MIC5211-1.8/2.5BM6 MICREL [Micrel Semiconductor], MIC5211-1.8/2.5BM6 Datasheet - Page 8

• Manufacturer Part Number: MIC5211-1.8/2.5BM6
• Description: Dual ?Cap 80mA LDO Regulator Preliminary Information
• Manufacturer: MICREL [Micrel Semiconductor]

MIC5211
is operating from a 7.2V-nominal two-cell lithium-ion battery
and both regulators are dropping the voltage to 3.0V, then
output current will be limited at higher ambient temperatures.
For example, at 70 C ambient the first regulator can supply
3.0V at 50mA output from a 7.2V supply; however, the
second regulator will have limitations on output current to
avoid thermal shutdown. The dissipation of the first regulator
is:
Since maximum power dissipation for the dual regulator is
250mW at 70 C, the second regulator can only dissipate up
to 34mW without going into thermal shutdown. The amount
of current the second regulator can supply is:
The second regulator can provide up to 8mA output current,
suitable for the keep-alive circuitry often required in hand-
held applications.
Refer to Application Hint 17 for heat sink requirements when
higher power dissipation capability is needed. Refer to De-
signing with Low Dropout Voltage Regulators for a more
thorough discussion of regulator thermal characteristics.
Dual-Voltage Considerations
For configurations where two different voltages are needed in
the system, the MIC5211 has the option of having two
independent output voltages from the same input. For ex-
ample, a 3.3V rail and a 5.0V rail can be supplied from the
MIC5211 for systems that require both voltages. Important
MIC5211
P
P
P
I
4.2V I
OUT2(max)
7.2V 3V I
D1
D1
D2(max)
216mW
7.2V 3V 50mA 7.2V 0.85mA
OUT2(max)
34mW
OUT2(max)
8mA
34mW
34mW
8
considerations must be taken to ensure proper functionality
of the part. The input voltage must be high enough for the 5V
section to operate correctly, this will ensure the 3.3V section
proper operation as well.
Both regulators live off of the same input voltage, therefore
the amount of output current each regulator supplies may be
limited thermally. The maximum power the MIC5211 can
dissipate at room temperature is 455mW, as shown in the
“Thermal Considerations” section. If we assume 6V input
voltage and 50mA of output current for the 3.3V section of the
regulator, then the amount of output current the 5V section
can provide can be calculated based on the power dissipa-
tion.
Based on the power dissipation allowed for the 5V section,
the amount of output current it can source is easily calculated.
(I
tion and in this case can be ignored)
I
Therefore, for this condition, the MIC5211 can supply 50mA
of output current from each section of the regulator.
MAX
GND
exceeds the maximum current rating of the device.
P
P
P
P
P
P
P
P
314.9mW = (6V – 5V) I
314.9mW = (6V – 5V) I
I
typically adds less than 5% to the total power dissipa-
MAX
D
D(3.3V)
D(3.3V)
D(max)
D(max)
D(5V)
D(5V)
D(5V)
= (V
= 314.9mA
= 455mW – 140.1mW
= 314.9mW
= 314.9mW
GND
= 455mW
– P
= (6V – 3.3V) 50mA + 6V · 0.85mA
= 140.1mW
D(3.3V)
– V
OUT
= P
) I
OUT
D(5V)
MAX
MAX
+ V
– 6V · I
GND
· I
GND
GND
November 2000
Micrel