AP62200/AP62201/AP62200T

Document number: DS41957 Rev. 4 - 2

13 of 23

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January 2021

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AP62200/AP62201/AP62200T

Application Information

1

Pulse Width Modulation (PWM) Operation

The AP62200/AP62201/AP62200T device is a 4.2V-to-18V input, 2A output, EMI friendly, fully integrated synchronous buck converter. Refer to

the block diagram in Figure 4. The device employs constant on-time control to provide fast transient response and easy loop stabilization. At the

beginning of each cycle, the one-shot pulse turns on the high-side power MOSFET, Q1, for a fixed on-time, tON. This one-shot on-pulse timing is

calculated by the converter’s input voltage and output voltage to maintain a pseudo-fixed frequency over the input voltage range. When Q1 is on,

the inductor current rises linearly and the device charges the output capacitor. Q1 turns off after the fixed on-time expires, and the low-side power

MOSFET, Q2, turns on. Once the output voltage drops below the output regulation, Q2 turns off. The one-shot timer is then reset and Q1 turns on

again. The on-time is inversely proportional to the input voltage and directly proportional to the output voltage. It is calculated by the following

equation:

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������������������ ∙ ������������������

Eq. 1

Where:



VIN is the input voltage



VOUT is the output voltage



fSW is the switching frequency

The off-time duration is tOFF and starts after the on-time expires. The off-time expires when the feedback voltage decreases below the reference

voltage, which then triggers the on-time duration to start again. The minimum off-time is 220ns typical.

In order to provide a small output ripple during light load conditions, the AP62201 operates in PWM regardless of output load.

2

Pulse Frequency Modulation (PFM) Operation

The AP62200/AP62200T enters PFM operation at light load conditions for high efficiency. During light load conditions, the regulator automatically

reduces the switching frequency. As the output current decreases, so too does the inductor current. The inductor current, IL, eventually reaches 0A,

marking the boundary between Continuous Conduction Mode (CCM) and Discontinuous Condition Mode (DCM). During this time, both Q1 and Q2

are off, and the load current is provided only by the output capacitor. When VFB becomes lower than 0.8V for AP62200 or 0.763V for AP62200T,

the next cycle begins, and Q1 turns on. Because the AP62200/AP62200T works in PFM during light load conditions, it can achieve power

efficiency of up to 84% at a 5mA load condition.

Likewise, as the output load increases from light load to heavy load, the switching frequency increases to maintain the regulation of the output

voltage. The transition point between light and heavy load conditions can be calculated using the following equation:

������������������������������ = (

������������������ − ������������������������

������������

) ∙ ������������������

Eq. 2

Where:



L is the inductor value

The quiescent current of AP62200/AP62200T is 135

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

3

Enable

When disabled, the device shutdown supply current is only 1.3

μA. When applying a voltage greater than the EN logic high threshold (typical 1.2V,

rising), the AP62200/AP62201/AP62200T enables all functions and the device initiates the soft-start phase. An internal 1.5µA pull-up current

source connected from the internal LDO-regulated VCC to the EN pin guarantees that if EN is left floating, the device still automatically enables

once the voltage reaches the EN logic high threshold. The AP62200/AP62201/AP62200T has a built-in 2.5ms soft-start time to prevent output

voltage overshoot and inrush current. When the EN voltage falls below its logic low threshold (typical 1.1V, falling), the internal SS voltage

discharges to ground and device operation disables.

The EN pin can also be used to program the undervoltage lockout thresholds. See Undervoltage Lockout (UVLO) section for more details.