MCP1710_12 Datasheet, PDF (15/26 Pages) Microchip Technology – Ultra-Low Quiescent Current LDO Regulator

5.0 APPLICATION
CIRCUITS/ISSUES
5.1 Typical Application
The MCP1710 is used for applications that require
ultra-low quiescent current draw.
+ ^CIN
-
V_IN
SHDN
GND
V_OUT
FB
C_OUT
FIGURE 5-1:
Typical Application Circuit.
5.2 Power Calculations
5.2.1 POWER DISSIPATION
The internal power dissipation within the MCP1710 is a
function of input voltage, output voltage, output current
and quiescent current. Equation 5-1 can be used to
calculate the internal power dissipation for the LDO.
EQUATION 5-1:
P_LDO = V_{INMAX} – V_{OUTMIN}  I_{OUTMAX}
Where:
P_LDO = LDO Pass device internal power
dissipation
V_IN(MAX) = Maximum input voltage
V_OUT(MIN) = LDO minimum output voltage
I_OUT(MAX) = Maximum output current
In addition to the LDO pass element power dissipation,
there is power dissipation within the MCP1710 as a
result of quiescent or ground current. The power
dissipation as a result of the ground current can be
calculated using Equation 5-2:
EQUATION 5-2:
Where:
P_{IGND} = V_{INMAX}  I_GND
P_I(GND) = Power dissipation due to the
quiescent current of the LDO
V_IN(MAX) = Maximum input voltage
I_GND = Current flowing in the GND pin
MCP1710
The total power dissipated within the MCP1710 is the
sum of the power dissipated in the LDO pass device
and the P(I_GND) term. Because of the CMOS
construction, the typical I_GND for the MCP1710 is
200 µA at full load. Operating at a maximum V_IN of 5.5V
results in a power dissipation of 1.1 mW. For most
applications, this is small compared to the LDO pass
device power dissipation, and can be neglected.
The maximum continuous operating junction
temperature specified for the MCP1710 is +85°C. To
estimate the internal junction temperature of the
MCP1710, the total internal power dissipation is
multiplied by the thermal resistance from junction-to-
ambient (R_JA) of the device. The thermal resistance
from junction-to-ambient for the 2 x 2 VDFN-8 package
is estimated at 73.1°C/W.
EQUATION 5-3:
T_{JMAX} = P_TOTAL  R_JA + T_{AMAX}
Where:
T_J(MAX) = Maximum continuous junction
temperature
P_TOTAL = Total device power dissipation
R_JA = Thermal resistance from junction to
ambient
T_AMAX = Maximum ambient temperature
The maximum power dissipation capability for a
package can be calculated given the junction-to-
ambient thermal resistance and the maximum ambient
temperature for the application. Equation 5-4 can be
used to determine the package maximum internal
power dissipation.
EQUATION 5-4:
P_{DMAX} = ^---T----^J--^--^M----^A---^X--R-^---_-^–---_J-T-_A---^A---^--^M----^A---^X---^---^
Where:
P_D(MAX) = Maximum device power dissipation
T_J(MAX) = maximum continuous junction
temperature
T_A(MAX) = maximum ambient temperature
R_JA = Thermal resistance from
junction-to-ambient
 2012 Microchip Technology Inc.
DS25158A-page 15