Hp 22uh Driver
Sebastian Thorndike
I am using the TPS61165 as a constant current boost driver for a TFT panel backlight. Part of the reason I chose this part was for the 'analog dimming' to eliminate audible noise from the inductor/caps.
It seems with these component values the converter is barely having to switch to maintain the boost voltage and current, when dimming this requirement is less. Therefore even at 100% PWM the converter switching duty cycle is just 16% maximum. Dimming puts the converter in pulse skipping mode as the switch minimum on time is not short enough to run continuously and maintain the desired current.
Is it safe for me to try a lower inductance value than the recommended 10 to 22uH? I presume this is recommended for devices with larger input to output step and higher current? In my application a lower inductance would probably keep the PWM constant (no audible noise) but I am concerned about loop stability.
I am trying to estimate the power consumption of the processor, driver and associated current sense circuits, for a 3-phase Permanent Magnet Synchronous Motor (with L-L resistance of 2.6 ohms at PWM freq of 25Khz at room temperature).
Hi Chuck,
You can use the MCF8316AEVM's integrated buck regulator with the 47uH inductor, 22uH inductor, or 22 ohm resistor as the buck filter to produce the buck output voltage. Each filtering component provides a range of possible buck output current:
Sometimes customers wish to minimize the BOM space on the buck. The buck components must be populated whether you are using the buck or not; but generally if a very small buck output current is required (
You are correct, VM needs to be at least 6V to feed LDO and the buck regulators. Some of our points are captured at VM=6V, which showed higher efficiency than points above VM=12V. Higher VM will result in much higher power losses that needs to be mitigated through PCB configurations (thick copper, increased area, more layers, etc.) to improve thermal dissipation.
However, if buck efficiency is low (such as VM = 35V), this is actually not the main contributor of power losses in the device, you'll have more losses through the LDO dropout losses as well as switching and conduction losses through the 6 MOSFETs.
You are indeed pushing the design to the limits. The chosen supply voltage does not provide much in the way of overhead. For a LED at full power, the duty cycle will dance around 100%. The driver MOSFET will have a small voltage as will the B560C-13-F Shottky diode. Together, their voltage drops represent the bulk of the 0.9 V you mentioned.
There is a relationship between the inductance and the PWM. May I recommend an empirical approach. Since the cost is relatively low, purchase 10, 22, and 33 uH devices. Conduct a few experiments with the inductor values and the R1 (master frequency). Use an oscilloscope to look for stable operation. Also look for best efficiency.
Do you have any remaining I/O to control the relay? You may or may not want to add this functionality as a master-enable for the circuit. Your solution may depend on how it is integrated into the remainder of the automotive / boat systems.
again, if I understand the DS, the max output individually for the three GPIO pins is 25 mA and I presume that is at whatever the PIC is operating at voltage wise? The 25 mA should be enough for the needs of the EN pin, should it not?
Yes, the PWM is formed by software as the chosen PIC10F does not feature a PWM hardware peripheral. The good news about the PIC family is that it has been around for decades. The designers have maintained consistency with the hardware design. Consequently, there are many tutorials you can follow. Not all will be directly applicable to your particular model, but they will all follow a general plan.
Yes, the PIC may operate within a range of voltages. The 2.0 to 5 VDC you mentioned is appropriate. However, do be careful as some microcontrollers do not operate at the full clock / peripheral speed at lower voltages. In your application this is likely not important.
Relative to the PWM frequency you will be using, the R7 / R6 combination show in in the demo board schematic is invisible. The resistor is installed to limit the current should the microcontroller have a higher voltage than the Allegro driver.
Recommend sending the potentiometer to a microcontroller Analog to Digital Converter (ADC). Unfortunately, there is no such hardware on the PIC10F200. However, the newer PIC10F222 does include this desirable feature. You then program the PIC to read the potentiometer and adjust the PWM duty cycle accordingly.
The PIC family is vast with many members that will meet your needs. The PIC10F200 is one of the smallest. Sincer you are prototyping, you may want to move up to a model with more features such as this EV09Z19A development board. This would give you access to more I/O and features such as hardware based ADC and PWM. There are similar offerings from other manufactures. If you are curious, you may want to thread this article about low-cost microcontrollers:
When there is square wave (PWM) input to the EN pin, the IC must be designed such that the duty cycle of the input takes precedence over the duty cycle determined by the Rsense resistor, thereby likely cutting current to, and brightness of, the LED. I suppose it could also increase the duty cycle and increase brightness?
Have you prototyped the unit? There may yet be value in purchasing the demo board to explore the operation before committing to a new PCB. You may want to study / reverse engineer the demo board to see how the designers routed the traces. With this high frequency design, you will want to take every advantage you can to prevent unstable operation.
APD, I have it prototyped in EasyEDA but have not had any boards made. I have some challenges with the component library but I can solve that when the time comes. Also, I need to add the potentiometer for conditioning the Rsense resistor.
An example circuit is shown in the PICkit5 Quick Start User Guide - this should be very close to the PICkit2 you mentioned. Notice that the debugger connects to your board via a 6 or 8-pin header as shown in this image:
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You need to increase the value of your shunt resistors, with 0.2 milliohms, 40V/V amplification, and 3.3V VREF the linear current range will be (3.3-0.25)/2/40/0.0002 = 190 amps. This is way more than your MOSFETs can handle and it means the resulting signal going into the ADC will be small and your current sense accuracy will be poor. I suggest using 1 milliohm resistors, which can sense up to 38 amps.
You have also mixed up the order of SNA, SPA, SNB, SPB, SNC, SPC. You need to swap the SNx with SPx. Also SLA, SLB, SLC are from another variant of the chip (DRV8350). Make sure to read the datasheet carefully, the mixing of different variants is not always obvious.
It is not recommended to add a lowpass filter to the CSA output, the datasheet rates the CSA slew rate at 10V/us for a 60pF load, if you add 1nF of capacitance it might slow down the CSA and you could get inaccurate current readings. Instead I suggest removing the low pass filter and setting your ADC sampling time to 2000ns (CSA settling time to 1% with 40V/V gain), during this time the CSA will charge the internal ADC capacitor.
You also need to add more capacitance to the motor supply, I suggest at least 1000uF. Look for electrolytic or polymer capacitors with low ESR and high ripple current rating. Using multiple capacitors in parallel is OK.
You have chosen TIM2 pins for the PWM signals, TIM2 is a general purpose 32bit timer. For motor control 32 bit timers are not necessary, with a 16 bit timer and 170MHz clock the minimum frequency is 2.6KHz. Usually motor PWM frequency is around 20-100KHz, so there is no need for a 32bit timer to achieve a lower frequency. I suggest moving the PWM pins to TIM1 or TIM8 which are advanced 16bit timers with more features than basic timers, and connecting the INL pins (to the N channels of the timer) as well. Alternatively you can use HRTIM (you chose a microcontroller with HRTIM as its main selling point), it allows complex waveform generation not possible with the other timers, but software support is not as good.
You should consider adding some communication interfaces so your motor driver can communicate with other electronics, such as exposing i2c, spi, canbus, etc. Also consider using the internal pullup resistor in the STM32 for the NFAULT pin, keep the external pullup for SDO if you want fast SPI speed.
You need to increase the value of your current sense resistors, not decrease them. Your new current sense resistors are 0.1 milliohms which is even smaller than the original 0.2 milliohms. I suggest 1 milliohm for the sense resistors as it will provide allow sensing up to 38 amps, and the MOSFETs you picked can do 29 amps continuously.
Regarding your power setup, it is uncommon to put ferrite beads on the input of your buck converters, they usually go on the output. Putting them on the input will not have any significant effect because the biggest contributor to noise on the power rails will be the motor MOSFETs, not the buck converter. Unless you are trying to reduce EMI ferrite beads are probably unnecessary on anything except analog supply rails.
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