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TPS54541 Datasheet, PDF (37/48 Pages) Texas Instruments – 4.5-V to 42-V Input, 5-A Step-Down DC-DC Converter With Soft-Start and Eco-mode
◁
TPS54541
www.ti.com
POWER DISSIPATION ESTIMATE
SLVSC57 – OCTOBER 2013
The following formulas estimate the TPS54541 power dissipation under CCM operation. These equations should
not be used if the device is operating in DCM.
The power dissipation of the IC includes conduction loss (PCOND), switching loss (PSW), gate drive loss (PGD), and
supply current (PQ). Example calculations are shown with the 12 V typical input voltage of the design example.
( ) PCOND
=
IOUT
2
´
RDS(on)
´
æ
ç
è
VOUT
VIN
ö
÷
ø
=
5
A2
´ 87 mW
´
5V
12 V
= 0.958 W
(56)
spacer
PSW = VIN ´ fSW ´ IOUT ´ trise = 12 V ´ 400 kHz ´ 5 A ´ 4.9 ns = 0.118 W
(57)
spacer
PGD = VIN ´ QG ´ fSW = 12 V ´ 3nC ´ 400 kHz = 0.014 W
(58)
spacer
PQ = VIN ´ IQ = 12 V ´ 146 mA = 0.0018 W
where (for Equation 56, Equation 57, Equation 58, and Equation 59)
• IOUT is the output current (A)
• RDS(on) is the on-resistance of the high-side MOSFET (Ω)
• VOUT is the output voltage (V)
• VIN is the input voltage (V)
• ƒsw is the switching frequency (Hz)
• trise is the SW pin voltage rise time and can be estimated by trise = VIN x 0.16 ns/V + 3 ns
• QG is the total gate charge of the internal MOSFET
• IQ is the operating nonswitching supply current
(59)
Therefore,
PTOT = PCOND + PSW + PGD + PQ = 0.958 W + 0.118 W + 0.014 W + 0.0018 W = 1.092 W
(60)
For given TA,
TJ = TA + RTH ´ PTOT
(61)
For given TJ(MAX) = 150°C
TA(max) = TJ(max) - RTH ´ PTOT
where (for Equation 60, Equation 61, and Equation 62)
• PTOT is the total device power dissipation (W)
• TA is the ambient temperature (°C)
• TJ is the junction temperature (°C)
• RTH is the thermal resistance of the package (°C/W)
• TJ(MAX) is maximum junction temperature (°C)
• TA(MAX) is maximum ambient temperature (°C)
(62)
Additional power loss occurs in the regulator circuit due to the inductor ac and dc losses and the catch diode and
PCB trace resistance impacting the overall efficiency of the regulator.
Copyright © 2013, Texas Instruments Incorporated
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