10.3.1 Power Save Mode

The device integrates a Power Save Mode with PFM to improve efficiency at light load. In Power Save Mode, the device only switches when the output voltage trips below a set threshold voltage. It ramps up the output voltage with several pulses and stops switching when the output voltage is higher than the set threshold voltage. PFM is exited and PWM mode entered in case the output current can no longer be supported in Power Save Mode. The threshold of the PFM comparator is typically 0.9% higher than the normal reference voltage. Figure 13 shows the details of PFM/PWM mode transition.

Figure 13. Output Voltage in PFM/PWM Mode

10.3.2 Enabling/Disabling the Device

The device is enabled by setting the EN input to a logic HIGH. Accordingly, a logic LOW disables the device. If the device is enabled, the internal power stage starts switching and regulates the output voltage to the set point voltage. The EN input must be terminated and should not be left floating.

10.3.3 Soft Start

After enabling the device, internal soft-start circuitry monotonically ramps up the output voltage which reaches nominal output voltage during a soft-start time of 250 µs (typical). This avoids excessive inrush current and creates a smooth output voltage rise slope. It also prevents excessive voltage drops of primary cells and rechargeable batteries with high internal impedance.

If the output voltage is not reached within the soft-start time, such as in the case of a heavy load, the converter enters regular operation. The TLV62565/6 are able to start into a pre-biased output capacitor. The converter starts with the applied bias voltage and ramps the output voltage to its nominal value.

10.3.4 Switch Current Limit

The switch current limit prevents the device from high inductor current and drawing excessive current from a battery or input voltage rail. Excessive current might occur with a heavy load or shorted output circuit condition.

The TLV62565/6 adopt valley current control by sensing the current of the low-side MOSFET. Once the low-side valley switch current limit is tripped, the low-side MOSFET is turned off and limits the inductor's valley current. The high-side current is also limited which is determined by the on time of the high-side MOSFET and inductor value calculated by Equation 1. For example, with 3.6 V_IN to 1.8 V_OUT and 2.2-µH specification, the peak current limit is approximately 1.97 A with a typical valley current limit of 1.7 A.

Additionally, there is a secondary high-side current limit (typical 2 A) to prevent the current from going too high, which is shown in Figure 14. Due to the internal propagation delay, the real current limit value might be higher than the static current limit in the electrical characteristics table.

Figure 14. Switch Current Limit

Equation 1.

where

• I_PEAK,LIMIT is the high-side peak current limit
• I_VALLEY,LIMIT is the low-side valley current limit

10.3.5 Power Good

The TLV62566 integrates a Power Good output going low when the output voltage is below its nominal value. The Power Good output stays high impedance once the output is above 95% of the regulated voltage and is low once the output voltage falls below typically 90% of the regulated voltage. The PG pin is an open drain output and is specified to sink typically up to 0.5 mA. The Power Good output requires a pull-up resistor connected to any voltage lower than 5.5 V. When the device is off due to UVLO or thermal shutdown, the PG pin is pulled to logic low.

10.4.1 Under Voltage Lockout

To avoid mis-operation of the device at low input voltages, under voltage lockout is implemented that shuts down the device at voltages lower than V_UVLO with V_{HYS_UVLO} hysteresis.

10.4.2 Thermal Shutdown

The device enters thermal shutdown once the junction temperature exceeds typically T_JSD. Once the device temperature falls below the threshold with hysteresis, the device returns to normal operation automatically. Power Good is pulled low when thermal protection is triggered.