SC5014 View Datasheet(PDF) - Semtech Corporation
Part Name
Description
MFG CO.
SC5014
Semtech Corporation
'SC5014' PDF : 34 Pages View PDF
SC5014
Applications Information (continued)
LED Short-Circuit Protection (SCP)
The SC5014 features a programmable LED short-circuit
protection (SCP). This allows the part to be customized
based on the LED forward voltage (VF) 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:
VSCP_Trip [V] = 20 X (1.23 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 10μs 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
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 (100pF ~ 8.2nF)
between IO pin to ground can help prevent the SC5014
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 SC5014 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 RISET resistor.
Extracted Duty
LED Frequency and Phase-Shifter Block
Cycle from
PWMI Input
PWM
PWM
Input
Duty Cycle
Extractor
10
0
10
PWM
Generator
10
Input
1
0
Phase Shifting
EN
1
4
1
PWM_ps[4:1]
All bits identical
when phase
shifting disabled
8
Soft-Start
PWM [4:1]
4
D[9:0] Bits
INT_DUTY Bit
FREQ Bits
FastFreq Bit
PH_SHIFT Bit
INT_PWM Bit
I2C Interface
Figure 1— LED PWM Dimming Control
14
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