BD9470AEFV Datasheet, PDF (11/39 Pages) Rohm – White LED driver for medium sized and large sized LCD back light

BD9470AFM・BD9470AEFV
○LED1-6 （HTSSOP-B28:18,19,20,22,23,24PIN / HSOP-M28：11,12,13,15,16,17PIN）
LED constant current output pins. Current value setting can be made by connecting a resistor to the ISET pin.
For the current value setting procedure, refer to the description of “ISET pin”.
If any of the LED pins is put in an abnormality state (short circuit mode, open circuit mode, ground short mode), the
relevant protection function will be activated.
・LED pin short circuit protection function ( LSP)
When any LED is in short state (more than LED=9.0V(typ)) the LED SHORT is detected.
After abnormal detection, the timer count starts. The LED that is abnormal detection after 2¹⁶ count is stopped and other
LED driver operates normally.
・LED pin open circuit protection function (LOP)
If any of the LED pins becomes open-circuited (0.2V (Typ.) or less), LED_OPEN will be detected. When this error is
detected, the timer will start counting, When it completes counting the preset period of time, only LED driver that detected
the error will stop operation and other LED driver will conduct normal operation.
・LED GND_SHORT protection function
When any LED pin is GND shorted the LED pin becomes less than 0.20V and the pin is latched because of LED_OPEN
detection. After that, the LED pin is pull upped by inner supply but it continues less than 0.2V state in grand shorted. After
detecting timer of open state, if the grand shorted (open) state continues 2⁷ counts all systems are latched.
To prevent the miss detection there is 4 count interval of mask before starting the timer count.
If PWM=H time is
PWM=H time < 4count・・・Not detect protection because it is in interval time
PWM=H time > 4count・・・Detect protection because it is out of interval time
Please verify enough to operate narrow PWM.
9V
LEDx
Interval of mask
Timer count
CLK
1 23 41 2
2¹⁶
FAIL
Figure 14. Timing chart of timer count
○LED_GND （HTSSOP-B28:21PIN / HSOP-M28：14PIN）
The LED_GND pin is a power ground pin used for the LED driver block.
○UVLO （HTSSOP-B28:25PIN / HSOP-M28：18PIN）
This pin is used to for step-up DC/DC converter. When UVLO pin voltage reaches 3.0V (Typ.) or more, IC will initiate
step-up operation. If it reaches 2.7V (Typ.) or less, the IC will stop the step-up operation.
The UVLO pin is of the high impedance type and involves no pull-down resistor, resulting in unstable potential in the
open-circuited state. To avoid this problem, be sure to make input voltage setting with the use of a resistive divider or
otherwise.
For calculation examples, refer to information in ’3.1 application explanation/UVLO setting procedure’
○LSP （HTSSOP-B28:26PIN / HSOP-M28：19PIN）
The setting pin for detection voltage of LED short circuit protection. The LED short circuit detection voltage is set to 9V
(Typ.) with the LSP pin being in the open-circuited state. However, making a change to the LSP pin input voltage will allow
the threshold for LED short circuit protection to be changed.
The relation between the LSP pin voltage and the LED short circuit protection detection voltage is given by the following
equation.
VLSP_SHORT
= ^VLEDSHORT
10
　[V ]
Here LEDSHORT：LED detection voltage
VLSP：LSP setting voltage
LSP pin input voltage setting should be made in the range of 0.3V to 2.5V.
For setting example, refer to information in’3.1 application explanation/LSP setting procedure’
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TSZ22111・15・001
11/35
TSZ02201-0F10C1002000-1-2
19.Oct.2013 Rev.003