SC5014 View Datasheet(PDF) - Semtech Corporation

Part Name

Description

MFG CO.

SC5014

High Efficiency 4-Channel HB LED Driver with I2C Interface and Phase-Shifted PWM Dimming

Semtech Corporation 

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SC5014

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 RSNS can be calculated using the

following equations.

PR_CS

=

I2

RMS

x

RCS

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

IO = Output DC Current, D = Duty Cycle

For the typical application circuit shown in the detailed

application circuit (page 23, 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.

PLL Filter Component Selection

The detailed application circuit on page 23, Figure 2 shows

the optimal R/C filter components for the PLL compensa-

tion. These are optimized for internal 1MHz switching fre-

quency. Please contact Semtech Power management

Application Group if a different switching frequency is

selected.

22

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