F

RT7204E

Copyright © 2024 Richtek Technology Corporation. All rights reserved.

is a registered trademark of Richtek Technology Corporation.

RT7204E_DS-00

May 2024

www.richtek.com

39

16.9

VIN Detection and LPS Protection

The RT7204E can detect the input voltage and implement LPS protection by sensing the drain voltage of the low-

side SR MOSFET, as shown in Figure 6. The recommended divider resistance, RVTR_H, between the SR MOSFET

drain terminal and the VTR pin is 150k

. Due to varying component stress and thermal considerations under AC

high/low line conditions, the power rating and OTP threshold can be adaptively customized through input voltage

detection for a more compact design. The VTR pin also provides AC OFF detection to prevent the RT7204E from

being reverse biased through the body diode of a blocking N-MOSFET. If there is no switching signal on the VTR

within the programmable delay time, a flag will be sent to the MCU to fulfill power saving requirements.

16.10

Thermal Considerations

The junction temperature should never exceed the absolute maximum junction temperature TJ(MAX), listed under

Absolute Maximum Ratings, to avoid permanent damage to the device. The maximum allowable power dissipation

depends on the thermal resistance of the IC package, the PCB layout, the rate of surrounding airflow, and the

difference between the junction and ambient temperatures. The maximum power dissipation can be calculated

using the following formula:

PD(MAX) = (TJ(MAX) - TA) /

JA

where TJ(MAX) is the maximum junction temperature, TA is the ambient temperature, and

JA is the junction-to-

ambient thermal resistance.

For continuous operation, the maximum operating junction temperature indicated under Recommended Operating

Conditions is 125°C. The junction-to-ambient thermal resistance,

JA, is highly package dependent. For a WQFN-

24L 4x4 package, the thermal resistance,

JA, is 39.6°C/W on a standard JEDEC low effective-thermal-conductivity

two-layer test board. The maximum power dissipation at TA = 25°C can be calculated as below:

PD(MAX) = (125°C - 25°C) / (39.6°C/W) = 2.52W for a WQFN-24L 4x4 package.

The maximum power dissipation depends on the operating ambient temperature for the fixed TJ(MAX) and the

thermal resistance,

JA. The derating curve in Figure 16 allows the designer to see the effect of rising ambient

temperature on the maximum power dissipation.

Figure 16. Derating Curve of Maximum Power Dissipation

0.0

0.5

1.0

1.5

2.0

2.5

3.0

0

25

50

75

100

125

Ambient Temperature (°C)

Two-Layer PCB

Note 8

. The information provided in this section is for reference only. The customer is solely responsible for the designing,

validating, and testing your product incorporating Richtek’s product and ensure such product meets applicable

standards and any safety, security, or other requirements.