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SM72442 Datenblatt(PDF) 11 Page - Texas Instruments |
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SM72442 Datenblatt(HTML) 11 Page - Texas Instruments |
11 / 21 page VIN VA C1 D1 D2 R1 C2 3 pF 30 pF Conversion Phase: Switch Open Track Phase: Switch Close SM72442 www.ti.com SNVS689H – OCTOBER 2010 – REVISED APRIL 2013 ANALOG INPUT An equivalent circuit for one of the ADC input channels is shown in Figure 9. Diode D1 and D2 provide ESD protection for the analog inputs. The operating range for the analog inputs is 0V to VA. Going beyond this range will cause the ESD diodes to conduct and result in erratic operation. The capacitor C1 in Figure 9 has a typical value of 3 pF and is mainly the package pin capacitance. Resistor R1 is the on resistance of the multiplexer and track / hold switch; it is typically 500 Ω. Capacitor C2 is the ADC sampling capacitor; it is typically 30 pF. The ADC will deliver best performance when driven by a low-impedance source (less than 100 Ω). This is specially important when sampling dynamic signals. Also important when sampling dynamic signals is a band-pass or low-pass filter which reduces harmonic and noise in the input. These filters are often referred to as anti-aliasing filters. Figure 9. Equivalent Input Circuit DIGITAL INPUTS and OUTPUTS The digital input signals have an operating range of 0V to VA, where VA = VDDA – VSSA. They are not prone to latch-up and may be asserted before the digital supply VD, where VD = VDDD – VSSD, without any risk. The digital output signals operating range is controlled by VD. The output high voltage is VD – 0.5V (min) while the output low voltage is 0.4V (max). SDA and SCL OPEN DRAIN OUTPUT SCL and SDA output is an open-drain output and does not have internal pull-ups. A “high” level will not be observed on this pin until pull-up current is provided by some external source, typically a pull-up resistor. Choice of resistor value depends on many system factors; load capacitance, trace length, etc. A typical value of pull- up resistor for SM72442 ranges from 2 k Ω to 10 kΩ. For more information, refer to the I2C Bus specification for selecting the pull-up resistor value . The SCL and SDA outputs can operate while being pulled up to 5V and 3.3V. I2C CONFIGURATION REGISTERS The operation of the SM72442 can be configured through its I2C interface. Complete register settings for I2C lines are shown below. Table 1. reg0 Register Description Bits Field Reset Value R/W Bit Field Description 55:40 RSVD 16'h0 R Reserved for future use. 39:30 ADC6 10'h0 R Analog Channel 6 (slew rate detection time constant, see adc config worksheet) 29:20 ADC4 10'h0 R Analog Channel 4 (iout_max: maximum allowed output current) 19:10 ADC2 10'h0 R Analog Channel 2 (operating mode, see adc_config worksheet) 9:0 ADC0 10'h0 R Analog Channel 0 (vout_max: maximum allowed output voltage) Copyright © 2010–2013, Texas Instruments Incorporated Submit Documentation Feedback 11 Product Folder Links: SM72442 |
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