MCP1801_09 Datasheet, PDF (17/26 Pages) Microchip Technology – 150 mA, High PSRR, Low Quiescent Current LDO

6.0 APPLICATION CIRCUITS &
ISSUES
6.1 Typical Application
The MCP1801 is most commonly used as a voltage
regulator. Its low quiescent current and low dropout
voltage make it ideal for many battery-powered
applications.
V_OUT
1.8V
I_OUT
50 mA
MCP1801
NC
SHDN
GND
V_OUT
V_IN
C_OUT
1 µF Ceramic
V_IN
2.4V to 5.0V
C_IN
1 µF
Ceramic
FIGURE 6-1:
Typical Application Circuit.
6.1.1 APPLICATION INPUT CONDITIONS
Package Type =
Input Voltage Range =
V_IN maximum =
V_OUT typical =
I_OUT =
SOT-23-5
2.4V to 5.0V
5.0V
1.8V
50 mA maximum
6.2 Power Calculations
6.2.1 POWER DISSIPATION
The internal power dissipation of the MCP1801 is a
function of input voltage, output voltage, and output
current. The power dissipation, as a result of the
quiescent current draw, is so low, it is insignificant
(25.0 µA x V_IN). The following equation can be used to
calculate the internal power dissipation of the LDO.
EQUATION 6-1:
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
The maximum continuous operating temperature
specified for the MCP1801 is +85°C. To estimate the
internal junction temperature of the MCP1801, the total
internal power dissipation is multiplied by the thermal
resistance from junction to ambient (Rθ_JA). The thermal
resistance from junction to ambient for the SOT-23-5
pin package is estimated at 256°C/W.
© 2009 Microchip Technology Inc.
MCP1801
EQUATION 6-2:
T_J(MAX) = P_TOTAL × Rθ_JA + T_AMAX
Where:
T_J(MAX) = Maximum continuous junction
temperature
P_TOTAL = Total device power dissipation
Rθ_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. The following equation
can be used to determine the package maximum
internal power dissipation.
EQUATION 6-3:
Where:
P_D(MAX)
=
-⁽--^T---^J---⁽--^M----^A---^X---⁾---–-----^T----^A---⁽--^M----^A---^X---⁾--⁾-
Rθ_JA
P_D(MAX) = Maximum device power
dissipation
T_J(MAX) = Maximum continuous junction
temperature
T_A(MAX) = Maximum ambient temperature
Rθ_JA = Thermal resistance from
junction to ambient
EQUATION 6-4:
T_J(RISE) = P_D(MAX) × Rθ_JA
Where:
T_J(RISE) = Rise in device junction
temperature over the ambient
temperature
P_TOTAL = Maximum device power
dissipation
Rθ_JA = Thermal resistance from
junction to ambient
EQUATION 6-5:
T_J = T_J(RISE) + T_A
Where:
T_J = Junction Temperature
T_J(RISE) = Rise in device junction
temperature over the ambient
temperature
T_A = Ambient temperature
DS22051C-page 17