MIC2954 Micrel Semiconductor, MIC2954 Datasheet - Page 10

• Manufacturer Part Number: MIC2954
• Description: 250mA Low-Dropout Regulator
• Manufacturer: Micrel Semiconductor

MIC2954
or about 0.01 F. When doing this, the output capacitor must
be increased to 3.3 F to maintain stability. These changes
reduce the output noise from 430 V to 100 V rms for a
100kHz bandwidth at 5V output. With the bypass capacitor
added, noise no longer scales with output voltage so that
improvements are more dramatic at higher output voltages.
Automotive Applications
The MIC2954 is ideally suited for automotive applications for
a variety of reasons. It will operate over a wide range of input
voltages with very low dropout voltages (40mV at light loads),
and
features are necessary for use in battery powered systems,
such as automobiles. It is a “bulletproof” device with the ability
to survive both reverse battery (negative transients up to 20V
below ground), and load dump (positive transients up to 60V)
conditions. A wide operating temperature range with low
temperature coefficients is yet another reason to use these
versatile regulators in automotive designs.
Thermal Calculations
Layout Considerations
The MIC2954-07BM/-08BM (8-pin surface-mount package)
has the following thermal characteristics when mounted on a
single layer copper-clad printed circuit board.
Schematic Diagram
MIC2954
very low quiescent currents (75 A typical). These
PC Board Dielectric Material
FR4
Ceramic
50 k
10 k
Q42
Q40
R30
k
Q6
30
50 k
20 k
Q41
R2
R1
10
Q1
Q3
50 k
R3
R11
18
k
ERROR
180
IN
R5
k
C1
20
pF
Q13
13 k
R4
140
R6
k
160 C/W
120 C/W
Q4
Q38
Q12
Q39
Q2
Q5
31.4 k
27.8 k
Q37
JA
20.6
R11
R8
R9
Q15A
k
R26
60 k
Q7
Q11
Q36
R10
150
k
Q8
R25
2.8 k
Q9
Q34
10
R12
110
Q20
k
Multilayer boards having a ground plane, wide traces near the
pads, and large supply bus lines provide better thermal
conductivity.
Our calculations will use the “worst case” value of 160 C/W,
which assumes no ground plane, minimum trace widths, and
a FR4 material board.
Pad Layout (minimum recommended geometry)
Nominal Power Dissipation and Die Temperature
The MIC2954-07BM/-08BM at a 55 C ambient temperature
will operate reliably at up to 440mW power dissipation when
mounted in the “worst case” manner described above. This
power level is equivalent to a die temperature of 125 C, the
recommended maximum temperature for nonmilitary grade
silicon integrated circuits.
Q18
R13
Q16
100
GND
k
R22
150 k
Q15B
Q17
R14
350
k
C2
40 pF
245 mil
Q30
Q19
DENOTES CONNECTION ON
MIC2954-02Bx/-03Bx ONLY
Q14
Q31
Q21
30 mil
12 k
Q29
FEEDBACK
R17
R24
50 k
Q28
Q22
R15
100 k
R16
30 k
Q25
R23 60 k
R21 8
R18
20k
Q26
10
R17
50 mil
Q23
SHDN
R27
182 k
R28
60 k
Q24
5V TAP
SENSE
OUT
150 mil
50 mil
August 1999
Micrel