SLAA977 October 2020 ADS7955-Q1
4 Pin Failure Mode Analysis (Pin FMA)
This section provides a Failure Mode Analysis (FMA) for the pins of the ADS7955-Q1. The failure modes covered in this document include the typical pin-by-pin failure scenarios:
- Pin short-circuited to Ground (see Table 4-2)
- Pin open-circuited (see Table 4-3)
- Pin short-circuited to an adjacent pin (see Table 4-4)
- Pin short-circuited to supply (see Table 4-5)
Table 4-2 through Table 4-5 also indicate how these pin conditions can affect the device as per the failure effects classification in Table 4-1.
Table 4-1 TI Classification of Failure
Effects
| Class | Failure Effects |
|---|---|
| A | Potential device damage that affects functionality |
| B | No device damage, but loss of functionality |
| C | No device damage, but performance degradation |
| D | No device damage, no impact to functionality or performance |
Figure 4-1 shows the ADS7955-Q1 pin diagram. For a detailed description of the device pins please refer to the Pin Configuration and Functions section in the ADS7955-Q1 data sheet.
Figure 4-1 Pin DiagramFollowing are the assumptions of use and the device configuration assumed for the pin FMA in this section:
- +VA and +VBD use the same supply voltage.
- AGND, REFM and BDGND use the same GND.
RC filters on every analog input, CHx. Series resistors are sized to limit the input currents into the analog inputs to <10mA in all circumstances, e.g. also in case device is unpowered and input signal is applied.
- Device is the only slave on the SPI bus.
Table 4-2 Pin FMA for Device Pins
Short-Circuited to Ground
| Pin Name | Pin No. | Description of Potential Failure Effect(s) | Failure Effect Class |
|---|---|---|---|
| GPIO2 | 1 | GPIO2 configured as digital output: GPIO2 stuck low. Increase in supply current when GPIO2 tries to drive high. Device damage may be plausible. | A |
| GPIO2 configured as digital input: GPIO2 stuck low. Readback value of GPIO2 will be 0b. | B | ||
| GPIO3 | 2 | GPIO3 configured as digital output: GPIO3 stuck low. Increase in supply current when GPIO3 tries to drive high. Device damage may be plausible. | A |
| GPIO3 configured as digital input: GPIO3 stuck low. Readback value of GPIO3 will be 0b. | B | ||
| REFM | 3 | No effect. Normal operation. | D |
| REFP | 4 | Reference voltage to the ADC will be 0 V as REFP = REFM = Ground. Incorrect conversion result for all channels. Conversion result for all channels will be close to 0x3FF. | B |
| +VA | 5 | Device unpowered and not functional. Observe that the absolute maximum ratings for all pins of the device are met, otherwise device damage may be plausible. | A |
| AGND | 6 | No effect. Normal operation. | D |
| MXO | 7 | Conversion results for all channels will be close to 0x000. Multiplexer's analog inputs CH7-CH0 will be connected to Ground through MXO. Increase in current sourced from the analog inputs. | B |
| AINP | 8 | External amplifier used between MXO and AINP: Conversion results for all channels will be close to 0x000. External amplifier's output will be connected to Ground. | B |
| MXO directly connected to AINP: Conversion results for all channels will be close to 0x000. Multiplexer's analog inputs CH7-CH0 will be connected to Ground through MXO and there will be increase in current sourced from the external circuits driving the analog inputs. | B | ||
| AINM | 9 | No effect. Normal operation. | D |
| AGND | 10 | No effect. Normal operation. | D |
| CH7 | 11 | Conversion result for this analog input channel will be close to 0x000. | B |
| CH6 | 12 | Conversion result for this analog input channel will be close to 0x000. | B |
| CH5 | 13 | Conversion result for this analog input channel will be close to 0x000. | B |
| CH4 | 14 | Conversion result for this analog input channel will be close to 0x000. | B |
| NC | 15 | No effect. Normal operation. | D |
| NC | 16 | No effect. Normal operation. | D |
| CH3 | 17 | Conversion result for this analog input channel will be close to 0x000. | B |
| CH2 | 18 | Conversion result for this analog input channel will be close to 0x000. | B |
| CH1 | 19 | Conversion result for this analog input channel will be close to 0x000. | B |
| CH0 | 20 | Conversion result for this analog input channel will be close to 0x000. | B |
| +VA | 21 | Device unpowered and not functional. Observe that the absolute maximum ratings for all pins of the device are met, otherwise device damage may be plausible. | A |
| AGND | 22 | No effect. Normal operation. | D |
| CS | 23 | CS stuck low. No SPI communication with the device possible. | B |
| SCLK | 24 | SCLK stuck low. No SPI communication with the device possible. | B |
| SDI | 25 | SDI stuck low. Device configuration cannot be modified. Device will remain in previously configured state until reset condition occurs. Device will remain in default configuration after power-up. | B |
| SDO | 26 | SDO stuck low. No data readback possible from the device. Increase in supply current when device tries to drive SDO high. Device damage may be plausible. | A |
| BDGND | 27 | No effect. Normal operation. | D |
| +VBD | 28 | Digital interface not powered up. No SPI communication with device possible. Observe that the absolute maximum ratings for all pins of the device are met, otherwise device damage may be plausible. | A |
| GPIO0 | 29 | GPIO0 configured as digital output: GPIO0 stuck low. Increase in supply current when GPIO0 tries to drive high. Device damage may be plausible. | A |
| GPIO0 configured as digital input: GPIO0 stuck low. Readback value of GPIO0 will be 0b. | B | ||
| GPIO1 | 30 | GPIO1 configured as digital output: GPIO1 stuck low. Increase in supply current when GPIO1 tries to drive high. Device damage may be plausible. | A |
| GPIO1 configured as digital input: GPIO1 stuck low. Readback value of GPIO1 will be 0b. | B |
Table 4-3 Pin FMA for Device Pins
Open-Circuited
| Pin Name | Pin No. | Description of Potential Failure Effect(s) | Failure Effect Class |
|---|---|---|---|
| GPIO2 | 1 | GPIO2 configured as digital output: No logic signaling between GPIO2 and external circuit possible. Otherwise normal operation. | B |
| GPIO2 configured as digital input: Readback value of GPIO2 will be unknown. | B | ||
| GPIO3 | 2 | GPIO3 configured as digital output: No logic signaling between GPIO3 and external circuit possible. Otherwise normal operation. | B |
| GPIO3 configured as digital input: Readback value of GPIO3 will be unknown. | B | ||
| REFM | 3 | Incorrect conversion result for all channels. The ADC reference will connect to ground internally through REFM pin ESD diode. Increased gain error for all channels due to reference voltage drop across ESD diode. | B |
| REFP | 4 | Incorrect and unknown conversion result for all channels. Unknown reference voltage to the ADC. The reference circuit may power-up through internal circuit to Power. | B |
| +VA | 5 | Device functionality unknown. Device unpowered and not
functional if all external analog pins are held low. Observe that
the absolute maximum ratings for all pins of the device are met,
otherwise device damage may be plausible. Device may power up through internal ESD diodes to +VA if voltages above the device's power-on reset threshold are present on any of the analog pins. | A |
| AGND | 6 | Device functionality unknown. Device may be unpowered or connect to ground internally through alternate pin ESD diode and power up. | B |
| MXO | 7 | External amplifier used between MXO and AINP: Multiplexer's analog inputs CH7-CH0 cannot be connected to the external amplifier's input. Conversion results for all channels will depend on the output voltage of the amplifier driving AINP. | B |
| MXO directly connected to AINP: Multiplexer's analog inputs CH7-CH0 cannot be connected to the ADC's input. Conversion results for all channels will be unknown. | B | ||
| AINP | 8 | Conversion results for all channels will be unknown. | B |
| AINM | 9 | Conversion results for all channels will be unknown. | B |
| AGND | 10 | Device functionality unknown. Device may be unpowered or connect to ground internally through alternate pin ESD diode and power up. | B |
| CH7 | 11 | Conversion result for this analog input channel will be unknown. | B |
| CH6 | 12 | Conversion result for this analog input channel will be unknown. | B |
| CH5 | 13 | Conversion result for this analog input channel will be unknown. | B |
| CH4 | 14 | Conversion result for this analog input channel will be unknown. | B |
| NC | 15 | No effect. Normal operation. | D |
| NC | 16 | No effect. Normal operation. | D |
| CH3 | 17 | Conversion result for this analog input channel will be unknown. | B |
| CH2 | 18 | Conversion result for this analog input channel will be unknown. | B |
| CH1 | 19 | Conversion result for this analog input channel will be unknown. | B |
| CH0 | 20 | Conversion result for this analog input channel will be unknown. | B |
| +VA | 21 | Device functionality unknown. Device unpowered and not
functional if all external analog pins are held low. Observe that
the absolute maximum ratings for all pins of the device are met,
otherwise device damage may be plausible. Device may power up through internal ESD diodes to +VA if voltages above the device's power-on reset threshold are present on any of the analog pins. | A |
| AGND | 22 | Device functionality unknown. Device may be unpowered or connect to ground internally through alternate pin ESD diode and power up. | B |
| CS | 23 | State of CS undetermined. No SPI communication with the device possible. | B |
| SCLK | 24 | State of SCLK undetermined. No SPI communication with the device possible. | B |
| SDI | 25 | State of SDI undetermined. Device configuration cannot be modified. Device will remain in previously configured state until reset condition occurs. Device will remain in default configuration after power-up. | B |
| SDO | 26 | No data readback possible from the device. | B |
| BDGND | 27 | Device functionality unknown. Digital interface may be unpowered or power up internally through alternate pin ESD diode to Ground. SPI communication may not be possible with the device. | B |
| +VBD | 28 | Digital interface not powered up if all external
digital pins are held low. No SPI communication with device
possible. Observe that the absolute maximum ratings for all pins of
the device are met, otherwise device damage may be plausible. Digital interface may power up through internal ESD diodes to DVDD if voltages above the device's power-on reset threshold are present on any of the digital pins. | A |
| GPIO0 | 29 | GPIO0 configured as digital output: No logic signaling between GPIO0 and external circuit possible. Otherwise normal operation. | B |
| GPIO0 configured as digital input: Readback value of GPIO0 will be unknown. | B | ||
| GPIO1 | 30 | GPIO1 configured as digital output: No logic signaling between GPIO1 and external circuit possible. Otherwise normal operation. | B |
| GPIO1 configured as digital input: Readback value of GPIO1 will be unknown. | B |
Table 4-4 Pin FMA for Device Pins
Short-Circuited to Adjacent Pin
| Pin Name | Pin No. | Shorted to | Description of Potential Failure Effect(s) | Failure Effect Class |
|---|---|---|---|---|
| GPIO2 | 1 | GPIO3 | GPIO2 configured as digital output and GPIO3 as digital output: Output voltage level unknown. Increase in supply current when GPIO2 tries to drive low and GPIO3 tries to drive high and vice versa. Device damage may be plausible. | A |
| GPIO2 configured as digital output and GPIO3 as digital input: Readback value of GPIO3 will depend on the output drive on GPIO2. | B | |||
| GPIO2 configured as digital input and GPIO3 as digital output: Readback value of GPIO2 will depend on the output drive on GPIO3. | B | |||
| GPIO2 configured as digital input and GPIO3 as digital input: Readback value of GPIO2 and GPIO3 will be the same. | B | |||
| GPIO3 | 2 | REFM | GPIO3 configured as digital output: GPIO3 stuck low. Increase in supply current when GPIO3 tries to drive high. Device damage may be plausible. | A |
| GPIO3 configured as digital input: GPIO3 stuck low. Readback value of GPIO3 will be 0b. | B | |||
| REFM | 3 | REFP | Incorrect conversion result for all channels. Conversion result will be close to 0x3FF for all channels. Reference voltage to the ADC will be 0 V as REFP = REFM = Ground. | B |
| REFP | 4 | +VA | Incorrect conversion result for all channels. Higher gain error for all channels because reference to the ADC is different from the intended REFP voltage. Reference voltage out of specification in case +VA > 3 V. | B |
| +VA | 5 | AGND | Device unpowered and not functional. Observe that the absolute maximum ratings for all pins of the device are met, otherwise device damage may be plausible. | A |
| AGND | 6 | MXO | Conversion results for all channels will be close to 0x000. Multiplexer's analog inputs CH7-CH0 will be connected to Ground through MXO. Increase in current sourced from the analog inputs. | B |
| MXO | 7 | AINP | External amplifier used between MXO and AINP: The external amplifier is bypassed. Increased gain error in conversion results if the external amplifier is configured for gain > 1. Conversion results for all channels may have higher error if there are ADC input settling errors when driving AINP directly with MXO. | B |
| MXO directly connected to AINP: No effect. Normal operation. | D | |||
| AINP | 8 | AINM | Conversion results for all channels will be close to 0x000. | B |
| AINM | 9 | AGND | No effect. Normal operation. | D |
| AGND | 10 | CH7 | Conversion result for CH7 will be close to 0x000. | B |
| CH7 | 11 | CH6 | Conversion results for CH7 and CH6 will be the same. The conversion results may be incorrect depending on the external drive circuits. | B |
| CH6 | 12 | CH5 | Conversion results for CH6 and CH5 will be the same. The conversion results may be incorrect depending on the external drive circuits. | B |
| CH5 | 13 | CH4 | Conversion results for CH5 and CH4 will be the same. The conversion results may be incorrect depending on the external drive circuits. | B |
| CH4 | 14 | NC | No effect. Normal operation. | D |
| NC | 15 | – | Not considered. Corner pin. | – |
| NC | 16 | CH3 | No effect. Normal operation. | D |
| CH3 | 17 | CH2 | Conversion results for CH3 and CH2 will be the same. The conversion results may be incorrect depending on the external drive circuits. | B |
| CH2 | 18 | CH1 | Conversion results for CH2 and CH1 will be the same. The conversion results may be incorrect depending on the external drive circuits. | B |
| CH1 | 19 | CH0 | Conversion results for CH1 and CH0 will be the same. The conversion results may be incorrect depending on the external drive circuits. | B |
| CH0 | 20 | +VA | Device configured for range 1: Conversion result for this analog input channel will be close to 0x3FF. | B |
| Device configured for range 2: Conversion result for this analog input channel will correspond to (+VA / (2xVREF)) * 1023. | B | |||
| +VA | 21 | AGND | Device unpowered and not functional. Observe that the absolute maximum ratings for all pins of the device are met, otherwise device damage may be plausible. | A |
| AGND | 22 | CS | CS stuck low. No SPI communication with the device possible. | B |
| CS | 23 | SCLK | SPI communication corrupted. No SPI communication with the device possible. | B |
| SCLK | 24 | SDI | SPI communication corrupted. No SPI communication with the device possible. | B |
| SDI | 25 | SDO | SPI communication corrupted. No SPI communication with
the device possible. Increase in supply current when host tries to drive SDI low while device tries to drive SDO high and vice versa. Device damage may be plausible. | A |
| SDO | 26 | BDGND | SDO stuck low. No data readback possible from the device. Increase in supply current when device tries to drive SDO high. Device damage may be plausible. | A |
| BDGND | 27 | +VBD | Digital interface not powered up. No SPI communication with device possible. Observe that the absolute maximum ratings for all pins of the device are met, otherwise device damage may be plausible. | A |
| +VBD | 28 | GPIO0 | GPIO0 configured as digital output: GPIO0 stuck high. Increase in supply current when GPIO0 tries to drive low. Device damage may be plausible. | A |
| GPIO0 configured as digital input: GPIO0 stuck high. Readback value of GPIO0 will be 1b. | B | |||
| GPIO0 | 29 | GPIO1 | GPIO0 configured as digital output and GPIO1 as digital output: Increase in supply current when GPIO0 tries to drive low and GPIO1 tries to drive high and vice versa. Device damage may be plausible. | A |
| GPIO0 configured as digital output and GPIO1 as digital input: Readback value of GPIO1 will depend on the output drive on GPIO0. | B | |||
| GPIO0 configured as digital input and GPIO1 as digital output: Readback value of GPIO0 will depend on the output drive on GPIO1. | B | |||
| GPIO0 configured as digital input and GPIO1 as digital input: Readback value of GPIO0 and GPIO1 will be the same. | B | |||
| GPIO1 | 30 | - | Not considered. Corner pin. | D |
Table 4-5 Pin FMA for Device Pins
Short-Circuited to
supply
| Pin Name | Pin No. | Description of Potential Failure Effect(s) | Failure Effect Class |
|---|---|---|---|
| GPIO2 | 1 | GPIO2 configured as digital output: GPIO2 stuck high. Increase in supply current when GPIO2 tries to drive low. Device damage may be plausible. | A |
| GPIO2 configured as digital input: GPIO2 stuck high. Readback value of GPIO2 will be 1b. | B | ||
| GPIO3 | 2 | GPIO3 configured as digital output: GPIO3 stuck high. Increase in supply current when GPIO3 tries to drive low. Device damage may be plausible. | A |
| GPIO3 configured as digital input: GPIO3 stuck high. Readback value of GPIO3 will be 1b. | B | ||
| REFM | 3 | Incorrect conversion result for all channels. The ADC reference will connect to ground internally through REFM pin ESD diode. Increased gain error for all channels due to reference voltage drop across ESD diode. Increase in supply current through ESD to Ground from REFM pin. Device damage may be plausible. | A |
| REFP | 4 | Incorrect conversion result for all channels. Higher gain error for all channels because reference to the ADC is different from the intended REFP voltage. Reference voltage out of specification in case +VA > 3 V. | B |
| +VA | 5 | No effect. Normal operation. | D |
| AGND | 6 | Device unpowered and not functional. Observe that the absolute maximum ratings for all pins of the device are met, otherwise device damage may be plausible. | A |
| MXO | 7 | Multiplexer's analog inputs
CH7-CH0 will be connected to Power through MXO. Increase in current
sinked by the external circuits driving the analog inputs.
|
B |
| AINP | 8 | If MXO is directly
connected to AINP, multiplexer's analog inputs CH7-CH0 will be
connected to Power through MXO and there will be increase in current
sinked by the external circuits driving the analog inputs.
|
B |
| AINM | 9 | Conversion result for all channels will be close to 0x000. | B |
| AGND | 10 | Device unpowered and not functional. Observe that the absolute maximum ratings for all pins of the device are met, otherwise device damage may be plausible. | A |
| CH7 | 11 | Device configured for range 1: Conversion result for this analog input channel will be close to 0x3FF. | B |
| Device configured for range 2: Conversion result for this analog input channel will correspond to (+VA / (2xVREF)) * 1023. | |||
| CH6 | 12 | Device configured for range 1: Conversion result for this analog input channel will be close to 0x3FF. | B |
| Device configured for range 2: Conversion result for this analog input channel will correspond to (+VA / (2xVREF)) * 1023. | |||
| CH5 | 13 | Device configured for range 1: Conversion result for this analog input channel will be close to 0x3FF. | B |
| Device configured for range 2: Conversion result for this analog input channel will correspond to (+VA / (2xVREF)) * 1023. | |||
| CH4 | 14 | Device configured for range 1: Conversion result for this analog input channel will be close to 0x3FF. | B |
| Device configured for range 2: Conversion result for this analog input channel will correspond to (+VA / (2xVREF)) * 1023. | |||
| NC | 15 | No effect. Normal operation. | D |
| NC | 16 | No effect. Normal operation. | D |
| CH3 | 17 | Device configured for range 1: Conversion result for this analog input channel will be close to 0x3FF. | B |
| Device configured for range 2: Conversion result for this analog input channel will correspond to (+VA / (2xVREF)) * 1023. | |||
| CH2 | 18 | Device configured for range 1: Conversion result for this analog input channel will be close to 0x3FF. | B |
| Device configured for range 2: Conversion result for this analog input channel will correspond to (+VA / (2xVREF)) * 1023. | |||
| CH1 | 19 | Device configured for range 1: Conversion result for this analog input channel will be close to 0x3FF. | B |
| Device configured for range 2: Conversion result for this analog input channel will correspond to (+VA / (2xVREF)) * 1023. | |||
| CH0 | 20 | Device configured for range 1: Conversion result for this analog input channel will be close to 0x3FF. | B |
| Device configured for range 2: Conversion result for this analog input channel will correspond to (+VA / (2xVREF)) * 1023. | |||
| +VA | 21 | No effect. Normal operation. | D |
| AGND | 22 | Device unpowered and not functional. Observe that the absolute maximum ratings for all pins of the device are met, otherwise device damage may be plausible. | A |
| CS | 23 | CS stuck high. No SPI communication with the device possible. SDO will be Hi-Z. | B |
| SCLK | 24 | SCLK stuck high. No SPI communication with the device possible. | B |
| SDI | 25 | SDI stuck high. Device configuration cannot be modified. Device will remain in previously configured state until reset condition occurs. Device will remain in default configuration after power-up. | B |
| SDO | 26 | SDO stuck high. No data readback possible from the device. Increase in supply current when device tries to drive SDO low. Device damage may be plausible. | A |
| BDGND | 27 | Device unpowered and not functional. Observe that the absolute maximum ratings for all pins of the device are met, otherwise device damage may be plausible. | A |
| +VBD | 28 | No effect. Normal operation. | D |
| GPIO0 | 29 | GPIO0 configured as digital output: GPIO0 stuck high. Increase in supply current when GPIO2 tries to drive low. Device damage may be plausible. | A |
| GPIO0 configured as digital input: GPIO0 stuck high. Readback value of GPIO0 will be 1b. | B | ||
| GPIO1 | 30 | GPIO1 configured as digital output: GPIO1 stuck high. Increase in supply current when GPIO1 tries to drive low. Device damage may be plausible. | A |
| GPIO1 configured as digital input: GPIO1 stuck high. Readback value of GPIO1 will be 1b. | B |