SPRUIY4B February 2023 – May 2024 TMS320F2800152-Q1 , TMS320F2800153-Q1 , TMS320F2800154-Q1 , TMS320F2800155 , TMS320F2800155-Q1 , TMS320F2800156-Q1 , TMS320F2800157 , TMS320F2800157-Q1
To achieve better accuracy, an external precision resistor can be used with INTOSC2. The external components required are:
Figure 4-7 shows an example illustration of these required external components.
In ExtR mode, the oscillator frequency error is directly proportional to the accuracy of the ExtR resistor.
The quality of the VDDIO supply directly affects the ExtR INTOSC performance. VDDIO capacitance values and circuit design must be decided with care to provide the cleanest supply possible to avoid jitter, noise, and other performance issues.
Placing a resistor on the ExtR pin prevents the pin from being used as a GPIO or X1.
Table 4-6 provides the ExtR specification values.
PARAMETER | TEST CONDITIONS | MIN | TYP | MAX | UNIT |
---|---|---|---|---|---|
fINTOSC2-ExtR-ERR-PERC | Ideal 0% error 100kΩ ExtR resistor | -0.7 | 0 | +0.7 | % |
fINTOSC2-ExtR | Ideal 0% error 100kΩ ExtR resistor | 9.93 | 10 | 10.07 | MHz |
fExtR-SETTLING | Switch to ExtR Mode | 1 | ms | ||
ExtR Resistance, RExtR | 100 | kΩ | |||
ExtR Decoupling Capacitance, CExtR | 10 | nF | |||
VDDIO Decoupling Capacitance, CVDDIO | 20 | μF |
Table 4-7 provides an example calculation for determining the total error of INTOSC2 given the parameters of a resistor.
PARAMETER | VALUE | UNIT |
---|---|---|
INTOSC2 Ideal Frequency Variation | 0.70 | % |
ExtR Resistor Tolerance | RTOLERANCE | % |
ExtR Resistor Temperature Coefficient | RTEMPCO | ppm/°C |
Operating Temperature | TOPERATING_POINT | °C |
ExtR Data Sheet Ambient Temperature | TAMBIENT | °C |
Total Frequency Error | [(0.70/100) + (RTOLERANCE/100) + ((RTEMPCO/1E6) * abs(TOPERATING_POINT-TAMBIENT))]*100 | % |
Table 4-8 provides example values using the above calculation.
PARAMETER | VALUE | UNIT |
---|---|---|
INTOSC2 Ideal Frequency Variation | 0.70 | % |
ExtR Resistor Tolerance | 0.10 | % |
ExtR Resistor Temperature Coefficient | 25 | ppm/°C |
Operating Temperature | 90 | °C |
ExtR Data Sheet Ambient Temperature | 25 | °C |
Total Frequency Error Calculation | ((0.70/100) + (0.10/100) + ((25/1E6) * abs(90-25)))*100 | % |
Total Frequency Error Calculation | 0.96 | % |
For best performance, use the following board layout guidelines: