LED Drivers/LCD Bias Forum - Recent Threads

I2C LED driver TLC59108

Eric van Hamelsveld — Sun, 26 May 2013 01:56:24 GMT

Hello,

Thank you in advance for any help offered. I am working with a software engineer who will help this end, but am currently am stuck for solutions.

Our circuit consists of 3x TLC59108 devices in a daisy chain, and to complete the design there are 2 sets of these in a rectangle (Surrounds a LCD monitor on a gaming console). (See URL below)

Control is by PWM through a PCA9516A I2C buffer. (See URL below)

Power supply is controlled by the TI chip TPS84620. (See URL below)

First samples built worked well. Production has started and around 100 of the first units preform well.

Then came a change of supply of the TLC59108 drivers and now the 'surround' crashes depending on where in the effect routine. We are able to exchange one TLC59108 to the older supply (Limited number left) and the circuit works well.

Any help with this would be much appreciated.

Regards,

Eric

SR#1-1025797424

Schematics can be viewed here.

https://sites.google.com/site/surrounddisplay/

LM3431Q / 5ch operation by 2pcs use

Ryuji Asaka — Fri, 24 May 2013 13:37:25 GMT

Hello,

My customer searching LED driver for Automotive of below requirement spec.

<Requirement>--------------------------

Rating : Automotive

Number of Channel : 5 channel

Vin : 5V or 8V

Vout : 4V(max)、30.1V(max)
Iout / ch : 50mA(typ)、55mA(max)

------------------------------------------------

I can find LM3431Q as 3ch of LED driver IC.

I thought that if I can use 2pcs of LM3431Q , we can make above requirement LED driver circuit.

Can LM3431Q operate above ?

If I use 2 device of LM3431Q for 5channel , are there LED current variation ?

Are there any application note for control the LED current variation ?

If there are any other device for this requiremnt , please kindly let me know?

Best Regards,

Ryuji Asaka

TPS92075

Hiranthini Alles — Thu, 23 May 2013 03:23:51 GMT

In the buck-boost option as shown in the User guide SLVU813 evaluation board (inductor based), since there is no open load protection, I have designed in a simple zener/resistor to bias a pnp transistor, and with an npn to pull the regulator FET gate off which depowers the IC. Is there any pin of the TPS92075 that can be either driven high or driven low to latch the device off in case of open load? I would like to use minimum components to address the open load protection....thanks.

Lcd backlight driver

vinoth pandiyan — Fri, 24 May 2013 08:26:18 GMT

Hello sir/madam

we using TPS61080 IC for LCD back light supply now we design the schematic with the reference of beagle bone black 7 inc display board here we need some clarification about how to determine the output voltage ,

Because in our schematic we using flash light type circuit design and we are not use same display what there in beagle bone. we using Densitron display of maximum LED voltage is 20V with 25 mAh rail but we don't know the output voltage of our circuit .for your reference here i attach our Schematic and display data sheet .So Please Guide us any change will made in the circuit because it is Prototype Board only .(Please visit the site to view this file)(Please visit the site to view this file)

Thanks&Regards,

vinoth.pandiyan

Any way to disable/bypass Flash Pulse Safety Timer on LM3553 LED driver?

Mike Fournier1 — Thu, 23 May 2013 15:05:15 GMT

Hello!

I'm using an LM3553 in a heavily heatsinked environment and require a higher continuous amperage sink than Torch mode can provide. Flash mode is providing the current levels I need, but of course only for a maximum of 3200 seconds before the safety pulse timer kills it.

Is there a method to:

disable the safety pulse timer entirely?
'reset' the timer mid-flash (it must be storing the elapsed vs. target clock ticks in a memory address somewhere?)
trigger the flash event again (via the i2c interface) before the first flash event has completed?

Sending a series of Flash->Torch->Flash->Torch... events over i2c does work, but leads to unpleasant flickering in LED output due to the time needed to send the serial command.

Any suggestions?

LM3409 sense resistor power

Paul Bar — Wed, 22 May 2013 13:50:22 GMT

Hi,

I designed a nice circuit with the LM3409 that works very well with Imax=1A for one LED with Rd=0.7 and Vf=2.9V. Now I would like to use the same circuit, but with the option of setting 2 maximum led current with a relay.

So, using a switch to control the relay, I would have the Imax=1A option and the Imax=2A option. I do not want to use the dimming function because I want to keep the dimming range intact at Imax=1A.

However, looking at the data sheet, I cannot find the current that flow in the resistor. How to calculate that? In my case the resistor is 0.24ohm, so there would be two 0.24ohm resistor in parallel in the higher current mode. That would result in a certain amount of current that need to flow in the relay. I want to choose the smallest relay to help noise rejection, but I need the current first.

Thanks for your help.

TL4242 Questions

David Hildebrand — Tue, 21 May 2013 13:36:24 GMT

I have a customer (Raytheon) using the TL4242 LED driver. He is driving a single LED at 20mA, using a 9.1 ohm resistor for the current sense resistor. The LED forward voltage varies from 2.2 to 3.8 and the power supply is 5V. The PWM frequency is 200 Hz.

He wants to see if he could reduce the turn-on transient during Pulse Width Modulation. He has a number of these devices and has staggered the PWM inputs to reduce the size of the transient, but if he could reduce the edge rate it would limit the extent of the harmonics. He observed that the TL4242 looks to be a feedback amplifier, so he thought that adding a small capacitor (0.1uf) in parallel with the LED would produce an integrator effect that would slow the current rise during turn on. He is also looking at paralleling the capacitor with 5k ohms to discharge the capacitor while the LED is off.

Any comments or potential gotchas?

Thanks, David

---------------------------------
David Hildebrand
Analog Field Applications
South Region
Texas Instruments, Inc.
Office: 214-479-0917
Cell: 972-841-6499
david.hildebrand@ti.com

---------------------------------

MTBF

Guilherme Farenzena — Tue, 21 May 2013 19:35:26 GMT

Gentleman

The TI provides MTBF for all your components ???

Best Regards

TPS92210

Roopesh Ghatke80441 — Tue, 21 May 2013 12:05:42 GMT

I want to shutdown TPS92210 using my microcontroller... Which pin do I use to do so?

Rgds/

Maverick

TPS61181 Is "Analog Dimming" control possible?

Tom Evans — Tue, 21 May 2013 02:08:02 GMT

We have a product using the TPS61181 to run four LED strings in a 5" display product. I saw one of them on broadcast TV last Sunday, and the 220Hz PWM backlight modulation is strobing very badly with the TV cameras. We can't increase the frequency enough to get around this, so I was wondering if I can put a "variable resistor" on the ISET pin, and control the brightness that way.

There's nothing obvious in the specifications giving the minimum LED current (corresponding to the maximum ISET resistance) that the chip will work at. I'm guessing that's implied by the switching power supply design and inductor selection, but a quick pointer would help here.

The easiest "variable resistor" would be a current mirror driven from a filtered PWM voltage. I could design this with discretes, but a pointer to a TI chip that can act as a "voltage controlled current sink" over the range of 15uA (replacing 82k) down to zero and App Notes demonstrating this function would also help a lot.

Tom

NEMA SSL-7 Compatibility for LM3450A-LM3409HV Combo?

Michael Lu (ACAT) — Fri, 17 May 2013 16:19:58 GMT

Hi,

I have a design that incorporates the suggested LM3450A-LM3409HV two-stage reference design for an LED driver (http://www.ti.com/tool/lm3450aev120v30). From a national standard of SSL compliance, do you know if this design has NEMA SSL-7 compatibility, in particular, compatibility with regards to the dimming curve?

Thanks,

Michael

TLC59116 Global Dimming (GRPPWM) problem

Bernard McDavitt — Sun, 15 Jul 2012 15:22:09 GMT

Hi,

A while back I designed a system which uses multiple TLC59108 and TLC59116 to play back patterns etc on many LED's. The customer is very happy with performance etc, but now would like a global dimming feature implemented to reduce brightness. I thought this should be quite straight forward, since as the dimming switch is pressed I could simply re-initialise the drivers but use a new GRPPWM value.

The TLC59108 are all off one I2C channel of the microcontroller, the TLC59116 off the other. I made all the modifications to both channels. The TLC59108 are dimming as expected, but for the life of me I can't seem to get the TLC59116 to respond. It is like they are ignoring the GRPPWM value.

Below is the data which is being sent out as part of the initialisation:

-----------------------------------------------------------------------------------------------------

#define TLC59116_INIT_DATA_LENGTH       25

// Data payload to initialise TLC59116.
unsigned char TLC59116_INIT_DATA[TLC59116_INIT_DATA_LENGTH] = {
   0b10000000,       // Control Register.                                   // TLC59116 Internal Register:
   0b10000001,       // Mode 1.                                               // [0x00]
   0b00000000,       // Mode 2.                                               // [0x01]
    0xFF,           // Brightness control LED0.                               // [0x02]
   0x00,           // Brightness control LED1.                               // [0x03]
   0x00,           // Brightness control LED2.                               // [0x04]
   0x00,           // Brightness control LED3.                               // [0x05]
   0x00,           // Brightness control LED4.                               // [0x06]
   0x00,           // Brightness control LED5.                               // [0x07]
   0x00,           // Brightness control LED6.                               // [0x08]
   0x00,           // Brightness control LED7.                               // [0x09]
   0x00,           // Brightness control LED8.                               // [0x0A]
   0x00,           // Brightness control LED9.                               // [0x0B]
   0x00,           // Brightness control LED10.                           // [0x0C]
   0x00,           // Brightness control LED11.                           // [0x0D]
   0x00,           // Brightness control LED12.                           // [0x0E]
    0xFF,           // Brightness control LED13.                           // [0x0F]
   0x00,           // Brightness control LED14.                           // [0x10]
    0xFF,           // Brightness control LED15.                           // [0x11]
   10,//0b11111111,       // Group Duty Cycle Control Register (GRPPWM).           // [0x12]
   0b11111111,       // Group Frequency Register (GRPFREQ).                   // [0x13]
   0b11111111,       // LED Driver Output State Register 0 (LEDOUT0).       // [0x14]
   0b11111111,       // LED Driver Output State Register 1 (LEDOUT1).       // [0x15]
   0b11111111,       // LED Driver Output State Register 2 (LEDOUT2).       // [0x16]
   0b11111111       // LED Driver Output State Register 3 (LEDOUT3).       // [0x17]
   };
-----------------------------------------------------------------------------------------------------

As part of my fault-finding, I have stripped the code back and have removed all but one TLC59116 device from my board and it is configured as:
A0 = 0
A1 = 0
A2 = 1
A3 = 0

So a write will be: 0b11001000 = 0xC8
And a read will be: 0b11001001 = 0xC9

The control register should be set to auto-inrement all registers starting from register 0b0000.
Mode1 register has 100 for the auto-increment, not sure if this matters since it is a read-only register? OSC = ON, ignore subaddr, listen to all-call.
Mode2 register has error status enabled, Group Control = dimming, outputs change on stop.

My test board has all 16 outputs connected, but the final product has only 14 so for the purposes of testing I have LED0, 13, 15, ON at full brightness.

I can see all the above data going out, and can even read back all registers and see the GRPPWM register saying it has the value 10 stored in it... If I change the DMBLNK to '1', the outputs will blink (when GRPFREQ is set lower) which proves the LEDOUT options are set correctly, ie responds to dimming/blinking. At the moment all the code is doing is sending the initialisation, and then either some test data, or doing a read back depending on my testing.

I did come across another thread talking about issues with the GRPPWM which had no answer:

http://e2e.ti.com/support/power_management/led_driverslcd_bias/f/192/t/153172.aspx

Are there any differences (other than more outputs) between the 8-channel TLC59108 and 16-channel TLC59116, I did not come across anything in the datasheet?

Can anyone provide any insight into what could be going wrong? If needed I can provide a I2C trace of the data going out/in.

Thanks,

Bernard.

cable length between TLC 5940 chips

Mirko Nuncium — Tue, 20 Mar 2012 18:15:01 GMT

Hi, Is there a limitation of cable length between daisy chained TLC5940's? I am trying to connect 14 chips using ethernet cable of 6 meters distance and encountering problems.

TPS61196

Kathleen Clare — Wed, 15 May 2013 16:15:22 GMT

TPS61196 chip. What should the UVLO pin be tied to if not using a higher under voltage lockout?

1W Dimmable LED driver solution

Utpal — Thu, 16 May 2013 13:20:05 GMT

Hello,

I am looking out for a 1W LED driver solution with dimming capacity.

Minimum of two-stage dimming is required.

Operational input voltage is 1.2V to 3.0V.

Which chip could be the optimum choice?

Regards,

--Utpal

TLC5971

Julio Aguirre — Thu, 25 Apr 2013 17:23:38 GMT

I am planning to use this driver TLC5971, to handle strings of HB RGBW LED from Cree, Inc. RGBW means the 3 color plus Cool White in one single die, HB means high Bright LED, the typical forward current is 350 mA. The maximum current from the TLC5971 is 60 ma per channel. There is any suggestion on how to handle more current without loosing linear control if I need to add for example a MOSFET transistor? Or there is another TLC driver that can handle by itself those RGBW LEDs.?

Thank you for your reply.

Julio

TLC59116 Changing GRPPWM causes erractic flashing

Johnd2225 — Thu, 15 Dec 2011 17:31:50 GMT

Hi,

I designed and built the LED system shown in the link.

http://www.autoartisans.com/rings/Barge1a.jpg

I'm finally trying to track down a problem we ran into back in 2009/2010. When we change the GRPPWM register from a larger value to a smaller value to dim the 12 channels we have connected to RGB and White LEDs. The scenario is as follows. We'll set the PWM registers to create a specific colour. Then we may want to slowly dim this colour to dark using the GRPPWM register. We do this by periodically sending out a smaller GRPPWM value to dim the overall intensity. Each time we send out an IIC message with 18 bytes. The Control/Address(0x82), 16 PWM channels and the GRPPWM value.

If, every 40mS, I send out a new GRPPWM value that is smaller by 4, it works most of the time but there are occasional errratic flashes where the RGB channels are suddenly quite bright as it happens at the lower PWM value. We're certain our IIC communications is functioning since we don't have any trouble changing any of the regular PWM registers. If we did the flashes would be coloured differently.

Needless to say the flashing is disconcerting and we've had clients comment negatively about it so I've been asked to see if we can fix it.

Thanks

John

LM3409HV: wide-short-wide pulses at switch node

Christopher Richardson — Thu, 16 May 2013 09:20:12 GMT

Dear LED Forum,

I´m working on an LM3409HV circuit that always drives 12 LEDs at around 35V at 330 mA, switching at a theoretical 330 kHz and an input voltage of 48VDC. The trouble is that the pulses on the switch node show a wide-narrow-wide behavior. Another inexplicable behavior is the average voltage across the current sense resistor, which is only 178 mV despite the IADJ pin being open circuit. (There is a 100nF MLCC on that pin to GND). The IADJ pin voltage is a proper 1.249V.

To get rid of the wide-narrow-wide I´ve tried:

- Adjusting the inductor value

- Adjusting the ROFF resistor value

- Optimizing the layout,

- Adding more input (VIN to GND) capacitance (small MLCC values and large Al-E value)

- Adding 1uF MLCC in parallel to the LEDs (the original design had no output cap)

None of this has had even the slightest effect. I´m attaching a scope shot showing the switch node in Ch.1 and the COFF pin voltage in Ch.2. This plot was taken using the spring tip attachment for both waveforms, so you can see that the switch node is well-behaved in terms of ringing/overshoot. What´s driving me nuts is that the COFF pin seems to work perfectly the first time - but when it falls again something appears to confuse the control loop, causing a minimum on-time pulse. I´ve looked at the current sense voltage, though it´s difficult to sense it properly, and this waveform along with everything else seem to be the results of the COFF pin commanding that short pulse. I can´t figure out what the cause is.

I haven´t tried putting filter cap or R-C snubber across the sense resistor - could this help?

Any ideas appreciated!

Many thanks,

chris

TPS65150 setup delays

Yu-Li — Tue, 02 Oct 2012 15:04:50 GMT

Hello,

I am using a 9" TFT LCD with the power sequence that is shown below:

I am thinking to use the TPS65150 device that controls the delays between Vs (this is my AVDD) -VGL and VGL-VGH.

Although I am happy with the delay setting for VGL-VGH I am not entirely certain whether it is possible to use this device and set the delay between Vs-VGL as during power-on, the sequence of the supplies for my display seems to be : dvdd->vgl->avdd->vgh->write data-> BL on when the datasheet for the supplies for the TPS65150 seems to be first Vs (avdd) and then VGH.

I ahve looked a few similar devices and all seem to go first VGL and then Vs or at the same time. Do I mis something or misunderstood the datasheets?

Forgot to mention the supplies values:

DVDD - 3.3v

AVDD (Vs) - 10.4V

VGL - (-5V)

VGH - 17V

VCOM - 4.2V

Thanks.

Yu-Li

Ext MOSFET for TPS61500 to let it supply 60V output

Sky Lee — Wed, 15 May 2013 10:13:26 GMT

Hi,

Currently we are designing TPS61500 for their 40V LED driver, we plan to modify it to 60V output, but understand that TPS61500 has an internal MOSFET that limit the Voltage to 40V.

Is it possible to add an external MOSFET on this IC to let it handle higher output Voltage? or any suggestion?

Do Ti have any similar reference design(I have searched online but cannot find) or application note that adding in ext MOSFET for this kind of driver?

Thanks.

LED DRIVER

Alex Getman1 — Tue, 14 May 2013 20:01:44 GMT

Hello,

I am looking for a LED DRIVER for separately switching on/off 4 LEDS (up to 150mA each one) high efficient, V_in = 3...5V. Who knows?

Alex

LM3447 Output power

Diego Luis Fernandez — Tue, 14 May 2013 05:58:12 GMT

Hello. I'm designing a 20-25W dimmable LED driver with LM3447 based on Flyback topology. The prototypes that I have realized have a very good performance. My question is: Can i use LM3447 for 55w dimmable led driver? What problems would I have?

Thanks.

TLC59108I, maximal output voltage

Thomas Best — Tue, 07 May 2013 09:21:08 GMT

Hi everyone,

i want to use the TLC59108IPWR to drive several LEDs.

The Supply voltage of the TLC59108 is 3.3V and the supply voltage for the LEDs is 5V.

Will the IC take harm if I the 3.3V supply voltage is switched off and the voltage for the LEDs is kept at 5V?

Is the maximal Output voltage stated in the datasheet (17V) only valid when the IC is powered on?

Thanks a lot and have a nice time!

Tom

HTSSOP28 / PWP package Step model link broken

Rowan Doherty — Tue, 23 Apr 2013 14:13:11 GMT

The link to the .stp model on the TLC5940 page for the HTSSOP28 package device appears to be broken:

http://webench.ti.com/cad/dlbxl.cgi/step/mxa28a.stp

Not Found

The requested object does not exist on this server. The link you followed is either outdated, inaccurate, or the server has been instructed not to let you have it.

Could I please have a model and could the link please be fixed.

-15V output not working in TPS65131RGET

Devendhiran Kumar — Fri, 26 Apr 2013 07:42:34 GMT

Hi,

I am using TPS65131RGET positive and negative output DC-DC converter in my proto design. In that the negative output was measured at initial power on and noted as -14.9V and positive output as 14.8V.

After few days we are again powered on and measured the output as 0.3V at negative output. But the +15V output section was working fine. Then the switching waveforms are probed and noted that switching was not done. The switching frequency waveform taken at power on was attached with this mail.

What are all the causes which stops the switching in IC?.