| ??? 08/07/05 11:45 Modified: 08/07/05 11:54 Read: times |
#98951 - calculations Responding to: ???'s previous message |
dear Prahlad,
if i would be you then i would have calculated the resistor values as follows the listed input leakage current is 10 ua , the input impedence Rin becomes 5(VDD)/10e-6 = 0.5 Meg. as a thumb rule the reference setting divider should show the resultant 1/100 (firm) of the input impedance which is 0.005 meg or 5K. we can take R19 as 4.7K you decided to keep ref voltage 1/10 of the VCC then R19/RQ+R19 = 4.7K/R1+4.7K = 0.1 (1/10) RQ = 47K to balance other input RP = 47K and the R53+R54 = 4.7k or R53 = R54 = 2.2K (varify if 1n914 can take the worst case currebt with R53) Now R21 it will for a divider with R19 and can be calculated using desired hystresis voltage. if you deside a 10 mv hyst voltage VCC*4.7k/R21+4.7K = 10 mv R21 = 2.2 M R21 is required if comparataor output does not has the internal pullups. Abhishek |
| Topic | Author | Date |
| LPC9xx Comparators and Hysterisis | 01/01/70 00:00 | |
| Feedback resistor is not enough | 01/01/70 00:00 | |
| Is this allright | 01/01/70 00:00 | |
| Tested it. | 01/01/70 00:00 | |
| calculations | 01/01/70 00:00 | |
| Re: Calculations. | 01/01/70 00:00 | |
| step down rartio | 01/01/70 00:00 | |
| Values need a change | 01/01/70 00:00 | |
| Please show the analyses | 01/01/70 00:00 | |
| Re: Value Changes. | 01/01/70 00:00 | |
| my doubt is | 01/01/70 00:00 | |
| Answers | 01/01/70 00:00 | |
| 1N914 not Zener. | 01/01/70 00:00 | |
| Silent at many places | 01/01/70 00:00 | |
| Low pass filter | 01/01/70 00:00 | |
| Answer | 01/01/70 00:00 | |
| Zero crossing detection | 01/01/70 00:00 | |
Thanks | 01/01/70 00:00 |