AP72250

Document number: DS44135 Rev. 1 - 2

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January 2022

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AP72250

Application Information

1

Pulse Width Modulation (PWM) Operation

The AP72250 device is a 0.6V-to-5.5V input, fully integrated synchronous boost converter with 1.0V minimum startup. Refer to the block diagram in

Figure 3. The device employs fixed-

frequency peak current mode control. The internal clock’s rising edge initiates turning on the integrated low-side

power MOSFET, Q1, for each cycle. When Q1 is on, the inductor current rises linearly. The current across Q1 is sensed and converted to a voltage

with a ratio of RT via the CSA block. The CSA output is combined with an internal slope compensation, SE, resulting in VSUM. When VSUM rises

higher than the COMP node, the device turns off Q1 and turns on the high-side power MOSFET, Q2. The inductor current decreases when Q2 is

on and charges the output capacitor. On the rising edge of next clock cycle, Q2 turns off and Q1 turns on. This sequence repeats every clock cycle.

The error amplifier generates the COMP voltage by comparing the voltage on the FB pin with an internal 0.8V reference. An increase in load current

causes the feedback voltage to drop. The error amplifier thus raises the COMP voltage until the average inductor current matches the increased

load current. This feedback loop regulates the output voltage. The internal slope compensation circuitry prevents subharmonic oscillation when the

duty cycle is greater than 50% for peak current mode control.

When the input voltage is above 90% of the output voltage, the AP72250 rapidly and smoothly transits from boost to pass-through mode by keeping

the high-side MOSFET, Q2, on.

The peak current mode control, integrated loop compensation network simplifies the AP72250 footprint as well as minimizing the external component

count.

Connecting the MODE pin to VIN sets the AP72250 to operate in Forced PWM Mode regardless of output load.

2

Pulse Frequency Modulation (PFM) and Ultrasonic Mode (USM) Operation

AP72250 enters PFM operation during light load conditions when the MODE pin is tied to GND. In heavy load conditions, the AP72250 operates in

PWM mode. As the load current decreases, the internal COMP node voltage also decreases. At a certain limit, if the load current is low enough, the

COMP node voltage is clamped and is prevented from decreasing any further. The voltage at which COMP is clamped corresponds to the 1.5A PFM

peak inductor current limit. As the load current approaches zero, the AP72250 enters PFM mode to increase the converter power efficiency at light

load conditions. When the inductor current decreases to 30mA, zero cross detection circuitry on the high-side power MOSFET, Q2, forces it off. The

boost converter does not sink current from the output when the output load is light and while the device is in PFM. Since the AP72250 works in PFM

during light load conditions, it can achieve power efficiency of up to 89% at a 5mA load condition.

AP72250 enters USM operation during light load conditions when the MODE pin is left floating. USM is similar to PFM operation but with one key

difference. Unlike in PFM, operating in USM limits the switching frequency of the device from falling below 20.5kHz. This prevents the device from

switching in the audible frequency range. When the regulator detects that no switching has occurred within the last 37

μs, it turns on Q2 for a fixed

amount of time (~50ns) to induce a negative inductor current and force switching action on the SW pin.

The quiescent current of AP72250 is 20

μA typical under a no-load, non-switching condition.

3

Enable

When the EN voltage falls below its logic low threshold (maximum 0.2V, falling), the internal SS voltage discharges to ground and device operation

disables. When disabled, the device shutdown supply current is only 2.5

μA. When applying a voltage greater than the EN logic high threshold

(minimum 0.90V, rising when VIN > 1.6V), the AP72250 enables all functions and the device initiates the soft-start phase. Alternatively, leave the

EN pin floating to allow the AP72250 to soft-start automatically when VIN > 1V. During the soft-start period when VOUT < VIN, the inductor current

is regulated at 250mA. Therefore, the load current should not exceed 100mA during startup.