MCP1701A Microchip Technology, MCP1701A Datasheet - Page 11

• Manufacturer Part Number: MCP1701A
• Description: 2 uA Low-Dropout Positive Voltage Regulator
• Manufacturer: Microchip Technology

5.0
5.1
The amount of power dissipated internal to the LDO
linear regulator is the sum of the power dissipation
within the linear pass device (P-channel MOSFET) and
the quiescent current required to bias the internal
reference and error amplifier. The internal linear pass
device power dissipation is calculated as shown in
Equation 5-1.
EQUATION 5-1:
The internal power dissipation, as a result of the bias
current for the LDO internal reference and error
amplifier, is calculated as shown in Equation 5-2.
EQUATION 5-2:
The total internal power dissipation is the sum of P
(pass device) and P
EQUATION 5-3:
For the MCP1701A, the internal quiescent bias current
is so low (2 μA, typ.) that the P
power dissipation equation can be ignored. The
maximum power dissipation can be estimated by using
the maximum input voltage and the minimum output
voltage to obtain a maximum voltage differential
between input and output. The next step would be to
multiply the maximum voltage differential by the
maximum output current.
EQUATION 5-4:
© 2006 Microchip Technology Inc.
Given:
T
P
P
V
AMAX
I
MAX
MAX
OUT
OUT
V
IN
P
TOTAL
THERMAL CONSIDERATIONS
Power Dissipation
P
P
D
= 3.3V to 4.1V
= 3.0V ± 2%
= 1 mA to 100 mA
= 55°C
= (4.1V – (3.0V x 0.98)) x 100 mA
= 116.0 milliwatts
D
(Pass Device) = (V
= (V
= P
P
INMAX
D
D
(Pass Device) + P
(Bias) = V
D
(bias).
– V
OUTMIN
IN
IN
– V
x I
) x I
D
GND
OUT
(bias) term of the
D
OUTMAX
(Bias)
) x I
OUT
Preliminary
D
To determine the junction temperature of the device, the
thermal resistance from junction-to-ambient must be
known. The 3-pin SOT-23 thermal resistance from
junction-to-air (R
335° C/W. The SOT-89 R
approximately 52° C/W when mounted on 1 square inch
of copper. The R
and other application-specific conditions.
The device junction temperature is determined by
calculating the junction temperature rise above
ambient, then adding the rise to the ambient
temperature.
EQUATION 5-5:
EQUATION 5-6:
T
T
T
T
T
J
J
J
J
J
=
=
=
=
=
P
116.0 milliwatts 335°C/W
93.9°C
116.0 milliwatts 52°C/W
61°C
DMAX
JA
JA
will vary with physical layout, airflow
) is estimated to be approximately
JUNCTION
TEMPERATURE – SOT-23
EXAMPLE:
JUNCTION
TEMPERATURE – SOT-89
EXAMPLE:
R
JA
MCP1701A
+
T
JA
A
is estimated to be
DS21990A-page 11
+
+
55°C
55°C