SC5014 datasheet(14/34 Pages) SEMTECH

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SC5014

LED Short-Circuit Protection (SCP)

The SC504 features a programmable LED short-circuit

protection (SCP). This allows the part to be customized

based on the LED forward voltage (V

F) mismatches between

the LED strings. If one or more LEDs are detected as short-

circuited, the corresponding string will be latched off. The

voltages on all IO pins are monitored to check if any IO pin

exceeds the SCP trip point. The IO voltage for LED string(s)

with faulty short-circuit LED(s) will be higher than other

normal IO pin voltages. This LED short-circuit protection

trip level (see detailed application circuit on page 23,

Figure 2) is expressed by the following equation:

SCP_Trip [V] = 20 X (.23 X R4) / (R4 + R5)

If any IO pin voltage exceeds the trip voltage, the IO current

sink will be latched off and the FLT will go low.This latch can

be reset by cycling UVLO, VCC or EN. Other LED strings are

unaffected and continue in normal operation. This protec-

tion will be disabled if SCP is tied to VCC.

There is a typical 0μs SCP detection time in PWM dimming

applications. If the PWM dimming on-time is less than the

SCP detection time, the SCP cannot be enabled.

In many applications, LED strings are connected to the IO

pins through a mechanical connector, which cannot support

an electrical connection at specific times. This connection

Applications Information (continued)

might cause noise on the IO pins. If this noise is large

enough, it may trigger a false SCP mode. Under such condi-

tion, a ceramic decoupling capacitor (00pF ~ 8.2nF)

between IO pin to ground can help prevent the SC504

from entering the protection mode by false trigger. Or,

simply disable this feature by connecting SCP pin to VCC

pin.

LED Open-Circuit Protection

If any LED string becomes open, the respective IO pin

voltage will be pulled to ground. Consequently, the inter-

nal COMP node (output of error amplifier) is driven high,

which causes the boost output voltage to increase. The

output voltage will be eventually clamped to a voltage

set by the OVP resistor divider. Under this condition, the

faulty string is latched off and the FLT pin is pulled low.

The boost voltage gets regulated to the voltage required

to set all non-faulty IO pins above 0.9V (typ). The remain-

ing strings remain in normal operation. The FLT and the

fault-out LED current sink latch-off can be reset by cycling

UVLO, VCC or EN.

LED Analog Dimming Control

The LED current in SC504 can be dimmed via the 5-bit

analog dimming register (register address: 0x02). The LED

current can be adjusted in 32 steps from 0mA to maximum

value, which is determined by the R

ISET resistor.

Soft-Start

I2CInterface

INT_DUTYBit

D[9:0]Bits

PWM

Generator

FREQBits

PhaseShifting

FastFreqBit

PH_SHIFTBit

PWM

Input

INT_PWMBit

ExtractedDuty

Cyclefrom

PWMIInput

LEDFrequencyandPhase-ShifterBlock

PWM_ps[4:1]

Allbitsidentical

whenphase

shiftingdisabled

PWM[4:1]

DutyCycle

Extractor

PWM

Input

Figure 1— LED PWM Dimming Control

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