Tongjia introduces backlight driver IC - LD7890 is mainly boost topology, which can drive 4 Channel LED light bar, 10V MOSFETDRV output voltage, high conversion efficiency, external 4 Channel current balance drive, constant current LED. Wide input voltage range of 9V ~ 28V, can cooperate with various power sources to drive LED to produce uniform brightness, external 4 Channel current balance drive, application is not limited to LED light bar drive current or voltage, only need to select the corresponding External components are all right.
The LD7890 has built-in innovative patented technology to meet the specifications of the following system vendors.
(1) For the IC Thermal problem required by the system, the IC Package temperature can be lower than the customer's specifications.
(2) Flexible for 4 Channel LED light bar with the following drivers, parallel function for applications above 4 Channel LED light bar.
(3) LED Short Protection Threshold is adjustable, flexible, only need to use the resistor is not limited by the controller process.
(4) Single CH Fault detection, which can be used as single CH LED Open/Short protection. Other CHs maintain motion and use elasticity.
LD7890 backlight protection mechanism
Focusing on a larger LED TV, the LD7890 provides LED short-circuit and open-circuit protection, as well as an output protection signal for LED malfunction detection, allowing the system to determine the LED light bar usage.
When the LED is used as the backlight source of the LCD panel, since the area of ​​the LCD panel is relatively large, a large number of LEDs are required, and these LEDs are often connected in a series of strings, each of which is driven by a controllable current source. For example, the current flowing through each string of LEDs is controlled to be the same, so that the brightness of each LED is the same. As long as the light emitted by each LED is properly conducted, the LCD panel can obtain a substantially uniform backlight brightness. Among all the LEDs, no matter which LED is shorted or open, it will affect the brightness uniformity of the LCD panel. Therefore, the LD7890 has a good LED string drive circuit, and a suitable protection detection circuit to detect whether the LED is short-circuited or open circuit, and the corresponding protective measures are taken.
Easy to set LED short circuit protection
LEDs are short-circuited due to poor connection between the wirings or poor quality of the LEDs. When the LEDs are short-circuited, the excess voltage will cross the externally stabilized NMOS of the LED Driver; PD=ILEDx VLED-Short. When the number of LED Short is too large, the LED Driver and NMOS will have a high temperature phenomenon. The advantage of the LD7890 can be set by using only an external resistor. When the LED string is short-circuited, if the VD–ISP×RSP > VLEDSP is satisfied, the STATUS Pin will be Pull Low and the shorted LED string will be turned off. If the LED string tail-to-tail short-circuit condition occurs, only the energy at the time of short-circuit should be considered to select the suitable resistance wattage, and the calculation method refers to the block description.
Easy to set LED open circuit protection
When the LED is open due to poor quality or poor connection between the LED string connection system, the VD voltage will be close to 0V. At this time, the Boost boost converter will increase the output voltage Vout due to no detection of the feedback signal. The LED open circuit protects the abnormal loop from the boost converter feedback control, and the excess voltage crosses the external steady current NMOS of the LED driver that is working normally; PD=ILED×VD. A problem that will cause the component to overheat will occur.
When any LED string of the LD7890 is open, the Boost boost converter increases the output voltage Vout because it does not detect the feedback signal until the OVP pin reaches 2.5V. The IC detects that the VSENSE pin is lower than 0.2V, indicating that the LED If the string has an abnormal condition, the LED Driver will turn off the faulty LED string and STATUS Pin Pull Low.
VOUT short circuit protection function description
When the LED string drive circuit is just connected to the power supply, it is likely that the drive power supply is not ready, and the LED string drive circuit determines that the LED string cannot be driven, thus misidentifying the LED string open or short circuit event. This should also be prevented. The LD7890 provides VOUT short-circuit protection. When VSCP< SCPSET, the LD7890 turns off the LED Driver and PWM Controller to avoid irreparable damage to the entire system.
Easy to use multiple Chip parallel applications
LED Backlight does not have a fixed number of LED strings in different applications or designs. There are many combinations according to the specifications of the Panel module factory, and the LD7890 is flexible in use, and the number of serials can be more than 4 in use. String or more, the LD7890 PARL Pin can be connected to multiple LD7890 ICs. The PARL Pin has the best feedback potential when paralleling multiple LD7890 ICs. It provides the correct feedback potential for the boost topology. The PARL Pin has the LED string. The correct protection mechanism for short circuit and open circuit without malfunction.
in conclusion
LED replaces CCFL. When its backlight is applied to laptops, desktop monitors, TVs and other large-sized panels of more than 10 inches, the integration of Backlight Driver IC (Power Topology + LED Current Balance) protection function of LED backlight modules is exceptional. It is important to look at the above description to provide a complete and comprehensive protection for the input, output and LED Backlight of the topology, and it is a highly integrated LED solution that integrates the Boost architecture with Current Balance, providing high LED current for each string. Accuracy current balance (<3%), high LED current drive capability, also provides instantaneous high current LED drive capability for 3D applications. With its comprehensive fail-safe features and high precision for high LED drive current capability and current balance, the LD7890 is an excellent LED Backlight driver solution.
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