mic61300yml Micrel Semiconductor, mic61300yml Datasheet - Page 13

• Manufacturer Part Number: mic61300yml
• Description: Low Input Voltage, Single-supply High-current Ldo
• Manufacturer: Micrel Semiconductor

Adjustable Regulator Design
The MIC61300 adjustable version allows programming
the output voltage from 0.5V to 3.0V by placing a resistor
divider network (R1, R2) from V
Application Circuit). The high side of R1 should be
connected at the point-of-load for high-accuracy Kelvin
sensing. V
where V
The resistor (R2) value between the FB pin and GND is
selected to maintain a minimum 10mA load on the
output.
The resistor values are calculated from the previous
equation, resulting in the following:
Table 1 is a list of resistor combinations to set the output
voltage. A 1% tolerance is recommended for both R1
and R2. For a unity gain, 0.5V output voltage, connect
the FB pin directly to the output.
Micrel, Inc.
September 2010
Table 1. Resistor Selection for Specific V
OUT
R1
V
OUT
OUT
=
is the desired output voltage.
R2
is determined by the following equation:
=
0.5
×
V
0.5V
0.6V
0.7V
0.8V
0.9V
1.1V
1.2V
1.5V
1.8V
2.2V
1.0
⎛
⎜ ⎜
⎝
OUT
V
×
0.5
OUT
⎛
⎜
⎝
R2
R1
10.0Ω
20.0Ω
30.1Ω
40.2Ω
49.9Ω
60.4Ω
69.8Ω
−
100Ω
130Ω
169Ω
+
R1
1
−
1
⎞
⎟ ⎟
⎠
⎞
⎟
⎠
49.9Ω
49.9Ω
49.9Ω
49.9Ω
49.9Ω
49.9Ω
49.9Ω
49.9Ω
49.9Ω
49.9Ω
49.9Ω
R2
OUT
to GND (see
OUT
Eq. 1
Eq. 2
13
Thermal Design
Linear regulators are simple to use. The most
complicated design parameters to consider are thermal
characteristics. To help reduce the thermal resistance,
the ePad (underneath the IC) should be soldered to the
PCB ground and the placement of thermal vias either
underneath or near the ePad is highly recommended.
Thermal design requires the following application-
specific parameters:
• Maximum ambient temperature (T
• Output current (I
• Output voltage (V
• Input voltage (V
• Ground current (I
First, calculate the power dissipation of the regulator
from these numbers and the device parameters from this
datasheet:
where the ground current is approximated by using
numbers from the Electrical Characteristics or Typical
Characteristics sections
For example, given an expected maximum ambient
temperature (T
and I
Equation 1:
Next, determnine the junction temperature for the
expected power dissipation above using the thermal
resistance (θ
adhering to the following criteria for the PCB design:
OUT
P
P
1oz. copper and 100mm
MIC61300.
T
J
D
D
= 1.5A, first calculate the expected P
= (60.7°C/W × 0.468W) + 75°C
= 103.4°C
= (θ
= 0.468W
= (V
= (1.2V – 0.9V) × 1.5A + 1.2V × 0.015A
JA
) of the 10-pin 3mm × 3mm MLF
JA
A
IN
) of 75°C with V
× P
- V
IN
OUT
GND
)
OUT
OUT
D
) + T
)
)
)
) × I
A
OUT
+ (V
IN
2
IN
= 1.2V, V
copper area for the
A
)
× I
M9999-092910-A
GND
)
MIC61300
OUT
®
D
= 0.9V,
(YML)
using
Eq. 3
Eq. 4
Eq. 5