I'm searching for a buck regulator (could be controller too) that has programmable voltage and current. The first one shouldn't be a problem but for current it should have something like Imon and Iset/Ictrl pins. In that way I can use MCU's DAC/PWM output to set both voltage and current, and also ADC inputs to monitor them.
Input voltage is 12 VDC, and output should be variable e.g. 1-5 V and up to 4-5 A (max. power 25-30 W). So far I found only one candidate LT8613. It looks fine but its tiny QFN package is not so DIY-friendly or it is? Another possibility is regulator/controller with I2C or SPI bus that can be used for programming and monitoring output voltage and current in above mentioned range.
Thanks!
Input voltage is 12 VDC, and output should be variable e.g. 1-5 V and up to 4-5 A (max. power 25-30 W). So far I found only one candidate LT8613. It looks fine but its tiny QFN package is not so DIY-friendly or it is? Another possibility is regulator/controller with I2C or SPI bus that can be used for programming and monitoring output voltage and current in above mentioned range.
Thanks!
it's actually quite a difficult job to get right. My first inclination is to pick one which suits, then use a uC with DAC output to feed the voltage feedback pin. However, noise may well become an issue with this idea as the buck converters need to be a balanced circuit with specific voltage/currents in mind: the moment you deviate from this, the output ripple unbalances the design. I've spent ages with various controllers (LTC3810, LTC3895, LM4116) trying to balance the output using the RC feedback network.
As for controlling current, well, the current is pulled from the reg, not controlled by it. Best you can achieve is controlling the current limit; but again this is fraut with issues given the peak/spike limits.
Probably the simplest way to go is a two-stage solution: use a Buck to perform the main drop 12-5v efficiently, then use a programmable LDO to make the final adjustments.
I can't recommend a specific component set, other than to look at Linear Tech and download their PowerCAD software: their devices rock, as does PowerCAD. LTC3895 would certainly do the first step, but it's overkill for your voltage requirements.
Mat
As for controlling current, well, the current is pulled from the reg, not controlled by it. Best you can achieve is controlling the current limit; but again this is fraut with issues given the peak/spike limits.
Probably the simplest way to go is a two-stage solution: use a Buck to perform the main drop 12-5v efficiently, then use a programmable LDO to make the final adjustments.
I can't recommend a specific component set, other than to look at Linear Tech and download their PowerCAD software: their devices rock, as does PowerCAD. LTC3895 would certainly do the first step, but it's overkill for your voltage requirements.
Mat
Quick back of the envelope calculation says at 300KHz you need about 6uH for the Inductance yielding 18-40% DeltaI for 1.5V-5V @4A. The NCP1589A uses a scalable R.OCP (use a digital pot here to set the OCP) from the gate to GND to set the OCP trip point. You would need to use a digital pot or voltage controlled current sink (DAC output to a opamp/transistor/resistor) on the bottom resistor of the feedback pin resistive divider to adjust the voltage up or down. You can't change change the upper resistor on the feed back without changing the overall loop crossover and polls and zeros.
Hope that helps.
Hope that helps.
I planned to test the following circuit. Sync buck controller is LT3741. Voltage programming is accomplished by injecting DAC output (MCP4822) 2.048 to 0 V for 0 to 6.3 V via R185. For current programming another DAC output is used. It's 0 to 1.5 V limits output current in range from 0 to 5 A. For voltage monitoring MCU ADC input is used (AUX_U_MON). Voltage divider R187, R188 is set to provide almost full scale for max output voltage. For current monitoring INA282 (gain 50V/V) is used that gives 2.5 V for max output current.
Possibly I will add dual op amp into the picture one for buffering voltage monitoring divider output (R187, R188) and another one to extend current shunt monitor output from 2.5 V to MCU's ADC full scale (3.3 V).
The LTspice model is shown below and you can also find it into attachment. According to it planned voltage and current limitation works as expected.
Possibly I will add dual op amp into the picture one for buffering voltage monitoring divider output (R187, R188) and another one to extend current shunt monitor output from 2.5 V to MCU's ADC full scale (3.3 V).
The LTspice model is shown below and you can also find it into attachment. According to it planned voltage and current limitation works as expected.
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