For AutoRanging, the MAX_LEAKAGE constants indicate the maximum expected leakage for the final product. These values should be set according to each product. The four values are the LowLight configuration leakage, the High Sensitivity configuration leakage, the High Signal configuration leakage, and the Sunlight configuration leakage levels. Please contact Silicon Labs support for more information on setting these values for your final product.
5) Finally go to QS_Config.c and delete the final element of each of the following arrays: QS_ChannelInfo, QS_IRConfig, and QS_MuxInput. The final element is the configuration data for the second PS channel which we are disabling.
The code should work on an Si1141 after these changes. Please contact Silicon Labs support if you are experiencing issues with this process.
After configuring the Si1132 or Si114x device and issuing the command to start measurements, the measurement values are always zero and never update.
Assuming proper configuration bits have been sent, there are two common scenarios that will yield measurement values of zero:
1) The device is being reset upon taking a measurement. If the power supply system cannot source the current necessary to drive the IR LEDs, VDD may droop and cause the Si114x to reset. If the device resets, all registers are reset so the measurement data registers will be zero. Check the VDD line and make sure VDD is not dropping. You can also read any registers you previously wrote to and make sure the registers have not been reset to default.
2) The second scenario that will yield measurement values of zero is if the device is not executing all configuration commands. When a PARAM_SET command is sent, no further writes should be made to the PARAM_WR or COMMAND registers until the RESPONSE register is incremented. The RESPONSE register increments upon the completion of a COMMAND. The RESPONSE register should be read until it is incremented to guarantee that no previous commands fail or are interrupted by following writes. Datasheet section 4.2 discusses the proper COMMAND Protocol to follow.
Q: Does Silicon Labs offer an ac line current sensor?
A: The Silicon Labs Si890x family of isolated 10-bit monitoring ADCs can be used to measure ac line voltage and current. These products integrate a 10-bit ADC with isolated UART, I2C or SPI serial ports in a single 16SOW package. The Si890x EVB is a turn-key evaluation board that measures ac line voltage and current. This board includes all 3 serial port product versions and a low-cost, discrete 115/220Vac line interface circuit for easy product evaluation.
Q: Does Silicon Labs make an ac current sensing chip that operates in the 60hz range?
A: Yes, there are two approaches to sensing ac mains current:
1) Silicon Labs offers an ISOlinear reference design that enables the user to build a low cost, analog isolation amplifier circuit rated up to 5KVACrms. This simple, low cost circuit can be combined with a simple resistive shunt sensor to accurately measure ac line current. The ISOlinear reference design kit (part number Si86IsoLin) is currently available at www.silabs.com/isolation.
The second approach is to use one of the Si890x isolated serial monitoring ADCs. These devices integrate a 10-bit SAR ADC (2uS conversion time) with an isolated serial port (options include UART, I2C/SMBus and SPI port). The Si890x connects to the ac mains using a simple external line voltage interface circuit (typically a dual opamp and passives). The incoming analog current waveform is digitized by the Si890x ADC, and the resulting data is isolated from the ac line and transmitted to the user's master processor or DAC.
Why doesn't the device respond to any I2C commands to an address of 0x5A?
The I2C address of the device is 0x5A, but a common mistake is not taking into account the fact that the I2C protocol shifts the address to the left one bit. The final bit of the first byte is a read/write indicator. This means that the I2C command should be writing to 0x5A << 1 = 0xB4.
If communication is still not functioning with an address of 0xB4, please make sure that the device is properly soldered down and making good connections on all pins. Pull-ups are required on SDA, SCL, and INT, and any unused LED pins must be connected to VDD as specified in the datasheet. If you are still having connection issues, please contact Silicon Labs technical support.
How do I achieve long range detection (>30cm) with the Si114x?
If you are not satisfied with the range of the Si114x using the default settings with the Large Photodiode and maximum LED current, there are a few things you can do to extend the range.
First, be sure to look at Knowledge Base articles 311549 and 311557 for information on how to properly optically isolate and filter your system for longer range. These two articles discuss how isolation and filtering can help achieve longer ranges of detection.
The next step you can take to increase the range is to increase the IR LED pulse width to allow for more infrared light to be emitted and thus have more infrared light to be reflected back by the object of detection. The pulse width is modified through the register named PS_ADC_GAIN. Please refer to the Si114x datasheet for more information on the settings of this register. You can increase the gain as much as you need to achieve your range of detection, but the trade-off is that the device will be more susceptible to photodiode saturation. Optical isolation and filtering can help avoid saturation.
More range can also be achieved in the host-side firmware. For systems that do not need a very fast response time, a rolling average can be applied to the PS measurements. The more samples you average together, the more stable the output will be. With less noise on the output, a ranged detection can be triggered off of less PS counts, which in turn gives more range.
Can infrared proximity sensing systems have equal distances of detection for different colored objects?
Color is, by definition, the quality of an object with respect to light reflected by the object. In other words, the amount of light reflected by an object is determined by its color. Since an infrared proximity measurement is measuring the amount of light reflected by an object, different color objects will give different infrared proximity measurements. Therefore, it is not possible for an active infrared proximity sensing system to have equal distances of detection for objects of varying colors.
Can multiple Si114x devices be implemented in a single system? What pins can be shared between these devices?
When using multiple Si114x’s in a system, the devices can share the same I2C lines and the LED pins can be connected to the same LED since the LED pins are tri-stated when not taking a measurement. However, the Si114x’s all power on with the same I2C address. This means that the Si114x’s cannot share VDD lines, nor can they both just be directly connected to the VDD of the main system.
In order to function properly, a system with multiple Si114x devices must individually power up devices and change their I2C address before another Si114x can be powered on. The simplest way to do this is by powering each Si114x by a port pin of the host MCU. This way the host MCU can power the first device, change its I2C address, then power on the next device, and so on. The same can be done with mosfets if the host processor cannot supply the current needed by the Si114x.
Due to the nature of these devices, the Si114x’s cannot be used in autonomous mode when multiple devices are implemented in the system. Since the Si114x devices cannot synchronize with each other, the devices can end up in a situation where multiple Si114x’s are taking measurements at the same time, and this will be bad for the power system as well as the measurements being taken. Therefore, the devices can only be used in Polled mode. The host MCU must manually force each Si114x to take a measurement to guarantee that no two Si114x devices are taking measurements at the same time.
When using multiple Si1120's in a system, which pins can be shared between these devices?
When using multiple Si1120’s in a single system, some of the pins can be shared between all Si1120’s in order to minimize the number of pins needed on the host. Excluding the two GND pins and the VDD pin, there are five pins of each Si1120 that we are concerned about their abilities to be shared. The five pins are TXO, PRX, SC, MD, and STX.
TXO – Multiple Si1120 TXO pins can be connected to the same LED as long as the Si1120’s will never be driving the LED’s at the same time. The TXO pins are tri-stated when not taking a measurement.
PRX – As long as only one Si1120 is taking a measurement at a time, the PRX pins can be shared to one input into the host device. While not taking measurements, the PRX pin is tri-stated.
SC – The SC pins act as a chip select in a system with multiple Si1120’s. Since only one Si1120 should be taking a PRX measurement at a time, the SC pins cannot be shared. The best way to optimize the usage of the SC pins with systems with more than two Si1120’s is to use a decoder. For example, a system with four Si1120’s can use a 2-to-4 decoder to determine which Si1120’s SC will be active.
MD – Since only one Si1120 will be active at a time, the MD pins can be shared because they are inputs to the device only when they are active. If your system is not using an Si1120 mode that requires toggling of MD, it is okay to connect all MD’s to GND.
STX – The STX pin is an input to start taking a measurement. If only one Si1120 is active at a time, the STX lines can be shared. If a system wants to take measurements from multiple Si1120’s at a time, STX should not be shared for these devices.
What is optical filtering? Is optical filtering necessary for infrared proximity sensing systems?
Optical filtering is the idea of using light filters to keep certain wavelengths of light from passing through a media. For infrared proximity sensing applications, filtering can help reduce noise caused by ambient light and also reduce the chances of ambient light causing the photodiode of the sensing device from saturating.
The optimal type of filter for this application is an infrared pass filter. These filters let only infrared light pass through and filter out all other wavelengths of light. With ambient visible light being filtered away from the device, the measurements will be much less noisy and provide for a higher signal to noise ratio. This will allow a system to safely rely on smaller changes in proximity measurements to determine when an object is detected, which effectively means the system can have much greater range of detection since the feedback at long range is small.
The filter also has another effect on proximity measurements – high ambient light performance is greatly improved. With the filter keeping visible ambient light away from the photodiode, the photodiode will be much less saturated than systems without the filter. This means that functionality will be much less affected by high ambient light conditions.
The only drawback of using infrared pass filtering is that the system can no longer take ambient visible light measurements since there is little to no ambient visible light on the sensor anymore.
Is optical isolation required for all proximity sensing applications? What material is best for optical isolation?
Optical isolation describes any material used to block the direct path of light between an infrared LED and an infrared sensing device used for proximity sensing. The coupling of light between the sensor and emitter will bring the sensor closer to saturation, cut into its maximum dynamic range, and cause noisier measurements. Also, the magnitude of the optical coupling is directly related to the distance between the LED and the sensor. If the LED is very close to the sensor, the coupling will be very high.
High optical isolation is required for long range applications (> 25 cm) that need high dynamic range and high signal to noise ratio while also putting the LED very close to the sensor. For applications not needing long range, optical isolation is not required when the LED is farther than 2 cm from the sensor.
Most material that is dense and dark colored is good for optical isolation. Rubber is the best for isolation because it is nonporous to light and its black color absorbs most light. Rubber is also good because it is soft and when pressure is applied it fills open gaps between the objects it is against. Buna-N rubber O-rings are what Silicon Labs reference designs use for optical isolation. The part number for this O-ring is 4061T111 at www.mcmaster.com.
Q: What limits the Si85xx ac current sensor to a minimum frequency of 50kHz?
A: In short, it is rated accuracy that limits the Si85xx ac current sensor to a minimum frequency of 50khz. Operating this device at frequencies below 50Khz increases the measurement error of the device beyond its rated +/-5% of measurement accuracy. At frequencies in the 10.5khz range, the Si85xx measurement error increases to approximately +/-9% due to integrator non-linearity. At frequencies of 10khz or less, an internal watchdog timer disables measurement.
Q. What happens when sensed AC current exceeds the nominal range (5A/10/20A) of a selected Si85xx current sensor? Does it damage the current sensor?
A. No, the Si85xx AC current sensor can be overranged more than 50% with no adverse effect on functionality and accuracy. However the output headroom of Si85xx will depend on operating voltage, and is limited to VDD-1.4V. Therefore, it may be necessary to increase VDD to 5V, depending on how hard the current sensor is overdriven. Also, package thermal limits limit the maximum current through the Si85xx current sensor to 20Amps max.
How does the reset of the Si850x/1x AC current sensor differ from that of a current sense transformer (CT)?
Current sense transformer (CT) reset circuits can be relatively simple or complex depending on the end application. A simple, low frequency power application may require an CT reset using only 1 diode, 2 resistors and 1 capacitor. However a high frequency or high duty cycle power delivery system may require a dedicated controller and more than a dozen discrete transistors and passives.
Can the Si850x/1x AC current sensor measure currents above 20A?
Yes, the Si850x/1x can measure currents much larger than 20A. 20A device versions transduce input currents at 100mV/Amp and a nominal full-scale output of 2V. However, if current is increased to 30A, the output rises to a 3V (assuming a 5V supply). The factors which limit the maximum measurable current measured are: 1) the thermal limitations of the device package; and 2) the magnitude of Vdd.
Why does the Si851x AC current sensor have two outputs?
The Si851x series is designed for use with more complex power systems having multiple switches (such as a full-bridge), where transformer currents flow in both directions. To maintain transformer flux balance (i.e. avoid saturating the transformer core), many systems use two current transformers (CT) - one in each leg of the full bridge. The CT output signals are then used by dedicated control circuits to force the currents into and out of the transformer to be equal thereby maintaining transformer flux balance.
Why do the Si851x AC current sensors have four reset inputs (R1-R4)?
A: The Si851x products are targeted at more complex power applications containing multiple power switches (a full bridge for example). These products have four reset inputs enabling the sensor to observe up to four different gate drive signals at the same time. This information is used by the sensor to optimally the sensor reset period for maximum accuracy.
Are there any special layout techniques that must be observed when applying the Si850x/1x AC current sensor?
Yes. The 20-pin wide-body versions of the Si850x/1x requires special layout considerations to avoid erroneous reset events that may cause the sensor to intermittantly halt operation. These layout techniques are not complex, and are documented in the Si85xx AC Current Sensor datasheet available at www.silabs.com.
Is the Si850x/1x AC current sensor QFN package safety certified to 1KVrms?
Although the Si850x/1x QFN package provides 1KVrms of isolation, this device is NOT safety certified by UL, VDE and CSA. The performance of QFN package versions of the Si850x/1x are guaranteed by design and/or characterization.