AAT1162_08 Datasheet, PDF (17/18 Pages) Advanced Analogic Technologies – 12V, 1.5A Step-Down DC/DC Converter

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PRODUCT DATASHEET
AAT1162
12V, 1.5A Step-Down DC/DC Converter
AAT1162 Losses
Total losses can be estimated by calculating the dropout (V_IN = V_O) losses where the power MOSFET R_DS(ON) will be at
the maximum value. All values assume an 85°C ambient temperature and a 140°C junction temperature with the TDFN
37°C/W package.
P_LOSS = I_LOAD2 · R_DS(ON)H = 1.5A² · 0.158Ω = 0.355W
T_J(MAX) = T_AMB + Θ_JA · P_LOSS = 85°C + (37°C/W) · 355mW = 96.6°C
The total losses are also investigated at the nominal input voltage (12V). The simplified version of the R_DS(ON) losses
assumes that the N-channel and P-channel R_DS(ON) are equal.
P_TOTAL = I_LOAD2 · R_DS(ON) + [(t_sw · F_OSC · I_LOAD + I_Q) · V_IN]
= 1.5A² · 100mΩ + [(5ns · 800kHz · 1.5A + 150µA) · 12V] = 299mW
T_J(MAX) = T_AMB + Θ_JA · P_LOSS = 85°C + (37°C/W) · 299mW = 96°C
1162.2008.01.1.3
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