AN2713 datasheet(13/40 Pages) STMICROELECTRONICS

13 / 40 page

AN2713

Component selection guidelines

Doc ID 14431 Rev 1

13/40

The most important parameter for the output capacitors is the effective series resistance

(ESR). The DC-DC converter control loop circuit has been designed to work properly with

low-cost electrolytic capacitors which have ESR in the range of 200 m

Ω. A 100 µF output

filter capacitor with ESR between 150 m

Ω and 350 mΩ is a good choice in most application

conditions. It is also possible to use electrolytic capacitors up to 220 µF with ESR between

100 m

Ω and 300 mΩ. The capacitor voltage rating must be at least 25 V, but if the highest

voltage selection condition is used (AUX=1), 35 V or higher voltage capacitors are

suggested.

3.4

DC-DC converter Schottky diode

In typical application conditions it is beneficial to use a 1 A Schottky diode which is suitable

for the LNBH23 DC-DC converter. Taking into consideration that the DC-DC converter

Schottky diode must be selected depending on the application conditions (VRRM > 25 V), an

N-channel Schottky diode like the STPS130A is recommended.

The average current flowing through the Schottky diode is lower than IPEAK and can be

calculated using Equation 1. In worst-case conditions, such as low input voltage and higher

output current, a Schottky diode capable of supporting the IPEAK should be selected. IPEAK

can be calculated using Equation 2.

Equation 1

3.5

DC-DC converter inductor

The LNBH23 operates with a standard 22 µH inductor for the entire range of supply voltages

and load current. The inductor saturation current rating (where inductance is approximately

70% of zero current inductance) must be greater than the switch peak current (IPEAK)

calculated at:

●

maximum load (Ioutmax)

●

minimum input voltage (Vinmin)

●

maximum DC-DC output voltage (VUPmax =Voutmax +0.75 V)

Table 3.

Recommended Schottky diode

Vendor

Part number

IF(av)

VF(max)

STMicroelectronics

1N5818

1 A

0.50 V

1N5819

1 A

0.55 V

STPS130A

1 A

0.46 V

STPS1L30A

1 A

0.30 V

STPS2L30A

2 A

0.45 V

1N5822

3 A

0.52 V

STPS340

3 A

0.63 V

STPS3L40A

3 A

0.5 V

Iout

Vout

Vin

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⋅

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