The TPS6281x-Q1 synchronous switch mode DC/DC converters are based on a peak current mode control topology. The control loop is internally compensated. To optimize the bandwidth of the control loop to the wide range of output capacitance that can be used with TPS6281x-Q1, one of three internal compensation settings can be selected. See the COMP/FSET section. The compensation setting is selected either by a resistor from COMP/FSET to GND, or by the logic state of this pin. The regulation network achieves fast and stable operation with small external components and low ESR ceramic output capacitors. The device can be operated without a feedforward capacitor on the output voltage divider, however, using a typically 10-pF feedforward capacitor improves transient response.
The devices support forced fixed frequency PWM operation with the MODE pin tied to a logic high level. The frequency is defined as either 2.25 MHz internally fixed when COMP/FSET is tied to GND or VIN, or in a range of 1.8 MHz to 4 MHz defined by a resistor from COMP/FSET to GND. Alternatively, the devices can be synchronized to an external clock signal in a range from 1.8 MHz to 4 MHz, applied to the MODE pin with no need for additional passive components. External synchronization is only possible if a resistor from COMP/FSET to GND is used. If COMP/FSET is directly tied to GND or VIN, the TPS6281x-Q1 cannot be synchronized externally. An internal PLL allows to change from internal clock to external clock during operation. The synchronization to the external clock is done on a falling edge of the clock applied at MODE to the rising edge on the SW pin. This allows a roughly 180° phase shift when the SW pin is used to generate the synchronization signal for a second converter. When the MODE pin is set to a logic low level, the device operates in power save mode (PFM) at low output current and automatically transfers to fixed frequency PWM mode at higher output current. In PFM mode, the switching frequency decreases linearly based on the load to sustain high efficiency down to very low output current.