MIC2169BMM datasheet(13/15 Pages) MICREL

13 / 15 page

March 2009

M9999-032409

MIC2169

Micrel

Design Example

Layout and Checklist:

1. Connect the current limiting (R2) resistor directly

to the drain of top MOSFET Q3.

2. Use a 5

Ω resistor from the input supply to the VIN

pin on the MIC2169. Also, place a 1

μF 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 1.4

Ω 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 10

Ω or less should be used.

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 10

μF ceramic capacitor should be placed

between the drain of the top MOSFET and the

source of the bottom MOSFET.

10.The 10

μF 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 0.01

μF to 0.1μF ceramic capacitor in parallel

with the CS resistor to ﬁlter any switching noise.

330uF/6.3V

330uF

68uF/20V

IRF7821

0.1uF/25V

C12

0.1uF/25V

Open

COMP/EN

BST

LSD

HSD

VSW

MIC2169

JP2

HEADER 3X2

470 ohm

+VIN

C11

Open

10uF/6V

SD103BWS

C13

1uF/16V

C15

100pF

C16

0.1uF

1.5V

2.5V

3.3V

Cout=AVX TPSD337M006R0045

Cin=AVX TPSD686M020R0070

C10

0.1uF

68uF

1.0uH

10K

4.64K

11.3K

4.02K

100K

R10

4R02 Ohm

R12

3.16k

SHDN

Open

R14

Open

CDRH127 / LD-1R0-MC

CBA

20V

10uF/16V

C14

DIN

2N7002E

0 Ohm

R11

RES

R13

RES

+Vin 5-12V

GND

Vout

MIC2169BMM Evaluation Board Schematic

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