MAX25232ATCH datasheet(14/21 Pages) MAXIM

14 / 21 page

Applications Information

Setting the Output Voltage

MAX25232 comes with fixed VOUT options (set internally) of 5V and 3.3V. For setting the output voltage between 3V

- 10V externally using resistor-dividers, chose MAX25232ATCF and MAX25232ATCG. Connect a resistor-divider from

output (OUT) to FB to AGND (see Figure 1). Select RFB2 (FB to AGND resistor) ≤ 500kΩ. Calculate RFB1 (OUT to FB

resistor) with the following equation:

RFB1 = RFB2

[[VOUT

VFB

]−1

]

where VFB = 1V (see Electrical Characteristics).

Other fixed-output voltage options (set internally) between 3V - 5.5V in 50mV steps are also available. Contact the factory

if your application requires fixed output voltage in this range.

MAX25232ATCF

MAX25232ATCG

RFB1

RFB2

VOUT

Figure 1. Setting the Output Voltage with External Resistor-Dividers

Input Capacitor

A 4.7μF low-ESR ceramic input capacitor is recommended for proper device operation. This value can be adjusted based

on application input-voltage-ripple requirements.

The discontinuous input current of the buck converter causes large input-ripple current. Switching frequency, peak

inductor current, and the allowable peak-to-peak input-voltage ripple dictate the input-capacitance requirement.

Increasing the switching frequency or the inductor value lowers the peak-to-average current ratio, yielding a lower input-

capacitance requirement. The input ripple is mainly comprised of ΔVQ (caused by the capacitor discharge) and ΔVESR

(caused by the ESR of the input capacitor). The total voltage ripple is the sum of ΔVQ and ΔVESR. Assume that input-

voltage ripple from the ESR and the capacitor discharge is equal to 50% each. The following equations show the ESR

and capacitor requirement for a target voltage ripple at the input:

Equation 1:

MAX25232

36V, 3A Mini Buck Converters with 3.5μA IQ

www.maximintegrated.com

Maxim Integrated | 14

MAX25232ATCH датащи(PDF) 14 Page - Maxim Integrated Products