MAX1945S 查看數據表（PDF） - Maxim Integrated

零件编号

产品描述 (功能)

生产厂家

MAX1945S

1MHz, 1% Accurate, 6A Internal Switch Step-Down Regulators

Maxim Integrated 

1MHz, 1% Accurate, 6A Internal Switch

Step-Down Regulators

fzESR = [1/(2π ✕ COUT RESR)] = [1/(2 ✕ π ✕ 94 ✕10-6 ✕

0.005)] = 339kHz.

For a 0.68µH output inductor, choose the closed-loop

unity-gain crossover frequency (fc) at 120kHz.

Determine the switching regulator DC gain:

GDC = gmc ✕ ROUT = 18.2 ✕ 0.3 = 5.46

then:

RC = (VOUT ✕ fC)/(gmEA ✕ VFB ✕ GDC ✕ fpLOAD) =

(1.8 ✕ 120kHz)/(50 ✕ 10-6 ✕ 0.8 ✕ 5.46 ✕ 5.554kHz) ≈

178kΩ (1%)

CC = (COUT ✕ ROUT)/RC =(94µF ✕ 0.3)/178kΩ ≈ 156pF,

choose CC = 100pF, 10%

Output Inductor: 0.68µH/12A, 5mΩ ESR (max), Coilcraft

DO3316P-681HC

Output Capacitor C5: 2XJMK432BJ476MM

Input Capacitor C1: LMK432BJ226MM

VCC = 3.3V OR 5V

C4

1µF

VIN = 2.5V

R1

10Ω

C1

3 x 22µF

C6

0.1µF

IN

BST

IN

IN MAX1945R LX

MAX1945S LX

IN

LX

VDD

LX

VCC

LX

LX

CTL1

LX

CTL2

LX

SYNCOUT

FB

SYNC

RC

178kΩ

COMP

REF

FBSEL

CC

100pF

GND

D1

C3

0.1µF

L1

0.68µF

1.8V, 6A

C5

2 x 47µF

C4

0.22µF

PGND

PC Board Layout

Considerations

Careful PC board layout is critical to achieve clean and

stable operation. The switching power stage requires

particular attention. Follow these guidelines for good

PC board layout:

1) Place decoupling capacitors as close to the IC as

possible. Keep power ground plane (connected to

PGND) and signal ground plane (connected to

GND) separate. Star connect both ground plane at

output capacitor.

2) Connect input and output capacitors to the power

ground plane; connect all other capacitors to the

signal ground plane.

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 the high-side

MOSFET, the low side MOSFET, and the input

capacitors. Avoid vias in the switching paths.

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 as close to the

IC as possible.

6) Route high-speed switching nodes away from sen-

sitive analog areas (FB, COMP).

Chip Information

TRANSISTOR COUNT: 5000

PROCESS: BiCMOS

Figure 3. Typical Application Circuit with all ceramic capacitors

(1MHz)

______________________________________________________________________________________ 17

Share Link: