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MAX12557 | 3.3V |
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0.1∝F |
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| 0.1∝F | 2.2∝F | |
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| 20kΩ |
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| REF_P | VDD |
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| MAX6029 | 1% |
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| 0.1∝F |
| REFOUT |
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| 1% |
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| 2 |
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| 2.413V |
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| 4 | 47Ω |
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| REF_N |
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| 0.1∝F |
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| MAX4230 |
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| 0.47∝F |
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| 330∝F |
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| 10∝F |
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| 6V | 1.47kΩ | 6V |
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| 52.3kΩ |
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| COM_ |
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| REFIN |
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| 1% |
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| GND |
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| 1.647V |
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| 1 |
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| 4 | 47Ω |
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| MAX4230 |
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| 3.3V |
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| 3 |
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| 52.3kΩ | 6V | 1.47kΩ | 6V |
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| 1% |
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| 0.1∝F | 2.2∝F | |
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| 0.880V |
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| VDD |
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| 4 | 47Ω |
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| 20kΩ |
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| 0.1∝F |
| REFOUT |
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| 1% | 3 |
| 330∝F |
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| 6V |
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| 1.47kΩ |
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| 20kΩ |
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| 1% |
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| REF_N |
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| 0.1∝F |
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| 20kΩ |
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| 1% |
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| COM_ | REFIN |
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| 0.1∝F |
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Figure 13. External Unbuffered Reference Driving Multiple ADCs
ence, allowing REF_P, REF_N, and COM_ to be driven directly by a set of external reference sources.
Figure 13 uses a MAX6029 precision 3.000V bandgap reference as a common reference for multiple convert- ers. A seven-component resistive divider chain follows the MAX6029 voltage reference. The 0.47µF capacitor along this chain creates a 10Hz LP filter. Three MAX4230 amplifiers buffer taps along this resistor chain providing 2.413V, 1.647V, and 0.880V to the MAX12557 REF_P, REF_N, and COM_ reference inputs. The feedback around the MAX4230 op amps provides additional 10Hz LP filtering. Reference volt- ages 2.413V and 0.880V set the full-scale analog input
range for the converter to ±1.022V (±[VREF_P - VREF_N] x 2/3).
Note that one single power supply for all active circuit components removes any concern regarding power- supply sequencing when powering up or down.
Grounding, Bypassing, and Board Layout
The MAX12557 requires
24 ______________________________________________________________________________________