MIC2169_09 Datasheet, PDF (13/15 Pages) Micrel Semiconductor – 500kHz PWM Synchronous Buck Control IC

MIC2169
Design Example
Layout and Checklist:
1. Connect the current limiting (R2) resistor directly
to the drain of top MOSFET Q3.
2. Use a 5Ω resistor from the input supply to the VIN
pin on the MIC2169. Also, place a 1μF ceramic
capacitor from this pin to GND, preferably not thru
a via.
3. The feedback resistors R3 and R4/R5/R6 should
be placed close to the FB pin. The top side of R3
should connect directly to the output node. Run
this trace away from the switch node (junction of
Q3, Q2, and L1). The bottom side of R3 should
connect to the GND pin on the MIC2169.
4. The compensation resistor and capacitors should
be placed right next to the COMP pin and the other
side should connect directly to the GND pin on the
MIC2169 rather than going to the plane.
5. Add a 1.4Ω resistor and a 1000pF capacitor from
the switch node to ground pin. See page 7, Current
Limiting section for more detail.
6. Add place holders for gate resistors on the top and
bottom MOSFET gate drives. If necessary, gate
resistors of 10Ω or less should be used.
Micrel
7. Low gate charge MOSFETs should be used to
maximize efficiency, such as Si4800, Si4804BDY,
IRF7821, IRF8910, FDS6680A and FDS6912A,
etc.
8. Compensation component GND, feedback resistor
ground, chip ground should all run together and
connect to the output capacitor ground. See demo
board layout, top layer.
9. The 10μF ceramic capacitor should be placed
between the drain of the top MOSFET and the
source of the bottom MOSFET.
10.The 10μF ceramic capacitor should be placed right
on the VDD pin without any vias.
11. The source of the bottom MOSFET should connect
directly to the input capacitor GND with a thick
trace. The output capacitor and the input capacitor
should connect directly to the GND plane.
12.Place a 0.01μF to 0.1μF ceramic capacitor in parallel
with the CS resistor to filter any switching noise.
J1
+Vin 5-12V
1
Cin=AVX TPSD686M020R0070
+VIN
C2 + C3
68uF
68uF/20V ^20V
+
C1
10uF/16V
C13
1uF/16V
C14
DIN
J2
SHDN
1
J3
1
GND
Q1
2N7002E
R1 ₁
0 Ohm
R7
100K
4
C9 C10
Open 0.1uF
R8
4.02K
R9
R2
10 470 ohm
C16
0.1uF
C4
10uF/6V
BST ¹⁰
D1
SD103BWS
C5
0.1uF/25V
4
Q3
IRF7821
HSD
9
R11
RES
U1
VSW ⁸
MIC2169
COMP/EN
LSD
7
R13
RES
FB
5
R10
4R02 Ohm
Q2
4
IRF7821
R12
47
C15
100pF
L1
Cout=AVX TPSD337M006R0045
CDRH127 / LD-1R0-MC
1.0uH
2
1
+
+
+
C6
C7
C8
330uF/6.3V 330uF Open
R3
10K
D2
C11
J4
1
Vout
R14
Open
C12
0.1uF/25V
Open
R4
3.16k
R5 R6
4.64K 11.3K
C
3.3V
B
2.5V
A
1.5V
JP2
HEADER 3X2
J5
1
GND
MIC2169BMM Evaluation Board Schematic
March 2009
13
M9999-032409