TPS61040-Q1: TPS61040QDBVRQ1

Hi ilya,

What's the forward voltage (min, typ, max) of a single led in your application?

Regards

Lei

Hi Lei

typ - 3.1V

max - 3.7V

my vcc in the circuit can be either 3.3V or 5V, what should i chose ?

Hi ilya,

5V VCC(Vin) is recommended, because with higher Vin, the max output capacity can be also higher, so more LEDs can be driven.

Here is the rough calculation for your reference when VCC = 5V.

• When the LED current is 15-20mA, L = 10μH, then the most LEDs that can be driven is 4;
• When the LED current is 15mA, L = 22μH, then the most LEDs that can be driven is 6;

Regards

Lei

Hi Lei

thank you for your reply, so to drive 6 leds L needs to be changed to 22μH but what about the RS (82 ohm) does it also needs to be changed ?

also if i need to drive 8 leds is it possible with this IC ?

Hi ilya,

I'll check and reply to you today.

Regards

Lei

Hi ilya,

ilya tashaev said:

L needs to be changed to 22μH but what about the RS (82 ohm) does it also needs to be changed ?

Higher inductance can output  higher max Iout. As my rough calculation, when 10μH inductor is used, only 4 LEDs can be driven. 

The resistance of Rs is decided by the TPS61040 Vref and LED current. Rs = 1.233V/I_LED

ilya tashaev said:

also if i need to drive 8 leds is it possible with this IC ?

TPS61040 can't drive 8 LEDs when the max forward voltage is 3.7V.

TPS61170 can be the option which drive 8 LEDs with the same topology.

Regards

Lei