MIC2954
or about 0.01µF. When doing this, the output capacitor must
be increased to 3.3µF to maintain stability. These changes
reduce the output noise from 430µV to 100µV 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 very low quiescent currents (75µA typical). These
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.
Micrel
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)
50 mil
245 mil
150 mil
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.
PC Board Dielectric Material
FR4
Ceramic
θ
JA
160°C/W
120°C/W
30 mil
50 mil
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.
Schematic Diagram
IN
FEEDBACK
R18
20kΩ
Q15A
Q15B
Q24
Q26
Q25
Q9
Q3
OUT
R11
18
kΩ
Q4
Q7
Q5
Q8
SENSE
Q14
Q6
Q1
10
R1
20 kΩ
C1
20
pF
R11
20.6
kΩ
Q2
Q20
Q16
Q17
R17
12 kΩ
R27
182 kΩ
5V TAP
R28
60 kΩ
Q22
Q21
C2
40 pF
Q42
R8
31.4 kΩ
R10
150
kΩ
Q23
R2
50 kΩ
R5
180
kΩ
Q13
R6
140
kΩ
Q12
R9
27.8 kΩ
R15
100 kΩ
Q40
Q41
R12
110
kΩ
Q11
R13
100
kΩ
R14
350
kΩ
Q29
R16
30 kΩ
R17
10
Ω
R30
30
kΩ
Q18
Q19
Q28
R3
50 kΩ
R4
13 kΩ
R21 8
Ω
50 kΩ
Q37
Q36
Q30 Q31
SHDN
R22
150 kΩ
R24
50 kΩ
R23 60 kΩ
10 kΩ
ERROR
Q38
R26
60 kΩ
Q34
R25
2.8 kΩ
DENOTES CONNECTION ON
MIC2954-02Bx/-03Bx ONLY
Q39
GND
MIC2954
10
August 1999
MICREL [ MICREL SEMICONDUCTOR ]
