Application Hint 7 Micrel
3
1997 3-187
0.78 (0.031)
0.61 (0.024)
5.0 (0.197)
4.8 (0.188) 0.37 (0.015)
BSC 45° 7° (4 PLCS)
0.77 (0.030)
0.64 (0.025)
3°–6°
7° (4 PLCS)
0.22 (0.009)
0.19 (0.007)
1.75 (0.069)
1.35 (0.053)
0.20 (0.008)
0.10 (0.004)
1.27 (0.50)
BSC
0.56 (0.022)
0.49 (0.019)
0.45 (0.018)
0.35 (0.014)
5.2 (0.205)
4.6 (0.181)
4.0 (0.158)
3.8 (0.150) 6.2 (0.244)
5.8 (0.228)
General Description
The MIC2951 brings the benefits of linear regulation to
surface mountable packaging. High accuracy, high effi-
ciency, very low ripple, and excellent protective features are
combined into a useful device for laptop/notebook comput-
ers, communications equipment, and battery operated in-
strumentation.
Features
• High accuracy +5V or adjustable output voltage
• Extremely small size; up to 150mA output current
• Low dropout voltage and quiescent curent
• Thermal and over-current protection
• Error flag warns of output dropout
• Logic-controlled electronic shutdown
MIC Versus LP Benefits
• Lower dropout voltage
• 150mA output current vs. 100mA
• One-sixth the ground current
• Reverse battery protection for load
• Survives automotive "Load Dump" transient (60V)
MIC2951 Configured as a selectable 3.3V or 5.0V
output regulator.
SD
V
GND
47
8
OUT
+VIN
FB
1
3
SHUTDOWN
INPUT
100pF
2N2222
1%
300kΩ
+7V
1%
180kΩ
+3.3µF
470 kΩ
0V
ON
5V
3.3V
220kΩ
1%
VCC OUT
MIC2951
Dimensions in mm (inch)
1
2
3
4
8
7
6
5
OUTPUT
SENSE
SHUTDOWN
GROUND ERROR
5V TAP
FEEDBACK
INPUT
Pin 1
Package Dimensions
Thermal Considerations
Pin Configuration
Ordering Information
Part Number Temperature Range Package Accuracy
LP2951-02BM –40°C to + 85°C 8-Pin SOIC 0.5%
LP2951-03BM –40°C to + 85°C 8-Pin SOIC 1.0%
MIC2951-02BM –40°C to + 85°C 8-Pin SOIC 0.5%
MIC2951-03BM –40°C to + 85°C 8-Pin SOIC 1.0%
Multi-layer boards having a ground
plane, wide traces near the pads, and
large supply bus lines provide better
thermal conductivity.
The "worst case" value of 160°C/W
assumes no ground plane, minimum
trace widths, and a FR4 material board. Minimum recom-
mended board pad size
Part II. Nominal Power Dissipation and Die Temperature
The MIC2951-02/-03BM at a 25°C ambient temperature will operate
reliably at up to 625mW power dissipation when mounted in the
"worst case" manner described above. At an ambient temperature
of 55°C, the device may safely dissipate 440mW. These power
levels are equivalent to a die temperature of 125°C, the recom-
mended maximum temperature for non-military grade silicon inte-
grated circuits.
Part I. Layout
The MIC2951-02/03BM (8-pin surface mount package) has the
following thermal characteristics when mounted on a single layer
copper-clad printed circuit board.
PC Board θJA
Dielectric
FR4 160°C/W
Ceramic 120°C/W
245 mil
30 mil 50 mil
50 mil
150 mil
Application Hint 7
by Bob Wolbert
Using Low Current LDO Regulators
Application Hint 7 Micrel
3-188 1997
SD
V
GND
47
8
OUT
+VIN
FB
1
3
SHUTDOWN
INPUT
100pF 1%
1.13MΩ
+18V
(+15.3V to +21V)
1%
102kΩ
+3.3µF
0V
ON
VOUT (+15V)
MIC2951
3.3µF
+
MIC2951 +3.3V RegulatorMIC2951 +3.0V Regulator
MIC2951 +2.85V Regulator
(Note: no external resistors are necessary)
MIC2951-02/-03BM common voltage applications. Calcula-
tions assume 100mA of output current, 25°C ambient tem-
perature, 100% duty cycle, and 160°C/W mounting. The
Shutdown Input may be left floating if it is not used.
Typical Applications
SD
V
GND
47
8
OUT
+VIN
FB
1
3
SHUTDOWN
INPUT
+18V
(+15.3V to +21V)
+3.3µF
0V
ON
VOUT (+5V)
MIC2951
3.3µF
+
2
SENSE
5V
TAP
6
SD
V
GND
47
8
OUT
+VIN
FB
1
3
SHUTDOWN
INPUT
100pF 1%
130kΩ
+5V
(+3.15V to +8.9V)
1%
100kΩ
+3.3µF
0V
ON
VOUT (+2.85V)
MIC2951
3.3µF
+
SD
V
GND
47
8
OUT
+VIN
FB
1
3
SHUTDOWN
INPUT
100pF 1%
143kΩ
+5V
(+3.3V to +9.0V)
1%
100kΩ
+3.3µF
0V
ON
VOUT (+3.0V)
MIC2951
3.3µF
+
SD
V
GND
47
8
OUT
+VIN
FB
1
3
SHUTDOWN
INPUT
100pF 1%
300kΩ
+5V
(+3.6V to +9.3V)
1%
180kΩ
+3.3µF
0V
ON
VOUT (+3.3V)
MIC2951
3.3µF
+
MIC2951 +12.0V Regulator
SD
V
GND
47
8
OUT
+VIN
FB
1
3
SHUTDOWN
INPUT
100pF 1%
2.21MΩ
+30V
(+28.3V to +30V)
1%
102kΩ
+3.3µF
0V
ON
VOUT (+28V)
MIC2951
3.3µF
+
SD
V
GND
47
8
OUT
+VIN
FB
1
3
SHUTDOWN
INPUT
100pF 1%
887kΩ
+15V
(+12.3V to +17.8V)
1%
102kΩ
+3.3µF
0V
ON
VOUT (+12V)
MIC2951
3.3µF
+
MIC2951 +28.0V RegulatorMIC2951 +15.0V
MIC2951 +5.0V Regulator
