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SC5014 View Datasheet(PDF) - Semtech Corporation

Part Name
Description
MFG CO.
'SC5014' PDF : 34 Pages View PDF
SC5014
Applications Information (continued)
The SC5014 has a unique DAC architecture which allows it
to have excellent LED current accuracy and string-to-string
matching over the entire DAC range.
The analog dimming method can be used in conjunction
with PWM dimming to increase the dimming resolution.
The fast loop response of the SC5014 allows the LED
current to transition to a new value within 160µs or so.
Please refer to the graphs in the typical characteristics
section.
LED PWM Dimming Control
The SC5014 supports three PWM dimming modes for
controlling the brightness of the LEDs.
The dimming modes are:
(1) PWM direct,
(2) PWM indirect and
(3) I2C control
It provides flexibility in setting the duty cycle and fre-
quency of the LED PWM signal. The PWM dimming mode
is set through the device control register (register address:
0x01) DCR [1:0] bits. Refer to Table 1 for more details.
(1) PWM Direct Control
The PWM input needs to be held high for normal opera-
tion. PWM dimming can be achieved by cycling the PWM
input at a given frequency where a “low” on the PWM
input turns off all IO current sinks and a “high” turns on all
IO current sinks. The PWM pin can be toggled by external
circuitry to allow PWM dimming. In a typical application,
a microcontroller sets a register or counter that varies the
pulse width on a GPIO pin. The SC5014 allows dimming
over a wide frequency range (100Hz-30kHz) in order to
allow compatibility with a wide range of devices. This
includes the newest dimming strategies that avoid the
audio band by using high frequency PWM dimming. In
this manner, a wide range of illumination can be gener-
ated while keeping the instantaneous LED current at its
peak value for high efficiency and color temperature. The
SC5014 provides a 1000:1 dimming range at 1kHz PWM
frequency. The LED current sinks turn on/off very rapidly
(<25ns, typical). This allows a wide dimming ratio. An addi-
tional advantage of PWM dimming is that it avoids in-rush
currents when filling the boost output capacitor. Simply
apply the PWM signal to the device at 10% duty for a milli-
second or two, and in-rush current is reduced. This
dimming time will vary based on the number of LEDs and
the size of the output capacitor. This can be easily deter-
mined during testing and programmed into the microcon-
troller firmware.
Table 1 — LED Dimming Control Methods
PWM Dim-
ming Mode
PWM Direct
Control
PWM Indirect
Control
(Default
Option)
Register
Settings
DCR[1:0]
00
01
PWM
Input
Source
PWMI Pin
Input
PWMI Pin
Input
I2C
Control
I2C
11
Control
LED PWM Output
PWM Frequency
PWM Duty Cycle
Phase
Shift
Option
Same as the PWMI Input
(Range 100 Hz to 30kHz)
Same as the PWMI Input
NO
Set via the FREQ Register
(0x05) and FAST_FREQ Bit
10kHz (max): FAST_FREQ=0
20kHz (max): FAST_FREQ=1
Same as the Duty Cycle of the PWM Input YES
Set via the FREQ Register
(0x05) and FAST_FREQ bit
10kHz (max): FAST_FREQ=0
20kHz (max): FAST_FREQ=1
Set Via the Duty Cycle Control
Register (0x03, 0x04)
YES
10-Bits @ 10kHz Output
9-Bits @ 20kHz Output
15
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