today, I had to program another 50 SX28 chips in a row. So I thought this would be a good chance for collecting some statistic data.
For programming the first 25 devices, I used a standard SXTech board, i.e. one with a 1µF output filter cap connected to the LM2940. While programming these devices, I got a total of nine "Chip Connection Failed" errors.
For programming ther next 25 devices, I used an SXTech board that I have modified before by adding a 22 µF aluminum electrolytic capacitor in parallel. The LM2940 data sheet discusses the output capacitor as follows:
The output capacitor is critical to maintaining regulator stability, and must meet the required conditions for both ESR (Equivalent Series Resistance) and minimum amount of capacitance.
MINIMUM CAPACITANCE:
The minimum output capacitance required to maintain stability is 22 µF (this value may be increased without limit). Larger values of output capacitance will give improved transient response.
ESR LIMITS:
The ESR of the output capacitor will cause loop instability if it is too high or too low. The acceptable range of ESR plotted versus load current is shown in the graph below. It is essential that the output capacitor meet these requirements, or oscillations can result.
It is important to note that for most capacitors, ESR is specified only at room temperature. However, the designer must ensure that the ESR will stay inside the limits shown
over the entire operating temperature range for the design.
For aluminum electrolytic capacitors, ESR will increase by about 30X as the temperature is reduced from 25°C to −40°C. This type of capacitor is not well-suited for low temperature operation.
Solid tantalum capacitors have a more stable ESR over temperature, but are more expensive than aluminum electrolytics.
A cost-effective approach sometimes used is to parallel an aluminum electrolytic with a solid Tantalum, with the total capacitance split about 75/25% with the Aluminum being the larger value. If two capacitors are paralleled, the effective ESR is the parallel of the two individual values. The “flatter” ESR of the Tantalum will keep the effective ESR from rising as quickly at low temperatures.
As I did not have a 22 µF tantalum on hand, I used an aluminum type with the original 1 µF tantalum in parallel.
While programming the next 25 devices using this modified SXTech board, I got no "Chip Connection Failed" errors at all.
Comments
today, I had to program another 50 SX28 chips in a row. So I thought this would be a good chance for collecting some statistic data.
For programming the first 25 devices, I used a standard SXTech board, i.e. one with a 1µF output filter cap connected to the LM2940. While programming these devices, I got a total of nine "Chip Connection Failed" errors.
For programming ther next 25 devices, I used an SXTech board that I have modified before by adding a 22 µF aluminum electrolytic capacitor in parallel. The LM2940 data sheet discusses the output capacitor as follows:
The output capacitor is critical to maintaining regulator stability, and must meet the required conditions for both ESR (Equivalent Series Resistance) and minimum amount of capacitance.
MINIMUM CAPACITANCE:
The minimum output capacitance required to maintain stability is 22 µF (this value may be increased without limit). Larger values of output capacitance will give improved transient response.
ESR LIMITS:
The ESR of the output capacitor will cause loop instability if it is too high or too low. The acceptable range of ESR plotted versus load current is shown in the graph below. It is essential that the output capacitor meet these requirements, or oscillations can result.
It is important to note that for most capacitors, ESR is specified only at room temperature. However, the designer must ensure that the ESR will stay inside the limits shown
over the entire operating temperature range for the design.
For aluminum electrolytic capacitors, ESR will increase by about 30X as the temperature is reduced from 25°C to −40°C. This type of capacitor is not well-suited for low temperature operation.
Solid tantalum capacitors have a more stable ESR over temperature, but are more expensive than aluminum electrolytics.
A cost-effective approach sometimes used is to parallel an aluminum electrolytic with a solid Tantalum, with the total capacitance split about 75/25% with the Aluminum being the larger value. If two capacitors are paralleled, the effective ESR is the parallel of the two individual values. The “flatter” ESR of the Tantalum will keep the effective ESR from rising as quickly at low temperatures.
As I did not have a 22 µF tantalum on hand, I used an aluminum type with the original 1 µF tantalum in parallel.
While programming the next 25 devices using this modified SXTech board, I got no "Chip Connection Failed" errors at all.
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Greetings from Germany,
Günther