS54J060 is enabled, an internal discharge resistance turns on to discharge external capacitance on the SS/REFIN pin and ensure soft start from 0 V. When the device is enabled with both VIN and EN above the rising thresholds, 100 Ω of resistance is connected from the SS/REFIN pin to ground. After the device detects the VCC pin is in regulation, the discharge resistance is increased to 300 Ω. The 300-Ω discharge resistance is connected to the SS/REFIN until the MODE detection time is completed. After the MODE detection time is completed, the TPS54J060 detects if an external reference is connected.