RT6203ENGSP datasheet(17/21 Pages) RICHTEK

17 / 21 page

RT6203E

DS6203E-00 January 2019

www.richtek.com

is a registered trademark of Richtek Technology Corporation.

Figure 5. External Bootstrap Diode and BOOT Capacitor

Series Resistor

BOOT

0.1µF

RT6203E

Thermal Considerations

In many applications, the RT6203E does not generate

much heat due to its high efficiency and low thermal

resistance of its SOP-8 package. However, in applications

in which the RT6203E is running at a high ambient

temperature and high input voltage, the generated heat

may exceed the maximum junction temperature of the

part.

The RT6203E includes a programmable over-temperature

protection (OTP) circuitry to prevent overheating due to

excessive power dissipation. If the junction temperature

reaches approximately 150

°C(default), the RT6203E stop

switching the power MOSFETs until the temperature drops

about 20

°C cooler.

Note that the over temperature protection is intended to

protect the device during momentary overload conditions.

The protection is activated outside of the absolute

maximum range of operation as a secondary fail-safe and

therefore should not be relied upon operationally.

Continuous operation above the specified absolute

maximum operating junction temperature may impair

device reliability or permanently damage the device.

The maximum power dissipation can be calculated by

the following formula :









D MAX

J MAX

JA EFFECTIVE

P= T

/ θ



where TJ(MAX) is the maximum allowed junction temperature

of the die. For recommended operating condition

specifications, the maximum junction temperature is

125

°C. TA is the ambient operating temperature,

θJA(EFFECTIVE) is the system-level junction to ambient

thermal resistance. It can be estimated from thermal

modeling or measurements in the system.

The device thermal resistance depends strongly 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.

As an example, consider the case when the RT6203E is

used in applications where VIN = 12V, IOUT = 6A, fSW =

700kHz, VOUT = 1.1V. The efficiency at 1.1V, 6A is 75.8%

by using WE -744770015 (1.5

μH, 5mΩ DCR) as the

inductor and measured at room temperature. The core

loss can be obtained from its website of 37.4mW in this

case. In this case, the power dissipation of the RT6203E





D, RT

OUT

CORE

1 η

DCR + P

= 1.89W







Considering the system-level

θJA(EFFECTIVE) is 34.8°C/W

(other heat sources are also considered), the junction

temperature of the regulator operating in a 25

°C ambient

temperature is approximately :

T = 1.89W 34.8 C/W + 25 C = 90.7 C





Figure 6 shows the RT6203E RDS(ON) versus different

junction temperature. If the application calls for a higher

ambient temperature, we might recalculate the device

power dissipation and the junction temperature based on

a higher RDS(ON) since it increases with temperature.

Using 50

°C ambient temperature as an example. Due to

the variation of junction temperature is dominated by the

ambient temperature, the TJ' at 50

°C ambient temperature

can be pre-estimated as





T ' = 90.7 C + 50 C 25 C = 115.7 C

 



According to Figure 6, the increasing RDS(ON) can be found









DS ON _H

DS ON _L

= 61.8m

(at 115.7 C) 56.7m

90.7 C = 5.1m

= 28.1m

(at 115.7 C) 25.7m

90.7 C = 2.4m



 









 







The external power dissipation caused by the increasing

RDS(ON) at higher temperature can be calculated as



D,RDS ON

1.1

= 6A

5.1m

+ 6A

2.4m

= 0.096W









 







As a result, the new power dissipation due to the variation

of RDS(ON) is 1.986W. Therefore, the estimated new

junction temperature is

T ' = 1.986W 34.8 C/W + 50 C = 119.1 C





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