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LED Drivers/LCD Bias
LED Drivers/LCD Bias Forum
5.7" TFT backlight
i have one 5.7" TFT lcd. In which LED's arangement in a backlight is as shown in an attached file.i am looking for it's driver.i zeroed down on TPS61041 & TPS61161
1. TPS61041 if i put RS=8.1 ohm (1.230 v / 150ma backlight max current limit is upto 210 ma.) across FB pin
2 TPS61161 if i put Rset=1.5 ohm (200 mv / 133ma backlight max current limit is upto 210 ma) across FB pin
Will it work for my BACKLIGHT i am confused because they are for series LEDS & my backlight have 3 series leds in 7 parallel rows.my backlight connector has 2 pins only as shown in attached file. If not someone give me some suggestions which led driver i should use. I want to use PWM method only not analog method for dimming.waiting for your reply.
Since your backlight connector has only two pins, you only need a LED driver that can drive a single string, like the TPS61161 or TPS61165 or TPS61500, and not one of the multi-string drivers like TPS61181, TPS61185, TPS61195. The TPS61041 cannot provide the output power that you need. Depending on your input voltage the TPS61161 may not be able to provide the output power that you need either. I suggest moving to the TPS61165. What is your input voltage to power the backlight driver, 3.3V, 5V, etc?
thanxs for the prompt reply,
input voltage is 5V
Doing a quick power balance of efficiency = (Vo*Io)/(Vin*Iin) = VLED*ILED/(5V * Iin) and assuming the LED driver will have a worst case efficiency of 87% and each LED has max drop of 3.6V, then the LED driver's current limit needs to be higher than Iin > (3*3.6V*140mA)/(5V*0.87) =348mA. So TPS61160 or 60A should work for you.
Well i am not good at hardware,should i go for TPS61160 or TPS61165?If you don't mind, Mostly both are same apart from led difference 6/10 & FET 26 V / .7A 38V / 1.2A ,switching freq. 600/1200(khz)
any specific reasons in choosing one over the other?Does the starting current limit is the concern since it is .4 amp in TPS 61160 & .7 amp in TPS61165 ? & finally if TPS61160
should work then why TPS61161 not?
The TPS61160 and TPS61161 are the same except for the over-voltage protection limit. The 60 has the 26V OVP limit, which is all that you will need for the 3 LEDs in series which produce < 12V. The TPS61161 and TPS61165 are the same except for the current limit. Assuming that you only need the 140mA total current per the attached schematic, you don't need the TPS61165 with its much higher current limit. So out of the three potential devices, the TPS61160 with is lower OVP threshold and lower current limit is the best fit for your application. If you want to use either 61 or the 65, you may. The 65 is higher priced than the 60/61.
Ok, thanxs for the prompt reply. will use TPS 61160.
If my system need 558mA, TPS61160 still be good choice or I have to move to hign switch current TPS61165?
You will need the TPS61165.
we will drive 9 string parallel of 3 leds in series or 3 strings parallel of 8 leds in series and considering to use TPS61165 for both configuration. Do you have app note how to choose switch current of DC-DC boost relative to output current?
Datasheet equation 4 on page 14 computes the maximum current for any boost converter. Ilim is the switch current limit specification.
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