You can set either the voltage OR the amperage. Not both.

Wait! Re-reading your question.

This is incorrect, look at the TPS61088 or TPS61178, you can indeed set both.

 

What I mean to convey is that you can not set a voltage AND a current if the load is too big for that voltage/current setting. Suppose you set 5 volts and 5 amps but your device will only draw 1 amp. IF you want your device to operate at 5 amps then the voltage must be allowed to vary until it reaches the desired amperage.

At the end of my statement I went on to say that you can set a voltage and specify a max amperage. In that case, suppose you set it for 1 amp but your device wants to draw 4.8 amps. The voltage can not regulate at 6.5 volts. The voltage would have to go up in order to deliver 4.8 amps, as you had initially stated.

I'm not saying you can't set both parameters, it was misleading for me to sound like I was saying you can't. But Ohms Law will not allow you to regulate 6.5 volts at 4.8 amps. You can do one or the other. Regardless of the settings on the machine.

Trying to think of a good way to explain it:

OK, your LED can be set to operate at 1 amp. The voltage will vary until the 1 amp is achieved. But the point is that the voltage varies. IF you set it to operate at 6.5 volts then you will get whatever amperage the LED wants to draw. IF you set a voltage to operate at AND specify a cut off amperage, in this case, 1 amp, the voltage CAN NOT be maintained. The LED is drawing too much current for that specified setting.

Maybe someone else can explain it better. Clearer. I'm struggling with a good definition.

 

You are conflating two separate concepts.

They are “limit” and “regulate”.

When you talk about setting 1mA, you are limiting current to that value. The voltage at 1mA can change, but current is expected to vary along with changes until it exceeds the 1mA “limit”.

When you are attempt to “regulate”current, the current will be kept constant. In order to do this without breaking the laws of physics (ie Ohms Law), the voltage in a current regulator must change.

So, try to understand the difference between “limit” and “regulate”.

 

This is incorrect, look at the TPS61088 or TPS61178, you can indeed set both.

Wrong. You are not understanding what the data sheets are saying.

The chip DOES NOT regulate or limit the current delivered to the load, specifically; it limits the peak current through its internal switch by abruptly turning off the switch the instant the current through the switch exceeds a preset value. It does this on a cycle-by-cycle basis, and it does so to protect the switch from overheating-- not to regulate, or even limit, load current.

Although that will certainly have some sort of effect on preventing excessive load current, it is nonetheless NOT the same as explicitly regulating the load current to a constant value.

 

Please note the TPS61088 and TPS61178 are boost voltage (!!!) converters. Voltage in, Voltage out. For driving any high-power LED you need Current out. Neither of your parts is intended, or appropriate, to do the job you are attempting. At least alone. If you insist on using a voltage boost converter it needs to be followed by a Voltage to Current conversion stage specifically designed to drive a LED.

 

Here is a buck PWM set to measure the LED current via Rs with a voltage of 0.1V.

1.5A buck led driver

Almost every company that make LED power supplies make one of these.
It is a little hard to see how the LED current is measured. Current flows from Vin, through R3, through LED, L1 and transistors to ground. When the transistors are open the current in L1 circles through D1, R3, LED.
Weather you are measuring LED current or L1 current it comes out about the same.

Another option: I have used many of these.
Current flows from Vin through L1, Q1, R1, ground. (this current is measured)
When Q1 opens up this current flows through D1 and into C1&LED9(s).
The LED current is indirectly regulated.

 

Another option: I have used many of these.
Current flows from Vin through L1, Q1, R1, ground. (this current is measured)
When Q1 opens up this current flows through D1 and into C1&LED9(s).
The LED current is indirectly regulated.
View attachment 194473

Note that in the ZXSC310 it is the inductor peak current that is controlled, which only somewhat regulates the LED current. Duty cycle is determined by L1 inductance and applied voltage and, being a constant-off-time controller, frequency varies with duty cycle and depends on input voltage regulation, Q1 drop, and L1 resistance. Current pulses to the D1 diode may be consistent, but with varying frequency the power to the LEDs varies. So it's really hard to truly "control" LED current with this scheme. Much better to start with a higher voltage than the LED needs and implement a proper buck current controller. The ZXLD1320 is just such a buck controller, but unfortunately not big enough current wise to meet the OP's needs.