ZXLD1370

ZXLD1370

Document number: DS32165 Rev. 4 - 2

19 of 36

www.diodes.com

March 2011

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A Product Line of

Diodes Incorporated

 

ZXLD1370 Boost Mode 350mA Minimum Recommended Inductor

Target Switching frequency > 500kHz

0

10

2030

405060

1

3

5

7

9

11

13

15

Supply Voltage (V)

L=22µH

L=33µH

L=47µH

Figure 26. 350mA Buck-Boost mode inductor selection for target frequency > 500kHz

Suitable coils for use with the ZXLD1370 may be selected from the MSS range manufactured by Coilcraft, or the NPIS range

manufactured by NIC components.

The following websites may be useful in finding suitable components

www.coilcraft.com

www.niccomp.com

www.wuerth-elektronik.de

MOSFET Selection

The ZXLD130 requires an external NMOS FET as the main power switch with a voltage rating at least 15% higher than the

maximum transistor voltage to ensure safe operation during the ringing of the switch node.

The current rating is

recommended to be at least 10% higher than the average transistor current. The power rating is then verified by calculating

the resistive and switching power losses.

switching

P

resistive

P

P

+

=

Resistive power losses

The resistive power losses are calculated using the RMS transistor current and the MOSFET on-resistance.

Calculate the current for the different topologies as follows:

Buck mode

LED

I

x

MAX

D

MAX

MOSFET

I

=

−

Boost / Buck-boost mode

LED

I

x

MAX

D

1

MAX

D

MAX

MOSFET

I

−

=

−

The approximate RMS current in the MOSFET will be:

Buck mode

D

LED

I

RMS

MOSFET

I

=

−