AP62250

Document number: DS42701 Rev. 2 - 2

13 of 21

www.diodes.com

January 2021

© Diodes Incorporated

AP62250

Application Information (continued)

6

Overcurrent Protection (OCP)

The AP62250 has cycle-by-cycle valley current limit protection by sensing the current through the internal low-side power MOSFET, Q2. While Q2

is on, the internal sensing circuitry monitors its conduction current. The overcurrent limit has a corresponding voltage limit, VLIMIT. When the

voltage between GND and SW is lower than VLIMIT due to excessive current through Q2, the OCP triggers, and the controller turns off Q2. During

this time, both Q1 and Q2 remain off. A new switching cycle begins only when the voltage between GND and SW rises above VLIMIT. If Q2

consistently hits the valley current limit for 2.5ms, the buck converter enters hiccup mode and shuts down. After 20ms of down time, the buck

converter restarts powering up. Hiccup mode reduces the power dissipation in the overcurrent condition.

Because the RDS(ON) values of the power MOSFETs increase with temperature, VLIMIT has a temperature coefficient of 0.4%/°C to compensate for

the temperature dependency of RDS(ON).

7

Thermal Shutdown (TSD)

If the junction temperature of the device reaches the thermal shutdown limit of +160°C, the AP62250 shuts down both its high-side and low-side

power MOSFETs. When the junction temperature reduces to the required level (+140°C typical), the device initiates a normal power-up cycle with

soft-start.

8

Power Derating Characteristics

To prevent the regulator from exceeding the maximum recommended operating junction temperature, some thermal analysis is required. The

regulator’s temperature rise is given by:

������������������������������ = ������������ ∙ (������������������)

Eq. 6

Where:



PD is the power dissipated by the regulator



θJA is the thermal resistance from the junction of the die to the ambient temperature

The junction temperature, TJ, is given by:

������������ = ������������ + ������������������������������

Eq. 7

Where:



TA is the ambient temperature of the environment