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How to properly set up A/D converter?

Latest Updated:03/31/2009

Question:

I do not understand the linkage between the setup of the conversion time of the A/D converter, and minimum conversion time, which is on the A/D conversion characteristics section of electrical characteristics of the hardware manual.

When in setting up, I can set up the conversion time of the A/D converter faster rate than the minimum conversion time of electrical characteristics.

Answer:

Depending on the operating frequency and the setting value that you are using, it can be possible to setup the conversion time, which is lower than the minimum conversion time of electrical characteristics, but in that case, accurate conversion result will not be guaranteed.

All the A/D converters of H8 and H8S are the converters of successive approximation method. Successive approximation method A/D converters save electric charge, which is equivalent to the input voltage, into the condenser located in sample & hold circuit first, and then convert it to the digital value. Therefore, to get the accurate conversion result, it is necessary to charge/discharge as much electric charge as input voltage in internal sample & hold circuit.

When the conversion time is shorter than the guaranteed minimum conversion time of electrical characteristics, it is not guaranteed to have the accurate conversion result.  This happens because enough charge could not be saved, or it could not finish being discharged.

Therefore, please setup the A/D conversion time to become more than the minimum conversion time, which is guaranteed at the A/D conversion characteristics section of electrical characteristics of the hardware manual.

Suitable Products
H8 Family
H8/300H
H8/3069R
H8/3068
H8/3067(H8/3065, H8/3066, H8/3067)
H8/3062(H8/3060, H8/3061, H8/3062)
H8/3052B
H8/3048B
H8/3048(H8/3044, H8/3045, H8/3047, H8/3048)
H8/3042(H8/3040, H8/3041, H8/3042)
H8/3039(H8/3036, H8/3037, H8/3038, H8/3039)
H8/3035(H8/3033, H8/3034, H8/3035)
H8/3032(H8/3030, H8/3031, H8/3032)
H8/3029F
H8/3029
H8/3028(H8/3028, H8/3028F)
H8/3024(H8/3024, H8/3026)
H8/3022(H8/3020, H8/3021, H8/3022)
H8/3008
H8/3006(H8/3006, H8/3007)
H8/3004(H8/3004, H8/3005)
H8/3003
H8/3002
H8/3001
H8S Family
H8S/2600
H8S/2678, 2678R
H8S/2668
H8S/2655
H8S/2649
H8S/2648, 2646
H8S/2643
H8S/2630, 2639, 2638, 2636, 2635
H8S/2633
H8S/2628
H8S/2626, 2623
H8S/2615
H8S/2612
H8S/2500
H8S/2556, 2552, 2506
H8S/2400
H8S/2437
H8S/2300
H8S/2378, 2378R
H8S/2368
H8S/2398, 2357
H8S/2355
H8S/2350
H8S/2345
H8S/2339
H8S/2329
H8S/2319
H8S/2200
H8S/2282, 2280
H8S/2276
H8S/2268, 2264
H8S/2258, 2239, 2238, 2237, 2227
H8S/2245
H8S/2215
H8S/2214
H8S/2218, 2212
H8S/2100
H8S/2199R
H8S/2194
H8S/2189R
H8S/2172
H8S/2168
H8S/2169, 2149
H8S/2158
H8S/2148, 2144
H8S/2144B,2134B
H8S/2140B
H8S/2138, 2134
H8S/2128, 2124
H8S/2116
H8S/2114R
H8S/2111B
H8S/2110B