MAX26402/MAX26403

36V, 2.5A/3.5A, Fully Integrated Synchronous

Silent Switcher Buck Converters

www.analog.com

Analog Devices | 12

Input Capacitor

The input filter capacitor reduces peak currents drawn from the power source and reduces noise and voltage ripple on

the input caused by the circuit's switching. The MAX26402/MAX26403 incorporate a symmetrical pinout to improve EMI

performance. It is recommended to split the input capacitors symmetrically between the two SUP pins. Connect a 2.2μF

(min) ceramic capacitor on each SUP pin for low-input voltage ripple. For additional noise immunity, a high-frequency

0603 or smaller capacitor can be added on each SUP pin. A bulk capacitor is typically required to provide the remaining

capacitance needed to minimize input voltage ripple and to improve load transient response.

Output Capacitor

The output capacitor is selected to meet output voltage ripple, load-transient response, and loop stability requirements.

During a load step, the output current changes almost instantaneously, whereas the inductor is slow to react. During this

transition time, the load-change requirements are supplied by the output capacitor, which causes an undershoot/

overshoot in the output voltage. Output capacitance also affects the control-loop stability.

The optimal phase margin for the fixed-output IC is achieved by using the effective output capacitance shown in Table 2.

Table 2. Recommended Output Capacitance for Fixed Output-Voltage Versions

PART NUMBER

FREQUENCY

EFFECTIVE COUT (μF)

TYP

MIN

MAX26402

400kHz

42

34

2.1MHz

23

18

3MHz

18

16

MAX26403

400kHz

42

34

2.1MHz

23

18

3MHz

18

16

Inductor Selection

Inductor design is a compromise between the size, efficiency, control-loop bandwidth, and stability of the converter.

Insufficient inductance increases the inductor current ripple causing higher conduction losses and higher output voltage

ripple. Since the slope compensation is fixed internally for MAX26402/MAX26403, it might also cause current-mode

control instability. A large inductor reduces the ripple, but increases the size and cost of the solution and slows the

response. Table 3 provides optimized inductor values for the respective switching frequency of the fixed-output IC.

Table 3. Recommended Inductor for Fixed Output-Voltage Versions

PART NUMBER

FREQUENCY

INDUCTANCE (μH)

TYP

MIN

MAX

MAX26402

400kHz

8.2

6.8

10

2.1MHz

2.2

1.5

3.3

3MHz

1.5

1

2.2

MAX26403

400kHz

6.8

4.7

8.2

2.1MHz

1.5

1.0

2.2

3MHz

1.0

0.8

1.5

PCB Layout Guidelines

Careful PCB layout is critical to achieve low switching-power losses and clean, stable operation. Use a multilayer board

whenever possible for better noise immunity and power dissipation. The package for the MAX26402/MAX26403 offers a

unique symmetrical design, which helps cancel the magnetic field generated in the opposite direction. See Figure 1 for

an example layout figure and the following guidelines for good PCB layout:

• Place as many copper planes as possible under the IC footprint to ensure efficient heat transfer.