Datasheet

19
MSL2023/2024 [DATASHEET]
42063A–LED–02/2013
Table 10-1. Fault conditions, response and recovery.
11. Applications Information
11.1 Turn-On Sequence
When power is applied the EEPROM contents copy into the control registers, setting up the device for operation; any
previously programmed control register settings are lost unless they are programmed into the EEPROM (page 25). The
MSL2023/24 wait for 250ms to allow the AC/DC or DC/DC input stage to establish the default voltage. The MSL2023/24
then starts to optimize the LED string voltage (V
LED
), and then begin to drive the LED strings. It is critical that the AC/DC
or DC/DC converter that powers the LED strings reaches its nominal output voltage in less than 250ms after power is
applied. When the 250ms start-up delay is complete the Efficiency Optimizer adjusts the LED voltage to the proper level
to drive the main string. After the voltage is set, normal PWM operation begins for both the Main and Color-Adjust strings.
11.2 Setting the Main String Current with R
S
The main string LED current regulates by monitoring the voltage at the S pin, the main string MOSFET source resistor
connection. The default feedback voltage at the S pin is 200mV. Choose the string current sense resistor R
S
using:
where I
LED
is the main string regulation current. The main string reference voltage (MREF) register 0x20 sets the
feedback voltage to 200mV, at 2mV per LSB. The regulation voltage, V
S(FB)
, is:
where MREF is the decimal equivalent of the value in register 0x20. The default value for MREF is 0x64, for a feedback
voltage of 0.2V. Change the feedback voltage by changing the value in register 0x20 using the serial interface. LED
average current is within ±3% of targeted value when a 1% resistor is used for R
S
.
11.3 Setting AC/DC Output Voltage
The efficiency optimizer output, FBO, connects to the AC/DC or DC/DC converter’s output voltage feedback node, and
pulls current from the node to force the converter’s output voltage up. The MSL2023/24 works with any input power
converter topology that uses a resistor divider to set its output voltage. Additionally, the two strings will operate off of
independent rails. Operation with and AC/DC PFC converter is described below.
Select the two resistors that set the nominal LED power supply’s output voltage by first determining the minimum output
voltage using:
Fault Response Recovery action
Die Temperature > 147°C Asleep (I
2
C still active)
When die temperature falls below
127°C operation resumes
Color-Adjust String has Shorted LEDs
Color-Adjust string turns off, FLTB pulls
low, and bit 0 of the Fault Status
register 0x23 sets high
Correct the short condition in LED
string. Toggle EN low to high to resume
operation, or clear faults using register
0x22 (page 27)
Color-Adjust String is Open Circuit
Color-Adjust string turns off, FLTB pulls
low, and bit 1of the Fault Status register
0x23 sets high
Correct the open condition in LED
string. Toggle EN low to high resume
operation, or clear faults using register
0x22 (page 27)
R
S
0.2
I
LED
----------- -
=
V
SFB
0.002 MREFV=