RT6203E
5V
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.
BOOT
R
RT6203E
SW
As an example, consider the case when the RT6203E is
0.1µF
used in applications where VIN = 12V, IOUT = 6A, fSW
=
700kHz, VOUT = 1.1V. The efficiency at 1.1V, 6Ais 75.8%
by using WE -744770015 (1.5μH, 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
Figure 5. External BootstrapDiode and BOOT Capacitor
Series Resistor
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.
is
1 η
η
PD, RT
=
POUT I2 DCR + PCORE = 1.89W
O
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 :
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.
TJ = 1.89W 34.8C/W + 25C = 90.7C
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.
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.
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 ' = 90.7C + 50C 25C = 115.7C
J
According to Figure 6, the increasing RDS(ON) can be found
as
RDS ON _H = 61.8m (at 115.7C) 56.7m 90.7C = 5.1m
The maximum power dissipation can be calculated by
the following formula :
RDS ON _L = 28.1m (at 115.7C) 25.7m 90.7C = 2.4m
The external power dissipation caused by the increasing
RDS(ON) at higher temperature can be calculated as
P
= T
T / θ
A
D MAX
J MAX
JA EFFECTIVE
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.
1.1
12
1.1
12
PD,RDS ON = 6A 2
5.1m + 6A 2 1
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
TJ' = 1.986W 34.8C/W + 50C = 119.1C
The device thermal resistance depends strongly on the
Copyright 2019 Richtek Technology Corporation. All rights reserved.
©
is a registered trademark of Richtek Technology Corporation.
DS6203E-00 January 2019
www.richtek.com
17
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