Hi,
I have question.
The data sheet P18, 7.3.8 Low Dropout Operation states "The device can operate at 100% duty cycle (no switching; regulator switch completely on) for low dropout support."
But, the data sheet P7, 6.6 Electrical Characteristics – Buck 1 states “(3) BUCK normal operation is ensured if VIN ≥ VOUT + 1 V.”.
1. Is it possible to operate with 100% duty cycle during normal operation? (Ex. Vin = 3.5V, Vout = 3.25V)
Best Regards,
Nishie
Hi Nishie,
If you are operating the device such that the drop between VIN/VOUT are close together, you will want BUCK1 operating in Bypass mode. This will happen as long as the input voltage is greater than 3.5V (see below). The electrical characteristics footnote (3) states that the Buck will transition to "normal operation" once the dropout exceeds 1V. Thus, it is not possible for 100% duty cycle during normal operation; you would need the bucks configured for bypass mode, which will allow Vout to follow Vin minus the drop across the FET and inductor.
Best,
Emily
