LP38853_15 Datasheet, PDF (17/30 Pages) Texas Instruments – LP38853 3A Fast-Response High-Accuracy Adjustable LDO Linear Regulator with Enable and Soft-Start

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LP38853
SNVS335E – DECEMBER 2006 – REVISED NOVEMBER 2015
Figure 24. F_ZERO and F_POLE vs Gain
8.2.2.2 Power Dissipation and Heat Sinking
Additional copper area for heat sinking may be required, depending on the maximum device dissipation (P_D) and
the maximum anticipated ambient temperature (T_A) for the device. Under all possible conditions, the junction
temperature must be within the range specified under operating conditions.
The total power dissipation of the device is the sum of three different points of dissipation in the device.
The first part is the power that is dissipated in the NMOS pass element and can be determined with Equation 8:
P_D(PASS) = (V_IN – V_OUT) × I_OUT
(8)
The second part is the power that is dissipated in the bias and control circuitry and can be determined with
Equation 9:
P_D(BIAS) = V_BIAS × I_GND(BIAS)
where
• I_GND(BIAS) is the portion of the operating ground current of the device that is related to V_BIAS.
(9)
The third part is the power that is dissipated in portions of the output stage circuitry and can be determined with
Equation 10:
P_D(IN) = V_IN × I_GND(IN)
where
• I_GND(IN) is the portion of the operating ground current of the device that is related to V_IN.
(10)
The total power dissipation is shown by Equation 11:
P_D = P_D(PASS) + P_D(BIAS) + P_D(IN)
(11)
The maximum allowable junction temperature rise (ΔT_J) depends on the maximum anticipated ambient
temperature (T_A(MAX)) for the application, and the maximum allowable operating junction temperature
(T_J(MAX))(see Equation 12):
ΔT_J = T_J(MAX) – T_A(MAX)
(12)
The maximum allowable value for junction-to-ambient thermal resistance, R_θJA, can be calculated using
Equation 13:
R _TJA
d
'T_J
P_D
(13)
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