# MAX16834 LED Driver

#### timur.hal

Joined Jan 29, 2022
19
Hello,

I have a question regarding the usage of the LED Driver for High Power LEDs

At the moment I am using MAX16834 LED Driver https://www.maximintegrated.com/en/...rs/MAX16834.html/design-development/tb-tabs-2 to drive this LED https://www.osram.com/ecat/OSRAM OS...im_web_catalog_103489/prd_pim_device_8160601/

The LED is 23V and 10A - 230W

When I drive this LED in a Boost configuration everything works fine, I can turn ON, OFF and dim LED without any issues

Now I need to change configuration to Buck-Boost and drive it from 24V

When I placed all components and modified board to this configuration LED Driver itself got burned when the voltage reaches around 22V on the input

Is there any fundamental issues driving LED in a Buck-Boost mode having around 1V headroom from input to output?
Is there anything obvious from the datasheet that I am missing?

Best regards,
Tim

#### Papabravo

Joined Feb 24, 2006
18,834
The term buck-boost does not benefit from a single well-defined definition. It seems that it can refer to either an inverting or non-inverting configuration. Which one are we talking about? I'm asking because the link is to a list of application notes that I'm not motivated to pour over and reversing voltages when you don't expect them to be reversed is often a sure-fire way to let the magic smoke out.

Last edited:

#### timur.hal

Joined Jan 29, 2022
19
The term buck-boost does not benefit from a single well-defined definition. It seems that it can refer to either an inverting or non-inverting configuration. Which one are we talking about? I'm asking because the link is to a list of application notes that I'm not motivated to pour over and reversing voltages when you don't expect them to be reversed is often a sure-fire way to let the magic smoke out.
Here is a link for a datasheet: https://datasheets.maximintegrated.com/en/ds/MAX16834.pdf

It only specifies Buck-Boost, I referred to the schematics on Page 13

Best regards,
Timur

#### ElectricSpidey

Joined Dec 2, 2017
2,147
I do not know if this applies in this case, but sometimes a person may use the maximum current and voltage values and keep them within limits, but neglect to consider the wattage.

Not to mention that wattage can be difficult to calculate in a DC to DC converter.

#### Papabravo

Joined Feb 24, 2006
18,834
Here is a link for a datasheet: https://datasheets.maximintegrated.com/en/ds/MAX16834.pdf

It only specifies Buck-Boost, I referred to the schematics on Page 13

Best regards,
Timur
I need to make a minor correction; the datasheet uses the term "boost-buck". I don't know if this was intentional or accidental, but at least it does not appear to be an inverting configuration.

OK, so I see the schematic in the datasheet, but where is the one that corresponds to how you built the circuit, complete with component values and how you derived those values, and any substitutions you may have made?

#### timur.hal

Joined Jan 29, 2022
19
I need to make a minor correction; the datasheet uses the term "boost-buck". I don't know if this was intentional or accidental, but at least it does not appear to be an inverting configuration.

OK, so I see the schematic in the datasheet, but where is the one that corresponds to how you built the circuit, complete with component values and how you derived those values, and any substitutions you may have made?
I am a bit confused as well with this datasheet and not sure how does this circuit supposed to work, if that would be an inverting Buck-Boost it is more cleared how it is operating

I have attached schematics for the Boost-Buck configuration

Best regards,
Tim

#### Attachments

• 199.1 KB Views: 5

#### Papabravo

Joined Feb 24, 2006
18,834
I am a bit confused as well with this datasheet and not sure how does this circuit supposed to work, if that would be an inverting Buck-Boost it is more cleared how it is operating

I have attached schematics for the Boost-Buck configuration

Best regards,
Tim
I don't see a power connection for LED_PWR_IN, only test points. WTH kind of schematic is this -- a fragment?
When the switch is closed, the side of the inductor connected to the diode is at ground potential. When the switch is opened the current in the inductor cannot change instantaneously and so the voltage rises, the diode conducts, and the downstream capacitors get charged.
The relationship between input and output voltage should be approximately:
$$V_o\;=\;\cfrac{V_{in}}{1-D}\text{, where D is the duty cycle}$$

Last edited:

#### timur.hal

Joined Jan 29, 2022
19
I don't see a power connection for LED_PWR_IN, only test points. WTH kind of schematic is this -- a fragment?
Yes, this is LED Driver part

Power comes directly from the connector into the LED Driver - LED_PWR_IN, so the voltage can be from 19-24V

#### Papabravo

Joined Feb 24, 2006
18,834
Yes, this is LED Driver part

Power comes directly from the connector into the LED Driver - LED_PWR_IN, so the voltage can be from 19-24V
Is that clear from the schematic that you presented?
OK, so 19-24V in, and now what is the output of the boost converter supposed to be? Does this value exceed the limitations of the part?
Note that in a boost converter, while you are boosting the voltage you are cutting the output current by a similar amount AND there may be a large current flowing in the inductor which must be delt with.

The immutable rule of DC-DC conversion schemes is that: Power out will always be less than power in. Sometimes it will be much less.

Edit: According to ABSOLUTE MAXIMUM RATINGS in the datasheet, the maximum voltage on the HV pin should be +30V. Did you observe that limit in your boost scheme? Perhaps not.

Edit2: Double checking your schematic, it is not evident that LED_PWR_IN is associated with any connector. When you need help, clear and concise and COMPLETE engineering documentation is essential.

Edit3: So, what did you set the duty cycle to, and is that output voltage greater than +30 volts?

Last edited:

#### timur.hal

Joined Jan 29, 2022
19
Is that clear from the schematic that you presented?
OK, so 19-24V in, and now what is the output of the boost converter supposed to be? Does this value exceed the limitations of the part?
Note that in a boost converter, while you are boosting the voltage you are cutting the output current by a similar amount AND there may be a large current flowing in the inductor which must be delt with.

The immutable rule of DC-DC conversion schemes is that: Power out will always be less than power in. Sometimes it will be much less.

Edit: According to ABSOLUTE MAXIMUM RATINGS in the datasheet, the maximum voltage on the HV pin should be +30V. Did you observe that limit in your boost scheme? Perhaps not.

Edit2: Double checking your schematic, it is not evident that LED_PWR_IN is associated with any connector. When you need help, clear and concise and COMPLETE engineering documentation is essential.

Edit3: So, what did you set the duty cycle to, and is that output voltage greater than +30 volts?

The load is obviously LED that I have mentioned in my first post 23V and 10A - 230W . It is HV reference to LV and LED voltage is 23V

#### timur.hal

Joined Jan 29, 2022
19
Does this schematics help? I do not believe that connector will help you a lot?

How this is related to my question:
"The immutable rule of DC-DC conversion schemes is that: Power out will always be less than power in. Sometimes it will be much less. "

According to the calculations duty cycle is 33% voltage on the LED at 19V input I measured to be 41V, so the voltage across the LED is 22V and current is 7.8A, but as soon as I increase voltage to 22V LED driver does not work

Best regards,
Tim

#### Attachments

• 189.4 KB Views: 3

#### Papabravo

Joined Feb 24, 2006
18,834
Does this schematics help? I do not believe that connector will help you a lot?

How this is related to my question:
"The immutable rule of DC-DC conversion schemes is that: Power out will always be less than power in. Sometimes it will be much less. "

According to the calculations duty cycle is 33% voltage on the LED at 19V input I measured to be 41V, so the voltage across the LED is 22V and current is 7.8A, but as soon as I increase voltage to 22V LED driver does not work

Best regards,
Tim
My point was two fold:
1. High output current from a boost converter requires much larger input current
2. 41V on the HV pin exceeds the ABSOLUT MAXIMUM RATINGS for that pin as documented in the datasheet.
3. For a duty cycle of 33% and an input of 19V, the output on the HV pin should be 28.5 Volts -- all fine
4. For a duty cycle of 33% and an input of 22V, the output on the HV pin should be 33 Volts -- NOT AT ALL FINE, exceeds the absolute maximum rating.
Exceeding an ABSOLUTE MAXIMUM RATING by 10% is pretty much guaranteed to be fatal. What the heck was your intention anyway?

#### timur.hal

Joined Jan 29, 2022
19
My point was two fold:
1. High output current from a boost converter requires much larger input current
2. 41V on the HV pin exceeds the ABSOLUT MAXIMUM RATINGS for that pin as documented in the datasheet.
3. For a duty cycle of 33% and an input of 19V, the output on the HV pin should be 28.5 Volts -- all fine
4. For a duty cycle of 33% and an input of 22V, the output on the HV pin should be 33 Volts -- NOT AT ALL FINE, exceeds the absolute maximum rating.
Exceeding an ABSOLUTE MAXIMUM RATING by 10% is pretty much guaranteed to be fatal. What the heck was your intention anyway?
The configuration I am trying to implement is Boost-Buck, as I mentioned in my first post

Can you please share how did you make your calculations and I believe you have made them for the Boost converted?

From the tests at 19V input using Boost-Buck configuration I got voltage on HV pin reference to GND 41V and part operates without any damage and also this will give 22V on HV pin referenced to LV

Best regards,
Tim

#### timur.hal

Joined Jan 29, 2022
19
The configuration I am trying to implement is Boost-Buck, as I mentioned in my first post

Can you please share how did you make your calculations and I believe you have made them for the Boost converted?

From the tests at 19V input using Boost-Buck configuration I got voltage on HV pin reference to GND 41V and part operates without any damage and also this will give 22V on HV pin referenced to LV

Best regards,
Tim
Sorry I have missed this message from you:
When the switch is closed, the side of the inductor connected to the diode is at ground potential. When the switch is opened the current in the inductor cannot change instantaneously and so the voltage rises, the diode conducts, and the downstream capacitors get charged.
The relationship between input and output voltage should be approximately:
Vo=Vin1−D, where D is the duty cycle

This is the operational principle of the Boost Converter and it does makes sense, but I need to work out for the in the Boost-Buck configuration you need to Boost your voltage on the LED_PWR pin higher than the input voltage by 23V (forward voltage of the LED)

But I need this circuit to operate from 24V input, so the Driver in theory should operate as a Buck Converted, but I can't understand the principle of the operation of this Boost-Buck Configuration

Best regards,
Tim

#### Papabravo

Joined Feb 24, 2006
18,834
I see a circuit that looks like a boost converter based on the arrangement of the switch (MOSFET), the inductor, and the diode. They can call it whatever they want, but it may take somebody smarter than me to decode what the datasheet is actually talking about. In particular, a buck converter will NEVER connect one end of the switch to ground. I don't know what to tell you.

#### timur.hal

Joined Jan 29, 2022
19
I see a circuit that looks like a boost converter based on the arrangement of the switch (MOSFET), the inductor, and the diode. They can call it whatever they want, but it may take somebody smarter than me to decode what the datasheet is actually talking about. In particular, a buck converter will NEVER connect one end of the switch to ground. I don't know what to tell you.
This is what I am trying yo understand. I understand how Boost, Buck and Buck-Boost operate, but I can't get my head around how this circuit supposed to work, this image if from their evaluation board, but it is the same configuration as I have sent earlier:

I see that it is an obvious Boost converter configuration on the input side, but in the datasheet they specify that : "Connecting the negative terminal of a boost converter's output to the input-positive supply results in a buck-boost converter (input-voltage referenced)."

This is what I am trying to understand in here and if it will work with my LED?

Best regards,
Tim