TMS320F280025C: TMS320F280025C

Yogini Joshi

Part Number: TMS320F280025C
Other Parts Discussed in Thread: LAUNCHXL-F280025C, REF6025, OPA320, C2000WARE

Currently we are getting offset error in ADC results. Every time, we are getting different value in ADC results when constant input vtg is applied to ADC input.

We tried below things;

- We have made an forceful call to (*Device_cal) , as suggested in TRM.

Also called below APIs forcefully ;

- - ADC_setOffsetTrim
  - ADC_setINLTrim
- Also, tried to get the offset value , by applying 0v to ADC input channel (nothing is provided to Adc input.), and tried changing the OFFSET_TRIM register for particular ADC module. But what we observed is, we are always getting a different value of offset when nothing is applied.
- We checked with example code adc_ex10_multiple_soc_epwm, but we are observing same offset error with sample code as well.

We have below configurations in ADC;

Internal reference vtg = 3.3 V
ADC A and ADC C modules have been configured for 4 SOCs each.
Trigger source = PWM trigger for 4 channels and software trigger for 4 channels (PWM with 20KHZ freq and 50% duty cycle)
SYSCLOCK = 100 MHZ and ADCLK = 50 MHZ

I tried the procedure mentioned at below link for ADC calibration ; with internal reference voltage = 3V3,

https://e2e.ti.com/support/microcontrollers/c2000-microcontrollers-group/c2000/f/c2000-microcontrollers-forum/707204/tms320f280049-adc-calibration

Below are my observations;

When I sample VREFLO with A13 channel, and follow the below mentioned procedure, I get the offset value at 4^th step as, -40 (decimal.)
If I set the same value in OFFSET_TRIM register, I get 1 (decimal) LSB, for VREFLO. But with same value in register when I apply ADCin as 1.4V, (1737 LSB) and I tired 512 conversions , average count I got is 1629. This average count value for applied voltage (1.4V) remains same even if I change the OFFSET_TRIM to any value.
So, overall conclusion is , whatever value we set in OFFSET_TRIM register, we always get the approx. -100 to -110 offset error in the ADC result count.

Do you suggest, what can be the reason for this error?

Note: we have same observations when we apply external reference voltage 3V3 , by taking vtg from the eval board pins itself.

Do you think that , there might be issue in the hardware connections or issue in ADC configuration?

over 2 years ago

0 Devin Cottier over 2 years ago

TI__Guru 60865 points

Hi Yogini,

If the fundamental issue is that you are applying 1.4V and sampling with 3.3V internal reference, but getting a result that is over 100 LSBs too low, then the issue is probably not offset error.

The typical offset error for this device is +/-2 LSBs and the min/max is +/-5 LSBs (and self-calibration is not required or recommended on this device, since it will not be able to get results much better than this). Note also that for the offset trim register, each step is not 1 LSBs (at 12-bit resolution), but instead 1/16 of an LSBs (to be compatible with other devices with similar ADCs that can also operate with 16 bit resolution in addition to 12 bit resolution). Also the trim range is only +7 LSBs / -8 LSBs @ 12-bit resolution, so self trim is not going to be able to help with your 100 LSBs of error.

An offset error would also be a fixed error regardless of the input voltage, so you'd expect say -100 LSBs of error whether you applied 0V, 0.3V, 1.4V, or 3.2V. I'd recommend that you try a variety of input voltages to determine if you have an offset error (fixed error regardless of input voltage), gain error (fixed ratio w.r.t. to the input voltage...e.g. you might expect 200 LSBs of error with a 2.8V input), or something non-linear.

If you have a gain error, you'd be looking at issues with the reference. For instance, if you are trying to using internal reference mode, but something is externally pulling on or otherwise conflicting with the VREF voltage the device is trying to drive out onto the VREFHI pin.

If you have a non-linear error, a good place to start would be looking at the impedance of the driving source vs. the configured S+H time (sample-and-hold time, set by ACQPS register). For instance, if your source impedance is extremely high (say your DC voltage is generated by a voltage divider) then you may need to greatly increase the S+H time from the minimum (which assumes a high bandwidth op-amp driving with 10's of ohms of source impedance). The following app. notes may be helpful if you need to go deeper into this topic: https://www.ti.com/lit/an/spract6/spract6.pdf and https://www.ti.com/lit/an/spracv0/spracv0.pdf.

0 Yogini Joshi over 2 years ago in reply to Devin Cottier

Prodigy 220 points

Hello Devin,

As per your recommendation I tried to measure multiple input values on single channel. Below are my observations

0 Yogini Joshi over 2 years ago in reply to Yogini Joshi

Prodigy 220 points

I am not able to get if the error is offset error or gain error. or there is something missing in our HW connections.

0 Yogini Joshi over 2 years ago in reply to Yogini Joshi

Prodigy 220 points

can you check the same at your side with your hardware setup?

0 Devin Cottier over 2 years ago in reply to Yogini Joshi

TI__Guru 60865 points

Hi Yogini,

Are you using a TI EVM, or is this a custom board? Is the signal buffered locally on the PCB with an op-amp? Do you have any capacitance on the ADC input (a couple 100 pF would be ideal, unless you are sampling relatively slow, in which case you can use 100nF or so to do a "charge-sharing" input design)?

What does the distribution of your 512 ADC results look like? For a good low-noise source, you might expect a max spread of maybe 3-6 LSBs with a standard deviation of maybe 0.5 to 1.0 LSBs.

Have you tried increasing the S+H duration? For 100ns I would expect that you are using a high-bandwidth op-amp to buffer the voltage.

0 Yogini Joshi over 2 years ago in reply to Devin Cottier

Prodigy 220 points

Hello Devin,

We are using LAUNCHXL-F280025C evaluation board. And currently for testing purpose I am directly applying the input voltage to the controller pin from power supply.

I tried increasing the S-H window to 15 sysclock cycles. But still there is no visible change in the output.

0 Yogini Joshi over 2 years ago in reply to Devin Cottier

Prodigy 220 points

Hello Devin,

Please find attached excel sheet for reference wherein I have copied the results for ADC conversion count for 512 conversions with input voltage = 2.733 V.

I directly applied 2.7V to the controller pin A0 from the power supply and observed the ADC counts for the same.

Note: I have measured the vtg from power supply on multimeter and then applied to the controller pin to supply the accurate vtg.

adcbuff	unsigned long[512]	[3450,3459,3451,3431,3457...]	0x0000B126@Data
	[0 ... 99]
		[0]	unsigned long	3450	0x0000B126@Data
		[1]	unsigned long	3459	0x0000B128@Data
		[2]	unsigned long	3451	0x0000B12A@Data
		[3]	unsigned long	3431	0x0000B12C@Data	Number of conversions		512
		[4]	unsigned long	3457	0x0000B12E@Data
		[5]	unsigned long	3443	0x0000B130@Data
		[6]	unsigned long	3462	0x0000B132@Data		count	vtg
		[7]	unsigned long	3462	0x0000B134@Data	Vin	3392	2.733
		[8]	unsigned long	3441	0x0000B136@Data	Sum
		[9]	unsigned long	3475	0x0000B138@Data	avg	3459.519	2.787
		[10]	unsigned long	3437	0x0000B13A@Data
		[11]	unsigned long	3467	0x0000B13C@Data	error	67.519	0.054
		[12]	unsigned long	3474	0x0000B13E@Data
		[13]	unsigned long	3447	0x0000B140@Data
		[14]	unsigned long	3464	0x0000B142@Data
		[15]	unsigned long	3415	0x0000B144@Data
		[16]	unsigned long	3450	0x0000B146@Data
		[17]	unsigned long	3361	0x0000B148@Data
		[18]	unsigned long	3371	0x0000B14A@Data
		[19]	unsigned long	3457	0x0000B14C@Data
		[20]	unsigned long	3466	0x0000B14E@Data
		[21]	unsigned long	3486	0x0000B150@Data
		[22]	unsigned long	3460	0x0000B152@Data
		[23]	unsigned long	3443	0x0000B154@Data
		[24]	unsigned long	3470	0x0000B156@Data
		[25]	unsigned long	3469	0x0000B158@Data
		[26]	unsigned long	3479	0x0000B15A@Data
		[27]	unsigned long	3458	0x0000B15C@Data
		[28]	unsigned long	3439	0x0000B15E@Data
		[29]	unsigned long	3468	0x0000B160@Data
		[30]	unsigned long	3457	0x0000B162@Data
		[31]	unsigned long	3474	0x0000B164@Data
		[32]	unsigned long	3460	0x0000B166@Data
		[33]	unsigned long	3439	0x0000B168@Data
		[34]	unsigned long	3467	0x0000B16A@Data
		[35]	unsigned long	3435	0x0000B16C@Data
		[36]	unsigned long	3451	0x0000B16E@Data
		[37]	unsigned long	3481	0x0000B170@Data
		[38]	unsigned long	3439	0x0000B172@Data
		[39]	unsigned long	3461	0x0000B174@Data
		[40]	unsigned long	3431	0x0000B176@Data
		[41]	unsigned long	3486	0x0000B178@Data
		[42]	unsigned long	3453	0x0000B17A@Data
		[43]	unsigned long	3443	0x0000B17C@Data
		[44]	unsigned long	3462	0x0000B17E@Data
		[45]	unsigned long	3445	0x0000B180@Data
		[46]	unsigned long	3460	0x0000B182@Data
		[47]	unsigned long	3463	0x0000B184@Data
		[48]	unsigned long	3439	0x0000B186@Data
		[49]	unsigned long	3471	0x0000B188@Data
		[50]	unsigned long	3435	0x0000B18A@Data
		[51]	unsigned long	3460	0x0000B18C@Data
		[52]	unsigned long	3462	0x0000B18E@Data
		[53]	unsigned long	3442	0x0000B190@Data
		[54]	unsigned long	3462	0x0000B192@Data
		[55]	unsigned long	3438	0x0000B194@Data
		[56]	unsigned long	3460	0x0000B196@Data
		[57]	unsigned long	3497	0x0000B198@Data
		[58]	unsigned long	3450	0x0000B19A@Data
		[59]	unsigned long	3431	0x0000B19C@Data
		[60]	unsigned long	3424	0x0000B19E@Data
		[61]	unsigned long	3427	0x0000B1A0@Data
		[62]	unsigned long	3472	0x0000B1A2@Data
		[63]	unsigned long	3431	0x0000B1A4@Data
		[64]	unsigned long	3479	0x0000B1A6@Data
		[65]	unsigned long	3467	0x0000B1A8@Data
		[66]	unsigned long	3451	0x0000B1AA@Data
		[67]	unsigned long	3467	0x0000B1AC@Data
		[68]	unsigned long	3445	0x0000B1AE@Data
		[69]	unsigned long	3466	0x0000B1B0@Data
		[70]	unsigned long	3443	0x0000B1B2@Data
		[71]	unsigned long	3466	0x0000B1B4@Data
		[72]	unsigned long	3465	0x0000B1B6@Data
		[73]	unsigned long	3426	0x0000B1B8@Data
		[74]	unsigned long	3463	0x0000B1BA@Data
		[75]	unsigned long	3442	0x0000B1BC@Data
		[76]	unsigned long	3458	0x0000B1BE@Data
		[77]	unsigned long	3471	0x0000B1C0@Data
		[78]	unsigned long	3461	0x0000B1C2@Data
		[79]	unsigned long	3513	0x0000B1C4@Data
		[80]	unsigned long	3449	0x0000B1C6@Data
		[81]	unsigned long	3463	0x0000B1C8@Data
		[82]	unsigned long	3458	0x0000B1CA@Data
		[83]	unsigned long	3451	0x0000B1CC@Data
		[84]	unsigned long	3458	0x0000B1CE@Data
		[85]	unsigned long	3443	0x0000B1D0@Data
		[86]	unsigned long	3451	0x0000B1D2@Data
		[87]	unsigned long	3473	0x0000B1D4@Data
		[88]	unsigned long	3490	0x0000B1D6@Data
		[89]	unsigned long	3527	0x0000B1D8@Data
		[90]	unsigned long	3465	0x0000B1DA@Data
		[91]	unsigned long	3478	0x0000B1DC@Data
		[92]	unsigned long	3484	0x0000B1DE@Data
		[93]	unsigned long	3487	0x0000B1E0@Data
		[94]	unsigned long	3450	0x0000B1E2@Data
		[95]	unsigned long	3470	0x0000B1E4@Data
		[96]	unsigned long	3467	0x0000B1E6@Data
		[97]	unsigned long	3485	0x0000B1E8@Data
		[98]	unsigned long	3463	0x0000B1EA@Data
		[99]	unsigned long	3464	0x0000B1EC@Data
	[100 ... 199]
		[100]	unsigned long	3460	0x0000B1EE@Data
		[101]	unsigned long	3476	0x0000B1F0@Data
		[102]	unsigned long	3470	0x0000B1F2@Data
		[103]	unsigned long	3465	0x0000B1F4@Data
		[104]	unsigned long	3455	0x0000B1F6@Data
		[105]	unsigned long	3458	0x0000B1F8@Data
		[106]	unsigned long	3463	0x0000B1FA@Data
		[107]	unsigned long	3462	0x0000B1FC@Data
		[108]	unsigned long	3479	0x0000B1FE@Data
		[109]	unsigned long	3479	0x0000B200@Data
		[110]	unsigned long	3463	0x0000B202@Data
		[111]	unsigned long	3463	0x0000B204@Data
		[112]	unsigned long	3455	0x0000B206@Data
		[113]	unsigned long	3473	0x0000B208@Data
		[114]	unsigned long	3459	0x0000B20A@Data
		[115]	unsigned long	3471	0x0000B20C@Data
		[116]	unsigned long	3457	0x0000B20E@Data
		[117]	unsigned long	3454	0x0000B210@Data
		[118]	unsigned long	3449	0x0000B212@Data
		[119]	unsigned long	3448	0x0000B214@Data
		[120]	unsigned long	3459	0x0000B216@Data
		[121]	unsigned long	3467	0x0000B218@Data
		[122]	unsigned long	3466	0x0000B21A@Data
		[123]	unsigned long	3472	0x0000B21C@Data
		[124]	unsigned long	3473	0x0000B21E@Data
		[125]	unsigned long	3512	0x0000B220@Data
		[126]	unsigned long	3463	0x0000B222@Data
		[127]	unsigned long	3474	0x0000B224@Data
		[128]	unsigned long	3469	0x0000B226@Data
		[129]	unsigned long	3462	0x0000B228@Data
		[130]	unsigned long	3462	0x0000B22A@Data
		[131]	unsigned long	3437	0x0000B22C@Data
		[132]	unsigned long	3494	0x0000B22E@Data
		[133]	unsigned long	3499	0x0000B230@Data
		[134]	unsigned long	3468	0x0000B232@Data
		[135]	unsigned long	3478	0x0000B234@Data
		[136]	unsigned long	3447	0x0000B236@Data
		[137]	unsigned long	3458	0x0000B238@Data
		[138]	unsigned long	3429	0x0000B23A@Data
		[139]	unsigned long	3471	0x0000B23C@Data
		[140]	unsigned long	3487	0x0000B23E@Data
		[141]	unsigned long	3463	0x0000B240@Data
		[142]	unsigned long	3451	0x0000B242@Data
		[143]	unsigned long	3470	0x0000B244@Data
		[144]	unsigned long	3471	0x0000B246@Data
		[145]	unsigned long	3421	0x0000B248@Data
		[146]	unsigned long	3465	0x0000B24A@Data
		[147]	unsigned long	3455	0x0000B24C@Data
		[148]	unsigned long	3469	0x0000B24E@Data
		[149]	unsigned long	3466	0x0000B250@Data
		[150]	unsigned long	3490	0x0000B252@Data
		[151]	unsigned long	3461	0x0000B254@Data
		[152]	unsigned long	3463	0x0000B256@Data
		[153]	unsigned long	3438	0x0000B258@Data
		[154]	unsigned long	3452	0x0000B25A@Data
		[155]	unsigned long	3475	0x0000B25C@Data
		[156]	unsigned long	3461	0x0000B25E@Data
		[157]	unsigned long	3465	0x0000B260@Data
		[158]	unsigned long	3456	0x0000B262@Data
		[159]	unsigned long	3452	0x0000B264@Data
		[160]	unsigned long	3367	0x0000B266@Data
		[161]	unsigned long	3362	0x0000B268@Data
		[162]	unsigned long	3455	0x0000B26A@Data
		[163]	unsigned long	3527	0x0000B26C@Data
		[164]	unsigned long	3433	0x0000B26E@Data
		[165]	unsigned long	3485	0x0000B270@Data
		[166]	unsigned long	3456	0x0000B272@Data
		[167]	unsigned long	3455	0x0000B274@Data
		[168]	unsigned long	3518	0x0000B276@Data
		[169]	unsigned long	3451	0x0000B278@Data
		[170]	unsigned long	3503	0x0000B27A@Data
		[171]	unsigned long	3453	0x0000B27C@Data
		[172]	unsigned long	3450	0x0000B27E@Data
		[173]	unsigned long	3495	0x0000B280@Data
		[174]	unsigned long	3467	0x0000B282@Data
		[175]	unsigned long	3461	0x0000B284@Data
		[176]	unsigned long	3455	0x0000B286@Data
		[177]	unsigned long	3462	0x0000B288@Data
		[178]	unsigned long	3467	0x0000B28A@Data
		[179]	unsigned long	3458	0x0000B28C@Data
		[180]	unsigned long	3485	0x0000B28E@Data
		[181]	unsigned long	3470	0x0000B290@Data
		[182]	unsigned long	3462	0x0000B292@Data
		[183]	unsigned long	3453	0x0000B294@Data
		[184]	unsigned long	3462	0x0000B296@Data
		[185]	unsigned long	3484	0x0000B298@Data
		[186]	unsigned long	3493	0x0000B29A@Data
		[187]	unsigned long	3461	0x0000B29C@Data
		[188]	unsigned long	3483	0x0000B29E@Data
		[189]	unsigned long	3452	0x0000B2A0@Data
		[190]	unsigned long	3475	0x0000B2A2@Data
		[191]	unsigned long	3468	0x0000B2A4@Data
		[192]	unsigned long	3457	0x0000B2A6@Data
		[193]	unsigned long	3515	0x0000B2A8@Data
		[194]	unsigned long	3471	0x0000B2AA@Data
		[195]	unsigned long	3507	0x0000B2AC@Data
		[196]	unsigned long	3453	0x0000B2AE@Data
		[197]	unsigned long	3459	0x0000B2B0@Data
		[198]	unsigned long	3471	0x0000B2B2@Data
		[199]	unsigned long	3463	0x0000B2B4@Data
	[200 ... 299]
		[200]	unsigned long	3485	0x0000B2B6@Data
		[201]	unsigned long	3455	0x0000B2B8@Data
		[202]	unsigned long	3442	0x0000B2BA@Data
		[203]	unsigned long	3467	0x0000B2BC@Data
		[204]	unsigned long	3427	0x0000B2BE@Data
		[205]	unsigned long	3525	0x0000B2C0@Data
		[206]	unsigned long	3461	0x0000B2C2@Data
		[207]	unsigned long	3445	0x0000B2C4@Data
		[208]	unsigned long	3458	0x0000B2C6@Data
		[209]	unsigned long	3458	0x0000B2C8@Data
		[210]	unsigned long	3483	0x0000B2CA@Data
		[211]	unsigned long	3466	0x0000B2CC@Data
		[212]	unsigned long	3478	0x0000B2CE@Data
		[213]	unsigned long	3454	0x0000B2D0@Data
		[214]	unsigned long	3436	0x0000B2D2@Data
		[215]	unsigned long	3459	0x0000B2D4@Data
		[216]	unsigned long	3467	0x0000B2D6@Data
		[217]	unsigned long	3463	0x0000B2D8@Data
		[218]	unsigned long	3472	0x0000B2DA@Data
		[219]	unsigned long	3448	0x0000B2DC@Data
		[220]	unsigned long	3455	0x0000B2DE@Data
		[221]	unsigned long	3459	0x0000B2E0@Data
		[222]	unsigned long	3456	0x0000B2E2@Data
		[223]	unsigned long	3503	0x0000B2E4@Data
		[224]	unsigned long	3463	0x0000B2E6@Data
		[225]	unsigned long	3506	0x0000B2E8@Data
		[226]	unsigned long	3464	0x0000B2EA@Data
		[227]	unsigned long	3525	0x0000B2EC@Data
		[228]	unsigned long	3455	0x0000B2EE@Data
		[229]	unsigned long	3463	0x0000B2F0@Data
		[230]	unsigned long	3488	0x0000B2F2@Data
		[231]	unsigned long	3467	0x0000B2F4@Data
		[232]	unsigned long	3468	0x0000B2F6@Data
		[233]	unsigned long	3444	0x0000B2F8@Data
		[234]	unsigned long	3468	0x0000B2FA@Data
		[235]	unsigned long	3460	0x0000B2FC@Data
		[236]	unsigned long	3425	0x0000B2FE@Data
		[237]	unsigned long	3451	0x0000B300@Data
		[238]	unsigned long	3451	0x0000B302@Data
		[239]	unsigned long	3441	0x0000B304@Data
		[240]	unsigned long	3440	0x0000B306@Data
		[241]	unsigned long	3449	0x0000B308@Data
		[242]	unsigned long	3469	0x0000B30A@Data
		[243]	unsigned long	3458	0x0000B30C@Data
		[244]	unsigned long	3453	0x0000B30E@Data
		[245]	unsigned long	3491	0x0000B310@Data
		[246]	unsigned long	3464	0x0000B312@Data
		[247]	unsigned long	3454	0x0000B314@Data
		[248]	unsigned long	3459	0x0000B316@Data
		[249]	unsigned long	3465	0x0000B318@Data
		[250]	unsigned long	3458	0x0000B31A@Data
		[251]	unsigned long	3458	0x0000B31C@Data
		[252]	unsigned long	3462	0x0000B31E@Data
		[253]	unsigned long	3455	0x0000B320@Data
		[254]	unsigned long	3450	0x0000B322@Data
		[255]	unsigned long	3467	0x0000B324@Data
		[256]	unsigned long	3462	0x0000B326@Data
		[257]	unsigned long	3462	0x0000B328@Data
		[258]	unsigned long	3451	0x0000B32A@Data
		[259]	unsigned long	3467	0x0000B32C@Data
		[260]	unsigned long	3459	0x0000B32E@Data
		[261]	unsigned long	3466	0x0000B330@Data
		[262]	unsigned long	3465	0x0000B332@Data
		[263]	unsigned long	3460	0x0000B334@Data
		[264]	unsigned long	3462	0x0000B336@Data
		[265]	unsigned long	3450	0x0000B338@Data
		[266]	unsigned long	3466	0x0000B33A@Data
		[267]	unsigned long	3463	0x0000B33C@Data
		[268]	unsigned long	3461	0x0000B33E@Data
		[269]	unsigned long	3479	0x0000B340@Data
		[270]	unsigned long	3476	0x0000B342@Data
		[271]	unsigned long	3461	0x0000B344@Data
		[272]	unsigned long	3460	0x0000B346@Data
		[273]	unsigned long	3461	0x0000B348@Data
		[274]	unsigned long	3461	0x0000B34A@Data
		[275]	unsigned long	3445	0x0000B34C@Data
		[276]	unsigned long	3451	0x0000B34E@Data
		[277]	unsigned long	3489	0x0000B350@Data
		[278]	unsigned long	3453	0x0000B352@Data
		[279]	unsigned long	3443	0x0000B354@Data
		[280]	unsigned long	3472	0x0000B356@Data
		[281]	unsigned long	3455	0x0000B358@Data
		[282]	unsigned long	3446	0x0000B35A@Data
		[283]	unsigned long	3470	0x0000B35C@Data
		[284]	unsigned long	3462	0x0000B35E@Data
		[285]	unsigned long	3446	0x0000B360@Data
		[286]	unsigned long	3460	0x0000B362@Data
		[287]	unsigned long	3477	0x0000B364@Data
		[288]	unsigned long	3457	0x0000B366@Data
		[289]	unsigned long	3454	0x0000B368@Data
		[290]	unsigned long	3442	0x0000B36A@Data
		[291]	unsigned long	3459	0x0000B36C@Data
		[292]	unsigned long	3468	0x0000B36E@Data
		[293]	unsigned long	3462	0x0000B370@Data
		[294]	unsigned long	3468	0x0000B372@Data
		[295]	unsigned long	3485	0x0000B374@Data
		[296]	unsigned long	3459	0x0000B376@Data
		[297]	unsigned long	3458	0x0000B378@Data
		[298]	unsigned long	3462	0x0000B37A@Data
		[299]	unsigned long	3458	0x0000B37C@Data
	[300 ... 399]
		[300]	unsigned long	3430	0x0000B37E@Data
		[301]	unsigned long	3455	0x0000B380@Data
		[302]	unsigned long	3460	0x0000B382@Data
		[303]	unsigned long	3457	0x0000B384@Data
		[304]	unsigned long	3365	0x0000B386@Data
		[305]	unsigned long	3370	0x0000B388@Data
		[306]	unsigned long	3459	0x0000B38A@Data
		[307]	unsigned long	3518	0x0000B38C@Data
		[308]	unsigned long	3465	0x0000B38E@Data
		[309]	unsigned long	3478	0x0000B390@Data
		[310]	unsigned long	3477	0x0000B392@Data
		[311]	unsigned long	3470	0x0000B394@Data
		[312]	unsigned long	3459	0x0000B396@Data
		[313]	unsigned long	3449	0x0000B398@Data
		[314]	unsigned long	3459	0x0000B39A@Data
		[315]	unsigned long	3451	0x0000B39C@Data
		[316]	unsigned long	3463	0x0000B39E@Data
		[317]	unsigned long	3454	0x0000B3A0@Data
		[318]	unsigned long	3461	0x0000B3A2@Data
		[319]	unsigned long	3465	0x0000B3A4@Data
		[320]	unsigned long	3466	0x0000B3A6@Data
		[321]	unsigned long	3463	0x0000B3A8@Data
		[322]	unsigned long	3460	0x0000B3AA@Data
		[323]	unsigned long	3456	0x0000B3AC@Data
		[324]	unsigned long	3465	0x0000B3AE@Data
		[325]	unsigned long	3467	0x0000B3B0@Data
		[326]	unsigned long	3456	0x0000B3B2@Data
		[327]	unsigned long	3463	0x0000B3B4@Data
		[328]	unsigned long	3468	0x0000B3B6@Data
		[329]	unsigned long	3458	0x0000B3B8@Data
		[330]	unsigned long	3471	0x0000B3BA@Data
		[331]	unsigned long	3464	0x0000B3BC@Data
		[332]	unsigned long	3459	0x0000B3BE@Data
		[333]	unsigned long	3469	0x0000B3C0@Data
		[334]	unsigned long	3465	0x0000B3C2@Data
		[335]	unsigned long	3457	0x0000B3C4@Data
		[336]	unsigned long	3461	0x0000B3C6@Data
		[337]	unsigned long	3466	0x0000B3C8@Data
		[338]	unsigned long	3466	0x0000B3CA@Data
		[339]	unsigned long	3462	0x0000B3CC@Data
		[340]	unsigned long	3474	0x0000B3CE@Data
		[341]	unsigned long	3463	0x0000B3D0@Data
		[342]	unsigned long	3462	0x0000B3D2@Data
		[343]	unsigned long	3464	0x0000B3D4@Data
		[344]	unsigned long	3458	0x0000B3D6@Data
		[345]	unsigned long	3461	0x0000B3D8@Data
		[346]	unsigned long	3471	0x0000B3DA@Data
		[347]	unsigned long	3441	0x0000B3DC@Data
		[348]	unsigned long	3502	0x0000B3DE@Data
		[349]	unsigned long	3457	0x0000B3E0@Data
		[350]	unsigned long	3491	0x0000B3E2@Data
		[351]	unsigned long	3459	0x0000B3E4@Data
		[352]	unsigned long	3480	0x0000B3E6@Data
		[353]	unsigned long	3474	0x0000B3E8@Data
		[354]	unsigned long	3443	0x0000B3EA@Data
		[355]	unsigned long	3471	0x0000B3EC@Data
		[356]	unsigned long	3459	0x0000B3EE@Data
		[357]	unsigned long	3458	0x0000B3F0@Data
		[358]	unsigned long	3449	0x0000B3F2@Data
		[359]	unsigned long	3460	0x0000B3F4@Data
		[360]	unsigned long	3460	0x0000B3F6@Data
		[361]	unsigned long	3433	0x0000B3F8@Data
		[362]	unsigned long	3453	0x0000B3FA@Data
		[363]	unsigned long	3455	0x0000B3FC@Data
		[364]	unsigned long	3451	0x0000B3FE@Data
		[365]	unsigned long	3477	0x0000B400@Data
		[366]	unsigned long	3442	0x0000B402@Data
		[367]	unsigned long	3400	0x0000B404@Data
		[368]	unsigned long	3464	0x0000B406@Data
		[369]	unsigned long	3455	0x0000B408@Data
		[370]	unsigned long	3463	0x0000B40A@Data
		[371]	unsigned long	3445	0x0000B40C@Data
		[372]	unsigned long	3459	0x0000B40E@Data
		[373]	unsigned long	3466	0x0000B410@Data
		[374]	unsigned long	3457	0x0000B412@Data
		[375]	unsigned long	3459	0x0000B414@Data
		[376]	unsigned long	3453	0x0000B416@Data
		[377]	unsigned long	3352	0x0000B418@Data
		[378]	unsigned long	3370	0x0000B41A@Data
		[379]	unsigned long	3462	0x0000B41C@Data
		[380]	unsigned long	3510	0x0000B41E@Data
		[381]	unsigned long	3490	0x0000B420@Data
		[382]	unsigned long	3483	0x0000B422@Data
		[383]	unsigned long	3474	0x0000B424@Data
		[384]	unsigned long	3449	0x0000B426@Data
		[385]	unsigned long	3466	0x0000B428@Data
		[386]	unsigned long	3453	0x0000B42A@Data
		[387]	unsigned long	3467	0x0000B42C@Data
		[388]	unsigned long	3455	0x0000B42E@Data
		[389]	unsigned long	3463	0x0000B430@Data
		[390]	unsigned long	3459	0x0000B432@Data
		[391]	unsigned long	3462	0x0000B434@Data
		[392]	unsigned long	3458	0x0000B436@Data
		[393]	unsigned long	3457	0x0000B438@Data
		[394]	unsigned long	3454	0x0000B43A@Data
		[395]	unsigned long	3458	0x0000B43C@Data
		[396]	unsigned long	3474	0x0000B43E@Data
		[397]	unsigned long	3463	0x0000B440@Data
		[398]	unsigned long	3459	0x0000B442@Data
		[399]	unsigned long	3460	0x0000B444@Data
	[400 ... 499]
		[400]	unsigned long	3470	0x0000B446@Data
		[401]	unsigned long	3461	0x0000B448@Data
		[402]	unsigned long	3539	0x0000B44A@Data
		[403]	unsigned long	3461	0x0000B44C@Data
		[404]	unsigned long	3463	0x0000B44E@Data
		[405]	unsigned long	3463	0x0000B450@Data
		[406]	unsigned long	3466	0x0000B452@Data
		[407]	unsigned long	3514	0x0000B454@Data
		[408]	unsigned long	3463	0x0000B456@Data
		[409]	unsigned long	3453	0x0000B458@Data
		[410]	unsigned long	3460	0x0000B45A@Data
		[411]	unsigned long	3464	0x0000B45C@Data
		[412]	unsigned long	3457	0x0000B45E@Data
		[413]	unsigned long	3450	0x0000B460@Data
		[414]	unsigned long	3464	0x0000B462@Data
		[415]	unsigned long	3461	0x0000B464@Data
		[416]	unsigned long	3417	0x0000B466@Data
		[417]	unsigned long	3459	0x0000B468@Data
		[418]	unsigned long	3474	0x0000B46A@Data
		[419]	unsigned long	3449	0x0000B46C@Data
		[420]	unsigned long	3453	0x0000B46E@Data
		[421]	unsigned long	3414	0x0000B470@Data
		[422]	unsigned long	3451	0x0000B472@Data
		[423]	unsigned long	3478	0x0000B474@Data
		[424]	unsigned long	3458	0x0000B476@Data
		[425]	unsigned long	3474	0x0000B478@Data
		[426]	unsigned long	3459	0x0000B47A@Data
		[427]	unsigned long	3449	0x0000B47C@Data
		[428]	unsigned long	3467	0x0000B47E@Data
		[429]	unsigned long	3462	0x0000B480@Data
		[430]	unsigned long	3468	0x0000B482@Data
		[431]	unsigned long	3417	0x0000B484@Data
		[432]	unsigned long	3448	0x0000B486@Data
		[433]	unsigned long	3454	0x0000B488@Data
		[434]	unsigned long	3463	0x0000B48A@Data
		[435]	unsigned long	3452	0x0000B48C@Data
		[436]	unsigned long	3411	0x0000B48E@Data
		[437]	unsigned long	3457	0x0000B490@Data
		[438]	unsigned long	3435	0x0000B492@Data
		[439]	unsigned long	3461	0x0000B494@Data
		[440]	unsigned long	3454	0x0000B496@Data
		[441]	unsigned long	3423	0x0000B498@Data
		[442]	unsigned long	3463	0x0000B49A@Data
		[443]	unsigned long	3475	0x0000B49C@Data
		[444]	unsigned long	3455	0x0000B49E@Data
		[445]	unsigned long	3464	0x0000B4A0@Data
		[446]	unsigned long	3463	0x0000B4A2@Data
		[447]	unsigned long	3464	0x0000B4A4@Data
		[448]	unsigned long	3463	0x0000B4A6@Data
		[449]	unsigned long	3454	0x0000B4A8@Data
		[450]	unsigned long	3441	0x0000B4AA@Data
		[451]	unsigned long	3351	0x0000B4AC@Data
		[452]	unsigned long	3471	0x0000B4AE@Data
		[453]	unsigned long	3510	0x0000B4B0@Data
		[454]	unsigned long	3491	0x0000B4B2@Data
		[455]	unsigned long	3475	0x0000B4B4@Data
		[456]	unsigned long	3448	0x0000B4B6@Data
		[457]	unsigned long	3478	0x0000B4B8@Data
		[458]	unsigned long	3436	0x0000B4BA@Data
		[459]	unsigned long	3459	0x0000B4BC@Data
		[460]	unsigned long	3463	0x0000B4BE@Data
		[461]	unsigned long	3446	0x0000B4C0@Data
		[462]	unsigned long	3479	0x0000B4C2@Data
		[463]	unsigned long	3435	0x0000B4C4@Data
		[464]	unsigned long	3464	0x0000B4C6@Data
		[465]	unsigned long	3460	0x0000B4C8@Data
		[466]	unsigned long	3430	0x0000B4CA@Data
		[467]	unsigned long	3467	0x0000B4CC@Data
		[468]	unsigned long	3445	0x0000B4CE@Data
		[469]	unsigned long	3461	0x0000B4D0@Data
		[470]	unsigned long	3468	0x0000B4D2@Data
		[471]	unsigned long	3400	0x0000B4D4@Data
		[472]	unsigned long	3459	0x0000B4D6@Data
		[473]	unsigned long	3459	0x0000B4D8@Data
		[474]	unsigned long	3462	0x0000B4DA@Data
		[475]	unsigned long	3460	0x0000B4DC@Data
		[476]	unsigned long	3422	0x0000B4DE@Data
		[477]	unsigned long	3459	0x0000B4E0@Data
		[478]	unsigned long	3397	0x0000B4E2@Data
		[479]	unsigned long	3453	0x0000B4E4@Data
		[480]	unsigned long	3466	0x0000B4E6@Data
		[481]	unsigned long	3431	0x0000B4E8@Data
		[482]	unsigned long	3463	0x0000B4EA@Data
		[483]	unsigned long	3467	0x0000B4EC@Data
		[484]	unsigned long	3459	0x0000B4EE@Data
		[485]	unsigned long	3455	0x0000B4F0@Data
		[486]	unsigned long	3440	0x0000B4F2@Data
		[487]	unsigned long	3463	0x0000B4F4@Data
		[488]	unsigned long	3445	0x0000B4F6@Data
		[489]	unsigned long	3462	0x0000B4F8@Data
		[490]	unsigned long	3458	0x0000B4FA@Data
		[491]	unsigned long	3428	0x0000B4FC@Data
		[492]	unsigned long	3478	0x0000B4FE@Data
		[493]	unsigned long	3444	0x0000B500@Data
		[494]	unsigned long	3482	0x0000B502@Data
		[495]	unsigned long	3474	0x0000B504@Data
		[496]	unsigned long	3449	0x0000B506@Data
		[497]	unsigned long	3467	0x0000B508@Data
		[498]	unsigned long	3450	0x0000B50A@Data
		[499]	unsigned long	3468	0x0000B50C@Data
	[500 ... 511]
		[500]	unsigned long	3465	0x0000B50E@Data
		[501]	unsigned long	3449	0x0000B510@Data
		[502]	unsigned long	3465	0x0000B512@Data
		[503]	unsigned long	3419	0x0000B514@Data
		[504]	unsigned long	3463	0x0000B516@Data
		[505]	unsigned long	3472	0x0000B518@Data
		[506]	unsigned long	3462	0x0000B51A@Data
		[507]	unsigned long	3454	0x0000B51C@Data
		[508]	unsigned long	3467	0x0000B51E@Data
		[509]	unsigned long	3466	0x0000B520@Data
		[510]	unsigned long	3454	0x0000B522@Data
		[511]	unsigned long	3450	0x0000B524@Data
i	unsigned long	512	0x0000B536@Data
Add new expression

0 Devin Cottier over 2 years ago in reply to Yogini Joshi

TI__Guru 60865 points

Hi Yogini,

Based on the results I don't think you have a good connection between the signal source and the ADC. I think you will want to improve your setup to get your results to be much less noisy and chaotic before worrying about the accuracy. Some things you can try, either in isolation or in combinations, are:

Use a function generator, precision signal injector EVM (https://www.ti.com/tool/PSIEVM), or precision reference IC (e.g. REF6025) to generate the DC test voltage instead of a power supply
Add a capacitor to the ADC input. The recommended value of this capacitor would be 200-300pF for fastest sampling (assuming a very good driver like a high bandwidth op-amp) or a ~100nF capacitor for slower "charge-sharing" based sampling
- High speed ADC input design is explored in the app. note: https://www.ti.com/lit/an/spract6/spract6.pdf
- Charge-sharing ADC input design is explored in the app. note: https://www.ti.com/lit/an/spracv0/spracv0.pdf
- Note that on the LAUNCHXL-F280025C, capacitor footprints are provided on ADC inputs at C25-C40 for the user to populate as needed
Add a high-speed low-noise op-amp (e.g. OPA320) to locally buffer the signal near the ADC input pin
- I'm not sure if there is a good boosterpack to do this for the launchpad, but if you can find an SMT prototyping launchpad you can build an op-amp circuit on it, or even just use some .100 protoboard
- On the ControlCard EVM, we sometimes use the protoboard area along with https://www.ti.com/tool/DIP-ADAPTER-EVM to build ADC buffers
Pay careful attention to cabling and signal return path
- Use as short of cables as possible
- Use shielded cables where possible
- For unshielded cables or unshielded portions of the cable connection, twist the signal and ground cables together for as much of the distance as possible to reduce the loop area between the signal and its return path
- Ensure that the ground connection to the board is made as close to the signal connection as possible
Increase the S+H duration
- Note: the max S+H duration is 512 SYSCLKs = 5.12us. If you are using a cable to connect from off-board and no buffer or capacitor, then you are probably closer to needing the max possible value than the min value

It is also always worth going back and double and triple checking the values of the device power rails (VDDIO, VDDA, VDD) and clocks (SYSCLK and ADCCLK) and running only the unmodified ADC examples provided in C2000ware

C2000™︎ microcontrollers

C2000 microcontrollers forum

TMS320F280025C: TMS320F280025C