SLVSAA4G June 2010 – February 2018 TPS65251
TPS65251 is a power management IC with three step-down buck converters. Both high-side and low-side MOSFETs are integrated to provide fully synchronous conversion with higher efficiency. TPS65251 can support 4.5-V to 18-V input supply, high load current, 300-kHz to 2.2-MHz clocking. The buck converters have an optional PSM mode, which can improve power dissipation during light loads. Alternatively, the device implements a constant frequency mode by connecting the LOW_P pin to ground. The wide switching frequency of 300 kHz to 2.2 MHz allows for efficiency and size optimization. The switching frequency is adjustable by selecting a resistor to ground on the ROSC pin. The SYNC pin also provides a means to synchronize the power converter to an external signal. Input ripple is reduced by 180 degree out-of-phase operation between Buck 1 and Buck 2. Buck 3 operates in phase with Buck 2.
All three buck converters have peak current mode control which simplifies external frequency compensation. A traditional type II compensation network can stabilize the system and achieve fast transient response. Moreover, an optional capacitor in parallel with the upper resistor of the feedback divider provides one more zero and makes the crossover frequency over 100 kHz.
Each buck converter has an individual current limit, which can be set up by a resistor to ground from the RLIM pin. The adjustable current limiting enables high efficiency design with smaller and less expensive inductors.
The device has two built-in LDO regulators. During a standby mode, the 3.3-V LDO and the 6.5-V LDO can be used to drive MCU and other active loads. By this, the system is able to turn off the three buck converters and improve the standby efficiency.
The device has a powergood comparator monitoring the output voltage. Each converter has its own soft-start and enable pins, which provide independent control and programmable soft-start.