BD9206EFV_14 Datasheet, PDF (8/21 Pages) Rohm – Simple Structure Constant Current Backlight Driver for LCD panels

BD9206EFV
Datasheet
Application Information
1. Block Functional Descriptions
(1) PREREG, REF, 5VREG
The PREREG is a circuit that generates a constant voltage using the VCC supply voltage and supplies it to REF and
5VREG blocks.
The REF is a temperature-compensated reference voltage source. Its output is used as the reference voltage for the
TSD (Thermal Shutdown Circuit) block.
The 5VREG is a 5V constant-voltage source. It is used as a power supply to the constant-current driver.
The 5V constant voltage is connected to the VREG terminal. Moreover, it is recommended to attach a 1μF ceramic
capacitor to VREG terminal for phase compensation.
(2) UVLO (Under Voltage Lock Out)
The LED driver is turned OFF when the VREG voltage is less than 2.9V (typ). The operation resumes when VREG is
more than 3.0V (typ).
(3) TSD (Thermal Shutdown Circuit)
The TSD circuit protects the IC from thermal damage.
This circuit detects the chip temperature and turns the circuit OFF when the chip temperature reaches 175°C.
A hysteresis of 20°C is set for TSD detection and release to prevent malfunction caused by temperature fluctuations.
(4) Current Driver (Constant-Current Driver), Driver Current Setting
The Current Driver (Constant-current driver) is a circuit that generates a constant current for turning ON the LEDs.
The Constant-current circuit of BD9206EFV consists of the constant-current setting and the constant-current
driver parts.
The constant-current driver part forces the voltage at point b to be equal to the voltage at point a, which is the
voltage VX that is set by the constant-current setting part.
Therefore, the current ILED that flows into the VLED terminal is as follows:
I _LED  V_b / R_SET  V_a / R_SET  V_X / R_SET  V_SET  A / R_SET  V_SET  B
where:
A and B are numerical constants
For BD9206EFV, the numerical constants inside the IC are set to satisfy the equation below:
ILED(mA) = VSET x 10 (VSET=0.6V to 3.0V)
If VSET is fixed, then Vb is fixed, therefore the current ILED always flows independently of the fixed voltage of VLED.
However, the constant current operation is stopped if the voltage of VLED terminal is less than 0.6V,
so please ensure that VLED>0.6V.
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Figure 12
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