PWM mode at medium / heavy load

Output

Voltage

t

PFM mode at light load

TLV62565, TLV62566

www.ti.com

SLVSBC1C – OCTOBER 2013 – REVISED JULY 2015

10.3 Feature Description

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

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.

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