SC5014A View Datasheet(PDF) - Semtech Corporation

Part Name

Description

MFG CO.

SC5014A

High Efficiency 2-Channel HB LED Driver with I2C Interface and Direct PWM Dimming

Semtech Corporation 

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SC5014A

Components Selection (continued)

Current Sensing Resistor Selection

The switch current is sensed via the current sensing resis-

tor, RCS. The sensed voltage at this pin is used to set the

peak switch current limit and also used for steady state

regulation of the inductor current. The current limit com-

parator has a trip voltage of 0.4V (typical). RCS value is

chosen to set the peak inductor and switch current using

the following equation.

I2

SW(Peak)

=

0.4/RCS

The power dissipation in RCS can be calculated using the

following equations.

For the typical application circuit shown in the detailed

application circuit (page 20, Figure 2), the power dissipa-

tion on the sensing resistor is shown by the following

equations.

Assuming VIN = 6V and VOUT = 31.5V, thus D = 81%,

PR_CS = 0.81 X (0.48/0.19)2 X 0.08 = 0.414(W)

For this example, a 0.08 Ω 1% thick-film chip resistor rated

at 1W can be used.

PR_CS

=

I2

RMS

x

RCS

IRMS = D x [IO/(1-D)]2

IO = Output DC Current, D = Duty Cycle

19

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