ams TMD2755 Temperature Sensor Function
Introduction
The purpose of this document is to describe TMD2755 registers that are related to the temperature sensor functionality and how to use them correctly. These registers are not published in the TMD2755 datasheet.
Register Descriptions
Settings for the Temperature Sensor
CFG1 Register (0x91) Bit 7
enab_temp_sensor (Bit7)
Access RW
Description: Enable or disable the comparator for temp sensor
Default 0: Disable temp sensor comparator
Set to 1: Enable temp sensor comparator
ADCCFG Register (0xBF) Bit [1:0]
adc_sel (Bit [1:0])
Access RW
Description: ADC input selection
Default 0: ADC input path for normal prox operation
Set to 1: ADC input path for temp sensor
ADCCFG Register (0xBF) Bit [3:2]
adc_settling (Bit [3:2])
Access RW
Description: ADC settling time selection
Default 1: 2 µs for normal prox operation
Set to 3: 8 µs for temp sensor
CALIB Register (0xD7) Bit 1
start_adc (Bit 1)
Access WS_SC (Write to start self clearing)
Description: Manually start ADC conversion
Default 0: No manual ADC start
Set to 1: Manually start ADC conversion for temp sensor (ADC conversion is automatic for prox when PEN is enabled)
Recommended Sequences in SW Driver
In some applications, there is a need to get the chip temperature information by reading out temp sensor ADCs periodically. At each time of setting up temp sensor and reading 10-bit temp ADCs from PDATA registers, the ongoing prox operation is affected. The sequences in the SW driver have to be optimized to reduce turnaround time, and avoid unwanted prox related interrupts if it operates in interrupt mode.
Sequences from Prox to Temp Sensor
Figure 1 below shows a recommended sequence from normal prox operation to temp sensor operation. The minimum lengths of the timers required are related to some of the prox configurations being used in an application.
Figure 1:
Sequences from Prox to Temp Sensor
| Sequence Step | Actions/States | Notes |
| 0 | Ongoing prox operation | |
| 1 | Disable PEN | Enable Register (x80) |
| 2 | Start timer1 | |
| 3 | Timer1 expires | |
| 4 | Disable prox-related INTs | INTENAB Register (0xDD) |
| 5 | Clear prox-related flags | STATUS Register (0x94) |
| 6 | Disable PWEN | Enable Register (x80) |
| 7 | Disable hw prox_avg | CALIBCFG Register (0xD9) |
| 8 | Set enab_temp_sensor bit to 1 | CFG1 Register (0x91) Bit 7 |
| 9 | Set adc_sel to 1 | ADCCFG Register (0xBF) Bit [1:0] |
| 10 | Set adc_settling to 3 (8µs) | ADCCFG Register (0xBF) Bit [3:2] |
| 11 | Set start_adc bit to 1 | CALIB Register (0xD7) Bit 1 |
| 12 | Start timer2 | |
| 13 | Timer2 expires | |
| 14 | Read 10-bit temp ADC from Pdata registers | Pdata Registers 0x99 and 0x9A |
Sequences from Temp Sensor to Prox
Figure 2 below shows a recommended sequence from temp sensor operation to prox operation. The minimum lengths of the timer required are related to some of the prox configurations being used in an application.
Figure 2:
Sequences from Temp Sensor to Prox
| Sequence Step | Actions/States | Notes |
| 0 | Temp sensor option just finished | |
| 1 | Set enab_temp_sensor bit to 0 | CFG1 Register (0x91) Bit 7 |
| 2 | Set adc_sel to 0 | ADCCFG Register (0xBF) Bit [1:0] |
| 3 | Set adc_settling to 1 (2µs) | ADCCFG Register (0xBF) Bit [3:2] |
| 4 | Clear prox-related flags | STATUS Register (0x94) |
| 5 | Enable prox-related INTs | INTENAB Register (0xDD) |
| 6 | Set hw prox_avg to its original setting | CALIBCFG Register (0xD9) |
| 7 | Enable PWEN | Enable Register (x80) |
| 8 | Enable PEN | Enable Register (x80) |
| 9 | Start timer | |
| 10 | Timer expires | |
| 11 | First valid Pdata available. Prox now running | Pdata Registers 0x99 and 0x9A |
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