7.3.1 Enable

The TPS80010 includes two DC-DC converters, a load switch, post-regulation LDO, and battery monitoring switch. Each of these circuits has a dedicated enable pin with an internal pulldown resistor, R_PULLDOWN, that can be driven by standard logic or by an open-drain driver. The EN_BUCK pin not only enables the buck converter, but also serves as the master enable for the device. No other circuitry in the TPS80010 can operate without EN_BUCK set high.

7.3.2 Buck DC-DC Converter and Load Switch

The synchronous step-down (buck) converter in the TPS80010 provides a fixed 1.8-V output with a load capacity of 150 mA. This converter operates with a fixed switching frequency of 2.25 MHz during pulse-width-modulation (PWM) operation at moderate to heavy loads. As the load current decreases, the converter automatically switches to a power-save mode and operates in pulse-frequency-modulation (PFM) mode to maximize power efficiency. During PFM operation, the converter positions the output at a voltage about 1% greater than the nominal output voltage. This feature minimizes the output voltage drops during sudden load transients. The power-save mode can be disabled by setting the MODE_BUCK pin high.

The buck converter has internal soft-start circuitry that limits the inrush current during startup to 150 mA, allowing a slow and controlled output-voltage ramp. Once the output voltage reaches 1.7 V, the output monitoring circuitry generates a Power Good (PG) output signal.

The TPS80010 also includes a load switch that is to be connected externally to the buck output voltage. This switch provides flexibility in the design and power distribution of the end application by allowing several loads (such as memory, I/O, Bluetooth, and so forth) to be connected to the same supply while being able to power down or disconnect some of these loads selectively when the end application goes to a low-power mode of operation. This switch has a controlled turnon to limit the inrush current caused by the load, and hence the load transient to the buck converter.

7.3.3 Boost DC-DC Converter and Post-Regulation LDO

The TPS80010 includes a synchronous step-up (boost) converter that provides a 3.1-V fixed output at 50-mA load current. The boost converter is controlled by a hysteretic current-mode controller. This controller regulates the output voltage by keeping the inductor ripple current constant and adjusting the offset of this inductor current depending on the output load. If the required average input current is lower than the average inductor current defined by this constant ripple, the converter goes into discontinuous-current mode (DCM) to keep the efficiency high at low-load conditions. The boost also has a soft-start circuit that limits the inrush current to 150 mA.

To provide a clean, low-noise supply when V_BAT > 3.1 V, the output of the boost is post-regulated by a
3-V LDO. This post-regulation allows the TPS80010 to provide a solid 3-V supply rail to the end application across the full input or battery-voltage range while minimizing the number of external components. To minimize power loss through the power path, the LDO allows for 100-mV input-voltage headroom at 50-mA load.

7.3.4 Battery Monitoring Switch and False Load

The TPS80010 implements a battery-voltage monitor switch to briefly check battery lifetime. The integrated false-load switch connects a specified load to the battery. When this false load is applied, the battery monitor switch is turned on, gating the sensed battery voltage to the ADC in the system. Based on this measurement, the system can determine the battery impedance and, therefore, battery health.