RT5752 datasheet(24/32 Pages) RICHTEK

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RT5752

DS5752-03 November 2023

www.richtek.com

is a registered trademark of Richtek Technology Corporation.

Thermal Considerations

In many applications, the RT5752 does not generate much

heat due to its high efficiency and low thermal resistance

of its TSOT-23-5 and TSOT-23-6 packages. However, in

applications which the RT5752 runs at a high ambient

temperature and high input voltage or high switching

frequency, the generated heat may exceed the maximum

junction temperature of the part. The junction temperature

should never exceed the absolute maximum junction

temperature of the part.

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. If the junction temperature reaches

approximately 150

°C, the RT5752 stops switching the

power MOSFETs until the temperature cools down by

°C.

The maximum power dissipation can be calculated by

the following formula :

PD(MAX) = (TJ(MAX)

− TA) / θJA(EFFECTIVE)





D, RT

OUT

CORE

1 η

DCR + P

= 0.439W







Considering the

θJA(EFFECTIVE) is 93.79°C/W by using the

RT5752 evaluation board with 4 layers PCB, all layers

with 1 oz. Cu, the junction temperature of the regulator

operating in a 25

°C ambient temperature is approximately :

TJ = 0.439W x 93.79

°C/W + 25°C = 66.1°C

Figure 11. Load Transient Response with and without

Feedforward Capactior

Note that, after defining the CFF, please also check the

load regulation because the feedforward capacitor might

inject an offset voltage into VOUT to cause VOUT inaccuracy.

If the output voltage is over specification caused by

calculated CFF, please decrease the value of feedforward

capacitor CFF.

Figure 11. shows the transient performance with and

without feedforward capacitor.

where TJ(MAX) is the maximum junction temperature of the

die. For recommended operating condition specifications,

the maximum junction temperature is 150

°C. TA is the

ambient temperature, and

θJA(EFFECTIVE) is the system-

level junction to ambient thermal resistance. It can be

estimated from thermal modeling or measurements in the

system.

The thermal resistance of the device strongly depends on

the surrounding PCB layout and can be improved by

providing a heat sink of surrounding copper ground. The

addition of backside copper with thermal vias, stiffeners,

and other enhancements can also help reduce thermal

resistance.

Experiments in the Richtek thermal lab show that simply

set

θJA(EFFECTIVE) as 110% to 120% of the θJA is reasonable

to obtain the allowed PD(MAX).

As an example, consider the case when the RT5752 is

used in TSOT-23-6 package applications where VIN = 5V,

IOUT = 2A, fSW = 1.2MHz, VOUT = 1.2V. The efficiency at

1.2V, 2A is 78.7% by using VCTA25201B-1R5MS6 (1.5

μH,

50m

Ω DCR) as the inductor and measured at room

temperature. The core loss, 10.3mW, can be obtained

from its website in this case. In this case, the power

dissipation of the RT5752 is

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