Datasheet LTC2452 (Analog Devices) - 8

LTC2452
applicaTions inForMaTion
of magnitude when compared to traditional delta-sigma 20 architectures. This allows external filter networks to in- 16 terface directly to the LTC2452. Since the average input 12 8 sampling current is 50nA, an external RC lowpass filter 4 using 1kΩ and 0.1µF results in <1LSB additional error. 0 Additionally, there is negligible leakage current between –4 OUTPUT CODE IN+ and IN–. –8 SIGNALS BELOW –12 GND
Reference Voltage Range
–16 –20 The LTC2453 reference input range is 2.5V to V –0.001 –0.005 0 0.005 0.001 0.0015 CC. For the V + + IN /VREF simplest operation, REF can be shorted to VCC. 2452 F03
Figure 3. Output Code vs V + – IN with VIN = 0 Input Voltage Range
capability. For example, if the underrange capability is As mentioned in the Output Data Format section, the out- 8LSB, the overrange capability is typically 31 – 8 = 23LSB. put code is given as 32768 • VIN/VREF + 32768. For VIN ≥ V
Output Data Format
REF, the output code is clamped at 65535 (all ones). For VIN ≤ –VREF, the output code is clamped at 0 (all zeroes). The LTC2452 generates a 16-bit direct binary encoded The LTC2452 includes a proprietary system that can, result. It is provided as a 16-bit serial stream through the typically, digitize each input 8LSB above V SDO output pin under the control of the SCK input pin REF and below GND, if the differential input is within ±V (see Figure 4). REF. As an ex- ample (Figure 3), if the user desires to measure a signal Letting V + – IN = (VIN – VIN ), the output code is given as slightly below ground, the user could set V – IN = GND, 32768 • VIN/VREF + 32768. The first bit output by the and V + REF = 5V. If VIN = GND, the output code would be LTC2452, D15, is the MSB, which is 1 for V + – IN ≥ VIN and approximately 32768. If V + IN = GND – 8LSB = –1.22 mV, 0 for V + – IN < VIN . This bit is followed by successively less the output code would be approximately 32760. significant bits (D14, D13...) until the LSB is output by the The total amount of overrange and underrange capability LTC2452. Table 1 shows some example output codes. is typically 31LSB for a given device. The 31LSB total During the data output operation the CS input pin must is distributed between the overrange and underrange be pulled low (CS = LOW). The data output process starts
Table 1. LTC2452 Output Data Format DIFFERENTIAL INPUT D15 D14 D13 D12...D2 D1 D0 CORRESPONDING VOLTAGE V + – IN – VIN (MSB) (LSB) DECIMAL VALUE
≥VREF 1 1 1 1 1 1 65535 VREF – 1LSB 1 1 1 1 1 0 65534 0.5•VREF 1 1 0 0 0 0 49152 0.5•VREF – 1LSB 1 0 1 1 1 1 49151 0 1 0 0 0 0 0 32768 –1LSB 0 1 1 1 1 1 32767 –0.5•VREF 0 1 0 0 0 0 16384 –0.5•VREF – 1LSB 0 0 1 1 1 1 16383 ≤ –VREF 0 0 0 0 0 0 0 2452fd 8 For more information www.linear.com/LTC2452