MAX8654_09 Datasheet, PDF(15/17 Page) Maxim Integrated Products

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MAX8654_09 Datasheet, PDF (15/17 Pages) Maxim Integrated Products – 12V, 8A 1.2MHz Step-Down Regulator

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12V, 8A 1.2MHz

Step-Down Regulator

The above equations provide accurate compensation

when the zero-cross frequency is significantly higher

than the double-pole frequency. When the zero-cross

frequency is near the double-pole frequency, the actual

zero-cross frequency is higher than the calculated fre-

quency. In this case, lowering the value of R1 reduces the

zero-cross frequency. Also, set the third pole of the type 3

compensation close to the switching frequency if the

zero-cross frequency is above 200kHz to boost the phase

margin. Note that the value of R4 can be altered to make

the values of the compensation components practical.

The recommended range for R3 is 2kâ¦ to 10kâ¦.

PCB Layout Considerations and Thermal

Performance

Careful PCB layout is critical to achieve clean and sta-

ble operation. It is highly recommended to duplicate

the MAX8654 EV kit layout for optimum performance. If

deviation is necessary, follow these guidelines for good

PCB layout:

1) Connect input and output capacitors, VVP and VVDL

capacitors to the power ground plane; connect all

other capacitors to the signal ground plane.

2) Place capacitors on VVP, VIN, VVL, VVDL, and SS as

close as possible to the IC and its corresponding pin

using direct traces. Keep power ground plane (con-

nected to PGND) and signal ground plane (connect-

ed to GND) separate.

3) Keep the high-current paths as short and wide as

possible. Keep the path of switching current short

and minimize the loop area formed by LX, the out-

put capacitors, and the input capacitors.

4) Connect IN, LX, and PGND separately to a large

copper area to help cool the IC to further improve

efficiency and long-term reliability.

5) Ensure all feedback connections are short and

direct. Place the feedback resistors and compensa-

tion components as close to the IC as possible.

6) Route high-speed switching nodes, such as LX,

away from sensitive analog areas (FB, COMP).

COMPENSATION

TRANSFER

FUNCTION

DOUBLE POLE

OPEN-LOOP

GAIN

THIRD

POLE

POWER-STAGE

TRANSFER FUNCTION

FIRST AND

SECOND ZEROS

Figure 4. Transfer Function for Type 3 Compensation

SECOND

POLE

ESR

ZERO

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