AP64352

Document number: DS41978 Rev. 5 - 2

13 of 21

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August 2019

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AP64352

Application Information (cont.)

7

Overcurrent Protection (OCP)

The AP64352 has cycle-by-cycle peak current limit protection by sensing the current through the internal high-side power MOSFET, Q1. While Q1

is on, the internal sensing circuitry monitors its conduction current. Once the current through Q1 exceeds the peak current limit, Q1 immediately

turns off. If Q1 consistently hits the peak current limit for 512 cycles, the buck converter enters hiccup mode and shuts down. After 8192 cycles of

down time, the buck converter restarts powering up. Hiccup mode reduces the power dissipation in the overcurrent condition.

8

Thermal Shutdown (TSD)

If the junction temperature of the device reaches the thermal shutdown limit of 160°C, the AP64352 shuts down both its high-side and low-side

power MOSFETs. When the junction temperature reduces to the required level (135°C typical), the device initiates a normal power-up cycle with

soft-start.

9

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. 4

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. 5

Where:



TA is the ambient temperature of the environment

For the SO-8EP package, the

θJA is 45°C/W. The actual junction temperature should not exceed the maximum recommended operating junction

temperature of 125°C when considering the thermal design. Figure 24 shows a typical derating curve versus ambient temperature.

Figure 24. Output Current Derating Curve vs. Ambient Temperature, VIN = 12V, fsw = 500kHz

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

5.0

0

20

40

60

80

100

120

140

160

Ambient Temperature (

°C)

VOUT = 1.2V

VOUT = 1.5V

VOUT = 1.8V

VOUT = 2.5V

VOUT = 3.3V

VOUT = 5V