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LTC1293/LTC1294/LTC1296 Single Chip 12-Bit Data Acquisition System
FEATURES
s
DESCRIPTIO
s s s
s s
Software Programmable Features Unipolar/Bipolar Conversion Differential/Single Ended Inputs MSB-First or MSB/LSB Data Sequence Power Shutdown Built-In Sample and Hold Single Supply 5V or 5V Operation Direct 4-Wire Interface to Most MPU Serial Ports and All MPU Parallel Ports 46.5kHz Maximum Throughput Rate System Shutdown Output (LTC1296)
The LTC1293/4/6 is a family of data acquisition systems which contain a serial I/O successive approximation A/D converter. It uses LTCMOSTM switched capacitor technology to perform either 12-bit unipolar, or 11-bit plus sign bipolar A/D conversions. The input multiplexer can be configured for either single ended or differential inputs (or combinations thereof). An on-chip sample and hold is included for all single ended input channels. When the LTC1293/4/6 is idle it can be powered down in applications where low power consumption is desired. The LTC1296 includes a System Shutdown Output pin which can be used to power down external circuitry, such as signal conditioning circuitry prior to the input mux. The serial I/O is designed to communicate without external hardware to most MPU serial ports and all MPU parallel I/O ports allowing up to eight channels of data to be transmitted over as few as three wires.
LTCMOS TM is a trademark of Linear Technology Corporation
KEY SPECIFICATIO S
s s s
Resolution ..................................................... 12 Bits Fast Conversion Time ............ 12s Max Over Temp. Low Supply Current ........................................ 6.0mA
TYPICAL APPLICATI
12-Bit Data Acquisition System with Power Shutdown
RB 5.1k 2N3906
+
R1 10k 1/4 LT1014
R2 1.2M
CH0 CH1 CH2 CH3
VCC SSO CLK CS
-
R2 1.2M C2 1F
350 STRAIN GAUGE BRIDGE
CH4 CH5 CH6 CH7 COM LTC1296
DOUT DIN REF+ REF - AGND V-
THREE ADDITIONAL STRAIN GAUGE INPUTS CAN BE ACCOMMODATED USING THE OTHER AMPLIFIERS IN THE LT1014
DGND
U
74HC04 47F +5V MPU 1N4148
LTC1293 TA01
UO
U
1
LTC1293/LTC1294/LTC1296 ABSOLUTE AXI U RATI GS (Note 1 and 2)
Operating Temperature Range LTC1293/4/6BC, LTC1293/4/6CC, LTC1293/4/6DC ....................................... 0C to 70C LTC1293/4/6BI, LTC1293/4/6CI, LTC1293/4/6DI .................................... -40C to 85C LTC1293/4/6BM, LTC1293/4/6CM, LTC1293/4/6DM ............................... -55C to 125C Storage Temperature Range .................. -65C to 150C Lead Temperature (Soldering, 10 sec.)................ 300C Supply Voltage (VCC) to GND or V - ................................................... 12V Negative Supply Voltage (V -) ..................... -6V to GND Voltage Analog and Reference Inputs ............................ (V -) -0.3V to VCC + 0.3V Digital Inputs ......................................... -0.3V to 12V Digital Outputs........................... -0.3V to VCC + 0.3V Power Dissipation............................................. 500mW
PACKAGE/ORDER I FOR ATIO
TOP VIEW CH0 CH1 CH2 CH3 CH4 CH5 COM DGND 1 2 3 4 5 6 7 8 S PACKAGE 16-LEAD PLASTIC SOL
TOP VIEW CH0 CH1 CH2 CH3 CH4 CH5 CH6 CH7 COM 1 2 3 4 5 6 7 8 9 20 DVCC 19 AVCC 18 CLK 17 CS 16 DOUT 15 DIN 14 REF + 13 REF
-
16 VCC 15 CLK 14 CS 13 DOUT 12 DIN 11 VREF 10 AGND 9 V-
ORDER PART NUMBER LTC1293BCS LTC1293CCS LTC1293DCS
LTC1294BCS LTC1294CCS LTC1294DCS
12 AGND 11 V - S PACKAGE 20-LEAD PLASTIC SO
DGND 10
J PACKAGE 20-LEAD CERAMIC DIP
TOP VIEW CH0 CH1 CH2 CH3 CH4 CH5 CH6 CH7 COM 1 2 3 4 5 6 7 8 9 20 VCC 19 SSO 18 CLK 17 CS 16 DOUT 15 DIN 14 REF + 13 REF
-
LTC1296BCS LTC1296CCS LTC1296DCS
12 AGND 11 V - S PACKAGE 20-LEAD PLASTIC SO
DGND 10
J PACKAGE 20-LEAD CERAMIC DIP
2
U
U
W
WW
U
W
TOP VIEW CH0 CH1 CH2 CH3 CH4 CH5 COM DGND 1 2 3 4 5 6 7 8 16 VCC 15 CLK 14 CS 13 DOUT 12 DIN 11 VREF 10 AGND 9 V-
ORDER PART NUMBER LTC1293BMJ LTC1293CMJ LTC1293DMJ LTC1293BIJ LTC1293CIJ LTC1293DIJ LTC1293BIN LTC1293CIN LTC1293DIN LTC1293BCN LTC1293CCN LTC1293DCN
J PACKAGE N PACKAGE 16-LEAD CERAMIC DIP 16-LEAD PLASTIC DIP
TOP VIEW CH0 CH1 CH2 CH3 CH4 CH5 CH6 CH7 COM 1 2 3 4 5 6 7 8 9 20 DVCC 19 AVCC 18 CLK 17 CS 16 DOUT 15 DIN 14 REF+ 13 REF - 12 AGND 11 V - N PACKAGE 20-LEAD PLASTIC DIP
LTC1294BMJ LTC1294CMJ LTC1294DMJ LTC1294BIJ LTC1294CIJ LTC1294DIJ
LTC1294BIN LTC1294CIN LTC1294DIN LTC1294BCN LTC1294CCN LTC1294DCN
DGND 10
TOP VIEW CH0 CH1 CH2 CH3 CH4 CH5 CH6 CH7 COM 1 2 3 4 5 6 7 8 9 20 VCC 19 SSO 18 CLK 17 CS 16 DOUT 15 DIN 14 REF + 13 REF - 12 AGND 11 V - N PACKAGE 20-LEAD PLASTIC DIP
LTC1296BMJ LTC1296CMJ LTC1296DMJ LTC1296BIJ LTC1296CIJ LTC1296DIJ
LTC1296BIN LTC1296CIN LTC1296DIN LTC1296BCN LTC1296CCN LTC1296DCN
DGND 10
LTC1293/LTC1294/LTC1296
CO VERTER A D
PARAMETER Offset Error Linearity Error (INL) Gain Error Minimum Resolution for which No Missing Codes are Guaranteed Analog and REF Input Range On Channel Leakage Current (Note 8)
Off Channel Lekage Current (Note 8)
AC CHARACTERISTICS (Note 3)
SYMBOL fCLK tSMPL tCONV tCYC tdDO tdis ten thDI thDO tf tr tWHCLK tWLCLK tsuDI tsuCS twHCS twLCS tenSSO tdisSSO CIN PARAMETER Clock Frequency Analog Input Sample Time Conversion Time Total Cycle Time Delay Time, CLK to DOUT Data Valid Delay Time, CS to DOUT Hi-Z Delay Time, CLK to DOUT Enabled Hold Time, DIN after CLK Time Output Data Remains Valid After CLK DOUT Fall Time DOUT Rise Time CLK High Time CLK Low Time Set-up Time, DIN Stable Before CLK Set-up Time, CS before CLK CS High Time During Conversion CS Low Time During Data Transfer Delay Time, CLK to SSO Delay Time, CS to SSO Input Capacitance See Test Circuits See Test Circuits VCC = 5V (Note 6) VCC = 5V (Note 6) VCC = 5V (Note 6) VCC = 5V (Note 6) VCC = 5V (Note 6) VCC = 5V (Note 6) See Test Circuits See Test Circuits Analog Inputs On Channel Analog Inputs Off Channel Digital Inputs
q q q q
WU
U
ULTIPLEXER CHARACTERISTICS (Note 3)
LTC1293/4/6B LTC1293/4/6C
MIN TYP MAX 3.0 0.5 1.0 12 (V -)-0.05V to VCC + 0.05V
q q q q
LTC1293/4/6D
MIN TYP MAX 3.0 0.75 4.0 12 UNITS LSB LSB LSB Bits V 1 1 1 1 A A A A
CONDITIONS (Note 4) (Notes 4, 5) (Note 4)
q q q q
MIN
TYP MAX 3.0 0.5 0.5 12
(Note 7) On Channel = 5V Off Channel = 0V On Channel = 0V Off Channel = 5V On Channel = 5V Off Channel = 0V On Channel = 0V Off Channel = 5V 1 1 1 1
1 1 1 1
CONDITIONS VCC = 5V (Note 6) See Operating Sequence See Operating Sequence See Operating Sequence (Note 6) See Test Circuits See Test Circuits See Test Circuits VCC = 5V (Note 6)
q q q
LTC1293/4/6B LTC1293/4/6C LTC1293/4/6D MIN TYP MAX 0.1 2.5 12 21 CLK +500ns 160 80 80 50 130 65 25 300 400 50 50 500 21 750 250 100 5 5 1500 500 130 50 300 150 200 1.0
UNITS MHz CLK Cycles CLK Cycles Cycles ns ns ns ns ns ns ns ns ns ns ns ns CLK Cycles ns ns pF
3
LTC1293/LTC1294/LTC1296
DIGITAL A D DC ELECTRICAL CHARACTERISTICS (Note 3)
SYMBOL VIH VIL IIH IIL VOH VOL IOZ ISOURCE ISINK ICC ICC PARAMETER High Level Input Voltage Low Level Input Voltage High Level Input Current Low Level Input Current High Level Output Voltage Low Level Output Voltage High Z Output Leakage Output Source Current Output Sink Current Positive Supply Current Positive Supply Current CONDITIONS VCC = 5.25V VCC = 4.75V VIN = VCC VIN = 0V VCC = 4.75V, IO = -10mA IO = 360A VCC = 4.75V, IO = 1.6mA VOUT = VCC, CS High VOUT = 0V, CS High VOUT = 0V VOUT = VCC CS High CS High, Power Shutdown CLK Off IREF I
-
Reference Current Negative Supply Current SSO Source Current SSO Sink Current
ISOURCEs ISINKs
Note 1: Absolute Maximum Ratings are those values beyond which the life of a device may be impaired. Note 2: All voltage values are with respect to DGND, AGND and REF - wired together (unless otherwise noted). Note 3: VCC = 5V, VREF+ = 5V, VREF - = 0V, V - = 0V for unipolar mode and -5V for bipolar mode, CLK = 1.0MHz unless otherwise specified. The q denotes specifications which apply over the full operating temperature range; all other limits and typicals TA = 25C. Note 4: These specs apply for both unipolar and bipolar modes. In bipolar mode, one LSB is equal to the bipolar input span (2VREF) divided by 4096. For example, when VREF = 5V, 1LSB (bipolar) = 2 (5V)/4096 = 2.44mV. Note 5: Linearity error is specified between the actual end points of the A/D transfer curve. The deviation is measured from the center of the quantization band.
4
U
LTC1293/4/6B LTC1293/4/6C LTC1293/4/6D MIN TYP MAX
q q q q q q q q
UNITS V V A A V
2.0 0.8 2.5 -2.5 2.4 4.7 4.0 0.4 3 -3 -20 20
V A mA mA
q
6 5
12 10
mA A
LTC1294BC, LTC1294CC, LTC1294DC, LTC1294BI, LTC1294CI, LTC1294DI, LTC1294BM, LTC1294CM, LTC1294DM
q
q q q q q
5 10 1 0.8 0.5 1.5 1.0
15 50 50
A A A mA mA
CS High CS High VSSO = 0V VSSO = VCC
Note 6: Recommended operating conditions. Note 7: Two on-chip diodes are tied to each reference and analog input which will conduct for reference or analog input voltages one diode drop below V - or one diode drop above VCC. Be careful during testing at low VCC levels (4.5V), as high level reference or analog inputs (5V) can cause this input diode to conduct, especially at elevated temperatures, and cause errors for inputs near full scale. This spec allows 50mV forward bias of either diode. This means that as long as the reference or analog input does not exceed the supply voltage by more than 50mV, the output code will be correct. To achieve an absolute 0V to 5V input voltage range will therefore require a minimum supply voltage of 4.950V over initial tolerance, temperature variations and loading. Note 8: Channel leakage current is measured after the channel selection.
LTC1293/LTC1294/LTC1296
TYPICAL PERFOR A CE CHARACTERISTICS
Supply Current vs Supply Voltage
10 CLK = 1MHz TA = 25C 8
OFFSET (LSB = 1/4096 x VREF)
SUPPLY CURRENT (mA)
SUPPLY CURRENT (mA)
6
4
2
0
4
5 SUPPLY VOLTAGE (V)
Change in Linearity vs Reference Voltage
CHANGE IN LINEARITY (LSB = 1/4096 x VREF)
1.25
CHANGE IN GAIN (LSB = 1/4096 x VREF)
1.00
-0.2 -0.4 -0.6 -0.8 -1.0 -1.2
MAGNITUDE OF OFFSET CHANGE (LSB)
0.75
0.50
0.25
0
0
1
3 4 2 REFERENCE VOLTAGE (V)
Change in Linearity vs Temperature
0.5
MAGNITUDE OF LINEARITY CHANGE (LSB) MAGNITUDE OF GAIN CHANGE (LSB)
0.5
MINIMUM CLK FREQUENCY* (MHz)
0.4
VCC = 5V VREF = 5V CLK = 1MHz
0.3
0.2
0.1
0 -50
-25
25 50 75 100 0 AMBIENT TEMPERATURE (C)
UW
6
LTC1293 G01
Supply Current vs Temperature
10 9 8 7 6 5 4 3 -50 -30 -10 10 30 50 70 90 110 130 AMBIENT TEMPERATURE (C)
LTC1293 G02
Unadjusted Offset Voltage vs Reference Voltage
0.9 VCC = 5V 0.8 0.7 0.6 0.5 0.4 VOS = 0.250mV 0.3 0.2 0.1 1 VOS = 0.125mV 3 2 4 REFERENCE VOLTAGE (V) 5
LTC1293 G03
CLK = 1MHz VCC = 5V
Change in Gain vs Reference Voltage
0 VCC = 5V
Change in Offset vs Temperature
0.5 VCC = 5V VREF = 5V CLK = 1MHz
0.4
LTC1294/6
0.3
0.2
0.1
LTC1293 0 1 2 3 4 REFERENCE VOLTAGE (V) 5
LTC1293 G05
5
LTC1293 G04
0 -50
-25
25 50 75 100 0 AMBIENT TEMPERATURE (C)
125
LTC1293 G06
Change in Gain vs Temperature
VCC = 5V VREF = 5V CLK = 1MHz
Minimum Clock Rate for 0.1LSB Error
VCC = 5V 0.25 0.20 0.15 0.10 0.05
0.4
0.3
0.2
0.1
125
0 -50
-25
25 50 75 100 0 AMBIENT TEMPERATURE (C)
125
-50
-25
25 50 75 100 0 AMBIENT TEMPERATURE (C)
125
LTC1293 G07
LTC1293 G08
LTC1293 G09
* AS THE CLK FREQUENCY IS DECREASED FROM 1MHz, MINIMUM CLK FREQUENCY (ERROR 0.1LSB) REPRESENTS THE FREQUENCY AT WHICH A 0.1LSB SHIFT IN ANY CODE TRANSITION FROM ITS 1MHz VALUE IS FIRST DETECTED.
5
LTC1293/LTC1294/LTC1296
TYPICAL PERFOR A CE CHARACTERISTICS
DOUT Delay Time vs Temperature
250 VCC = 5V
MAXIMUM CLK FREQUENCY* (MHz) DOUT DELAY TIME FROM CLK (ns)
1.0
MAXIMUM RFILTER** ()
200
150
MSB FIRST DATA
100
LSB FIRST DATA
50
0 -50
-25
25 50 75 100 0 AMBIENT TEMPERATURE (C)
Sample and Hold Acquisition Time vs Source Resistance
100
S & H AQUISITION TIME TO 0.02% (s)
INPUT CHANNEL LEAKAGE CURRENT (nA)
800 700 600 500 400 300 200 100 ON CHANNEL OFF CHANNEL
PEAK-TO-PEAK NOISE ERROR (LSB)
VREF = 5V VCC = 5V TA = 25C 0V TO 5V INPUT STEP
10
VIN
RSOURCE+
+ -
1 100
1000 RSOURCE+ ()
LTC1296 SSO Source Current vs VCC - VSSO
500 VCC = 5V 400
ISOURCE (A)
400 300 500
200
ISINK (A)
300
100
0
0
0.1
0.5 0.6 0.2 0.3 0.4 VCC - VSSO VOLTAGE (V)
6
UW
LTC1293 G10
LTC1292 G13
Maximum Clock Rate vs Source Resistance
10k
VCC = 5V VREF = 5V CLK = 1MHz
Maximum Filter Resistor vs Cycle Time
RFILTER
0.8
+VIN
1k
+VIN
CFILTER 1F
+ -
0.6
+ +IN - -IN
RSOURCE-
100
0.4
10
0.2
125
0 100
1
1k 10k RSOURCE - () 100k
LTC1293 G11
10
100 1k CYCLE TIME (s)
10k
LTC1293 G12
Input Channel leakage Current vs Temperature
1000 900 GUARANTEED
2.25 2.00 1.75 1.50 1.25 1.00 0.75 0.50 0.25 0
Noise Error vs Reference Voltage
LTC1293/4/6 NOISE = 200Vp-p
10000
0 -50 -30 -10 10 30 50 70 90 110 130 AMBIENT TEMPERATURE (C)
LTC1293 G14
0
1
4 3 2 REFERENCE VOLTAGE (V)
5
LTC1293 G15
LTC1296 SSO Sink Current vs VSSO
VCC = 5V * MAXIMUM CLK FREQUENCY REPRESENTS THE CLK FREQUENCY AT WHICH A 0.1LSB SHIFT IN THE ERROR AT ANY CODE TRANSITION FROM ITS 1MHz VALUE IS FIRST DETECTED. ** MAXIMUM RFILTER REPRESENTS THE FILTER RESISTOR VALUE AT WHICH A 0.1LSB CHANGE IN FULL SCALE ERROR FROM ITS VALUE AT RFILTER = 0 IS FIRST DETECTED.
200
100
0
0.7
0
0.2
0.6 0.4 VSSO VOLTAGE (V)
0.8
1.0
LTC1293 G17
LTC1293 G16
LTC1293/LTC1294/LTC1296
PI FU CTIO S
LTC1293 #
1-6 7 8 9 10 11 12 13 14 15 16
PIN
CH0 - CH5 COM DGND V- AGND VREF DIN DOUT CS CLK VCC
FUNCTION
Analog Inputs Common
The analog inputs must be free of noise with respect to AGND. The common pin defines the zero reference point for all single ended inputs. It must be free of noise and is usually tied to the analog ground plane. Digital Ground This is the ground for the internal logic. Tie to the ground plane. Negative Supply Tie V - to most negative potential in the circuit (Ground in single supply applications). Analog Ground AGND should be tied directly to the analog ground plane. Ref. Input The reference inputs must be kept free of noise with respect to AGND. Data Input The A/D configuration word is shifted into this input. Digital Data Output The A/D conversion result is shifted out of this output. Chip Select Input A logic low on this input enables data transfer. Clock This clock synchronizes the serial data transfer and controls A/D conversion rate. Positive supply This supply must be kept free of noise and ripple by bypassing directly to the analog ground plane.
LTC1294 #
1 -8 9 10 11 12 13, 14 15 16 17 18 19, 20
PIN
CH0 - CH7 COM DGND V- AGND REF -, REF + DIN DOUT CS CLK AVCC, DVCC
FUNCTION
Analog Inputs Common
The analog inputs must be free of noise with respect to AGND. The common pin defines the zero reference point for all single ended inputs. It must be free of noise and is usually tied to the analog ground plane. Digital Ground This is the ground for the internal logic. Tie to the ground plane. Negative Supply Tie V - to most negative potential in the circuit (Ground in single supply applications). Analog Ground AGND should be tied directly to the analog ground plane. Ref. Inputs The reference inputs must be kept free of noise with respect to AGND. The A/D sees a reference voltage equal to the difference between REF + and REF -. Data Input The A/D configuration word is shifted into this input. Digital Data Output The A/D conversion result is shifted out of this output. Chip Select Input A logic low on this input enables data transfer. Clock This clock synchronizes the serial data transfer and controls A/D converion rate. Positive Supplies These supplies must be kept free of noise and ripple by bypassing directly to the analog ground plane. AVCC and DVCC must be tied together.
LTC1296 #
1 -8 9 10 11 12 13, 14 15 16 17 18 19 20
PIN
CH0 - CH7 COM DGND V- AGND REF -, REF + DIN DOUT CS CLK SSO VCC
FUNCTION
Analog Inputs Common
The analog inputs must be free of noise with respect to AGND. The common pin defines the zero reference point for all single ended inputs. It must be free of noise and is usually tied to the analog ground plane. Digital Ground This is the ground for the internal logic. Tie to the ground plane. Negative Supply Tie V - to most negative potential in the circuit (Ground in single supply applications). Analog Ground AGND should be tied directly to the analog ground plane. Ref. Inputs The reference inputs must be kept free of noise with respect to AGND. The A/D sees a reference voltage equal to the difference between REF + and REF -. Data Input The A/D configuration word is shifted into this input. Digital Data Output The A/D conversion result is shifted out of this output. Chip Select Input A logic low on this input enables data transfer. Clock This clock synchronizes the serial data transfer and controls A/D conversion rate. System Shutdown System Shutdown Output pin will go low when power shutdown is requested. Output Positive Supply This supply must be kept free of noise and ripple by bypassing directly to the analog ground plane.
U
U
U
DESCRIPTION
DESCRIPTION
DESCRIPTION
7
LTC1293/LTC1294/LTC1296
BLOCK DIAGRA
20 DVCC AVCC 19 DIN 15
INPUT SHIFT REGISTER
CH0 CH1 CH2 CH3 CH4 CH5 CH6 CH7 COM
1 2 3 4 5 6 7 8 9 12-BIT CAPACITIVE DAC ANALOG INPUT MUX SAMPLE AND HOLD
10 DGND
TEST CIRCUITS
Load Circuit for tdDO, tr and tf
1.4V
DOUT 100pF
Load Circuit for tdis and ten
TEST POINT
5V
3k DOUT 100pF
8
W
3k
(Pin numbers refer to LTC1294)
18 CLK
OUTPUT SHIFT REGISTER
16
DOUT
COMP 12-BIT SAR
11 V-
12 AGND
13 REF -
14 REF +
CONTROL AND TIMING
17
CS
LTC1293 BD
Load Circuit for tenSSO and tdisSSO
1.4V
3k
TEST POINT
SSO LT1296 100pF
TEST POINT
LTC1293 TC02
LTC1293 TC08
On and Off Channel Leakage Current
ION A ON CHANNEL
5V tdis WAVEFORM 2, ten tdis WAVEFORM 1
LTC1293 TC05
IOFF A OFF CHANNELS
POLARITY
LTC1293 TC1
LTC1293/LTC1294/LTC1296 TEST CIRCUITS
Voltage Waveforms for ten
CS
DIN
START
CLK
1
2
3
4
5
6
7
8
DOUT ten
0.8V
B11
LTC1293 TC07
Voltage Waveform for tdisSSO
Voltage Waveform for DOUT Rise and Fall Times, tr, tf
2.4V
CS
0.8V tdisSSO
DOUT
0.4V
SSO
2.4V
LTC1293 TC10
tr
tf
LTC1293 TC04
Voltage Waveform for for tenSSO
Voltage Waveform for tdis
CLK
0.8V tenSSO
CS
2.0V
SSO 0.8V
LTC1293 TC09
DOUT WAVEFORM 1 (SEE NOTE 1) tdis DOUT WAVEFORM 2 (SEE NOTE 2)
90%
10%
Voltage Waveform for DOUT Delay Time, tdDO
CLK
NOTE 1: WAVEFORM 1 IS FOR AN OUTPUT WITH INTERNAL CONDITIONS SUCH THAT THE OUTPUT IS HIGH UNLESS DISABLED BY THE OUTPUT CONTROL. NOTE 2: WAVEFORM 2 IS FOR AN OUTPUT WITH INTERNAL CONDITIONS SUCH THAT THE OUTPUT IS LOW UNLESS DISABLED BY THE OUTPUT CONTROL.
LTC1293 TC06
0.8V tdDO 2.4V
DOUT 0.4V
LTC1293 TC03
9
LTC1293/LTC1294/LTC1296
APPLICATI
S I FOR ATIO
The LTC 1293/4/6 is a data acquisition component which contains the following functional blocks: 1. 12-bit successive approximation capacitive A/D converter 2. Analog multiplexer (MUX) 3. Sample and hold (S/H) 4. Synchronous, half duplex serial interface 5. Control and timing logic DIGITAL CONSIDERATIONS Serial Interface The LTC1293/4/6 communicates with microprocessors and other external circuitry via a synchronous, half duplex, four-wire serial interface (see Operating Sequence). The clock (CLK) synchronizes the data transfer with each bit being transmitted on the falling CLK edge and captured on the rising CLK edge in both transmitting and receiving systems. The input data is first received and then the A/D conversion result is transmitted (half duplex). Because of
CS
DIN 1 DOUT 1
SHIFT MUX 1 NULL ADDRESS IN BIT
SHIFT A/D CONVERSION RESULT OUT
the half duplex operation DIN and DOUT may be tied together allowing transmission over just 3 wired: CS, CLK and DATA (DIN/DOUT). Data transfer is initiated by a falling chip select (CS) signal. After CS falls the LTC1293/4/6 looks for a start bit. After the start bit is received a 7-bit input word is shifted into the DIN input which configures the LTC1293/4/6 and starts the conversion. After one null bit, the result of the conversion is output on the DOUT line. With the half duplex serial interface the DOUT data is from the current conversion. After the end of the data exchange CS should be brought high. This resets the LTC1293/4/6 in preparation for the next data exchange.
10
U
INPUT DATA WORD The LTC1293/4/6 seven-bit data word is clocked into the DIN input on the rising edge of the clock after chip select goes low and the start bit has been recognized. Further inputs on the DIN pin are then ignored until the next CS cycle. The input word is defined as follows:
UNIPOLAR/ BIPOLAR SGL/ DIFF ODD/ SIGN SELECT 1 SELECT 0 UNI MSBF POWER SHUTDOWN START PS MUX ADDRESS MSB FIRST/ LSB FIRST
LTC1293 AI02
W
U
UO
Start Bit The first "logical one" clocked into the DIN input after CS goes low is the start bit. The start bit initiates the data transfer and all leading zeroes which precede this logical one will be ignored. After the start bit is received the remaining bits of the input word will be clocked in. Further inputs on the DIN pin are then ignored until the next CS cycle.
DIN 2 DOUT 2
LTC1293 AI01
MUX Address The four bits of the input word following the START BIT assign the MUX configuration for the requested conversion. For a given channel selection, the converter will measure the voltage between the two channels indicated by the + and - signs in the selected row of the following table. Note that in differential mode (SGL/DIFF = 0) measurements are limited to four adjacent input pairs with either polarity. In single ended mode, all input channels are measured with respect to COM. Only the +inputs have sample and holds. Signals applied at the -inputs must not change more than the required accuracy during the conversion.
LTC1293/LTC1294/LTC1296
APPLICATI
S I FOR ATIO
Table 1a. LTC1294/6 Multiplexer Channel Selection
MUX ADDRESS SGL/ ODD SELECT DIFF SIGN 1 0 0 0 00 0 0 01 0 0 10 0 0 11 0 1 00 0 1 01 0 1 10 0 1 11 DIFFERENTIAL CHANNEL SELECTION 0 + 1 - + - + - + - + - + - + - + - 2 3 4 5 6 7 MUX ADDRESS SGL/ ODD SELECT DIFF SIGN 1 0 1 0 00 1 0 01 1 0 10 1 0 11 1 1 00 1 1 01 1 1 10 1 1 11 SINGLE-ENDED CHANNEL SELECTION 0 + + + + + + + + 1 2 3 4 5 6 7 COM - - - - - - - -
Table 1b. LTC1293 Channel Selection
MUX ADDRESS SGL/ ODD SELECT DIFF SIGN 1 0 0 0 00 0 0 01 0 0 10 0 0 11 0 1 00 0 1 01 0 1 10 0 1 11 DIFFERENTIAL CHANNEL SELECTION 0 + 1 - + - + Not Used - + - + - Not Used + - 2 3 4 5 MUX ADDRESS SGL/ ODD SELECT DIFF SIGN 1 0 1 0 00 1 0 01 1 0 10 1 0 11 1 1 00 1 1 01 1 1 10 1 1 11 SINGLE-ENDED CHANNEL SELECTION 0 + + + Not Used + + + Not Used - - - 1 2 3 4 5 COM - - -
Unipolar/Bipolar (UNI) The UNI bit determines whether the conversion will be unipolar or bipolar. When UNI is a logical one, a unipolar conversion will be performed on the selected input voltUnipolar Transfer Curve (UNI = 1)
OUTPUT CODE 111111111111 111111111110 * * * 000000000001 000000000000
INPUT VOLTAGE VREF - 1LSB VREF - 2LSB * * * 1LSB 0V
INPUT VOLTAGE (VREF = 5V) 4.9988V 4.9976V * * * 0.0012V 0V
LTC1293 AI03a
U
age. When UNI is a logical zero, a bipolar conversion will result. The input span and code assignment for each conversion type are shown in the figures below:
Unipolar Output Code (UNI = 1)
111111111111 111111111110
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* * *
000000000001 000000000000 VIN
0V
1LSB
VREF-1LSB
VREF
VREF-2LSB
LTC1293 AI03b
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LTC1293/LTC1294/LTC1296
APPLICATI
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INPUT VOLTAGE VREF - 1LSB VREF - 2LSB * * * 1LSB 0V
Bipolar Transfer Curve (UNI = 0)
OUTPUT CODE 011111111111 011111111110 * * * 000000000001 000000000000 INPUT VOLTAGE (VREF = 5V) 4.9976V 4.9851V * * * 0.0024V 0V OUTPUT CODE 111111111111 111111111110 * * * 100000000001 100000000000 INPUT VOLTAGE -1LSB -2LSB * * * -(VREF) + 1LSB - (VREF) INPUT VOLTAGE (VREF = 5V) -0.0024V -0.0048V * * * -4.9976V -5.00000V
LTC1293 AI04a
Bipolar Output Code (UNI = 0)
011111111111 011111111110
1LSB
* * * 000000000001 000000000000
The following discussion will demonstrate how the two reference pins are to be used in conjunction with the analog input multiplexer. In unipolar mode the input span of the A/D is set by the difference in voltage on the REF + pin and the REF - pin. In the bipolar mode the input span is twice the difference in voltage on the REF + pin and the REF - pin. In the unipolar mode the lower value of the input span is set by the voltage on the COM pin for single-ended inputs and by the voltage on the minus input pin for differential inputs. For the bipolar mode of operation the voltage on the COM pin or the minus input pin set the center of the input span. The upper and lower value of the input span can now be summarized in the following table:
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VIN
VREF-1LSB VREF VREF-2LSB
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-VREF
-VREF + 1LSB
111111111111 111111111110 * * * 100000000001 100000000000
-2LSB -1LSB
LTC1293 AI04b
INPUT CONFIGURATION
Single-Ended Differential
Lower Value COM -(REF + - REF - ) + COM + - Upper Value (REF - REF ) + COM (REF+ - REF - ) + COM Lower Value IN - Upper Value (REF + - REF - ) + IN - -(REF + - REF - ) + IN - (REF + - REF - ) + IN -
UNIPOLAR MODE
BIPOLAR MODE
The reference voltages REF + and REF - can fall between VCC and V -, but the difference (REF + - REF -) must be less than or equal to VCC. The input voltages must be less than or equal to VCC and greater than or equal to V -. For the LTC1293 REF - = 0V. The following examples are for a single-ended input configuration. Example 1: Let VCC = 5V, V - = 0V, REF + = 4V, REF - = 1V and COM = 0V. Unipolar mode of operation. The resulting input span is 0V IN + 3V.
LTC1293/LTC1294/LTC1296
APPLICATI
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Example 2: The same conditions as Example 1 except COM = 1V. The resulting input span is 1V IN + 4V. Note if IN + 4V the resulting DOUT word is all 1's. If IN + 1V then the resulting DOUT word is all 0's. Example 3: Let VCC = 5V, V - = -5V, REF + = 4V, REF - = 1V and COM = 1V. Bipolar mode of operation. The resulting input span is -2V IN + 4V. For differential input configurations with the same conditions as in the above three examples the resulting input spans are as follows: Example 1 (Diff.): IN - IN + IN - + 3V. Example 2 (Diff.): IN - IN + IN - + 3V. Example 3 (Diff.): IN - - 3V IN + IN - + 3V.
Operating Sequence Example: Differential Inputs (CH4 +, CH5-), Unipolar Mode
MSB-FIRST DATA (MSBF = 1) tCYC CS
CLK START DIN SGL/ ODD/ SEL0 DIFF SIGN HI-Z DOUT tSMPL SEL1 UNI MSBF B11 PS DON'T CARE B1 B0 FILLED WITH ZEROES tCONV
MSB-FIRST DATA (MSBF = 0) tCYC CS
CLK START DIN SGL/ ODD/ SEL0 DIFF SIGN MSBF B11 SEL1 UNI PS DON'T CARE B1 B0 B1 B11
DOUT
HI-Z
tSMPL
tCONV
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MSB-First/LSB-First (MSBF) The output data of the LTC1293/4/6 is programmed for MSB-first or LSB-first sequence using the MSB bit. When the MSBF bit is a logical one, data will appear on the DOUT line in MSB-first format. Logical zeroes will be filled in indefinitely following the last data bit to accommodate longer word lengths required by some microprocessors. When the MSBF bit is a logical zero, LSB first data will follow the normal MSB first data on the DOUT line. In the bipolar mode the sign bit will fill in after the MSB bit for MSBF = 0 (see Operating Sequence). Power Shutdowns (PS) The power shutdown feature of the LTC1293/4/6 is activated by making the PS bit a logical zero. If CS remains low after the PS bit has been received, a 12-bit DOUT word with
DON'T CARE DON'T CARE FILLED WITH ZEROES
LTC1293 AI05
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SHUTDOWN* NEW CONVERSION BEGINS START DON'T CARE SEL1/ ODD/ SEL0 MSBF DIFF SIGN HI-Z B11
* * * * * * * * * *
Power Shutdown Operating Sequence Example: Differential Inputs (CH4+, CH5 -), Unipolar Mode and MSB-First Data
CS
REQUEST POWER SHUTDOWN
CLK START DIN SEL1 UNI PS SEL1 UNI PS
DOUT
*STOPPING THE CLOCK WILL HELP REDUCE POWER CONSUMPTION. CS CAN BE BROUGHT HIGH ONCE THE DIN WORD HAS BEEN CLOCKED IN.
all logical ones will be shifted out followed by logical zeroes till CS goes high. Then the DOUT line will go into its high impedance state. The LTC 1293/4/6 will remain in the shutdown mode till the next CS cycle. There is no warmup or wait period required after coming out of the power shutdown cycle so a conversion can commence after CS goes low (see Power Shutdown Operating Sequence). The LTC1296 has a System Shutdown Output pin (SSO) which will go low when power shutdown is activated. The pin will stay low till next CS cycle. Microprocessor Interfaces The LTC1293/4/6 can interface directly (without external hardware) to most popular microprocessors (MPU) synchronous serial formats (see Table 1). If an MPU without a dedicated serial port is used, then three of the MPU's parallel port lines can be programmed to form the serial link to the LTC1293/4/6. Included here are one serial interface example and one example showing a parallel port programmed to form the serial interface. Microprocessor Interfaces The LTC1293/4/6 can interface directly (without external hardware) to most popular microprocessors (MPU) synchronous serial formats (see Table 1). If an MPU without a dedicated serial port is used, then three of the MPU's parallel port lines can be programmed to form the serial link to the LTC1293/4/6.
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MSBF B0 FILLED WITH ZEROES SEL1/ ODD/ SEL0 DIFF SIGN
HI-Z
LTC1293 AI06
Table 1. Microprocessor with Hardware Serial Interfaces Compatible with the LTC1293/4/6**
PART NUMBER Motorola MC6805S2, S3 MC68HC11 MC68HC05 RCA CDP68HC05 Hitachi HD6305 HD6301 HD63701 HD6303 HD64180 National Semiconductor COP400 Family COP800 Family NS8050U HPC16000 Family Texas Instruments TMS7002 TMS7042 TMS70C02 TMS70C42 TMS32011* TMS32020* TMS370C050 TYPE OF INTERFACE SPI SPI SPI SPI SCI Synchronous SCI Synchronous SCI Synchronous SCI Synchronous SCI Synchronous MICROWIRE MCROWIRE/PLUS MICROWIRE/PLUS MICROWIRE/PLUS Serial Port Serial Port Serial Port Serial Port Serial Port Serial Port SPI
* Requires external hardware ** Contact factory for interface information for processors not on this list MICROWIRE and MICROWIRE/PLUS are trademarks of National Semiconductor Corp.
LTC1293/LTC1294/LTC1296
APPLICATI
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Motorola SPI (MC68HC11) The MC68HC11 has been chosen as an example of an MPU with a dedicated serial port. This MPU transfers data MSBfirst and in 8-bit increments. The DIN word sent to the data register starts the SPI process. With three 8-bit transfers, the A/D result is read into the MPU. The second 8-bit transfer clocks B11 through B8 of the A/D conversion result into the processor. The third 8-bit transfer clocks the remaining bits B7 through B0 into the MPU. The data is right justified in the two memory locations. ANDing the second byte with 0DHEX clears the four most significant bits. This operation was not included in the code. It can be inserted in the data gathering loop or outside the loop when the data is processed.
Data Exchange Between LTC1294 and MC68HC11
CS
CLK
DIN
SGL/ START DIFF
ODD/ EVEN
SEL 1
SEL 0
UNI
DOUT START MPU TRANSMIT WORD
0
0
0
1 BYTE 1
SGL
ODD
SEL 1
SEL 0
UNI MSBF
MPU RECEIVED WORD
?
?
?
? BYTE 1
?
?
?
?
?
Hardware and Software Interface to Motorola MC68HC11
DOUT FROM LTC1294 STORED ON MC68HC11 RAM MSB #62 O O O O B11 B10 B9 B8 LSB #63 B7 B6 B5 B4 B3 B2 B1 B0 BYTE 2 DOUT MISO
LTC1293 TD01a
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Interfacing to the Parallel Port of the Intel 8051 Family The Intel 8051 has been chosen to show the interface between the LTC1293/4/6 and parallel port microprocessors. Usually the signals CS, DIN and CLK are generated on three port lines and the DOUT signal is read on a fourth port line. This works very well. One can save a line by tying the DIN and DOUT lines together. The 8051 first sends the start bit and DIN to the LTC1294 over the line connected to P1.2. Then P1.2 is reconfigured as an input and the 8051 reads back the 12-bit A/D result over the same data line.
MSBF PS DON'T CARE B11 B10 B9 B8 B7 B6 B5 B4 B3 B2 B1 B0 PS X X X X X X X X X X X X X BYTE 2 BYTE 3 (DUMMY) ? ? 0 B11 B10 B9 B8 B7 B6 B5 B4 B3 B2 B1 B0
LTC1293 TD01
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BYTE 2
BYTE 3
BYTE 1 ANALOG INPUTS LTC1294
CS CLK DIN
DO SCK MC68HC11 MOSI
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LTC1293/LTC1294/LTC1296
APPLICATI
MC68HC11 CODE
LABEL MNEMONIC LDAA STAA LDAA STAA LDAA STAA LDAA STAA LDAA STAA LDX LOOP BCLR LDAA STAA LDAA WAIT1 BPL LDAA
S I FOR ATIO
OPERAND #$50 $1028 #$1B $1009 #$10 $50 #$E0 $51 #$00 $52 #$1000 $08,X,$01 $50 $102A $1029 WAIT1 $51
COMMENTS CONFIGURATION DATA FOR SPCR LOAD DATA INTO SPCR ($1028) CONFIG. DATA FOR PORT D DDR LOAD DATA INTO PORT D DDR LOAD DIN WORD INTO ACC A LOAD DIN DATA INTO $50 LOAD DIN WORD INTO ACC A LOAD DIN DATA INTO $51 LOAD DUMMY DIN WORD INTO ACC A LOAD DUMMY DIN DATA INTO $52 LOAD INDEX REGISTER X WITH $1000 D0 GOES LOW (CS GOES LOW) LOAD DIN INTO ACC A FROM $50 LOAD DIN INTO SPI, START SCK CHECK SPI STATUS REG CHECK IF TRANSFER IS DONE LOAD DIN INTO ACC A FROM $51
Hardware and Software Interface to Intel 8051
PS BIT LATCHED INTO LTC1294 CS 1 CLK 2 3 4 5 6 7 8
DATA (DIN/DOUT)
SGL/ DIFF START
ODD/ SIGN
SEL 1
SEL 0
UNI
8051 P1.2 OUTPUT DATA TO LTC1294 8051 P1.2 RECONFIGURED AS INPUT AFTER THE 8TH RISING CLK BEFORE THE 8TH FALLING CLK
Hardware and Software Interface to Intel 8051
DOUT FROM LTC1294 STORED IN 8051 RAM MSB
R2
B11
B10
B9
B8
B7
B6
B5
LSB
R3
B3
B2
B1
B0
0
0
0
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LABEL MNEMONIC STAA WAIT2 LDAA BPL LDAA STAA LDAA STAA WAIT3 LDAA BPL BSET LDAA STAA JMP OPERAND COMMENTS $102A LOAD DIN INTO SPI, START SCK $1029 CHECK SPI STATUS REG WAIT2 CHECK IF TRANSFER IS DONE $102A LOAD LTC1294 MSBs INTO ACC A $62 STORE MSBs IN $62 $52 LOAD DUMMY DIN INTO ACC A FROM $52 $102A LOAD DUMMY DIN INTO SPI, START SCK $1029 CHECK SPI STATUS REG WAIT3 CHECK IF TRANSFER IS DONE $08,X,$01 D0 GOES HIGH (CS GOES HIGH) $102A LOAD LTC1294 LSBs IN ACC $63 STORE LSBs IN $63 LOOP START NEXT CONVERSION
B10 MSB PS B11 B9 B8 B7 B6 B5 B4 B3 B2 B1
LTC1293 TD02
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B0
LTC1294 SEND A/D RESULT BACK TO 8051 P1.2 LTC1294 TAKES CONTROL OF DATA LINE ON 8TH FALLING CLK
B4 ANALOG INPUTS 0 LTC1294
CS CLK DOUT DIN MUX ADDRESS A/D RESULT
P1.4 P1.3 8051 P1.2
LTC1293 TD02a
LTC1293/LTC1294/LTC1296
APPLICATI
8051 CODE
LABEL MNEMONIC SETB CONT MOV CLR MOV LOOP1 RLC CLR MOV SETB DJNZ MOV CLR MOV LOOP MOV RLC SETB CLR DJNZ MOV MOV SETB
S I FOR ATIO
OPERAND P1.4 A,#87H P1.4 R4,#08H A P1.3 P1.2,C P1.3 R4,LOOP1 P1,#04H P1.3 R4,#09H C,P1.2 A P1.3 P1.3 R4,LOOP R2,A C,P1.2 P1.3
COMMENTS CS GOES HIGH DIN WORD FOR LTC1294 CS GOES LOW LOAD COUNTER ROTATE DIN BIT INTO CARRY CLK GOES LOW OUTPUT DIN BIT TO LTC1294 CLK GOES HIGH NEXT DIN BIT P1.2 BECOMES AN INPUT CLK GOES LOW LOAD COUNTER READ DATA BIT INTO CARRY ROTATE DATA BIT (B3) INTO ACC CLK GOES HIGH CLK GOES LOW NEXT DOUT BIT STORE MSBs IN R2 READ DATA BIT INTO CARRY CLK GOES HIGH
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0 3-WIRE SERIAL INTERFACE TO OTHER PERIPHERALS OR LTC1293/4/6s CS LTC1294 8 CHANNELS
OUTPUT PORT SERIAL DATA 3 3 CS LTC1294 8 CHANNELS 3 CS LTC1294 8 CHANNELS 3
MPU
Figure 3. Several LTC1294 Sharing One 3-Wire Serial Interface
Sharing the Serial Interface The LTC1293/4/6 can share the same 3-wire serial interface with other peripheral components or other LTC1293/ 4/6's (Figure 3). Now, the CS signals decide which LTC1293/ 4/6 is being addressed by the MPU. ANALOG CONSIDERATIONS Grounding The LTC1293/4/6 should be used with an analog ground plane and single point grounding techniques. Do not use wire wrapping techniques to breadboard and evaluate the
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LABEL MNEMONIC CLR CLR RLC MOV RLC SETB CLR MOV RLC SETB CLR MOV SETB RRC RRC RRC RRC MOV AJMP OPERAND P1.3 A A C,P1.2 A P1.3 P1.3 C,P1.2 A P1.3 P1.3 C,P1.2 P1.4 A A A A R3,A CONT COMMENTS CLK GOES LOW CLEAR ACC ROTATE DATA BIT (B3) INTO ACC READ DATA BIT INTO CARRY ROTATE DATA BIT (B2) INTO ACC CLK GOES HIGH CLK GOES LOW READ DATA BIT INTO CARRY ROTATE DATA BIT (B1) INTO ACC CLK GOES HIGH CLK GOES LOW READ DATA BIT INTO CARRY CS GOES HIGH ROTATE DATA BIT (B0) INTO ACC ROTATE RIGHT INTO ACC ROTATE RIGHT INTO ACC ROTATE RIGHT INTO ACC STORE LSBs IN R3 START NEXT CONVERSION
LTC1293 F03
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device. To achieve the optimum performance use a PC board. The analog ground pin (AGND) should be tied directly to the ground plane with minimum lead length (a low profile socket is fine). The digital ground pin (DGND) also can be tied directly to this ground pin because minimal digital noise is generated within the chip itself. VCC should be bypassed to the ground plane with a 22F (minimum value) tantalum with leads as short as possible and as close as possible to the pin. A 0.1F ceramic disk also should be placed in parallel with the 22F and again with leads as short as possible and as close to VCC as possible. AVCC and DVCC should be tied together on the
17
LTC1293/LTC1294/LTC1296
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VERTICAL: 0.5mV/DIV HORIZONTAL: 10s/DIV
LTC1294. Figure 4 shows an example of an ideal LTC1293/ 4/6 ground plane design for a two sided board. Of course this much ground plane will not always be possible, but users should strive to get as close to this ideal as possible.
22F TANTALUM
VCC
1 2 3 4 5 6 7 8 9 10 ANALOG GROUND PLANE
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VERTICAL: 0.5mV/DIV
19 18 17 16 15 14 13 12 11 V- 0.1F CERAMIC DISK
LTC1293 F04
Figure 4. Ground Plane for the LTC1293/4/6
Bypassing For good performance, VCC must be free of noise and ripple. Any changes in the VCC voltage with respect to ground during a conversion cycle can induce errors or noise in the output code. VCC noise and ripple can be kept below 0.5mV by bypassing the VCC pin directly to the analog ground plane with a minimum of 22F tantalum capacitor and with leads as short as possible. The lead from the device to the VCC supply also should be kept to a minimum and the VCC supply should have a low output impedance such as obtained from a voltage regulator (e.g., LT323A). For high frequency bypassing a 0.1F ceramic disk placed in parallel with the 22F is recommended. Again the leads should be kept to a minimum. Figure 5 and 6 show the effects of good and poor VCC bypassing.
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0.1F CERAMIC
Figure 5. Poor VCC Bypassing. Noise and Ripple Can Cause A/D Errors.
CS
VCC
HORIZONTAL: 10s/DIV
Figure 6. Good VCC Bypassing Keeps Noise and Ripple on VCC Below 1mV
Analog Inputs Because of the capacitive redistribution A/D conversion techniques used, the analog inputs of the LTC1293/4/6 have capacitive switching input current spikes. These current spikes settle quickly and do not cause a problem. If large source resistances are used or if slow settling op amps drive the inputs, take care to insure the transients caused by the current spikes settle completely before the conversion begins.
RSOURCE + VIN + C1 "-" INPUT "+" INPUT LTC1293/4/6 6TH CLK RON = 500 8TH CLK CIN = 100pF
RSOURCE - VIN -
C2
LTC1293 F07
Figure 7. Analog Input Equivalent Circuit
LTC1293/LTC1294/LTC1296
APPLICATI
S I FOR ATIO
Source Resistance The analog inputs of the LTC1293/4/6 look like a 100pF capacitor (CIN) in series with a 500 resistor (RON). CIN gets switched between (+) and (-) inputs once during each conversion cycle. Large external source resistors and capacitances will slow the settling of the inputs. It is important that the overall RC time constant is short enough to allow the analog inputs to settle completely within the allowed time. "+" Input Settling The input capacitor is switched onto the "+" input during the sample phase (tSMPL, see Figure 8). The sample period 2 1/2 CLK cycles before a conversion starts. The voltage on the "+" input must settle completely within the sample period. Minimizing RSOURCE+ and C1 will improve the settling time. If large "+" input source resistance must be used, the sample time can be increased by using a slower CLK frequency. With the minimum possible sample time of 2.5s RSOURCE + < 1.5k and C1 < 20pF will provide adequate settling time.
CS
CLK
DIN
START
SGL/ DIFF
DOUT HI-Z
1ST BIT TEST (-) INPUT MUST SETTLE DURING THIS TIME
(+) INPUT
(-) INPUT
Figure 8. "+" and "-" Input Settling Windows
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"-" Input Settling At the end of the sample phase the input capacitor switches to the "-" input and the conversion starts (see Figure 8). During the conversion, the "+" input voltage is effectively "held" by the sample and hold and will not affect the conversion result. It is critical that the "-" input voltage be free of noise and settle completely during the first CLK cycle of the conversion. Minimizing RSOURCE - and C2 will improve settling time. If large "-" input source resistance must be used the time can be extended by using a slower CLK frequency. At the maximum CLK frequency of 1MHz, RSOURCE - < 250 and C2 < 20pF will provide adequate settling. Input Op Amps When driving the analog inputs with an op amp it is important that the op amp settles within the allowed time (see Figure 8). Again the "+" and "-" input sampling times can be extended as described above to accommodate slower op amps. Most op amps including the LT1006 and LT1013 single supply op amps can be made to settle
SAMPLE HOLD MSBF PS tSMPL (+) INPUT MUST SETTLE DURING THIS TIME B11
LTC1293 F08
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LTC1293/LTC1294/LTC1296
APPLICATI
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within the minimum settling windows of 2.5s ("+" input) and 1s("-" input) that occurs at the maximum clock rate of 1MHz. Figures 9 and 10 show examples of adequate and poor op amp settling.
VERTICAL: 5mV/DIV
HORIZONTAL: 500ns/DIV
Figure 9. Adequate Settling of Op Amp Driving Analog Input
VERTICAL: 5mV/DIV
HORIZONTAL: 20s/DIV
Figure 10. Poor Op Amp Settling Can Cause A/D Errors
RC Input Filtering It is possible to filter the inputs with an RC network as shown in Figure 11. For large values of CF (e.g., 1F) the capacitive input switching currents are averaged into a net DC current. A filter should be chosen with a small resistor and large capacitor to prevent DC drops across the resistor. The magnitude of the DC current is approximately IDC = 100pF x VIN/tCYC and is roughly proportional to VIN. When running at the minimum cycle time of 21.5s, the input current equals 23A at VIN = 5V. Here a filter resistor of 5 will cause 0.1LSB of full-scale error. If a larger filter resistor must be used, errors can be reduced by increasing
RFILTER VIN - CFILTER IIDC "+" LTC1293/4/6 "-"
LTC1293 F11
Figure 11. RC Input Filtering
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the cycle time as shown in the typical performance characteristic curve Maximum Filter Resistor vs Cycle Time. Input Leakage Current Input leakage currents also can create errors if the source resistance gets too large. For example, the maximum input leakage specification of 1A (at 125C) flowing through a source resistance of 1k will cause a voltage drop of 1mV or 0.8LSB. This error will be much reduced at lower temperatures because leakage drops rapidly (see typical performance characteristic curve Input Channel Leakage Current vs Temperature). SAMPLE AND HOLD Single-Ended Input The LTC1293/4/6 provides a built-in sample and hold (S&H) function for all signals acquired in the single-ended mode (COM pin grounded). The sample and hold allows the LTC1293/4/6 to convert rapidly varying signals (see typical performance characteristic curve of S&H Acquisition Time vs Source Resistance). The input voltage is sampled during the tSMPL time as shown in Figure 8. The sampling interval begins as the bit preceding the MSBF bit is shifted in and continues until the falling edge of the PS bit is received. On this falling edge the S&H goes into the hold mode and the conversion begins. Differential Input With a differential input the A/D no longer converts a single voltage but converts the difference between two voltages. The voltage on the selected "+" input is sampled and held and can be rapidly time varying. The voltage on the "-" pin must remain constant and be free of noise and ripple throughout the conversion time. Otherwise the differencing operation will not be done accurately. The conversion time is 12 CLK cycles. Therefore a change in the -IN input voltage during this interval can cause conversion errors. For a sinusoidal voltage on the -IN input this error would be: 12 VERROR (MAX) = 2f(-)VPEAK fCLK
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(
)
Where f(-) is the frequency of the "-" input voltage, VPEAK is its peak amplitude and fCLK is the frequency of the CLK.
LTC1293/LTC1294/LTC1296
APPLICATI
S I FOR ATIO
Usually VERROR will not be significant. For a 60Hz signal on the "-" input to generate a 0.25LSB error (300V) with the converter running at CLK = 1MHz, its peak value would have to be 66mV. Rearranging the above equation the maximum sinusoidal signal that can be digitized to a given accuracy is given as:
VERROR(MAX) fCLK f(-) MAX = 2VPEAK 12
VERTICAL: 0.5mV/DIV
For 0.25LSB error (300V) the maximum input sinusoid with a 5V peak amplitude that can be digitized is 0.8Hz. Unused inputs should be tied to the ground plane. Reference Input The voltage on the reference input of the LTC1293/4/6 determines the voltage span of the A/D converter. The reference input has transient capacitive switching currents due to the switched capacitor conversion technique (see Figure 12). During each bit test of the conversion (every CLK cycle) a capacitive current spike will be generated on the reference pin by the A/D. These current spikes settle quickly and do not cause a problem. If slow settling circuitry is used to drive the reference input, take care to insure that transients caused by these current spikes settle completely during each bit test of the conversion.
REF+ 14 ROUT VREF REF- 13 LTC1293/4/6 EVERY CLK CYCLE RON 8pF - 40pF
VERTICAL: 0.5mV/DIV
LTC 1293 F12
Figure 12. Reference Input Equivalent Circuit
Figure 13 and 14 show examples of both adequate and poor settling. Using a slower CLK will allow more time for the reference to settle. Even at the maximum CLK rate of 1MHz most references and op amps can be made to settle within the 1s bit time. For example the LT1027 will settle adequately or with a 10F bypass capacitor at VREF the LT1021 also can be used.
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Figure 13. Adequate Reference Settling (LT1027)
HORIZONTAL: 1s/DIV
Figure 14. Poor Reference Settling Can Cause A/D Errors
Reduced Reference Operation The effective resolution of the LTC1293/4/6 can be increased by reducing the input span of the converter. The LTC1293/4/6 exhibits good linearity over a range of reference voltages (see typical performance characteristics curves of Change in Linearity vs Reference Voltage and Change in Gain Error vs Reference Voltage). Care must be taken when operating at low values of VREF because of the reduced LSB step size and the resulting higher accuracy requirement placed on the converter. Offset and Noise are factors that must be considered when operating at low VREF values. For the LTC1293 REF - has been tied to the AGND pin. Any voltage drop from the AGND pin to the ground plane will cause a gain error. Offset with Reduced VREF The offset of the LTC1293/4/6 has a larger effect on the output code when the A/D is operated with a reduced reference voltage. The offset (which is typically a fixed voltage) becomes a larger fraction of an LSB as the size of the LSB is reduced. The typical performance characteristic curve of Unadjusted Offset Error vs Reference Voltage shows how offset in LSB's is related to reference voltage for a typical value of VOS. For example a VOS of 0.1mV, which is 0.1LSB with a 5V reference becomes 0.4LSB with
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LTC1293/LTC1294/LTC1296
APPLICATI
S I FOR ATIO
a 1.25 reference. If this offset is unacceptable, it can be corrected digitally by the receiving system or by offsetting the "-" input to the LTC1293/4/6. Noise with Reduced VREF The total input referred noise of the LTC1293/4/6 can be reduced to approximately 200V peak-to-peak using a ground plane, good bypassing, good layout techniques and minimizing noise on the reference inputs. This noise is insignificant with a 5V reference input but will become a larger fraction of an LSB as the size of the LSB is reduced. The typical performance characteristic curve of Noise Error vs Reference Voltage shows the LSB contribution of this 200V of noise. For operation with a 5V reference, the 200V noise is only 0.16LSB peak-to-peak. Here the LTC1293/4/6 noise will contribute virtually no uncertainty to the output code. For reduced references, the noise may become a significant fraction of an LSB and cause undesirable jitter in the output code. For example, with a 1.25V reference, this 200V noise is 0.64LSB peak-to-peak. This will reduce the range of input voltages over which a stable output code can be achieved by 0.64LSB. Now averaging readings may be necessary. This noise data was taken in a very clean test fixture. Any setup induced noise (noise or ripple on VCC, VREF or VIN) will add to the internal noise. The lower the reference voltage used, the more critical it becomes to have a noisefree setup. Gain Error due to Reduced VREF The gain error of the LTC1294/6 is very good over a wide range of reference voltages. The error component that is seen in the typical performance characteristics curve Change in Gain Error vs Reference Voltage for the LTC1293 is due the voltage drop on the AGND pin from the device to the ground plane. To minimize this error the LTC1293 should be soldered directly onto the PC board. The internal reference point for VREF is tied to AGND. Any voltage drop in the AGND pin will make the reference voltage, internal to the device, less than what is applied externally (Figure 15). This drop is typically 400V due to the product of the pin resistance (RPIN) and the LTC1293 supply current. For
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example, with VREF = 1.25V this will result in a gain error change of -1.0LSB from the gain error measured with VREF = 5V.
LTC1293 DAC REF - REF + AGND ICC RPIN VREF
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REFERENCE VOLTAGE
LTC1293 F15
Figure 15. Parasitic Pin Resistance (RPIN)
LTC1293/4/6 AC Characteristics Two commonly used figures of merit for specifying the dynamic performance of the A/Ds in digital signal processing applications are the Signal-to-Noise Ratio (SNR) and the "effective number of bits"(ENOB). SNR is the ratio of the RMS magnitude of the fundamental to the RMS magnitude of all the non-fundamental signals up to the Nyquist frequency (half the sampling frequency). The theoretical maximum SNR for a sine wave input is given by: SNR = (6.02N + 1.76dB) where N is the number of bits. Thus the SNR depends on the resolution of the A/D. For an ideal 12-bit A/D the SNR is equal to 74dB. A Fast Fourier Transform (FFT) plot of the output spectrum of the LTC1294 is shown in Figures 16a and 16b. The input (fIN) frequencies are 1kHz and 22kHz with the sampling frequency (fS) at 45.4kHz. The SNR obtained from the plot are 72.7dB and 72.5dB. Rewriting the SNR expression it is possible to obtain the equivalent resolution based on the SNR measurement. SNR - 1.76dB N= 6.02 This is the so-called effective number of bits (ENOB). For the example shown in Figures 16a and 16b, N = 11.8 bits. Figure 17 shows a plot of ENOB as a function of input frequency. The top curve shows the A/D's ENOB remains at 11.8 for input frequencies up to fS/2 with 5V supplies.
LTC1293/LTC1294/LTC1296
APPLICATI
0 -20
S I FOR ATIO
MAGNITUDE (dB)
MAGNITUDE (dB)
-40 -60 -80 -100 -120 -140 0 5 15 FREQUENCY (kHz) 10 20 25
1293 F16a
Figure 16a. LTC1294 FFT Plot fIN = 1kHz, fS = 45.4kHz, SNR = 72.7dB with 5V Supplies
0 -20 -40 -60 -80 -100 -120 -140 0 5 15 FREQUENCY (kHz) 10 20 25
1293 F16b
MAGNITUDE (dB)
Figure 16b. LTC1294 FFT Plot fIN = 22kHz, fS = 45.4kHz, SNR = 72.5dB with 5V Supplies
12.0 11.5 EFFECTIVE NUMBER OF BITS 11.0 10.5 10.0 9.5 +5V SUPPLY 9.0 8.5 fS = 45.4kHz 8.0 0 20 40 60 FREQUENCY (kHz) 80 100
LT1293 F17
5V SUPPLIES
Figure 17. LTC1294 ENOB vs Input Frequency
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0 -20 -40 -60 -80 -100 -120 -140 0 5 10 15 FREQUENCY (kHz) 20 25
1293 F8
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Figure 18. LTC1294 FFT Plot fIN1 = 5.1kHz, fIN2 = 5.6kHz, fS = 45.4kHz with 5V Supplies
For +5V supplies the ENOB decreases more rapidly. This is due predominantly to the 2nd harmonic distortion term. Figure 18 shows a FFT plot of the output spectrum for two tones applied to the input of the A/D. Nonlinearities in the A/D will cause distortion products at the sum and difference frequencies of the fundamentals and products of the fundamentals. This is classically referred to as intermodulation distortion (IMD). Overvoltage Protection Applying signals to the LTC1293/4/6's analog inputs that exceed the positive supply or that go below V - will degrade the accuracy of the A/D and possibly damage the device. For example this condition would occur if a signal is applied to the analog inputs before power is applied to the LTC1293/4/6. Another example is the input source is operating from different supplies of larger value than the LTC1293/4/6. These conditions should be prevented either with proper supply sequencing or by use of external circuitry to clamp or current limit the input source. There are two ways to protect the inputs. In Figure 19 diode clamps from the inputs to VCC and V - are used. The second method is to put resistors in series with the analog inputs for current limiting. As shown in Figure 20a, a 1k resistor is enough to stand off 15V (15mA for only one channel). If more than one channel exceeds the supplies than the following guidelines can be used. Limit the current to 7mA per channel and 28mA for all channels.
23
LTC1293/LTC1294/LTC1296
APPLICATI S I FOR ATIO U
1N4148 DIODES VCC 1k +5V
This means four channels can handle 7mA of input current each. Reducing CLK frequency from a maximum of 1MHz (See typical performance characteristics curves Maximum CLK Frequency vs Source Resistance and Sample and Hold Acquisition Time vs Source Resistance) allows the use of larger current limiting resistors. The "+" input can accept a resistor value of 1k but the "-" input cannot accept more than 250 when the maximum clock frequency of 1MHz is used. If the LTC1293/4/6 is clocked at the maximum clock frequency and 250 is not enough to current limit the "-" input source then the clamp diodes are recommended (Figures 20a and 20b). The reason for the limit on the resistor value is the MSB bit test is affected by the value of the resistor placed at the "-" input (see discussion on Analog Inputs and the typical performance characteristics curve Maximum CLK Frequency vs Source Resistance). If VCC and VREF are not tied together, then VCC should be turned on first, then VREF. If this sequence cannot be met connecting a diode from VREF to VCC is recommended (see Figure 21). For dual supplies (bipolar mode) placing two Schottky diodes from VCC and V - to ground (Figure 22) will prevent
1N4148 DIODES VCC +5V
LTC1293/4/6 AGND DGND V- -5V
LTC1293 F19
Figure 19. Overvoltage Protection for Inputs
VCC +5V 1N5817 LTC1293/4/6 AGND DGND V- -5V 1N5817
LTC1293 F22
VCC 1k 250
+
LTC1293/4/6
-
AGND DGND V- -5V
LTC1293 F20a
Figure 20a. Overvoltage Protection for Inputs
24
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+
LTC1293/4/6
-
AGND DGND V- -5V
LTC1293 F20b
Figure 20b. Overvoltage Protection for Inputs
power supply reversal from occuring when an input source is applied to the analog MUX before power is applied to the device. Power supply reversal occurs, for example, if the input is pulled below V -. VCC will then pull a diode drop below ground which could cause the device not to power up properly. Likewise, if the input is pulled above VCC, V - will be pulled a diode drop above ground. If no inputs are present on the MUX, the Schottky diodes are not required if V - is applied first then VCC. Because a unique input protection structure is used on the digital input pins, the signal levels on these pins can exceed the device VCC without damaging the device.
VCC
+5V 1N4148
LTC1293/4/6 REF+ AGND DGND
LTC1293 F21
+5V
Figure 21
+5V
Figure 22. Power Supply Reversal
LTC1293/LTC1294/LTC1296
APPLICATI
S I FOR ATIO
A "Quick Look" Circuit for the LTC1294/6 Users can get a quick look at the function and timing of the LTC1294/6 by using the following simple circuit (Figure 23). VREF is tied to VCC. DIN is tied high which means VIN should be applied to the CH7 with respect to COM. A
22F CH0 CH1 CH2 CH3 CH4 LTC1294 CH5 CH6 CH7 COM DGND DVCC AVCC CLK CS DOUT DIN REF+ REF- AGND V- f CLK VDD
VIN
TO OSCILLOSCOPE
Figure 23. "Quick Look" Circuit for the LTC1294/6
TYPICAL APPLICATI
5VOUT +15V LT1027
S
Digitally Linearized Platinum RTD Signal Conditioner
+
10F 500k 400C TRIM +15V +15V
12k*
12.5k*
+ -
1k* Rplat.
A1 LT1101 A=10
* TRW-IRC MAR-6 RESISTOR - 0.1% ** 1% FILM RESISTOR Rplat. = 1k AT 0C - ROSEMOUNT #118MF
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Unipolar conversion is requested and the data is output MSB first. CS is driven at 1/64 the clock rate by the CD4520 and DOUT outputs the data. The output data from the DOUT pin can be viewed on an oscilloscope that is set up to trigger on the falling edge of CS (Figure 24).
+5V f/64
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CLK CS DOUT
EN RESET Q1 Q4 Q2 Q3 CD4520 Q3 Q2 Q4 Q1 RESET EN VSS CLK
NULL BIT
MSB (B11)
LSB (B0)
FILLS ZEROES
VERTICAL: 5V/DIV HORIZONTAL: 2s/DIV
CLOCK IN 1MHz MAX
LTC1293 F23
Figure 24. Scope Trace of the LTC1294/6 "Quick Look" Circuit Showing A/D Output 101010101010 (AAAHEX)
+
A2 LT1006
1k CH0 CH1 CH2 CH3 CH4 LTC1294 CH5 CH6 CH7 COM DGND DVCC AVCC CLK CS DOUT DIN REF+ REF - AGND V- 22F TANTALUM TO/FROM 68HC11 PROCESSOR
-
30.1k** 1F
3.92M** 500k ZEROC TRIM
LTC1293 TA03
25
LTC1293/LTC1294/LTC1296
TYPICAL APPLICATI
LT1027
10F*
CH0 CH1 CH2 8 ANALOG INPUTS 0-5V RANGE CH3 CH4 CH5 CH6 CH7 COM DGND LTC1294
DVCC AVCC CLK CS DOUT DIN REF+ REF - AGND V- TO ADDITIONAL LTC1294s
*SOLID TANTALUM 4N28
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Micropower, 5000V Opto-Isolated, Multichannel,12-Bit Data Acquisition System is Accessed Once Every Two Seconds
4N28s 10k 9V 10k 2N3906 51k 2N3906 150 5V 10k 51k 150 SCK 5V 10k C1
5V 5.1k (3) 51k 150 10k C0 TO 68HC11 5V 10k 51k 150 MOSI
5.1k 300 4N28 10k 2N3904 ISOLATION BARRIER 5V MISO 51k
LT1292 TA02
NC
LTC1293/LTC1294/LTC1296
PACKAGE DESCRIPTIO
0.160 (4.064) MAX GLASS SEALANT
0.290 - 0.320 (7.366 - 8.128)
0.015 - 0.060 (0.380 - 1.520)
0.008 - 0.018 (0.203 - 0.460) 0.385 0.025 (9.779 0.635)
0 - 15
0.125 (3.175) MIN
0.290 - 0.320 (7.366 - 8.128)
GLASS SEALANT
0.160 (4.064) MAX
0.015 - 0.060 (0.381 - 1.524)
0 - 15
0.008 - 0.018 (0.203 - 0.457) 0.385 0.025 (9.779 0.635)
0.125 (3.175) MIN
0.080 (2.032) MAX
0.300 - 0.325 (7.620 - 8.255)
0.130 0.005 (3.302 0.127)
0.009 - 0.015 (0.229 - 0.381) +0.025 0.325 -0.015
0.015 (0.381) MIN
(
+0.635 8.255 -0.381
)
0.125 (3.175) MIN
Information furnished by Linear Technology Corporation is believed to be accurate and reliable. However, no responsibility is assumed for its use. Linear Technology Corporation makes no representation that the interconnection of circuits as described herein will not infringe on existing patent rights.
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Dimensions in inches (millimeters) unless otherwise noted. J Package 16-Lead Ceramic DIP
0.200 (5.080) MAX 0.005 (0.127) MIN 0.840 (21.336) MAX
16
15
14
13
12
11
10
9
0.025 (0.635) RAD TYP
0.220 - 0.310 (5.588 - 7.874)
1
0.080 (2.030) MAX 0.100 0.010 (2.540 0.254) 0.038 - 0.068 (0.965 - 1.727) 0.014 - 0.026 (0.360 - 0.660)
2
3
4
5
6
7
8
J16 1291
TJMAX 150C
JA 80C/W
J Package 20-Lead Ceramic DIP
20
0.200 (5.080) 0.220 - 0.310 0.025 MAX (5.588 - 7.874) (0.635) RAD TYP
1.060 (26.924) MAX
19
18
17
16
15
14
13
12
11
1
0.038 - 0.068 (0.965 - 1.727) 0.014 - 0.026 (0.356 - 0.660) 0.100 0.010 (2.540 0.254)
2
0.005 (0.127)
3
4
5
6
7
8
9
10
J20 12/91
TJMAX 150C
JA 80C/W
N Package 16-Lead Plastic DIP
0.045 - 0.065 (1.143 - 1.651) 0.770 (19.558) 16 15 14 13 12 11 10 9
0.065 (1.651) TYP
0.260 0.010 (6.604 0.254)
1 0.045 0.015 (1.143 0.381) 0.100 0.010 (2.540 0.254) 0.018 0.003 (0.457 0.076)
2
3
4
5
6
7
8
N16 1291
TJMAX 110C
JA 100C/W
27
LTC1293/LTC1294/LTC1296
PACKAGE DESCRIPTIO
0.300 - 0.325 (7.620 - 8.255)
0.130 0.005 (3.302 0.127)
0.015 (0.381) MIN 0.009 - 0.015 (0.229 - 0.381) +0.025 0.325 -0.015
(
+0.635 8.255 -0.381
)
0.125 (3.175) MIN
0.065 0.015 (1.651 0.381) 0.100 0.010 (2.540 0.254)
0.005 (0.127) RAD MIN
0.291 - 0.299 (7.391 - 7.595)
0.010 - 0.029 x 45 (0.254 - 0.737)
0.093 - 0.104 (2.362 - 2.642)
0 - 8 TYP
0.009 - 0.013 (0.229 - 0.330)
SEE NOTE 0.016 - 0.050 (0.406 - 1.270)
NOTE: PIN 1 IDENT, NOTCH ON TOP AND CAVITIES ON THE BOTTOM OF PACKAGES ARE THE MANUFACTURING OPTIONS. THE PART MAY BE SUPPLIED WITH OR WITHOUT ANY OF THE OPTIONS. 1 2 3 4 5 6 7 8
SOL16 12/91
0.005 (0.127) RAD MIN
0.291 - 0.299 (7.391 - 7.595) 0.010 - 0.029 x 45 (0.254 - 0.737) 0.093 - 0.104 (2.362 - 2.642) 0.037 - 0.045 (0.940 - 1.143) 20 19 18
0 - 8 TYP
0.009 - 0.013 (0.229 - 0.330)
SEE NOTE 0.016 - 0.050 (0.406 - 1.270)
0.050 (1.270) TYP
NOTE: PIN 1 IDENT, NOTCH ON TOP AND CAVITIES ON THE BOTTOM OF PACKAGES ARE THE MANUFACTURING OPTIONS. THE PART MAY BE SUPPLIED WITH OR WITHOUT ANY OF THE OPTIONS. 1 2 3 4 5 6 7 8 9 10
SOL20 12/91
28
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7487
(408) 432-1900 q FAX: (408) 434-0507 q TELEX: 499-3977
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Dimensions in inches (millimeters) unless otherwise noted. N Package 20-Lead Plastic DIP
0.045 - 0.065 (1.143 - 1.651) 1.040 (26.416) MAX
20
19
18
17
16
15
14
13
12
11
0.065 (1.651) TYP
0.260 0.010 (6.604 0.254)
1
0.018 0.003 (0.457 0.076)
2
3
4
5
6
7
8
9
10
N20 0192
TJMAX 110C
JA 100C/W
S Package 16-Lead Plastic SOL
0.398 - 0.413 (10.109 - 10.490) 0.037 - 0.045 (0.940 - 1.143) 16 15 14 13 12 11 10 9
0.050 (1.270) TYP
0.004 - 0.012 SEE NOTE (0.102 - 0.305)
0.394 - 0.419 (10.008 - 10.643)
0.014 - 0.019 (0.356 - 0.483) TYP
TJMAX 110C
JA 150C/W
S Package 20-Lead Plastic SOL
0.496 - 0.512 (12.598 - 13.995) 17 16 15 14 13 12 11
0.004 - 0.012 (0.102 - 0.305)
SEE NOTE
0.394 - 0.419 (10.008 - 10.643)
0.014 - 0.019 (0.356 - 0.483) TYP
TJMAX 110C
JA 150C/W
LT/GP 0392 10K REV 0
(c) LINEAR TECHNOLOGY CORPORATION 1992

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