SBOU024C august   2004  – july 2023 PGA309

 

  1.   1
  2.   Read This First
    1.     About This Manual
    2.     Related Documentation from Texas Instruments
    3.     If You Need Assistance
    4.     Information About Cautions and Warnings
    5.     FCC Warning
    6.     Trademarks
  3. 1Introduction
    1. 1.1  PGA309 Functional Description
    2. 1.2  Sensor Error Adjustment Range
    3. 1.3  Gain Scaling
    4. 1.4  Offset Adjustment
    5. 1.5  Voltage Reference
    6. 1.6  Sensor Excitation and Linearization
    7. 1.7  ADC for Temperature Sensing
    8. 1.8  External EEPROM and Temperature Coefficients
    9. 1.9  Fault Monitor
    10. 1.10 Over-Scale and Under-Scale Limits
    11. 1.11 Power-Up and Normal Operation
    12. 1.12 Digital Interface
    13. 1.13 Pin Configuration
  4. 2Detailed Description
    1. 2.1  Gain Scaling
      1. 2.1.1 PGA309 Transfer Function
      2. 2.1.2 Solving For Gain Settings
    2. 2.2  Offset Scaling
    3. 2.3  Zero DAC and Gain DAC Architecture
    4. 2.4  Output Amplifier
    5. 2.5  Reference Voltage
    6. 2.6  Linearization Function
      1. 2.6.1 System Definitions
      2. 2.6.2 Key Linearization Design Equations
        1. 2.6.2.1 Lin DAC Counts Conversion
      3. 2.6.3 Key Ideal Design Equations
        1. 2.6.3.1 Linearization Design
        2.       37
    7. 2.7  Temperature Measurement
      1. 2.7.1 Temp ADC Start-Convert Control
      2. 2.7.2 External Temperature Sensing with an Excitation Series Resistor
    8. 2.8  Fault Monitor
    9. 2.9  Over-Scale and Under-Scale
      1. 2.9.1 Over-Scale and Under-Scale Calculation
      2.      44
    10. 2.10 Noise and Coarse Offset Adjust
    11. 2.11 General AC Considerations
  5. 3Operating Modes
    1. 3.1 Power-On Sequence and Normal Stand-Alone Operation
    2. 3.2 EEPROM Content and Temperature Lookup Table Calculation
      1. 3.2.1 Temperature Lookup Table Calculation
        1. 3.2.1.1 Temperature Lookup Table Calculation
        2.       52
        3.       53
    3. 3.3 Checksum Error Event
    4. 3.4 Test Pin
    5. 3.5 Power-On Initial Register States
      1. 3.5.1 PGA309 Power-Up State
  6. 4Digital Interface
    1. 4.1  Description
    2. 4.2  Two-Wire Interface
      1. 4.2.1 Device Addressing
      2. 4.2.2 Two-Wire Access to PGA309
    3. 4.3  One-Wire Interface
    4. 4.4  One-Wire Interface Timeout
    5. 4.5  One-Wire Interface Timing Considerations
    6. 4.6  Two-Wire Access to External EEPROM
    7. 4.7  One-Wire Interface Initiated Two-Wire EEPROM Transactions
    8. 4.8  PGA309 Stand-Alone Mode and Two-Wire Transactions
    9. 4.9  PGA309 Two-Wire Bus Master Operation and Bus Sharing Considerations
    10. 4.10 One-Wire Operation with PRG Connected to VOUT
    11. 4.11 Four-Wire Modules and One-Wire Interface (PRG)
  7. 5Application Background
    1. 5.1 Bridge Sensors
    2. 5.2 System Scaling Options for Bridge Sensors
      1. 5.2.1 Absolute Scale
      2. 5.2.2 Ratiometric Scale
    3. 5.3 Trimming Real World Bridge Sensors for Linearity
    4. 5.4 PGA309 Calibration Procedure
  8. 6Register Descriptions
    1. 6.1 Internal Register Overview
    2. 6.2 Internal Register Map
      1. 6.2.1 Register 0: Temp ADC Output Register (Read Only, Address Pointer = 00000)
      2. 6.2.2 Register 1: Fine Offset Adjust (Zero DAC) Register (Read/Write, Address Pointer = 00001)
      3. 6.2.3 Register 2: Fine Gain Adjust (Gain DAC) Register (Read/Write, Address Pointer = 00010)
      4. 6.2.4 Register 3: Reference Control and Linearization Register (Read/Write, Address Pointer = 00011)
      5. 6.2.5 Register 4: PGA Coarse Offset Adjust and Gain Select/Output Amplifier Gain Select Register (Read/Write, Address Pointer = 00100)
      6. 6.2.6 Register 5: PGA Configuration and Over/Under-Scale Limit Register (Read/Write, Address Pointer = 00101)
      7. 6.2.7 Register 6: Temp ADC Control Register (Read/Write, Address Pointer = 00110)
      8. 6.2.8 Register 7: Output Enable Counter Control Register (Read/Write, Address Pointer = 00111)
      9. 6.2.9 Register 8: Alarm Status Register (Read Only, Address Pointer = 01000)
  9.   A External EEPROM Example
    1.     A.1 PGA309 External EEPROM Example
      1.      A.1.1 Gain and Offset Scaling for External EEPROM
      2.      94
  10.   B Detailed Block Diagram
    1.     B.1 Detailed Block Diagram
  11.   C Glossary
  12.   Revision History

The resolution for the Temp ADC in Internal Temperature Mode is 0.0625°C/count.

For positive temperatures (for example, 20°C):

(20°C)/(0.0625°C/count) = 320 → 140h → 0001 0100 0000

Twos Complement is not performed on positive numbers. Simply convert the number to binary code with 16-bit, right-justified format, and MSB = ‘0’ to denote a positive sign. Extend the sign to the upper 4 bits.

20°C will be read by the Temp ADC as 0000 0001 0100 0000 → 140h

For negative temperatures (that is, −20°C):

(|−20|)/(0.0625°C/count) = 320 → 140h → 0001 0100 0000

Generate the Twos Complement of a negative number by complementing the absolute value binary number and adding 1. Extend the sign, denoting a negative number by MSB = ‘1’. Extend the sign to the upper 4 bits to form the 16-bit word.

−20°C will be read by the Temp ADC as 1111 1110 1100 0000 → FEC0h.

Step 2:

Calculate Gain DAC temperature coefficients using Table 3-3.

For the Gain DAC desired counts (that is, G3 = 0.4):

Gx = (GainDESIRED − 1/3)(3/2)(65536)
G3 = (0.4 − 1/3)〈3/2)(65536) = 6553.6
0 ≤ Gx ≤ 65535
0.3333333 ≤ Gain DAC ≤ 0.9999898

For positive slopes (that is, GM5):

GM5 = [(G5 − G4)/(T5 − T4)][256]
GM5 = [(26214 − 7537)/(160 − 0)][256] = 29883.2
Integer [29883.2] = 29883
GM5 =29883 → 74BBh → 0111 0100 1101 1101
The allowed range for GM is: -32768 ≤ GM ≤ +32767 (16 bit signed integer)

For negative slopes (that is, GM2):

GM2 = [(G2 − G1)/(T2 − T1)][256]
GM2 = [(36044.8 − 55706)/(−320 − {−480})][256] = −31457.28
Integer [−31457.9] = −31457
Generate the Twos Complement of −31458:
GM2 = 851Eh → 1000 0101 0001 1110
The allowed range for GM is: -32768 ≤ GM ≤ +32767 (16 bit signed integer)

Note: Gain DAC Slopes

If the Gain DAC slope computes to a count > 65535, there is a problem. The Temp ADC must be reconfigured for lower resolution or the number of points in the Lookup Table must be increased to bring the slopes within the PGA309 computation region.

Table 3-3 Gain DAC Temperature Coefficient Calculation
Temp
(°C)		 Temp Index Temp ADC
(Counts)		 Gain DAC Desired Value Gain DAC Desired Index Gain DAC Desired
(Counts)		 Gain DAC Slope Gain DAC Slope Formula Gain DAC Slope(1)
(Counts)		 Gain DAC Slope
(Hex)
−40 T0 −640 1 G0 65535 G0 G0 = G0 65535 FFFF
−30 T1 −480 0.9 G1

55706

 GM1 GM1 = [(G1 − G0)/T1 − T0)][256]

-15726

 C292
−20 T2 −320 0.7 G2

36045

 GM2 GM2 = [(G2 − G1)/T2 − T1)][256]

-31458

851E
−10 T3 −160 0.55 G3

21299

 GM3 GM3 = [(G3 − G2)/T3 − T2)][256]

-23594

A3D6
0 T4 0 0.41 G4

7537

 GM4 GM4 = [(G4 − G3)/T4 − T3)][256]

-22019

A9FD
10 T5 160 0.6 G5

26214

 GM5 GM5 = [(G5 − G4)/T5 − T4)][256]

29883

74BB
20 T6 320 0.4756 G6

13985

 GM6 GM6 = [(G6 − G5)/T6 − T5)][256]

-19566

B392
30 T7 480 0.6543 G7

31552

 GM7 GM7 = [(G7 − G6)/T7 − T6)][256]

28107

6DCB
(1) Integer [Gain DAC Slope Formula]

Step 3:

Calculate Zero DAC temperature Coefficients using Table 3-4.

For the Zero DAC desired counts (for example, Z5 = 1.5):

Zx = (VZDESIRED/VREF)(65536)
Z5 = (1.5/5)(65536) = 19660.8
0 ≤ Zx ≤ 65535
0.1V ≤ Zero DAC Analog Range ≤ (VSA − 0.1V)
0V ≤ Zero DAC Programming Range ≤ VREF

For positive slopes (for example, ZM4):

ZM4 = [(Z4 − Z3)/(T4 − T3)][256]
ZM4 = [(26214.4 − 13107.2)/(0 − {−160})][256] = 20971.52
Integer [20971.52] = 20972
ZM4 = 20972 → 51ECh → 0101 0001 1110 1101
The allowed range for ZM is: -32768 ≤ ZM ≤ +32767 (16 bit signed integer)

For negative slopes (for example, ZM6):

ZM6 = [(Z6 − Z5)/(T6 − T5)][256]
ZM6 = [(13107.2 − 19660.8)/(320 − 160)][256] = −10485.76
Integer [−10485.76] = −10486
Generate the Twos Complement of −10486:
ZM6 = D70Ah → 1101 0111 0000 1010
The allowed range for ZM is: -32768 ≤ ZM ≤ +32767 (16 bit signed integer)

Note: Zero DAC Slopes outside allowed range

If the Zero DAC slope computes to a count outside the range -32768 < ZM < +32767, there is a problem. The Temp ADC must be reconfigured for lower resolution or the number of points in the Lookup Table must be increased to bring the slopes within the PGA309 computation region.

Table 3-4 Zero DAC Temperature Coefficient Calculation
Temp
(°C)		 Temp
Index		 Temp ADC
(Counts)		 Zero DAC Desired Value Zero DAC Desired Index Zero DAC Desired
(Counts)		 Zero DAC Slope Zero DAC Slope Formula Zero DAC Slope(1)
(Counts)		 Zero DAC Slope
(Hex)
−40 T0 −640 0.1 Z0 1310.7 Z0 Z0 = Z0 1311 051E
−30 T1 −480 0.2 Z1 2621.4 ZM1 ZM1 = [(Z1 − Z0)/T1 − T0)][256] 2097 0831
−20 T2 −320 1 Z2 13107.2 ZM2 ZM2 = [(Z2 − Z1)/T2 − T1)][256] 16777 4189
−10 T3 −160 1 Z3 13107.2 ZM3 ZM3 = [(Z3 − Z2)/T3 − T2)][256] 0 0000
0 T4 0 2 Z4 26214.4 ZM4 ZM4 = [(Z4 − Z3)/T4 − T3)][256] 20972 51EC
10 T5 160 1.5 Z5 19660.8 ZM5 ZM5 = [(Z5 − Z4)/T5 − T4)][256] −10486

D70A
20 T6 320 1 Z6 13107.2 ZM6 ZM6 = [(Z6 − Z5)/T6 − T5)][256] −10486

D70A
30 T7 480 2 Z7 26214.4 ZM7 ZM7 = [(Z7 − Z6)/T7 − T6)][256] 20972 51EC
(1) Integer [Zero DAC Slope Formula]

Step 4:

Assemble the Lookup Table, as shown in Table 3-5.

Table 3-5 Lookup Table Contents
Temp
(°C)		 Temp
Index		 Zero DAC
Slope		 Gain DAC
Slope		 EEPROM Tx
(Hex)		 EEPROM ZMi
(Hex)		 EEPROM GMi
(Hex)
−40 T0 Z0 G0 FD80 051E FFFF
−30 T1 ZM1 GM1 FE20 0831 C292
−20 T2 ZM2 GM2 FEC0 4189 851E
−10 T3 ZM3 GM3 FF60 0000 A3D6
0 T4 ZM4 GM4 0000 51EC A9FD
10 T5 ZM5 GM5 00A0 D70A 74BB
20 T6 ZM6 GM6 0140 D70A B392
30 T7 ZM7 GM7 01E0 51EC 6DCB
— TEND ZMEND GMEND 7FFF 0000 B5D8

Use the calculated values from Step 2 and Step 3.

Set TMEND to 7FFFh to indicate the end of the Lookup Table.

Set ZMEND to 0000h.

Calculate GMEND as Checksum2 (truncate results above 16-bit):

GMEND = Checksum2 = FFFFh − sum(Hex values of all entries in the Lookup Table except GMEND)
GMEND = FFFFh − C49DDh
GMEND = FFFFF4B622h
GMEND = Checksum2 = B622h

Step 5:

Calculate Ideal value for Gain DAC at TREAD = +25°C using Table 3-6.

Table 3-6 Gain DAC vs Temperature
Tx Temp (°C) Gx Gain DAC
T0 −40 G0 1
T1 −30 G1 0.9
T2 −20 G2 0.7
T3 −10 G3 0.4
T4 0 G4 0.3333
T5 10 G5 0.6
T6 20 G6 0.4756
TREAD 25 GREAD Calculated
T7 30 G7 0.6543

Linear Interpolation for Gain DAC (TREAD = 25°C):

GREAD = {[(G7 − G6)/(T7 − T6)] [TREAD − T6]} + G6
GREAD = {[(0.6543 − 0.4756)/(30 − 20)] [25 − 20]} +0.4756
GREAD = 0.56495

Step 6:

Reference calculation algorithm for Gain DAC using Lookup Table.

Table 3-7 outlines the calculation algorithm used inside the PGA309 for linear interpolation and calculation of the Gain DAC setting for TREAD = 25°C. From Table 3-3 the computations for GM1-GM7 at T1-T7, for given values at G1-G7, are known. In addition, the starting values (T0 and G0) were defined. Step 5 shows the Actual Gain DAC value for TREAD = 25°C should be 0.56495 V/V if the linear interpolation part of the calculation algorithm is working properly.

Table 3-7 Gain DAC Lookup Table Calculation Algorithm
Temp
(°C)		 Tx Temp
ADC
(Counts)		 GMi Gain DAC
Slope(1)
(Counts)		 GAC Calculation Running
GAC Value(1)
(Counts)		 Actual Gain
DAC (V/V)
−40 T0 −640 G0 65535 GAC0 = G0 65535 0.9999898
−30 T1 −480 GM1 −15727 GAC1 = GAC0 + [GM1(T1 − T0)/256] 55706 0.9000041
−20 T2 −320 GM2 −31457 GAC2 = GAC1 + [GM2(T2 − T1)/256] 36045 0.7000020
−10 T3 −160 GM3 −47104 GAC3 = GAC2 + [GM3(T3 − T2)/256] 6605 0.4005229
0 T4 0 GM4 −10496 GAC4 = GAC3 + [GM4(T4 − T3)/256] 45 0.3337911
10 T5 160 GM5 41943 GAC5 = GAC4 + [GM5(T5 − T4)/256] 26259 0.6004537
20 T6 320 GM6 −19566 GAC6 = GAC5 + [GM6(T6 − T5)/256] 14030 0.4760539
30 T7 480 GM7 28107 T7 > TREAD → YES! — —
25 TREAD 400 — — GAC_TREAD = GAC6 + [GM7(TREAD − T6)/256] 22813 0.565399169
— TEND 32767 (7FFFh) — — The Lookup Table is read to the end to verify Checksum2 — —
(1) Integer [GAC Calculation]

Each time the Temp ADC does a conversion, it reads the entire external EEPROM. The first part of the EEPROM is dedicated to fixed setup parameters for the PGA309 that do not change with temperature. As the PGA309 reads the second half of the EEPROM, it begins a running calculation of the Gain DAC setting with temperature (the PGA309 runs a similar calculation for the Zero DAC setting). The model in Table 3-7 includes an accumulator named GAC (G Accumulator). When the PGA309 reads T0, the initial Gain DAC setting (G0) is stored in GAC0 (GAC at T0READ). Next, T1 is read and slope GM1 is multiplied by the difference between T1 and T0 (a scale divisor of 256 is used to convert back to decimal counts for our model) and added to GAC0 to form the new accumulator value, GAC1 (GAC at T1READ). This process continues in a sequential fashion as the PGA309 reads through the entire Lookup Table. As each temperature index value (Tx) is read, it is compared against TREAD, the current Temp ADC conversion result. If Tx > TREAD, it is known that TREAD is between Tx and T(x − 1). In this example, it occurs after T7 is read. The accumulator contents, GAC6 (GAC at T6), are modified by the addition of (TREAD − T6)(GM7). The resulting GAC_TREAD is the linearly interpolated setting for the Gain DAC at TREAD = 25°C. The actual Gain DAC value is slightly different than the theoretical value calculated in Step 5 due to Gain DAC resolution and computation rounding. The rest of the EEPROM is read through TEND for error checking with Checksum2 at the end of the Lookup Table. If Checksum2 is valid then the Gain DAC is updated with the computed value GAC_TREAD = 0.565399169.

GAC Calculation (for example, GAC2):

GAC1 = 55706; GM2 = −31457; T2 = −320; T1 = −480
GAC2 = GAC1 + [GM2(T2 − T1)/256]
GAC2 = 55706 + [−31457(−320−{−480})/256] = 36045.375
Integer [GAC2] = Integer [36045.375] = 36045
GAC2 = 36045

Actual Gain DAC (for example, GAC2):

GAC2 = 36045
Gain DAC = [(GACx/65536)(2/3)] + 1/3
Gain DAC = [(36045 / 65536)(2/3)] + 1/3 = 0.7000020
Gain DAC at GAC2 = 0.7000020