MIC5311 MICREL [Micrel Semiconductor], MIC5311 Datasheet - Page 9

• Manufacturer Part Number: MIC5311
• Description: LowQ Mode Dual 300mA LDO
• Manufacturer: MICREL [Micrel Semiconductor]

February 2005
Micrel, Inc.
Functional Description
The MIC5311 is a high performance, low quiescent
current power management IC consisting of two µCap
low dropout regulators with a LowQ™ mode featuring
lower operating current. Both regulators are capable of
sourcing 300mA.
Enable 1 and 2
The enable inputs allow for logic control of both output
voltages with individual enable inputs. The enable input
is active high, requiring 1.0V for guaranteed operation.
The enable input is CMOS logic and cannot be left
floating.
LowQ™ Mode
The LowQ™ pin is logic level low, requiring <0.2V to
enter the LowQ™ mode. The LowQ™ pin cannot be left
floating. Features of the LowQ™ mode include lower
total quiescent current of typically 7uA.
Input Capacitor
Good bypassing is recommended from input to ground
to help improve AC performance. A 1µF capacitor or
greater located close to the IC is recommended. Larger
load currents may require larger capacitor values.
Bypass Capacitor
The internal reference voltage of the MIC5311 can be
bypassed with a capacitor to ground to reduce output
noise and increase input ripple rejection (PSRR). A
quick-start feature allows for quick turn-on of the output
voltage. The recommended nominal bypass capacitor is
0.01µF, but an increase will result in longer turn on
times t
Output Capacitor
Each regulator output requires a 2.2µF ceramic output
capacitor for stability. The output capacitor value can be
increased
performance has been optimized for a 2.2µF ceramic
type output capacitor. X7R/X5R dielectric-type ceramic
capacitors
temperature performance. X7R-type capacitors change
capacitance by 15% over their operating temperature
range and are the most stable type of ceramic
capacitors. Z5U and Y5V dielectric capacitors change
value by as much as 50% to 60% respectively over their
operating temperature ranges. To use a ceramic chip
capacitor with Y5V dielectric, the value must be much
higher than a X7R ceramic capacitor to ensure the same
minimum capacitance over the equivalent operating
temperature range.
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Thermal Considerations
The MIC5311 is designed to provide 300mA of
continuous current per channel in a very small MLF
package. Maximum power dissipation can be calculated
based on the output current and the voltage drop across
the part. To determine the maximum power dissipation
of the package, use the junction-to-ambient thermal
resistance of the device and the following basic
equation:
T
die,
temperature. θ
examples of the junction-to-ambient thermal resistance
for the MIC5311.
The actual power dissipation of the regulator circuit can
be determined using the equation:
Substituting P
conditions that are critical to the application will give the
maximum operating conditions for the regulator circuit.
For example, when operating the MIC5311 at 60°C with
a minimum footprint layout, the maximum load currents
can be calculated as follows:
The junction-to-ambient thermal resistance for the
minimum footprint is 63°C/W, from Table 1. The
maximum power dissipation must not be exceeded for
proper operation. Using a lithium-ion battery as the
supply voltage of 4.2V, 1.8V
and 2.8V
can be calculated as follows:
9
J
3x3 MLF™-10
(max) is the maximum junction temperature of the
Package
125°C,
OUT
Table 1. MLF™ Thermal Resistance
/100mA for channel 2, power dissipation
P
D(max)
D
JA
and
P
P
P
P
P
P
P
P
P
P
P
P
(max) = (T
DTOTAL
D LDO1
D LDO2
D
D
D
D LDO1
D LDO1
D LDO1
D LDO2
D LDO1
D LDO1
is layout dependent; Table 1 shows
(max) = (T
(max) = (125°C - 60°C) / 63°C/W
(max) = 1.03W
for P
Minimum Footprint
T
θ
JA
A
= (V
= (V
= (V
= (4.2V-1.8V) x 150mA
= 360mW
= (V
= (4.2V-2.8V) x 100mA
= 140mW
= P
D
Recommended
is
J
and solving for the operating
D LDO1
63°C/W
IN
IN
IN
IN
(max) - T
-V
-V
-V
-V
J
OUT
the
(max) - T
OUT1
OUT2
OUT1
OUT2
/150mA for channel 1
+ P
) x I
) x I
) x I
) x I
ambient
D LDO2
A
) /θ
OUT1
OUT2
OUT1
OUT2
A
) /θ
JA
[phone]
M9999-021105
JA
MIC5311
operating
2°C/W
θ
JC