ISL97678IRZ-TK Просмотр технического описания (PDF) - Renesas Electronics

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ISL97678IRZ-TK

8-Channel 45V, 50mA LED Driver

Renesas Electronics 

ISL97678

Inductor

The selection of the inductor should be based on its maximum

and saturation current (ISAT) characteristics, power dissipation

(DCR), EMI susceptibility (shielded vs unshielded), and size.

Inductor type and value influence many key parameters,

including ripple current, current limit, efficiency, transient

performance, and stability.

The inductor’s maximum current capability must be adequate

enough to handle the peak current at the worst case condition.

Additionally, if an inductor core is chosen with too low a current

rating, saturation in the core will cause the effective inductor

value to fall, leading to an increase in peak to average current

level, poor efficiency and overheating in the core. The series

resistance, DCR, within the inductor causes conduction loss and

heat dissipation. A shielded inductor is usually more suitable for

EMI susceptible applications, such as LED backlighting.

The peak current can be derived from the voltage across the

inductor during the Off-period, as expressed in Equation 10:

ILpeak = VO  IO   85%  VI  + 1  2VI  VO – VI   L  VO  fSW

(EQ. 10)

The choice of 85% is an average term for the efficiency

approximation. The first term is the average current, which is

inversely proportional to the input voltage. The second term is

the inductor current change, which is inversely proportional to L

and fSW as a result, for a given switching.

FN6998 Rev.3.00

Sep 8, 2017

Page 15 of 17

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