JAJSLP2A august 2021 – july 2023 AFE439A2 , AFE539A4 , AFE639D2
PRODUCTION DATA
This design example uses the TPS63020, a buck-boost converter, and connects the TEC element between the VIN and VOUT nodes to create bidirectional voltage control of the TEC element. The control voltage to the TPS63020 must be between 0 V and 1.8 V to achieve the full range of TEC current. As shown in Figure 8-1, the temperature is measured using the LMT70, a high-precision, analog temperature sensor. The LMT70 provides a voltage output between 1.38 V and 300 mV for the temperature range of –55ºC to +125ºC. Therefore, configure the PI controller output (DAC1) with the internal reference and a gain of 1.5 ×. Similarly, configure ADC0 to be in Hi-Z input mode (ADC-MODE = 0), with the internal reference, and 4 × gain. This configuration sets ADC0 at a full-scale input (VFS) range of (1.21 V × 4) / 3 = 1.613 V. With 10-bit resolution, 1 LSB of ADC0 code corresponds to (1.613 V / 1024) = 1.58 mV. The response slope of the LMT70 at 30ºC is 5.194 mV/ºC. Therefore, 1 LSB of the ADC0 corresponds to (1.58 / 5.194) = 0.3ºC.
The voltage output of the LMT70 corresponding to the temperature set point of 30ºC is 943.227 mV. Using Equation 4, calculate the SETPOINT input as 598d (0x256). For negative feedback, use an odd number of phase inversions in the feedback loop. The DAC1 output to the TPS63020 output has one phase inversion; the TPS63020 decreases when the DAC1 output increases. The TPS63020 output and the TEC cold-side temperature have the second phase inversion; the TEC cold-side temperature decreases when the TPS63020 output increases. The TEC cold-side and the LMT70 have the third phase inversion; when the TEC cold-side temperature decreases, the LMT70 output voltage increases. The external loop of the AFEx39xx has an odd number of phase inversions; therefore, make sure that the internal PI control loop has no phase inversion. To prevent the phase inversion, configure LOOP-POLARITY = 1. Choose the values of RF and CF in Figure 8-1 based on the noise level present in the sensing circuit.
When the output of the comparator is low, the PI controller output enters safe mode. Therefore, the current sense amplifier and the comparator setting must be configured to trigger fallback mode at the desired TEC current limit.
Follow the procedure described in Section 7.4.6.2 to configure the parameters listed in Table 8-37.
REGISTER FIELD NAME | STATIC ADDRESS | STATIC ADDRESS LOCATION | CONFIGURED VALUE (16-BIT) | DYNAMIC ADDRESS | DYNAMIC ADDRESS LOCATION |
---|---|---|---|---|---|
SETPOINT | 0x22[9:0] | SRAM | 0x0256 | 0x06[9:0] | Register |
KP | 0x23[15:0] | SRAM | 0x0FA0 | N/A | N/A |
KI | 0x26[15:0] | SRAM | 0x0001 | N/A | N/A |
MAX-OUTPUT | 0x20[15:6] | SRAM | 0xFFC0 | N/A | N/A |
MIN-OUTPUT | 0x21[15:6] | SRAM | 0x0000 | N/A | N/A |
COMMON-MODE | 0x25[11:2] | SRAM | 0x7FC0 | 0x0C[11:2] | Register |
LOOP-POLARITY | 0x27[0] | SRAM | 0x0001 | N/A | N/A |
FIXED-OUTPUT | 0x27[15:6] | SRAM | 0x0000 | N/A | N/A |
ADC-MODE | 0x27[1] | SRAM | 0x0002 | N/A | N/A |
CMP-THRESHOLD | 0x24[15:6] | SRAM | 0x7FC0 | N/A | N/A |