SNVSBL0A November 2020 – December 2021 TPS7H4010-SEP
PRODUCTION DATA
The voltage regulation loop in the TPS7H4010-SEP regulates the FB pin voltage to be the same as the internal reference voltage. The output voltage of the TPS7H4010-SEP is set by a resistor divider to program the ratio from VOUT to VFB. The resistor divider is connected from the output to ground with the mid-point connecting to the FB pin.
The internal voltage reference and feedback loop produce precise voltage regulation over temperature. TI recommends using divider resistors with 1% tolerance or better, and with temperature coefficient of 100 ppm or lower. Typically, RFBT = 10 kΩ to 100 kΩ is recommended. Larger RFBT and RFBB values reduce the quiescent current going through the divider, which help maintain high efficiency at very light load. But larger divider values also make the feedback path more susceptible to noise. If efficiency at very light load is critical in a certain application, RFBT up to 1 MΩ can be used.
RFBB can be calculated by Equation 7:
The minimum programmable VOUT equals VFB, with RFBB open. The maximum VOUT is limited by the maximum duty cycle at a given frequency:
where
Ideally, without frequency foldback, VOUT_MAX = VIN_MIN × DMAX.
Power losses in the circuit reduces the maximum output voltage. The TPS7H4010-SEP folds back switching frequency under tOFF_MIN condition to further extend VOUT_MAX. The device maintains output regulation with lower input voltage. The minimum fold-back frequency is limited by the maximum HS on-time, tON_MAX. Maximum output voltage with frequency foldback can be estimated by:
The voltage drops on the HS MOSFET and inductor DCR have been taken into account in Equation 9. The switching losses were not included.
If the resistor divider is not connected properly, the output voltage cannot be regulated because the feedback loop cannot obtain correct output voltage information. If the FB pin is shorted to ground or disconnected, the output voltage is driven close to VIN. The load connected to the output could be damaged under this condition. Do not short FB to ground or leave it open circuit during operation.
The FB pin is a noise sensitive node. It is important to place the resistor divider as close as possible to the FB pin, and route the feedback node with a short and thin trace. The trace connecting VOUT to RFBT can be long, but it must be routed away from the noisy area of the PCB. For more layout recommendations, see Layout section.