PG
A308
PGA308
PGA3
08
www.ti.com
SBOS440B – JULY 2008 – REVISED DECEMBER 2010
Single-Supply, Auto-Zero Sensor Amplifier
with Programmable Gain and Offset
Check for Samples: PGA308
FEATURES
DESCRIPTION
•
•
•
•
•
•
•
•
•
•
•
•
The PGA308 is a programmable analog sensor signal
conditioner. The analog signal path amplifies the
sensor signal and provides digital calibration for offset
and gain. Calibration is done via the 1W pin, a digital
One-Wire,
UART-compatible
interface.
For
three-terminal sensor modules, 1W may be
connected to VOUT and the assembly programmed
through the VOUT pin. Gain and offset calibration
parameters are stored onboard in seven banks of
one-time programmable (OTP) memory. The
power-on reset (POR) OTP bank may be
programmed a total of four times.
1
2
Digital Calibration for Bridge Sensors
Offset Select: Coarse and Fine
Gain Select: Coarse and Fine
Bridge Fault Monitor
Input Mux for Lead Swap
Over/Under Scale Limits
DOUT/ VOUT Clamp Function
Seven Banks OTP Memory
One-Wire Digital UART Interface
Operating Voltage: +2.7V to +5.5V
Temperature Range: –40°C to +125°C
MSOP-10 and 3mm × 4mm DFN-10 Packages
The all-analog signal path contains a 2×2 input
multiplexer (mux) to allow electronic sensor lead
swapping, a coarse offset adjust, an auto-zero
programmable gain instrumentation amplifier (PGA),
a fine gain adjust, a fine offset adjust, and a
programmable gain output amplifier. Fault monitor
circuitry detects and signals sensor burnout,
overload,
and
system
fault
conditions.
Over/under-scale limits provide additional means for
system level diagnostics. The dual-use DOUT/VCLAMP
pin can be used as a programmable digital output or
as a VOUT over-voltage clamp.
APPLICATIONS
•
•
•
•
Bridge Sensors
Remote 4-20mA Transmitters
Strain, Load, Weigh Scales
Automotive Sensors
EVALUATION TOOLS
•
PGA308EVM (Hardware and Software)
– Calibration and Configuration
– Sensor Emulation
For detailed application information, see the PGA308
User's Guide (SBOU069) available for download at
www.ti.com.
VREF
VS
VEXC
4
DOUT/VCLAMP
10
1
PGA308
Digital Interface
(One-Wire)
Fine Offset
RAM
3-Bit
DAC
Output Gain
VREF
VREF
OTP
(7 Banks)
Overscale
16-Bit
DAC
7-Bit + Sign
DAC
Ref(1)
8
7
VIN1
Output
Gain
Select
5
Input
Mux
Bridge
Sensor
VIN2
Fault
Monitor
Auto-Zero
PGA
6
1W
DOUT
Select
VREF
Coarse Offset
2
16-Bit
DAC
Output
Scale
Limit
Amplifier
9
VFB
VSJ
VOUT
Ref(1)
Fine Gain
3-Bit
DAC
Front-End
Gain Select
Underscale
3
GND
NOTE: (1) Ref = VREF or VS selectable.
1
2
Please be aware that an important notice concerning availability, standard warranty, and use in critical applications of Texas
Instruments semiconductor products and disclaimers thereto appears at the end of this data sheet.
All trademarks are the property of their respective owners.
PRODUCTION DATA information is current as of publication date.
Products conform to specifications per the terms of the Texas
Instruments standard warranty. Production processing does not
necessarily include testing of all parameters.
Copyright © 2008–2010, Texas Instruments Incorporated
PGA308
SBOS440B – JULY 2008 – REVISED DECEMBER 2010
www.ti.com
This integrated circuit can be damaged by ESD. Texas Instruments recommends that all integrated circuits be handled with
appropriate precautions. Failure to observe proper handling and installation procedures can cause damage.
ESD damage can range from subtle performance degradation to complete device failure. Precision integrated circuits may be more
susceptible to damage because very small parametric changes could cause the device not to meet its published specifications.
PACKAGE/ORDERING INFORMATION (1)
PRODUCT
PGA308
(1)
PACKAGE-LEAD
PACKAGE
DESIGNATOR
PACKAGE
MARKING
MSOP-10
DGS
P30A
3mm × 4mm DFN-10
DRK
P30B
For the most current package and ordering information see the Package Option Addendum at the end of this document, or see the TI
web site at www.ti.com.
ABSOLUTE MAXIMUM RATINGS (1)
Over operating free-air temperature range, unless otherwise noted.
PARAMETER
PGA308
UNIT
Supply Voltage, VS
+5.5
V
DOUT/VCLAMP Output Current Limit
±10
mA
–10 to +10
mA
GND – 0.3 to VS + 0.3
V
Input Current
VIN1, VIN2, VREF, 1W, DOUT/VCLAMP, VSJ
Pin Protection
(2)
VFB Terminal Voltage
–30 to 30
V
VFB Terminal Current
–10 to 10
mA
–160 to 160
mA
Operating Temperature Range
VOUT
–40 to +150
°C
Storage Temperature Range
–55 to +150
°C
Junction Temperature
+165
°C
ESD Ratings
2000
V
(1)
(2)
2
Human Body Model (HBM)
Stresses above these ratings may cause permanent damage. Exposure to absolute maximum conditions for extended periods may
degrade device reliability. These are stress ratings only, and functional operation of the device at these or any other conditions beyond
those specified is not implied.
Terminals are diode-clamped to the power-supply rails, VS and GND. Limit current to 10mA or less.
Submit Documentation Feedback
Copyright © 2008–2010, Texas Instruments Incorporated
Product Folder Link(s): PGA308
PGA308
www.ti.com
SBOS440B – JULY 2008 – REVISED DECEMBER 2010
ELECTRICAL CHARACTERISTICS
Boldface limits apply over the specified temperature range, TA = –40°C to +125°C.
At TA = +25°C, VS = +5V, GND = 0V, DOUT/VCLAMP = +5V, and VREF = +5V, unless otherwise noted.
PGA308
PARAMETER
VOUT/VIN Differential Signal Gains (1)
(Front-End PGA + Output Amplifier)
CONDITIONS
MIN
Front-End PGA gains (GF): 4, 6, 8, 12, 16, 32, 64, 100, 200,
400, 480, 600, 800, 960, 1200, 1600
Output Amplifier gains: 2, 2.4, 3, 3.6, 4, 4.5, 6
Fine Gain Adjust = 0.33 to 1
2.67
VOUT/VIN Slew Rate
(Front-End PGA + Output Amplifier)
VOUT/VIN Settling Time (0.01%FSR)
(Front-End PGA + Output Amplifier)
External Sensor Output Sensitivity
TYP
V/V
0.6
CMP_SEL [CFG1 register] = 1
0.3
VOUT/VIN differential gain = 8,
VOUT = +0.5V to +4.5V step, comp off, no capacitive load
13
VOUT/VIN differential gain = 200,
VOUT = +0.5V to +4.5V step, comp off, no capacitive load
15
VS = VREF = VCLAMP = +5V
UNIT
9600
CMP_SEL [CFG1 register] = 0
(2)
MAX
0.08
V/ms
V/ms
ms
ms
296
mV/V
FRONT-END PGA
Auto-Zero Internal Frequency
40
Offset Voltage (RTI) (3)
kHz
Coarse Offset Adjust disabled
±5
Coarse Offset Adjust disabled
±0.2
vs Supply Voltage, VS
Coarse Offset Adjust disabled
2 + 150/GF
10 + 1000/GF
mV/V
vs Common-Mode Voltage
GF = Front-End PGA gain,
Coarse Offset Adjust disabled
1 + 250/GF
10 + 2000/GF
mV/V
100
mV
vs Temperature
Offset Voltage Programming Range (RTI) (3)
Coarse Offset Adjust enabled,
Coarse Offset Adjust controls offset
vs Temperature
–100
±40
mV
mV/°C
Coarse Offset Adjust enabled
±0.2
mV/°C
vs Supply Voltage, VS
Coarse Offset Adjust enabled
2 + 150/GF
mV/V
vs Common-Mode Voltage
GF = Front-End PGA gain,
Coarse Offset Adjust enabled
1 + 250/GF
mV/V
Linear Input Voltage Range (4)
0.2
Input Bias Current
±0.3
vs Temperature
VS – 1.4
V
±1.5
nA
10
Input Offset Current
±0.1
vs Temperature
pA/°C
±1.5
nA
10
pA/°C
Input Impedance: Differential
30 ∥ 6
GΩ ∥ pF
Input Impedance: Common-Mode
50 ∥ 20
GΩ ∥ pF
Input Voltage Noise
Input Voltage Noise Density
Input EMI Filter Frequency
RTI, dc to 10Hz, GF = 100, RS = 0Ω
1.2
mVPP
RTI, voltage noise density, f = 1kHz, Coarse Offset Adjust =
0V
50
nV/√Hz
RTI, voltage noise density, f = 1kHz,
Coarse Offset Adjust = 100mV
80
nV/√Hz
Input EMI filter to GND, VIN1 and VIN2
40
MHz
f3dB
PGA Gain (5)
Gain Range Steps
4, 6, 8, 12, 16, 32, 64, 100, 200, 400, 480, 600, 800, 960,
1200, 1600
Initial Gain Error
4
GF ≤ 16
±0.03
±0.25
%
±0.1
±0.4
%
600 ≤ GF ≤ 1600
±0.3
±1
6
Output Voltage Range
(1)
(2)
(3)
(4)
(5)
V/V
32 ≤ GF ≤ 480
vs Temperature
Bandwidth
1600
0.05
%
ppm/°C
VS – 0.05
V
GF = 4
400
kHz
GF = 1600
10
kHz
PGA308 total differential gain from input (VIN1 – VIN2) to output (VOUT): VOUT / (VIN1 – VIN2) = (PGA gain) × (output amplifier gain) × (fine
gain adjust) with output amplifier internal gains used.
Based on bridge sensor excitation voltage of +5V and PGA308 output voltage span of 4V. Individual applications must consider noise,
small-signal bandwidth, and required system error to assess if the PGA308 will work for a given sensor sensitivity.
RTI = Referred-to-input.
Linear input range is the allowed min/max voltage on the VIN1 and VIN2 pins for the front-end PGA to continue to operate in a linear
region. The allowed common-mode and differential voltage depends on gain and offset settings. Refer to the PGA308 User's Guide
(SBOU069), for more information.
IREF current load is typically 100mA while in Shutdown mode. Although the output amplifier is disabled in Shutdown mode, RFO and
RGO (180kΩ typical total) remain connected in series between VFB and GND while in Shutdown mode. See Figure 37, Detailed Block
Diagram, for more information.
Submit Documentation Feedback
Copyright © 2008–2010, Texas Instruments Incorporated
Product Folder Link(s): PGA308
3
PGA308
SBOS440B – JULY 2008 – REVISED DECEMBER 2010
www.ti.com
ELECTRICAL CHARACTERISTICS (continued)
Boldface limits apply over the specified temperature range, TA = –40°C to +125°C.
At TA = +25°C, VS = +5V, GND = 0V, DOUT/VCLAMP = +5V, and VREF = +5V, unless otherwise noted.
PGA308
PARAMETER
CONDITIONS
MIN
VREF = +5V
–100
TYP
MAX
UNIT
+100
mV
Coarse Offset Adjust
(RTI of Front-End PGA) (6)
Range
Resolution
7 bit + sign, VREF = +5V
PSRR
CMRR
Drift
Coarse Offset Adjust = 100mV
1
mV
2
mV/V
1
mV/V
1.2
mV/°C
Fine Offset Adjust (Zero DAC)
Programming Range
RTO of Front-End PGA
Output Voltage Range
Resolution
–0.5VREF
+0.5VREF
0.1
VS – 0.1
65,536 steps, 16-bit DAC, VREF = +5V
Integral Nonlinearity
V
V
76
mV
±6
LSB
Differential Nonlinearity
±0.5
LSB
Gain Error
±0.5
%
±4
ppm/°C
Gain Error Drift
Offset
±4
mV
Offset Drift
±10
mV/°C
PSRR
±200
mV/V
Output Amplifier
Output Fine Gain Adjust (Gain DAC)
Range
0.33
Resolution
65,536 steps, 16-bit DAC
Integral Nonlinearity
Differential Nonlinearity
1
mV/V
±6
LSB
±0.5
Gain Error
LSB
±0.2
Gain Drift
V/V
10
3
%
ppm/°C
Output Amplifier
Offset Voltage (RTI of Output Amplifier) (6)
vs Temperature
vs Supply Voltage, VS
±3
mV
±5
mV/°C
±100
Common-Mode Input Range
0
Input Bias Current
mV/V
VS – 1.5
±100
V
pA
Amplifier Internal Gain
Gain Range Steps
2, 2.4, 3, 3.6, 4, 4.5, 6
vs Temperature
±1
Output Short-Circuit Current
ISC
Output Resistance
RO
V/V
%
ppm/°C
0.03
VS – 0.06
IOUT = 4mA (7)
0.1
VS – 0.1
Sourcing/sinking
10
V
V
mA
106
dB
2
MHz
Gain = 2, CL = 200pF
45
deg
AC small-signal, open-loop, f = 1MHz, IOUT = 0, see
Figure 28
500
Ω
Gain-Bandwidth Product
Phase Margin
±0.25
IOUT = 0.5mA (7)
Open-Loop Gain at 0.1Hz
4
6
±0.05
Output Voltage Range
(6)
(7)
2
Initial Gain Error
RTI = Referred-to-input.
Unless limited by the over/under-scale setting, or VCLAMP pin.
Submit Documentation Feedback
Copyright © 2008–2010, Texas Instruments Incorporated
Product Folder Link(s): PGA308
PGA308
www.ti.com
SBOS440B – JULY 2008 – REVISED DECEMBER 2010
ELECTRICAL CHARACTERISTICS (continued)
Boldface limits apply over the specified temperature range, TA = –40°C to +125°C.
At TA = +25°C, VS = +5V, GND = 0V, DOUT/VCLAMP = +5V, and VREF = +5V, unless otherwise noted.
PGA308
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNIT
Over- and Under-Scale Limits
Over-Scale Thresholds
VLIM = 4V, register-selectable ratio of VLIM
OS0
HL[2:0] (CFG1 register D[5:3]) = 000
0.97
0.9805
0.99
V/V
OS1
HL[2:0] (CFG1 register D[5:3]) = 001
0.9588
0.9688
0.9788
V/V
OS2
HL[2:0] (CFG1 register D[5:3]) = 010
0.9509
0.9609
0.9709
V/V
OS3
HL[2:0] (CFG1 register D[5:3]) = 011
0.9392
0.9492
0.9492
V/V
OS4
HL[2:0] (CFG1 register D[5:3]) = 100
0.8416
0.8516
0.8616
V/V
OS5
HL[2:0] (CFG1 register D[5:3]) = 101
0.7673
0.7773
0.7873
V/V
OS6
HL[2:0] (CFG1 register D[5:3]) = 110
0.6189
0.6289
0.6389
V/V
OS7
HL[2:0] (CFG1 register D[5:3]) = 111
0.5603
0.5703
0.5803
Over-Scale Threshold Tempco
±3
V/V
ppm/°C
Over-Scale Amplifier Offset
±9
mV
Over-Scale Amplifier Offset Drift
±10
mV/°C
Under-Scale Thresholds
VLIM = 5V, register-selectable ratio of VLIM
US7
LL[2:0] (CFG1 register D[2:0]) = 111
0.0487
0.0547
0.0607
V/V
US6
LL[2:0] (CFG1 register D[2:0]) = 110
0.04478
0.05078
0.05678
V/V
US5
LL[2:0] (CFG1 register D[2:0]) = 101
0.04088
0.04688
0.05288
V/V
US4
LL[2:0] (CFG1 register D[2:0]) = 100
0.03306
0.03906
0.04506
V/V
US3
LL[2:0] (CFG1 register D[2:0]) = 011
0.02916
0.03516
0.04116
V/V
US2
LL[2:0] (CFG1 register D[2:0]) = 010
0.02525
0.03125
0.03725
V/V
US1
LL[2:0] (CFG1 register D[2:0]) = 001
0.01743
0.02343
0.02943
V/V
US0
LL[2:0] (CFG1 register D[2:0]) = 000
0.01353
0.01953
0.02553
Under-Scale Threshold Tempco
±3
V/V
ppm/°C
Under-Scale Amplifier Offset
±9
mV
Under-Scale Amplifier Offset Drift
±10
mV/°C
Output Voltage Clamp
VCLAMP ≤ VS, VS = +5V
Input Voltage Range
1.25
4.95
Input Bias Current
±60
VOUT Clamp Point
VCLAMP – 0.05
VCLAMP
V
nA
VCLAMP + 0.05
V
Fault Monitor Circuit
(External Comparators)
INP_HI Comparator Threshold
INN_HI Comparator Threshold
Fault Detect Mode Select = 0 (bridge fault); see CFG1
register
Smaller of (VS – 1.2) or (0.65VFLT)
V
INP_LO Comparator Threshold
INN_LO Comparator Threshold
Fault Detect Mode Select = 0 (bridge fault); see CFG1
register
Larger of (0.1V) or (0.35VFLT)
V
Fault Monitor Reference; see CFG1 register, FLT REF bit
sets VFLT
VS or VREF
V
INP_HI Comparator Threshold
INN_HI Comparator Threshold
Fault Detect Mode Select = 1 (common-mode fault); see
CFG1 register
VS – 1.2
V
INP_LO Comparator Threshold
INN_LO Comparator Threshold
Fault Detect Mode Select = 1 (common-mode fault); see
CFG1 register
Fault Monitor Reference
VFLT
70
Comparator Hysteresis
Comparator Input Offset Voltage
100
130
mV
7
mV
±10
mV
Fault Monitor Circuit
(Internal Comparators)
A1SAT_LO Comparator Threshold
A2SAT_LO Comparator Threshold
Threshold is amplifier negative saturation voltage
100
mV
A1SAT_HI Comparator Threshold
A2SAT_HI Comparator Threshold
Threshold is amplifier positive saturation voltage
VS – 0.12
V
A3SAT_LO Comparator Threshold
Threshold is amplifier negative saturation voltage
50
mV
VIN1, VIN2 Pull-up Current Sources
Pull-Up Current Source
30
45
Current Source Matching
IPU
Register-selectable
15
±1.5
±7
Current Source Tempco
±5
Submit Documentation Feedback
Copyright © 2008–2010, Texas Instruments Incorporated
Product Folder Link(s): PGA308
nA
nA
pA/°C
5
PGA308
SBOS440B – JULY 2008 – REVISED DECEMBER 2010
www.ti.com
ELECTRICAL CHARACTERISTICS (continued)
Boldface limits apply over the specified temperature range, TA = –40°C to +125°C.
At TA = +25°C, VS = +5V, GND = 0V, DOUT/VCLAMP = +5V, and VREF = +5V, unless otherwise noted.
PGA308
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNIT
VREF
Input Range
1.8
Input Resistance
VS
43
V
kΩ
Digital Interface
One-Wire
Serial speed baud rate
4.8k
114k
bits/s
0.8
V
Logic Levels
Logic Levels (1W pin)
Low
High
2.0
Hysteresis
V
100
mV
Output Low Level (1W pin)
Open drain, ISINK = 4mA
0.4
V
Output Levels (DOUT/VCLAMP)
Low, DOUT mode selected, ISINK = 4mA and VS = +4.5V, or
ISINK = 2mA and VS = +2.7V
0.4
V
High, DOUT mode selected, ISOURCE = 4mA and VS = +4.5V,
or
ISOURCE = 2mA and VS = +2.7V
VS – 0.4
V
POWER SUPPLY
Supply Voltage
OTP Program Voltage
Quiescent Current
Shutdown Supply Current
VS
2.7
5.5
VS-PGM
4.5
5.5
V
1.6
mA
IQ
ISHDN
VS = +5V, does not include IREF
VS = +5V, does not include IREF
1.3
(8)
V
260
mA
POWER-ON RESET (POR)
Power-Up Threshold
VS rising
2.1
V
Power-Down Threshold
VS falling
1.7
V
TEMPERATURE RANGE
Specified Performance Range
–40
+125
°C
Operational-Degraded Performance Range
–40
+150
°C
Thermal Resistance
MSOP-10, Junction-to-Ambient
(8)
6
150
qJA
°C/W
IREF current load is typically 100mA while in Shutdown mode. Although the output amplifier is disabled in Shutdown mode, RFO and
RGO (180kΩ typical total) remain connected in series between VFB and GND while in Shutdown mode. See Figure 37, Detailed Block
Diagram, for more information.
Submit Documentation Feedback
Copyright © 2008–2010, Texas Instruments Incorporated
Product Folder Link(s): PGA308
PGA308
www.ti.com
SBOS440B – JULY 2008 – REVISED DECEMBER 2010
TYPICAL THREE-WIRE APPLICATION CIRCUIT
Power Supply
+
-
+5V
DOUT/
VCLAMP
VS
VREF
Sensor
Out
1W
Ground
PC
VCC
+5V
Easy-To-Use
Calibration
USB
One-Wire
GND
RISO
100W
VOUT
VCC
CF
10nF
PGA308
Bridge
Sensor
ADC
VIN2
VFB
VIN1
VSJ
RPU
CF
47pF
PGA308EVM
GND
Submit Documentation Feedback
Copyright © 2008–2010, Texas Instruments Incorporated
Product Folder Link(s): PGA308
7
PGA308
SBOS440B – JULY 2008 – REVISED DECEMBER 2010
www.ti.com
PIN CONFIGURATIONS
DGS PACKAGE
MSOP-10
(TOP VIEW)
DRK PACKAGE
3x4 DFN-10
(TOP VIEW)
DOUT/VCLAMP
1
10 VREF
1W
2
9
VOUT
GND
3
8
VFB
VS
4
7
VSJ
VIN1
5
6
VIN2
PGA308
DOUT/VCLAMP
1
10 VREF
1W
2
9
VOUT
GND
3
8
VFB
VS
4
7
VSJ
VIN1
5
6
VIN2
PGA308
PIN DESCRIPTIONS
PIN #
8
NAME
DESCRIPTION
1
DOUT/VCLAMP
Dual-use pin: Output voltage clamp limit for VOUT or programmable digital output. The output voltage
clamp function is for use in multiple supply systems where the PGA308 may be at VS = +5V and the
system analog-to-digital converter (ADC) is powered at +3V. Setting VCLAMP to +3.2V prevents
over-voltage and latch-up on the system ADC input. VCLAMP may be set through a resistor divider from
VS. If configured for digital output, the DOUT function allows for configuration plus calibration of a sensor
module either through the One-Wire interface (1W pin) or as a permanently configured module through
the power-on reset (POR) OTP memory setting.
2
1W
One-Wire interface program pin. UART interface for digital calibration of the PGA308 over a single
wire. Can be connected to VOUT for a three terminal (VS, GND, VOUT) programmable sensor assembly.
3
GND
4
VS
5
VIN1
Signal input voltage 1. Connect to + or – output of the sensor bridge. Internal multiplexer can change
connection internally to front-end PGA.
6
VIN2
Signal input voltage 2. Connect to + or – output of the sensor bridge. Internal multiplexer can change
connection internally to front-end PGA.
7
VSJ
Output amplifier summing junction. Use for output amplifier compensation when driving large capacitive
loads (> 200pF) and/or for using external gain setting resistors for the output amplifier.
8
VFB
VOUT feedback pin. Voltage feedback sense point for over-/under-scale limit circuitry. If internal gain set
resistors for the output amplifier are used, this pin is also the voltage feedback sense point for the
output amplifier. VFB in combination with VSJ allows for use of external filter and protection circuits
without degrading the PGA308 VOUT accuracy. VFB must always be connected to either VOUT or the
point of feedback for VOUT if external filtering is used.
9
VOUT
Analog output voltage of conditioned sensor.
10
VREF
Reference voltage input pin. VREF is used for coarse offset adjust and Zero DAC. VREF or VS may be
individually selected for over-/under-scale threshold reference and fault monitor comparator reference.
Ground.
+Voltage supply.
Submit Documentation Feedback
Copyright © 2008–2010, Texas Instruments Incorporated
Product Folder Link(s): PGA308
PGA308
www.ti.com
SBOS440B – JULY 2008 – REVISED DECEMBER 2010
TYPICAL CHARACTERISTICS
At TA = +25°C, VS = VREF = DOUT/VCLAMP = +5V, RL = 10kΩ and CL = 100pF connected to GND, unless otherwise noted.
Gain format is presented: G = FE-PGA × Fine Gain × Output Gain.
FRONT-END PGA INPUT BIAS CURRENT
WITH IPU DISABLED vs TEMPERATURE
40
900
35
800
Input Bias Current (pA)
Input Bias Current, Pull-Up Enabled (nA)
FRONT-END PGA INPUT BIAS CURRENT
WITH IPU ENABLED vs TEMPERATURE
30
25
20
15
10
5
700
600
500
400
300
200
100
0
-50
-25
0
25
50
75
100
125
0
-50
150
-25
0
25
Temperature (°C)
75
100
125
Figure 1.
Figure 2.
COARSE OFFSET ADJUST ERROR vs
TEMPERATURE
FRONT-END PGA OFFSET VOLTAGE vs
TEMPERATURE
0.6
150
50
+51mV to +99mV Offset Adjust
40
Three Typical Units Shown
0.5
30
+11mV Offset Adjust
Output Voltage (mV)
Error from Ideal Value (%)
50
Temperature (°C)
0.4
0.3
0.2
0.1
-50mV to -100mV Offset Adjust
-10mV Offset Adjust
3s
20
Unit 1
10
Unit 2
0
-10
Unit 3
-20
3s
-30
0
-50
-25
0
25
50
75
100
125
-40
-50
150
0
25
50
75
100
125
Temperature (°C)
Figure 3.
Figure 4.
0.1Hz TO 10Hz OUTPUT NOISE
(G = 1600)
INPUT-REFERRED FRONT-END NOISE vs
FREQUENCY
1
RTF Front-End Noise (mV/ÖHz)
Coarse Offset = 0V
0V
VOUT (500mV/div)
-25
Temperature (°C)
Coarse Offset = 2.5mV
0V
Time (2s/div)
Offset = 100mV, G = 4x1x1
Offset = 0V, G = 4x1x1
150
Clock
Feedthrough
Offset = 100mV, G = 32x1x1
Offset = 40mV, G = 100x1x1
0.1
Offset = 0V, G = 32x1x1
Offset = 0V, G = 100x1x1
0.01
100
Offset = 0V, G = 1600x1x1
1k
10k
100k
Frequency (Hz)
Figure 5.
Figure 6.
Submit Documentation Feedback
Copyright © 2008–2010, Texas Instruments Incorporated
Product Folder Link(s): PGA308
9
PGA308
SBOS440B – JULY 2008 – REVISED DECEMBER 2010
www.ti.com
TYPICAL CHARACTERISTICS (continued)
At TA = +25°C, VS = VREF = DOUT/VCLAMP = +5V, RL = 10kΩ and CL = 100pF connected to GND, unless otherwise noted.
Gain format is presented: G = FE-PGA × Fine Gain × Output Gain.
OVER-SCALE TOTAL ERROR vs TEMPERATURE
(5V Ref)
UNDER-SCALE TOTAL ERROR vs TEMPERATURE
(4V Ref)
0
14
Eight Programming Levels Shown
Eight Programming Levels Shown
OS6
-2
OS7
OS5
Under-Scale Total Error (mV)
Over-Scale Total Error (mV)
-1
-3
-4
-5
OS2
-6
OS0
-7
OS1
OS3, OS4
-8
-9
-10
-50
-25
0
50
75
100
125
8
US2
US4
US3
6
4
US5
US6
2
0
-50
150
US1
US0
10
US7
-25
0
25
50
75
100
125
Temperature (°C)
Temperature (°C)
Figure 7.
Figure 8.
ZERO DAC OFFSET ERROR vs
TEMPERATURE
COMMON-MODE REJECTION (RTI) vs
FREQUENCY
0.2
150
120
156mV
0
110
-0.2
G = 600x1x2
-0.4
100
2.344V
-0.6
CMR (dB)
Offset Error from Ideal Value (mV)
25
12
-0.8
-1.0
-1.2
G = 100x1x2
90
G = 32x1x2
80
70
-1.4
4.844V
-1.6
G = 4x1x2
60
-1.8
-2.0
-50
50
-25
0
25
50
75
100
125
10
150
100
1k
10k
Frequency (Hz)
Temperature (°C)
Figure 9.
Figure 10.
POWER-SUPPLY REJECTION RATIO (RTI) vs
FREQUENCY
GAIN vs
FREQUENCY
120
10000
110
G = 1600x1x6
G = 600x1x2
G = 100x1x2
G = 800x1x2
1000
G = 32x1x2
G = 400x1x2
100
90
Gain
PSRR (dB)
100
80
G = 32x1x3
10
G = 4x1x2
70
G = 4x1x2
1
60
50
0.1
10
10
100
1k
10k
1k
10k
100k
Frequency (Hz)
Frequency (Hz)
Figure 11.
Figure 12.
Submit Documentation Feedback
1M
10M
Copyright © 2008–2010, Texas Instruments Incorporated
Product Folder Link(s): PGA308
PGA308
www.ti.com
SBOS440B – JULY 2008 – REVISED DECEMBER 2010
TYPICAL CHARACTERISTICS (continued)
At TA = +25°C, VS = VREF = DOUT/VCLAMP = +5V, RL = 10kΩ and CL = 100pF connected to GND, unless otherwise noted.
Gain format is presented: G = FE-PGA × Fine Gain × Output Gain.
VOUT WITH VCLAMP LOW (1.25V) vs
TEMPERATURE
4.99
1.30
4.98
1.29
4.97
1.28
VOUT with VCLAMP Low (V)
VOUT with VCLAMP High (V)
VOUT WITH VCLAMP HIGH (4.94V) vs
TEMPERATURE
4.96
4.95
4.94
4.93
4.92
4.91
4.90
1.27
1.26
1.25
1.24
1.23
1.22
1.21
4.89
-50
-25
0
25
50
75
100
125
150
1.20
-50
Temperature (°C)
0
25
50
75
100
125
150
Temperature (°C)
Figure 13.
Figure 14.
COMMON-MODE OVER-VOLTAGE RECOVERY
VCLAMP RESPONSE
(No Cap Load, CMP SEL = 1)
VIN CM = 3V
50mV/div
VOUT (1V/div)
CMP SEL = 1 (Comp On),
2.5V VCLAMP, RL = 10kW,
G = 32x1x2, 300Hz Triangle Wave
VIN CM = 5V
VIN CM (2V/div)
-25
RL = 10kW, CMP SEL = 0,
CL = 0, CF = 0, Gain = 4x1x2
Time (25ms/div)
Time (250ms/div)
Figure 15.
Figure 16.
VCLAMP RESPONSE
(No Cap Load, CMP SEL = 0)
VCLAMP RESPONSE
(CL = 10nF, CMP SEL = 1)
CMP SEL = 1 (Comp On),
2.5V VCLAMP, RL = 10kW,
G = 32x1x2, 300Hz Triangle Wave
50mV/div
50mV/div
CMP SEL = 0 (Comp Off),
2.5V VCLAMP, RL = 10kW,
G = 32x1x2, 300Hz Triangle Wave
Time (250ms/div)
Time (250ms/div)
Figure 17.
Figure 18.
Submit Documentation Feedback
Copyright © 2008–2010, Texas Instruments Incorporated
Product Folder Link(s): PGA308
11
PGA308
SBOS440B – JULY 2008 – REVISED DECEMBER 2010
www.ti.com
TYPICAL CHARACTERISTICS (continued)
At TA = +25°C, VS = VREF = DOUT/VCLAMP = +5V, RL = 10kΩ and CL = 100pF connected to GND, unless otherwise noted.
Gain format is presented: G = FE-PGA × Fine Gain × Output Gain.
VCLAMP RESPONSE
(CL = 10nF, CMP SEL = 0)
OUTPUT VOLTAGE vs
OUTPUT CURRENT
VS
CMP SEL = 0 (Comp Off),
2.5V VCLAMP, RL = 10kW,
G = 32x1x2, 300Hz Triangle Wave
VS - 0.1
50mV/div
Output Voltage (V)
VS - 0.2
VS - 0.3
VS - 0.4
VS = 2.7V
VS = 3V
VS = 5V
VS = 5.5V
GND + 0.4
GND + 0.3
GND + 0.2
GND + 0.1
GND
Time (250ms/div)
0
3
6
9
12
15
| Output Current | (mA)
Figure 19.
Figure 20.
QUIESCENT CURRENT vs
TEMPERATURE
OUTPUT AMPLIFIER OPEN-LOOP GAIN vs
FREQUENCY (CMP SEL = 1)
120
Output Amplifier Open-Loop Gain (dB)
1.6
1.4
1.2
IQ (mA)
1.0
0.8
0.6
0.4
0.2
0
-50
-25
0
25
50
75
100
125
100
80
60
40
CL £ 100pF
20
CL = 10nF
RL = 10kW, CL = 10nF
0
-20
0.01
150
RL = 1kW, CL = 10nF
0.1
1
10
10k
100k
1M
Figure 22.
OUTPUT AMPLIFIER OPEN-LOOP GAIN vs
FREQUENCY (CMP SEL = 0)
OUTPUT AMPLIFIER OPEN-LOOP PHASE vs
FREQUENCY (CMP SEL = 1)
10M
180
100
80
60
40
CL £ 100pF
20
CL = 10nF
RL = 10kW, CL = 10nF
0
RL = 1kW, CL = 10nF
0.1
1
10
100
1k
10k
100k
1M
10M
Output Amplifier Open-Loop Phase (°)
Output Amplifier Open-Loop Gain (dB)
12
1k
Figure 21.
120
-20
0.01
100
Frequency (Hz)
Temperature (°C)
CL £ 100pF
160
140
120
100
80
60
CL = 10nF
40
20
RL = 10kW, CL = 10nF
0
RL = 1kW, CL = 10nF
-20
0.01
0.1
1
10
100
1k
Frequency (Hz)
Frequency (Hz)
Figure 23.
Figure 24.
Submit Documentation Feedback
10k
100k
1M
10M
Copyright © 2008–2010, Texas Instruments Incorporated
Product Folder Link(s): PGA308
PGA308
www.ti.com
SBOS440B – JULY 2008 – REVISED DECEMBER 2010
TYPICAL CHARACTERISTICS (continued)
At TA = +25°C, VS = VREF = DOUT/VCLAMP = +5V, RL = 10kΩ and CL = 100pF connected to GND, unless otherwise noted.
Gain format is presented: G = FE-PGA × Fine Gain × Output Gain.
OUTPUT AMPLIFIER OPEN-LOOP PHASE vs
FREQUENCY (CMP SEL = 0)
CAPACITIVE LOAD DRIVE
CL = 1nF
CMP SEL = 0 (Comp Off)
G = 4x1x2
VOPP = 100mV
RL = 10kW
160
140
CL £ 100pF
120
20mV/div
Output Amplifier Open-Loop Phase (°)
180
100
80
60
CL = 10nF
40
20
RL = 10kW, CL = 10nF
0
RL = 1kW, CL = 10nF
-20
0.01
0.1
1
10
100
1k
10k
100k
1M
Time (5ms/div)
10M
Frequency (Hz)
Figure 25.
Figure 26.
CAPACITIVE LOAD DRIVE
CL = 10pF
OPEN-LOOP OUTPUT IMPEDANCE vs
FREQUENCY
10k
20mV/div
Open-Loop Output Impedance (W)
CMP SEL = 0 (Comp Off)
G = 4x1x2
VOPP = 100mV
RL = 10kW
CMP SEL = 1
CMP SEL = 0
1k
IL = 0
IL = 500mA
100
IL = 5mA
10
Time (5ms/div)
10
100
1k
10k
100k
1M
10M
Frequency (Hz)
Figure 28.
SMALL-SIGNAL STEP RESPONSE
CMP SEL = 1
LARGE-SIGNAL STEP RESPONSE
CMP SEL = 1
VOUT (1V/div)
VOUT (50mV/div)
Figure 27.
CMP SEL = 1 (Comp On),
RL = 10kW, RISO = 100W, CL = 10nF, CF = 47pF,
G = 600x1x2, f = 4kHz, VOPP = 100mV
CMP SEL = 1 (Comp On),
RL = 10kW, RISO = 100W, CL = 10nF, CF = 47pF,
G = 600x1x2, f = 4kHz, VOPP = 4V
Time (50ms/div)
Time (50ms/div)
Figure 29.
Figure 30.
Submit Documentation Feedback
Copyright © 2008–2010, Texas Instruments Incorporated
Product Folder Link(s): PGA308
13
PGA308
SBOS440B – JULY 2008 – REVISED DECEMBER 2010
www.ti.com
TYPICAL CHARACTERISTICS (continued)
At TA = +25°C, VS = VREF = DOUT/VCLAMP = +5V, RL = 10kΩ and CL = 100pF connected to GND, unless otherwise noted.
Gain format is presented: G = FE-PGA × Fine Gain × Output Gain.
LARGE-SIGNAL STEP RESPONSE
CMP SEL = 1
VOUT (1V/div)
VOUT (50mV/div)
SMALL-SIGNAL STEP RESPONSE
CMP SEL = 1
CMP SEL = 1 (Comp On),
RL = 10kW, RISO = 100W, CL = 10nF, CF = 47pF,
G = 4x1x2, f = 4kHz, VOPP = 100mV
CMP SEL = 1 (Comp On),
RL = 10kW, RISO = 100W, CL = 10nF, CF = 47pF,
G = 4x1x2, f = 4kHz, VOPP = 4V
Time (50ms/div)
Figure 31.
Figure 32.
SMALL-SIGNAL STEP RESPONSE
CMP SEL = 0
LARGE-SIGNAL STEP RESPONSE
CMP SEL = 0
VOUT (1V/div)
VOUT (50mV/div)
Time (50ms/div)
CMP SEL = 0 (Comp Off),
RL = 10kW, CL = 0, CF = 0,
G = 600x1x2, f = 4kHz, VOPP = 100mV
Time (50ms/div)
Figure 33.
Figure 34.
SMALL-SIGNAL STEP RESPONSE
CMP SEL = 0
LARGE-SIGNAL STEP RESPONSE
CMP SEL = 0
VOUT (1V/div)
VOUT (50mV/div)
Time (50ms/div)
CMP SEL = 0 (Comp Off),
RL = 10kW, CL = 0, CF = 0,
G = 4x1x2, f = 4kHz, VOPP = 100mV
14
CMP SEL = 0 (Comp Off),
RL = 10kW, CL = 0, CF = 0,
G = 600x1x2, f = 4kHz, VOPP = 4V
CMP SEL = 0 (Comp Off),
RL = 10kW, CL = 0, CF = 0,
G = 4x1x2, f = 4kHz, VOPP = 4V
Time (50ms/div)
Time (50ms/div)
Figure 35.
Figure 36.
Submit Documentation Feedback
Copyright © 2008–2010, Texas Instruments Incorporated
Product Folder Link(s): PGA308
PGA308
www.ti.com
SBOS440B – JULY 2008 – REVISED DECEMBER 2010
FUNCTIONAL DESCRIPTION
OVERVIEW
VOLTAGE REFERENCE
The PGA308 is an ideal building block for resistive
bridge sensor conditioning and general data
acquisition. Digitally-programmable coarse offset, fine
offset, and gain may be controlled in real time or
permanently programmed into the PGA308.
The PGA308 VREF pin provides input from a
reference voltage. The reference voltage is used by
the Coarse Offset Adjust and Zero DACs. The fault
monitor circuitry trip points, as well as the over- and
under-scale limits, can be selected to be referenced
to either VS or VREF. This flexibility accommodates
absolute or ratiometric mode designs.
SENSOR ERROR ADJUSTMENT RANGE
The PGA308 is designed to readily accommodate the
following sensors:
Span25°C: 0.08mV/V to 296mV/V
Initial Offset: 20mV/V
Span and offset are based on a bridge sensor
excitation voltage of +5V, a PGA308 output voltage
span of 4V (+0.5V to +4.5V), VREF of +5V, and a
VOUT/VIN gain up to 9600. For proper PGA308 setup,
consider noise, small-signal bandwidth, VOUT/VIN
gain, and required system error.
AMPLIFICATION SIGNAL PATH
The core of the PGA308 is a precision, low drift, and
low noise front-end programmable gain amplifier
(PGA). This front-end PGA has gain capabilities from
x4 to x1600. The output amplifier has a gain range
from ×2 to ×6. A fine gain adjust in front of the output
amplifier offers a selectable ×0.33 to ×1.0 attenuation
factor. This architecture yields a VOUT/VIN gain range
for the PGA309 of ×2.67 to ×9600. Many applications
use overall gains of ×1600 or less. The selection of
gains in the front-end PGA and output amplifier,
although capable of up to ×9600 overall gain, are
intended to allow for gain distribution throughout the
PGA308; this design enables optimum span and
offset scaling from input to output. The polarity of the
inputs can be switched through the input mux to
accommodate sensors with unknown polarity output.
Higher gains reduce bandwidth and require more
analog filtering and/or system analog-to-digital
converter (ADC) averaging to reject noise.
COARSE AND FINE OFFSET ADJUSTMENT
The sensor offset adjustment is done in two stages.
The input-referred Coarse Offset Adjust DAC has a
±100mV offset adjustment range for a selected VREF
of +5V. Any residual input sensor offset is corrected
and any desired VOUT offset pedestal for zero-applied
sensor strain input is set by a Fine Offset Adjust
through the 16-bit Zero DAC that adds to the signal
from the output of the front-end PGA.
FAULT MONITOR CIRCUIT SENSOR FAULT
DETECTION
To detect sensor burnout and/or short, a set of four
comparators (external fault comparators) are
connected to the inputs of the front-end PGA. There
are two fault-detect modes of operation for these
comparators.
Common-Mode Fault
If either of the inputs are taken outside of the
common-mode range of the amplifier [greater than
(VS – 1.2V), or less than 100mV], then the
corresponding comparator sets a sensor fault flag
that can be programmed to drive the PGA308 VOUT to
within 100mV (IOUT < 4mA) of either VS (or VCLAMP if
VCLAMP is used) or ground. This level is well above
the set over-scale limit level or well below the set
under-scale limit level. The state of the fault condition
can be read in digital form in the ALRM register. If the
over-scale/under-scale limiting is disabled, the
PGA308 output voltage is also driven within 100mV
(IOUT < 4mA) of either VS (or VCLAMP if VCLAMP is used)
or ground, depending on the selected fault polarity
(high or low).
Bridge Fault
To assist in identifying mis-wiring, or open- or
short-circuit conditions, the PGA308 provides bridge
fault monitoring. For bridge fault detection, either VS
or VREF (whichever is used for bridge excitation) can
be chosen as VFLT. If either of the inputs are taken to
less than the larger of either 100mV or 0.35VFLT, then
a fault is signaled. Also, if either of the inputs is taken
to greater than the smaller of (VS – 1.2V) or 0.65VFLT,
then a fault is signaled. This fault detection allows for
operation with bridge differential voltages of up to
30% of the bridge excitation voltage. The
corresponding comparator sets a sensor fault flag
that can be programmed to drive the PGA308 VOUT to
within 100mV (IOUT < 4mA) of either VS (or VCLAMP if
VCLAMP is used) or ground. This level is well above
the set over-scale limit level or well below the set
Submit Documentation Feedback
Copyright © 2008–2010, Texas Instruments Incorporated
Product Folder Link(s): PGA308
15
PGA308
SBOS440B – JULY 2008 – REVISED DECEMBER 2010
www.ti.com
under-scale limit level. If over-scale/under-scale
limiting is disabled, the PGA308 output voltage is
driven within 100mV (IOUT < 4mA) of either VS or
ground, depending on the selected fault polarity (high
or low).
Additional Fault Detection
There are five additional fault detect comparators
(internal fault comparators) that help detect subtle
PGA308 front-end violations that could result in linear
voltages at VOUT and be interpreted as valid states.
These comparators are especially useful during
factory calibration and setup.
Alarm Register
Each of nine fault conditions sets a corresponding bit
in the Alarm register. The state of the fault condition
can be read digitally from the Alarm register.
OVER-SCALE AND UNDER-SCALE LIMITS
The over-scale and under-scale limit circuitry
provides a programmable upper and lower clip limit
for the PGA308 output voltage. When combined with
the fault monitor circuitry, system diagnostics can be
performed to determine if a conditioned sensor is
defective, or if the process being monitored by the
sensor is out of range. The selected PGA308 VLIM is
divided down by a precision resistor string to form the
over- and under-scale trip points. These resistor
ratios are extremely accurate and produce no
significant initial or temperature errors. An over-scale
amplifier driven by the over-scale threshold limits
(clips) the maximum PGA308 output, VOUT. Similarly,
an under-scale amplifier driven by the under-scale
threshold limits (clips) the minimum PGA308 output,
VOUT. The reference for the trip points, VLIM, is
register-selectable for either VREF or VS.
DOUT/VCLAMP PIN
The dual-use DOUT/VCLAMP pin functions either as a
VOUT clamp or as a digital push-pull output. The
voltage clamp function provides an output voltage
clamp, which is external-resistor programmable. In
mixed-voltage systems, where the PGA308 may run
from +5V with its output scaled for 0.1V to 2.9V,
VCLAMP can be set to 3.0V to prevent an over-voltage
lock-up/latch-up condition on a 3V system ADC or
microcontroller input. When programmed as a digital
output this pin can be used for sensor module
configuration. The value may be pre-programmed in
the one-time programmable (OTP) banks, or
controlled through the One-Wire interface (1W pin).
16
DIGITAL INTERFACE: ONE-WIRE PROGRAM
PROTOCOL
The PGA308 can be configured through a single-wire,
UART-compatible interface (1W pin). It is possible to
connect this single-wire communication pin to the
VOUT pin in true three-terminal modules (VS, ground,
and sensor out) and continue to allow for calibration
and configuration programming.
All communication transactions start with an
initialization byte transmitted by the controller. This
byte (55h) sets the baud rate used for the
communication transaction. The baud rate is sensed
during the initialization byte of every transaction, and
is used throughout the entire transaction. Each
transaction may use a different baud rate, if desired.
Baud rates of 4.8k to 114k bits/second are supported.
Each communication consists of several bytes of
data. Each byte consists of 10-bit periods. The first bit
is the start bit and is always '0'. When idle, the 1W
pin should always be high. The second through ninth
bits are the eight data bits for the byte and are
transferred LSB first. The 10th bit is the stop bit and
is always '1'.
The second byte is a command/address byte. The
last bit in this byte indicates either a read or write at
the address selected by the address pointer portion
of the byte. Additional data transfer occurs after the
command/address byte. The number of bytes and
direction of data transfer depend on the command
byte. For a read sequence, the PGA308 waits for a
2-bit delay (unless programmed otherwise) after the
completion of the command/address byte before
beginning to transmit. This wait allows time for the
controller to ensure that the PGA308 is able to control
the One-Wire interface. The first byte transmitted by
the PGA308 is the least significant byte of the register
and the second byte will be the most significant byte
of the register.
The recommended circuit implementation is to use a
pull-up resistor and/or current source with an open
drain (or open collector) output connected to the 1W
pin, which is also an open drain output. The single
wire can be driven high by the controller during
transmit from the controller, but some form of pull-up
is required to allow the signal to go high during
receive because the PGA308 1W pin can only pull
the output low.
Submit Documentation Feedback
Copyright © 2008–2010, Texas Instruments Incorporated
Product Folder Link(s): PGA308
PGA308
www.ti.com
SBOS440B – JULY 2008 – REVISED DECEMBER 2010
Timeout on the One-Wire Interface
The PGA308 includes a timeout mechanism. If
synchronization between the controller and the
PGA308 is lost for any reason, the timeout
mechanism allows the One-Wire interface to reset
communication. The timeout period is set to
approximately 28ms (typical). If the timeout period
expires between the initialization byte and the
command byte, between the command byte and any
data byte, or between any data bytes, the PGA308
resets the One-Wire interface circuitry so that it
expects an initialization byte. Every time that a byte is
transmitted on the single wire interface, this timeout
period restarts.
POWER-ON SEQUENCE
The PGA308 provides circuitry to detect when the
power supply is applied to the PGA308 and resets
the internal registers to a known power-on reset
(POR) state. This reset also occurs whenever the
supply is invalid so that the PGA308 is set to a known
state when the supply becomes valid again. The
threshold for this circuit is approximately 1.7V to
2.1V. After the power supply becomes valid, the
PGA308 waits for approximately 25ms, during which
VOUT is disabled, and then attempts to read the data
from the last valid OTP memory bank. If the memory
bank has the proper checksum, then the PGA308
RAM is loaded with the OTP data and VOUT enabled.
If the checksum is invalid, VOUT is set to disabled.
Unless disabled by the OWD bit in Configuration
Register 2 (CFG2), the One-Wire interface can
always communicate to the PGA308 and override the
contents of the current RAM in use by setting the
appropriate SWL[2:0] bits in the Software Control
Register (SFTC). For applications that require
instant-on for VOUT, the NOW bit in the CFG2 register
can be set to '1', which eliminates the 25ms disable
of VOUT on power-up.
ONE-WIRE OPERATION WITH 1W
CONNECTED TO VOUT
In some sensor applications, it is desired to provide
the end user of the sensor module with three pins:
VS, GND, and Sensor Out. It is also desired in these
applications to digitally calibrate the sensor module
after its final assembly of sensor and electronics. The
PGA308 has a mode that allows the One-Wire
interface pin (1W) to be tied directly to the PGA308
output pin (VOUT).
To calibrate the PGA308 in Three-Wire configuration,
program the internal registers and measure the
resulting VOUT. To do this while VOUT is connected to
1W requires the ability to enable and disable VOUT.
Thus, the 1W/VOUT line operates in a multiplexed
mode where 1W is used as a bidirectional digital
interface while VOUT is disabled, and VOUT drives the
line as a conditioned sensor output voltage when it is
enabled.
space
The PGA308 also provides a mode in which the
output amplifier can be enabled for a set time period
and then disabled again to allow sharing of the 1W
pin with the VOUT connection. This action is
accomplished by writing a value to bits OEN[7:0] in
the One-Wire Enable Control register (OENC). Any
non-zero value enables the output. This non-zero
value is decremented every 10ms until it becomes
zero. When this value becomes zero, VOUT is
disabled and a 1s timeout begins waiting for bus
activity on the digital interface (1W pin). As long as
there is activity on the 1W pin, the 1s timeout is
continually reset. After 1s of no bus activity, the
PGA308 checks for a correct checksum. If the
checksum is correct, the PGA308 runs with the
values that currently exist in RAM. If the checksum is
not valid, the PGA308 checks for written bank select
registers in OTP in the order of BANK SEL4, BANK
SEL3, BANK SEL2 then BANK SEL1. The highest
bank select register containing valid programmed
data is read. The value read from this register points
to one of the seven OTP banks, which is then loaded
into RAM.
space
space
space
space
space
space
space
space
space
Submit Documentation Feedback
Copyright © 2008–2010, Texas Instruments Incorporated
Product Folder Link(s): PGA308
17
PGA308
SBOS440B – JULY 2008 – REVISED DECEMBER 2010
www.ti.com
OTP MEMORY BANKS
PGA308 TRANSFER FUNCTION
There are four one-time programmable (OTP) bank
selection registers: BANK SEL1, BANK SEL2, BANK
SEL3, and BANK SEL4. Bank selection may be set
four times by programming the BANK SELx registers
in order (1, 2, 3, 4). The default OTP bank used on
POR is the location stored in the last programmed
BANK SELx register. Therefore, if programmed,
BANK SEL4 always has priority over lower-numbered
bank select registers.
Equation 1 shows the mathematical expression that is
used to compute the output voltage, VOUT. This
equation can also be rearranged algebraically to
solve for different terms. For example, during
calibration, this equation is rearranged to solve for
VIN.
The PGA308 contains seven OTP user memory
banks. All seven of these banks may be
independently programmed. However, the default
bank at POR can be set only four times. The seven
possible OTP user memory banks allow an end
product with a microcontroller interface between the
end-user and the PGA308 to select from up to seven
factory pre-programmed configurations. It also
provides total user flexibility for any other
configuration through software communication over
the One-Wire interface (1W pin). This flexibility allows
no-scrap recovery from miscalibration situations.
Where:
mux_sign: This term changes the polarity of the
input signal; value is ±1
VIN: The input signal for the PGA308; VIN1 = VINP,
VIN2 = VINN
VCoarse_Offset: The coarse offset DAC output
voltage
GI: Input stage gain
VZero_DAC: Zero DAC output voltage
GD: Gain DAC
GO: Output stage gain
18
(
(
VOUT = [ mux_sign ? VIN + VCoarse_Offset ? GI + VZero_DAC ] ? GD ? GO
(1)
Submit Documentation Feedback
Copyright © 2008–2010, Texas Instruments Incorporated
Product Folder Link(s): PGA308
PGA308
www.ti.com
SBOS440B – JULY 2008 – REVISED DECEMBER 2010
VS
VREF
VREF
VS
VS
OTP
(7 Banks)
PGA308
POR
Interface
and
Control
Circuitry
RAM
Control Registers
Alarm Register
Digital
Controls
Input Mux Control(1)
Bridge
Sensor
Fine Offset Adjust(1)
(16-Bit)
VREF
Front-End PGA Out
0 < VZDAC < VREF
Gain = x4 to x1600
16-Bit DAC
Offset Due to Zero DAC
-0.5VREF < Offset < +0.5VREF
Zero DAC
4R
A1
4R
R
Auto
Zero
VINN
RG
RF
Fault Ref
Select(1)
VS
Input Mux
Ref
Select
VREF
Fault Monitor
Circuit
VCLAMP
Mode
Only
RCL2
VS
2
Scale
Limit
1
VOUT
RISO
Clamp
VOUT FILT
VFB
RFO
8R
8R
3
RGO
VREF
7-Bit + Sign
DAC
Digital Out
3-Bit DAC
VREF
Auto
Zero
RCL1
DOUT/VCLAMP
1
Over-Scale Limit(1)
Auto
Zero
R
(2)
(3)
Output
Amplifier
A3
Front-End
PGA Gain
1W
VLIM
Gain DAC
PGA
Diff Amp
A2
VINP
Ref
Select
Fine Gain Adjust (16-Bit)(1)
RF
VOS
VLIM
VS
VIN1
VIN2
OS/US Ref Select(1)
VREF
DOUT/VCLAMP(1)
PGA Gain Select (1 of 16)(1)
Range of 4 to 1600
(w/PGA Diff Amp Gain = 4)
VLIM
CF
Under-Scale Limit(1)
INT/EXT FB Select(1)
CL
3-Bit DAC
VSJ
Output Gain Select (1-of-7)(1)
Range of 2 to 5
Alarm Register Inputs
Coarse Offset Range(1)
Fault Detect Mode(1)
Coarse Offset Adjust(1)
GND
NOTES: (1) User-adjustable feature.
(2) Optional connection; see the One-Wire Operation with 1W Connected to VOUT section for more information.
(3) Optional connection; see the PGA308 User's Guide for more information.
Figure 37. Detailed Block Diagram
Submit Documentation Feedback
Copyright © 2008–2010, Texas Instruments Incorporated
Product Folder Link(s): PGA308
19
PGA308
SBOS440B – JULY 2008 – REVISED DECEMBER 2010
www.ti.com
REVISION HISTORY
NOTE: Page numbers for previous revisions may differ from page numbers in the current version.
Changes from Revision A (April, 2009) to Revision B
Page
•
Updated front page format to current standards ................................................................................................................... 1
•
Added PGA Transfer Function section ............................................................................................................................... 18
20
Submit Documentation Feedback
Copyright © 2008–2010, Texas Instruments Incorporated
Product Folder Link(s): PGA308
PACKAGE OPTION ADDENDUM
www.ti.com
23-Dec-2021
PACKAGING INFORMATION
Orderable Device
Status
(1)
Package Type Package Pins Package
Drawing
Qty
Eco Plan
(2)
Lead finish/
Ball material
MSL Peak Temp
Op Temp (°C)
Device Marking
(3)
(4/5)
(6)
PGA308AIDGSR
ACTIVE
VSSOP
DGS
10
2500
RoHS & Green
NIPDAUAG | SN
Level-2-260C-1 YEAR
-40 to 125
P30A
PGA308AIDGSRG4
ACTIVE
VSSOP
DGS
10
2500
RoHS & Green
SN
Level-2-260C-1 YEAR
-40 to 125
P30A
PGA308AIDGST
ACTIVE
VSSOP
DGS
10
250
RoHS & Green
NIPDAUAG | SN
Level-2-260C-1 YEAR
-40 to 125
P30A
PGA308AIDRKR
ACTIVE
VSON
DRK
10
3000
RoHS & Green
NIPDAU
Level-2-260C-1 YEAR
-40 to 125
P30B
PGA308AIDRKT
ACTIVE
VSON
DRK
10
250
RoHS & Green
NIPDAU
Level-2-260C-1 YEAR
-40 to 125
P30B
(1)
The marketing status values are defined as follows:
ACTIVE: Product device recommended for new designs.
LIFEBUY: TI has announced that the device will be discontinued, and a lifetime-buy period is in effect.
NRND: Not recommended for new designs. Device is in production to support existing customers, but TI does not recommend using this part in a new design.
PREVIEW: Device has been announced but is not in production. Samples may or may not be available.
OBSOLETE: TI has discontinued the production of the device.
(2)
RoHS: TI defines "RoHS" to mean semiconductor products that are compliant with the current EU RoHS requirements for all 10 RoHS substances, including the requirement that RoHS substance
do not exceed 0.1% by weight in homogeneous materials. Where designed to be soldered at high temperatures, "RoHS" products are suitable for use in specified lead-free processes. TI may
reference these types of products as "Pb-Free".
RoHS Exempt: TI defines "RoHS Exempt" to mean products that contain lead but are compliant with EU RoHS pursuant to a specific EU RoHS exemption.
Green: TI defines "Green" to mean the content of Chlorine (Cl) and Bromine (Br) based flame retardants meet JS709B low halogen requirements of
工商网监
湘ICP备2023018690号
