LTC1404 Complete SO-8, 12-Bit, 600ksps ADC with Shutdown
FEATURES
s s s s s s s s s s s s
DESCRIPTION
The LTC ®1404 is a complete 600ksps, 12-bit A/D converter which draws only 75mW from a 5V or ± 5V supplies. This easy-to-use device comes complete with a 160ns sample-and-hold and a precision reference. Unipolar and bipolar conversion modes add to the flexibility of the ADC. The LTC1404 has two power saving modes: Nap and Sleep. In Nap mode, it consumes only 7.5mW of power and can wake up and convert immediately. In the Sleep mode, it consumes 60µW of power typically. Upon powerup from Sleep mode, a reference ready (REFRDY) signal is available in the serial data word to indicate that the reference has settled and the chip is ready to convert. The LTC1404 converts 0V to 4.096V unipolar inputs from a single 5V supply and ± 2.048V bipolar inputs from ± 5V supplies. Maximum DC specs include ± 1LSB INL, ± 1LSB DNL and 45ppm/°C full-scale drift over temperature. Guaranteed AC performance includes 69dB S/(N + D) and – 76dB THD at an input frequency of 100kHz over temperature. The 3-wire serial port allows compact and efficient data transfer to a wide range of microprocessors, microcontrollers and DSPs.
, LTC and LT are registered trademarks of Linear Technology Corporation. MICROWIRE is a trademark of National Semiconductor Corp.
Complete 12-Bit ADC in SO-8 Single Supply 5V or ±5V Operation Sample Rate: 600ksps Power Dissipation: 75mW (Typ) 72dB S/(N + D) and – 80dB THD at Nyquist No Missing Codes over Temperature Nap Mode with Instant Wake-Up: 7.5mW Sleep Mode: 60µW High Impedance Analog Input Input Range (1mV/LSB): 0V to 4.096V or ± 2.048V Internal Reference Can Be Overdriven Externally 3-Wire Interface to DSPs and Processors (SPI and MICROWIRETM Compatible)
APPLICATIONS
s s s s s s s s
High Speed Data Acquisition Digital Signal Processing Multiplexed Data Acquisition Systems Audio and Telecom Processing Digital Radio Spectrum Analysis Low Power and Battery-Operated Systems Handheld or Portable Instruments
TYPICAL APPLICATION
Single 5V Supply, 600kHz, 12-Bit Sampling A/D Converter
5V
Power Consumption vs Sample Rate
100 NORMAL CONVERSION 10
10µF*
0.1µF LTC1404 MPU 7 6 5 SERIAL DATA LINK
LTC1404 • TA01
SUPPLY CURRENT (mA)
+
ANALOG INPUT (0V TO 4.096V) REFOUT 2.43V + 10µF
1
VCC
VSS
8
2 3 0.1µF 4
1 SLEEP MODE BETWEEN CONVERSION
AIN VREF GND
CONV CLK DOUT
P1.4 P1.3 P1.2
0.1
0.01 9.6MHz CLOCK 0.001 0.01 0.1 1 10 100 1k 10k 100k 1M SAMPLE RATE (Hz)
LTC1404 • TA02
*AVX TPSD106M035R0300
U
U
U
NAP MODE BETWEEN CONVERSION
1
LTC1404
ABSOLUTE MAXIMUM RATINGS
(Notes 1, 2)
PACKAGE/ORDER INFORMATION
TOP VIEW VCC 1 AIN 2 VREF 3 GND 4 8 VSS 7 CONV 6 CLK 5 DOUT
Supply Voltage (VCC) ................................................. 7V Negative Supply Voltage (VSS).................... – 6V to GND Total Supply Voltage (VCC to VSS) Bipolar Operation Only ........................................ 12V Analog Input Voltage (Note 3) Unipolar Operation .................. – 0.3V to (VCC + 0.3V) Bipolar Operation........... (VSS – 0.3V) to (VCC + 0.3V) Digital Input Voltage (Note 4) Unipolar Operation ................................– 0.3V to 12V Bipolar Operation.........................(VSS – 0.3V) to 12V Digital Output Voltage Unipolar Operation .................. – 0.3V to (VCC + 0.3V) Bipolar Operation........... (VSS – 0.3V) to (VCC + 0.3V) Power Dissipation.............................................. 300mW Operating Ambient Temperature Range LTC1404C................................................ 0°C to 70°C LTC1404I............................................ – 40°C to 85°C Junction Temperature.......................................... 125°C Storage Temperature Range ................. – 65°C to 150°C Lead Temperature (Soldering, 10 sec).................. 300°C
ORDER PART NUMBER LTC1404CS8 LTC1404IS8
S8 PACKAGE 8-LEAD PLASTIC SO
TJMAX = 125°C, θJA = 130°C/ W
S8 PART MARKING 1404 1404I
Consult factory for PDIP packages and Military grade parts.
POWER REQUIRE E TS
SYMBOL VCC VSS ICC PARAMETER Positive Supply Voltage Negative Supply Voltage Positive Supply Current
(Note 5)
CONDITIONS Unipolar Bipolar Bipolar Only fSAMPLE = 600ksps Nap Mode Sleep Mode fSAMPLE = 600ksps, VSS = – 5V Nap Mode Sleep Mode fSAMPLE = 600ksps Nap Mode Sleep Mode MIN 4.75 4.75 – 2.45
q q q q q q q q q
TYP
ISS
Negative Supply Current
PD
Power Dissipation
15 1.3 8.0 0.2 0.2 4 75 7.5 60
MAX 5.25 5.25 – 5.25 30 3.0 20.0 0.6 0.5 10 160 20 150
UNITS V V V mA mA µA mA mA µA mW mW µW
A ALOG I PUT
SYMBOL PARAMETER VIN IIN CIN Analog Input Range
(Note 5)
CONDITIONS 4.75V ≤ VCC ≤ 5.25V (Unipolar) 4.75V ≤ VCC ≤ 5.25V, – 5.25V ≤ VSS ≤ – 2.45V (Bipolar) During Conversions (Hold Mode) Between Conversions (Sample Mode) During Conversions (Hold Mode)
q
MIN
TYP 0 to 4.096 0 to ± 2.048
MAX
UNITS V V
Analog Input Leakage Current Analog Input Capacitance
±1 45 5
2
U
W
U
U
UW
WW
W
U
U
µA pF pF
LTC1404 CO VERTER CHARACTERISTICS
PARAMETER Resolution (No Missing Codes) Integral Linearity Error Differential Linearity Error Offset Error Full-Scale Error Full-Scale Tempco IOUT(REF) = 0
q
DY A IC ACCURACY
SYMBOL PARAMETER S/(N + D) Signal-to-Noise THD Total Harmonic Distortion Up to 5th Harmonic Peak Harmonic or Spurious Noise IMD Intermodulation Distortion Full Power Bandwidth
I TER AL REFERE CE CHARACTERISTICS
PARAMETER VREF Output Voltage VREF Output Tempco VREF Line Regulation VREF Load Regulation VREF Wake-Up Time from Sleep Mode CONDITIONS IOUT = 0 IOUT = 0 4.75V ≤ VCC ≤ 5.25V – 5.25V ≤ VSS ≤ 0V 0 ≤ IOUT ≤ 1mA CVREF = 10µF
DIGITAL I PUTS AND OUTPUTS
SYMBOL PARAMETER VIH VIL IIN CIN VOH VOL High Level Input Voltage Low Level Input Voltage Digital Input Current Digital Input Capacitance High Level Output Voltage Low Level Output Voltage
U
U
U
WU
U
U
With internal reference (Notes 5, 7)
MIN
q
CONDITIONS (Note 8) (Note 9)
q q q
TYP
MAX ±1 ±1 ±6 ±8 ± 15
UNITS Bits LSB LSB LSB LSB LSB ppm/°C
12
± 10
± 45
VCC = 5V, VSS = – 5V, fSAMPLE = 600kHz
CONDITIONS 100kHz Input Signal 300kHz Input Signal 100kHz Input Signal 300kHz Input Signal 100kHz Input Signal 300kHz Input Signal fIN1 = 99.17kHz, fIN2 = 102.69kHz fIN1 = 298.68kHz, fIN2 = 304.83kHz
q q q
MIN 69
TYP 72 72 – 82 – 80 – 84 – 82 – 82 – 70 5 1
MAX
UNITS dB dB
– 76 – 76
dB dB dB dB dB dB MHz MHz
Full Linear Bandwidth (S/(N + D) ≥ 68dB)
U
(Note 5)
MIN 2.410
q
TYP 2.430 ± 10 0.5 0.01 1 2.5
MAX 2.450 ± 45
UNITS V ppm/°C LSB/ V LSB/ V LSB/mA ms
(Note 5)
MIN
q q q
CONDITIONS VCC = 5.25V VCC = 4.75V VIN = 0V to VCC VCC = 4.75V, IO = – 10µA VCC = 4.75V, IO = – 200µA VCC = 4.75V, IO = 160µA VCC = 4.75V, IO = 1.6mA
TYP
MAX 0.8 ± 10
UNITS V V µA pF V V
2.0
5 4.7
q q
4.0 0.05 0.10 0.4
V V
3
LTC1404
DIGITAL I PUTS AND OUTPUTS
SYMBOL PARAMETER IOZ COZ ISOURCE ISINK Hi-Z Output Leakage DOUT Hi-Z Output Capacitance DOUT Output Source Current Output Sink Current
TI I G CHARACTERISTICS
SYMBOL fSAMPLE(MAX) tCONV tACQ fCLK tCLK tWK(NAP) t1 t2 t3 t4 t5 t6 t7 t8 t9 t10 PARAMETER Maximum Sampling Frequency Conversion Time Acquisition Time (Unipolar Mode) (Bipolar Mode VSS = – 5V) CLK Frequency CLK Pulse Width Time to Wake Up from Nap Mode CLK Pulse Width to Return to Active Mode CONV↑ to CLK↑ Setup Time CONV↑ After Leading CLK↑ CONV Pulse Width Time from CLK↑ to Sample Mode Aperture Delay of Sample-and-Hold
Minimum Delay Between Conversion (Unipolar Mode) (Note 6) (Bipolar Mode VSS = – 5V) Delay Time, CLK↑ to DOUT Valid Delay Time, CLK↑ to DOUT Hi-Z Time from Previous Data Remains Valid After CLK↑ CLOAD = 20pF CLOAD = 20pF CLOAD = 20pF
The q denotes specifications which apply over the full operating temperature range; all other limits and typicals apply to TA = 25°C. 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 GND. Note 3: When these pin voltages are taken below VSS (ground for unipolar mode) or above VCC, they will be clamped by internal diodes. This product can handle input currents greater than 60mA without latch-up if the pin is driven below VSS (ground for unipolar mode) or above VCC. Note 4: When these pin voltages are taken below VSS (ground for unipolar mode), they will be clamped by internal diodes. This product can handle input currents greater than 60mA without latch-up if the pin is driven below VSS (ground for unipolar mode). These pins are not clamped to VCC. Note 5: VCC = 5V, fSAMPLE = 600kHz, tr = tf = 5ns unless otherwise specified.
4
U
U
(Note 5)
MIN
q
CONDITIONS VOUT = 0V to VCC VOUT = 0V VOUT = VCC
TYP 15 – 10 10
MAX ± 10
UNITS µA pF mA mA
UW
(Note 5, see Figures 12, 13, 14)
CONDITIONS
q
MIN 600
TYP 1.36 200 160
MAX
UNITS kHz µs ns ns
fCLK = 9.6MHz
q
0.1 40 350 40 70 0 40 60 40
9.6
MHz ns ns ns ns ns ns ns ns
(Note 6)
q
q q q
(Note 10) Jitter < 50ps
q
q q q q q
220 180 40 40 10 30
310 300 70 70
ns ns ns ns ns
Note 6: Guaranteed by design, not subject to test. Note 7: Linearity, offset and full-scale specifications apply for unipolar and bipolar modes. Note 8: Integral nonlinearity is defined as the deviation of a code from a straight line passing through the actual endpoints of the transfer curve. The deviation is measured from the center of the quantization band. Note 9: Bipolar offset is the offset voltage measured from – 0.5LSB when the output code flickers between 0000 0000 0000 and 1111 1111 1111. Note 10: The rising edge of CONV starts a conversion. If CONV returns low at a bit decision point during the conversion, it can create small errors. For best performance, ensure that CONV returns low either within 100ns after the conversion starts (i.e., before the first bit decision) or after the 14 clock cycles. (Figure 13 Timing Diagram).
LTC1404 TYPICAL PERFORMANCE CHARACTERISTICS
Unipolar Mode Differential Nonlinearity vs Output Code
1.00 1.00
INTEGRAL NONLINEARITY (LSBs)
DIFFERENTIAL NONLINEARITY (LSBs)
0.75 0.50 0.25 0 –0.25 –0.50 –0.75 –1.00 0 512 1024 1536 2048 2560 3072 3584 4096 OUTPUT CODE
1404 G01
0.75 0.50 0.25 0 –0.25 –0.50 –0.75 –1.00 0 512 1024 1536 2048 2560 3072 3584 4096 OUTPUT CODE
1404 G02
DIFFERENTIAL NONLINEARITY (LSBs)
fSAMPLE = 600kHz
Bipolar Mode Integral Nonlinearity vs Output Code
1.00 fSAMPLE = 600kHz
0 –10 –20 –30
INTEGRAL NONLINEARITY (LSBs)
0.75 0.50 AMPLITUDE (dB) 0.25 0 –0.25 –0.50 –0.75 –1.00 0 –2048 2048 –1024 1024 1536 –1536 –512 512 OUTPUT CODE
1404 G04
–50 – 60 –70 –80 –90 –100 –110 –120 0 30 60 90 120 150 180 210 240 270 300 FREQUENCY (kHz)
1404 G05
AMPLITUDE (dB)
Unipolar Mode ENOB and Signal/(Noise + Distortion) vs Input Frequency
12 11
EFFECTIVE NUMBER OF BITS
9 8 7 6 5 4 3 2 1 0 10
56 50
SIGNAL-TO-NOISE RATIO (dB)
SIGNAL-TO-NOISE RATIO (dB)
10
NYQUIST FREQUENCY
fSAMPLE = 600kHz 100 INPUT FREQUENCY (kHz) 1000
1404 G07
UW
Unipolar Mode Integral Nonlinearity vs Output Code
1.00 fSAMPLE = 600kHz 0.75 0.50 0.25 0 –0.25 –0.50 –0.75
Bipolar Mode Differential Nonlinearity vs Output Code
fSAMPLE = 600kHz
–1.00 0 –2048 2048 –1024 1024 1536 –1536 –512 512 OUTPUT CODE
1404 G03
Unipolar Mode 4096 Nonaverage FFT with 100kHz Signal
fSAMPLE = 600kHz fIN = 99.1699kHz SINAD = 71dB THD = –77dB 0 –10 –20 –30 –40 –50 –60 –70 –80 –90 –100 –110 –120
Unipolar Mode 4096 Nonaverage FFT with 300kHz Signal
fSAMPLE = 600kHz fIN = 298.681kHz SINAD = 71dB THD = –73dB
–40
0
30 60 90 120 150 180 210 240 270 300 FREQUENCY (kHz)
1404 G06
Unipolar Mode Signal-to-Noise Ratio (Without Harmonics) vs Input Frequency
74 68 62
SIGNAL/(NOISE + DISTORTION) (dB) 80 70 60 50 40 30 20 10 fSAMPLE = 600kHz 0 10 100 INPUT FREQUENCY (kHz) 1000
1404 G08
Bipolar Mode Signal-to-Noise Ratio (Without Harmonics) vs Input Frequency
80 70 60 50 40 30 20 10 fSAMPLE = 600kHz 0 10 100 INPUT FREQUENCY (kHz) 1000
1404 G09
5
LTC1404 TYPICAL PERFORMANCE CHARACTERISTICS
Unipolar Mode Distortion vs Input Frequency
AMPLITUDE (dB BELOW THE FUNDAMENTAL)
0 –10 –20 AMPLITUDE (dB) –30 –40 –50 –60 –70 –80 –90 –100 10 100 INPUT FREQUENCY (kHz) 1000
1404 G10
fSAMPLE = 600kHz
Unipolar Mode Intermodulation Distortion Plot at 300kHz
0 –10 –20 –30 fSAMPLE = 600kHz fa = 298.6816406kHz fb = 304.8339844kHz fa fb
AMPLITUDE (dB)
–40 –50 – 60 –70 –80 –90 –100 –110 –120 0 20 40 60 80 100 120 140 160 FREQUENCY (kHz) 180 200 220 240 260 2fa fa + fb 2fb
Bipolar Mode Intermodulation Distortion Plot at 300kHz
0 –10 –20 –30 fSAMPLE = 600kHz fa = 298.6816406kHz fb = 304.8339844kHz fa fb 2fa + fb 3fa
2fa
AMPLITUDE (dB)
–40 –50 – 60 –70 –80 –90 –100 –110 –120 0 20 40 60 80 100 120 140 160 FREQUENCY (kHz) 180 200 220 240 260 fa + fb fb – fa 2fb
6
UW
THD
Unipolar Mode Intermodulation Distortion Plot at 100kHz
0 –10 –20 –30 –40 –50 – 60 –70 –80 –90 –100 2fa – fb 2fa 2fb fa fb fSAMPLE = 600kHz fa = 99.16992188kHz fb = 102.6855469kHz
2ND HARMONIC
3RD HARMONIC
–110 –120 0 30 60 90 120 150 180 210 240 270 300 FREQUENCY (kHz)
1404 G11
2fa + fb 3fa 2fb – fa 3fb
280
300
1404 G12
2fb + fa 2fb – fa 3fb
280
300
1404 G12
LTC1404 TYPICAL PERFORMANCE CHARACTERISTICS
Unipolar Mode S/(N + D) vs Input Frequency and Amplitude
80 VIN = 0dB
SIGNAL/(NOISE + DISTORTION) (dB)
SPURIOUS-FREE DYNAMIC RANGE (dB)
SIGNAL/(NOISE + DISTORTION) (dB)
70 60 50 40 30 20 10 fSAMPLE = 600kHz 0 10 100 INPUT FREQUENCY (kHz) 1000
1404 G14
VIN = – 20dB
VIN = – 60dB
Bipolar Mode Peak Harmonic or Spurious Noise vs Input Frequency
0
0
SPURIOUS-FREE DYNAMIC RANGE (dB)
–20 –30 –40 –50 –60 –70 –80 –90 –100 10 100 INPUT FREQUENCY (kHz) 1000
1404 G17
POWER SUPPLY FEEDTHROUGH (dB)
POWER SUPPLY FEEDTHROUGH (dB)
–10
fSAMPLE = 600kHz
Reference Voltage vs Temperature
2.440 2.438
REFERENCE VOLTAGE (V)
REFERENCE VOLTAGE (V)
2.436 2.434 2.432 2.430 2.428 2.426 2.424 2.422 2.420 –50 –25 50 75 0 25 TEMPERATURE (°C) 100 125
2.43 2.42 2.41 2.40 2.39
ACQUISITION TIME (µs)
UW
1404 G20
Bipolar Mode S/(N + D) vs Input Frequency and Amplitude
80 VIN = 0dB 70 60 50 40 30 20 10 fSAMPLE = 600kHz 0 10 100 INPUT FREQUENCY (kHz) 1000
1404 G15
Unipolar Mode Peak Harmonic or Spurious Noise vs Input Frequency
0 –10 –20 –30 –40 –50 –60 –70 –80 –90 –100 10 100 INPUT FREQUENCY (kHz) 1000
1404 G16
fSAMPLE = 600kHz
VIN = – 20dB
VIN = – 60dB
Unipolar Mode Power Supply Feedthrough vs Ripple Frequency
0
AIN = 0dB AIN FREQUENCY = 100kHz fSAMPLE = 600kHz VCC (VRIPPLE = 1mV) –10 –20 –30 –40 –50 –60 –70 –80 –90 –100 1 10 100 RIPPLE FREQUENCY (kHz) 1000
1404 G18
Bipolar Mode Power Supply Feedthrough vs Ripple Frequency
–10 –20 –30 –40 –50 –60 –70 –80 –90 –100 1 10 100 RIPPLE FREQUENCY (kHz) 1000
1404 G19
AIN = 0dB AIN FREQUENCY = 100kHz fSAMPLE = 600kHz
VSS (VRIPPLE = 10mV)
VCC (VRIPPLE = 1mV)
Reference Voltage vs Load Current
2.45 2.44
Acquisition Time vs Source Impedance
4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0 10 100 1k SOURCE RESISTANCE (Ω) 10k
1404 G22
1404 G21
TA = 25°C
–8 –7
–6
–5 –4 –3 –2 –1 LOAD CURRENT (mA)
0
1
7
LTC1404 TYPICAL PERFORMANCE CHARACTERISTICS
Unipolar Mode VCC Supply Current vs Temperature
20 15.0 12.5 VCC CURRENT 200 VSS CURRENT 150 100 50 fSAMPLE = 600kHz 100 125 0 –50 –25 50 75 0 25 TEMPERATURE (°C) 100 0 125 10.0 7.5 5.0 2.5 fSAMPLE = 600kHz 0 –50 –25 0 25 50 75 TEMPERATURE (°C)
VCC SUPPLY CURRENT (mA)
VCC SUPPLY CURRENT (mA)
15
10
5
PIN FUNCTIONS
VCC (Pin 1): Positive Supply, 5V. Bypass to GND (10µF tantalum in parallel with 0.1µF ceramic). AIN (Pin 2): Analog Input. 0V to 4.096V (Unipolar), ± 2.048V (Bipolar). VREF (Pin 3): 2.43V Reference Output. Bypass to GND (10µF tantalum in parallel with 0.1µF ceramic). GND (Pin 4): Ground. GND should be tied directly to an analog ground plane. DOUT (Pin 5): The A/D conversion result is shifted out from this pin. CLK (Pin 6): Clock. This clock synchronizes the serial data transfer. A minimum CLK pulse of 40ns signals the ADC to wake up from Nap or Sleep mode. CONV (Pin 7): Conversion Start Signal. This active high signal starts a conversion on its rising edge. Keeping CLK low and pulsing CONV two/four times will put the ADC into Nap/Sleep mode. VSS (Pin 8): Negative Supply. – 5V for bipolar operation. Bypass to GND with 10µF tantalum in parallel with 0.1µF ceramic. VSS should be tied to GND for unipolar operation.
8
UW
Bipolar Mode Supply Current vs Temperature
300 250
VSS SUPPLY CURRENT (µA)
1404 G23
1404 G24
U
U
U
LTC1404
FUNCTIONAL BLOCK DIAGRA
AIN
VREF 2.43V REF
CLK CONV CONTROL LOGIC 12 SUCCESSIVE APPROXIMATION REGISTER/PARALLEL TO SERIAL CONVERTER
TEST CIRCUITS
5V 3k DOUT 3k CLOAD DOUT CLOAD
Hi-Z TO VOH VOL TO VOH VOH TO Hi-Z
W
CSAMPLE ZEROING SWITCH VCC GND VSS 12-BIT CAPACITIVE DAC COMP DOUT
1404 BD
U
U
Hi-Z TO VOL VOH TO VOL VOL TO Hi-Z
1404 TC01
9
LTC1404
APPLICATIONS INFORMATION
Conversion Details The LTC1404 uses a successive approximation algorithm and an internal sample-and-hold circuit to convert an analog signal to a 12-bit serial output based on a precision internal reference. The control logic provides easy interface to microprocessors and DSPs through 3-wire connections. A rising edge on the CONV input starts a conversion. At the start of a conversion the successive approximation register (SAR) is reset. Once a conversion cycle has begun, it cannot be restarted. During conversion, the internal 12-bit capacitive DAC output is sequenced by the SAR from the most significant bit (MSB) to the least significant bit (LSB). Referring to Figure 1, the AIN input connects to the sample-and-hold capacitor during the acquired phase and the comparator offset is nulled by the feedback switch. In this acquire phase, it typically takes 160ns for the sample-and-hold capacitor to acquire the analog signal. During the convert phase, the comparator feedback switch opens, putting the comparator into the compare mode. The input switches connect CSAMPLE to ground, injecting the analog input charge onto the summing junction. This input charge is successively compared with the binary-weighted charges supplied by the capacitive DAC. Bit decisions are made by the high speed comparator. At the end of a conversion, the DAC output balances the AIN input charge. The SAR contents (a 12-bit data word) which represent the input voltage, are presented through the serial pin DOUT.
SAMPLE S1 SAMPLE AIN HOLD DAC CDAC VDAC S A R DOUT
1404 F01
AMPLITUDE (dB)
AMPLITUDE (dB)
CSAMPLE
COMP
Figure 1. AIN Input
10
U
W
+ –
U
U
Dynamic Performance The LTC1404 has excellent high speed sampling capability. FFT (Fast Fourier Transform) test techniques are used to test the ADC’s frequency response, distortion and noise at the rated throughput. By applying a low distortion sine wave and analyzing the digital output using an FFT algorithm, the ADC’s spectral content can be examined for frequencies outside the fundamental. Figure 2a shows a typical LTC1404 FFT plot.
0 –10 –20 –30 –40 –50 – 60 –70 –80 –90 –100 –110 –120 0 30 60 90 120 150 180 210 240 270 300 FREQUENCY (kHz)
1404 F02a
fSAMPLE = 600kHz fIN = 99.169kHz SINAD = 72dB THD = – 88dB
Figure 2a. LTC1404 Nonaveraged, 4096 Point FFT Plot with 100kHz Input Frequency in Bipolar Mode
0 –10 –20 –30 –40 –50 – 60 –70 –80 –90 –100 –110 –120 0 30 60 90 120 150 180 210 240 270 300 FREQUENCY (kHz)
1404 F02b
fSAMPLE = 600kHz fIN = 298.681kHz SINAD = 71dB THD = – 84dB
Figure 2b. LTC1404 Nonaveraged, 4096 Point FFT Plot with 300kHz Input Frequency in Bipolar Mode
LTC1404
APPLICATIONS INFORMATION
Signal-to-Noise Ratio The signal-to-noise plus distortion ratio [S/(N + D)] is the ratio between the RMS amplitude of the fundamental input frequency to the RMS amplitude of all other frequency components at the A/D output. The output is band limited to frequencies from DC to half the sampling frequency. Figure 2a shows a typical spectral content with a 600kHz sampling rate and a 100kHz input. The dynamic performance is excellent for input frequencies up to the Nyquist limit of 300kHz as shown in Figure 2b. Effective Number of Bits The effective number of bits (ENOBs) is a measurement of the effective resolution of an ADC and is directly related to the S/(N + D) by the equation:
N= S /(N + D) – 1.76 6.02
AMPLITUDE (dB BELOW THE FUNDAMENTAL)
where N is the effective number of bits of resolution and S/(N + D) is expressed in dB. At the maximum sampling rate of 600kHz, the LTC1404 maintains very good ENOBs up to the Nyquist input frequency of 300kHz (refer to Figure 3).
12 11 10 9 8 7 6 5 4 3 2 1 fSAMPLE = 600kHz 100k INPUT FREQUENCY (Hz) 1M
1404 F03
74 68 NYQUIST FREQUENCY 62 56 50
EFFECTIVE NUMBER OF BITS
0 10k
Figure 3. Effective Bits and Signal-to-Noise + Distortion vs Input Frequency in Bipolar Mode
U
W
U
U
Total Harmonic Distortion Total harmonic distortion (THD) is the ratio of the RMS sum of all harmonics of the input signal to the fundamental itself. The out-of-band harmonics alias into the frequency band between DC and half of the sampling frequency. THD is expressed as: V22 + V32 + V42 + …Vn2 THD = 20 log V1 where V1 is the RMS amplitude of the fundamental frequency and V2 through Vn are the amplitudes of the second through nth harmonics. THD vs input frequency is shown in Figure 4. The LTC1404 has good distortion performance up to the Nyquist frequency and beyond.
0 –10 –20 –30 –40 –50 –60 –70 –80 –90 –100 10k 100k INPUT FREQUENCY (Hz) 1M
1404 F04
fSAMPLE = 600kHz
3RD HARMONIC 2ND HARMONIC
THD
SIGNAL/(NOISE + DISTORTION) (dB)
Figure 4. Distortion vs Input Frequency in Bipolar Mode
Intermodulation Distortion If the ADC input signal consists of more than one spectral component, the ADC transfer function nonlinearity can produce intermodulation distortion (IMD) in addition to THD. IMD is the change in one sinusoidal input caused by the presence of another sinusoidal input at a different frequency.
11
LTC1404
APPLICATIONS INFORMATION
If two pure sine waves of frequencies fa and fb are applied to the ADC input, nonlinearities in the ADC transfer function can create distortion products at sum and difference frequencies of mfa ± nfb, where m and n = 0, 1, 2, 3, etc. For example, the 2nd order IMD terms include (fa + fb) and (fa – fb) while the 3rd order IMD terms includes (2fa + fb), (2fa – fb), (fa + 2fb) and (fa – 2fb). If the two input sine waves are equal in magnitude, the value (in decibels) of the 2nd order IMD products can be expressed by the following formula.
IMD( fa ± fb) = 20log Amplitude at (fa ± fb) Amplitude at fa
Figure 5 shows the IMD performance at a 100kHz input.
0 –10 –20 –30
AMPLITUDE (dB)
fa
fb
fSAMPLE = 600kHz fa = 99.16992188kHz fb = 102.6855469kHz
–40 –50 –60 –70 –80 –90 –100 –110 –120 0 20 40 60 80 100 120 140 160 180 200 220 240 260 280 300 FREQUENCY (kHz)
1404 F05
fa + fb 2fa – fb 2fb – fa 2fa 2fb
Figure 5. Intermodulation Distortion Plot in Bipolar Mode
Peak Harmonic or Spurious Noise The peak harmonic or spurious noise is the largest spectral component excluding the input signal and DC. This value is expressed in decibels relative to the RMS value of a full-scale input signal. Full Power and Full Linear Bandwidth The full power bandwidth is the input frequency at which the amplitude of the reconstructed fundamental is reduced by 3dB for a full-scale input signal. The full linear bandwidth is the input frequency at which the S/(N + D) has dropped to 68dB (11 effective bits). The
12
U
W
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LTC1404 has been designed to optimize input bandwidth, allowing the ADC to undersample input signals with frequencies above the converter’s Nyquist Frequency. The noise floor stays very low at high frequencies; S/(N + D) becomes dominated by distortion at frequencies far beyond Nyquist. Driving the Analog Input The analog input of the LTC1404 is easy to drive. It draws only one small current spike while charging the sampleand-hold capacitor at the end of a conversion. During conversion, the analog input draws only a small leakage current. The only requirement is that the amplifier driving the analog input must settle after the small current spike before the next conversion starts. Any op amp that settles in 160ns to small load current transient will allow maximum speed operation. If a slower op amp is used, more settling time can be provided by increasing the time between conversions. Suitable devices capable of driving the ADC’s AIN input include the LT ® 1360 and the LT1363 op amps. The LTC1404 comes with a built-in unipolar/bipolar detection circuit. If the VSS potential is forced below GND, the internal circuitry will automatically switch to bipolar mode. The following list is a summary of the op amps that are suitable for driving the LTC1404, more detailed information is available in the Linear Technology databooks and the LinearViewTM CD-ROM. LT 1215/LT1216: Dual and quad 23MHz, 50V/µs single supply op amps. Single 5V to ± 15V supplies, 6.6mA specifications, 90ns settling to 0.5LSB. LT1223: 100MHz video current feedback amplifier. ± 5V to ± 15V supplies, 6mA supply current. Low distortion up to and above 600kHz. Low noise. Good for AC applications. LT1227: 140MHz video current feedback amplifier. ± 5V to ± 15V supplies, 10mA supply current. Lowest distortion at frequencies above 600kHz. Low noise. Best for AC applications.
2fa + fb 3fa 2fb + fa 3fb
LTC1404
APPLICATIONS INFORMATION
LT1229/LT1230: Dual and quad 100MHz current feedback amplifiers. ± 2V to ± 15V supplies, 6mA supply current each amplifier. Low noise. Good AC specs. LT1360: 37MHz voltage feedback amplifier. ± 5V to ± 15V supplies. 3.8mA supply current. Good AC and DC specs. 70ns settling to 0.5LSB. LT1363: 50MHz, 450V/µs op amps. ± 5V to ± 15V supplies. 6.3mA supply current. Good AC and DC specs. 60ns settling to 0.5LSB. LT1364/LT1365: Dual and quad 50MHz, 450V/µs op amps. ± 5V to ± 15V supplies, 6.3mA supply current per amplifier. 60ns settling to 0.5LSB. Internal Reference The LTC1404 has an on-chip, temperature compensated, curvature corrected, bandgap reference, which is factory trimmed to 2.43V. It is internally connected to the DAC and is available at Pin 3 to provide up to 1mA of current to an external load. For minimum code transition noise, the reference output should be decoupled with a capacitor to filter wideband noise from the reference (10µF tantalum in parallel with a 0.1µF ceramic). The VREF pin can be driven with a DAC or other means to provide input span adjustment in bipolar mode. The VREF pin must be driven to at least 2.46V to prevent conflict with the internal reference. The reference should not be driven to more than 5V. Figure 6 shows an LT 1360 op amp driving the reference pin. Figure 7 shows a typical reference, the LT1019A-5 connected to the LTC1404. This will provide an improved
5V INPUT RANGE ± 0.843 • VREF(OUT) AIN VCC
+
LT1360
VREF(OUT) ≥ 2.46V 3Ω 10µF
LTC1404 VREF
–
GND VSS
1404 F06
Figure 6. Driving the VREF with the LT1360 Op Amp
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5V INPUT RANGE ± 4.215V (= ±0.843 • VREF) AIN 10V VIN LTC1404 VOUT 3Ω 10µF GND GND VSS
1404 F07
VCC
VREF
LT1019A-5
–5V
Figure 7. Supplying a 5V Reference Voltage to the LTC1404 with the LT1019A-5
drift (equal to the maximum 5ppm/°C of the LT1019A-5) and a ± 4.215V full scale. If VREF is forced lower than 2.43V, the REFRDY bit in the serial data output will be forced to low. UNIPOLAR / BIPOLAR OPERATION AND ADJUSTMENT Figure 8 shows the ideal input/output characteristics for the LTC1404. The code transitions occur midway between successive integer LSB values (i.e., 0.5LSB, 1.5LSB, 2.5LSB, … FS – 1.5LSB). The output code is natural binary with 1LSB = 4.096/4096 = 1mV. Figure 9 shows the input/output transfer characteristics for the bipolar mode in two’s complement format. Unipolar Offset and Full-Scale Error Adjustments In applications where absolute accuracy is important, offset and full-scale errors can be adjusted to zero. Figure 10a shows the extra components required for full-scale error adjustment. Figure 10b shows offset and full-scale adjustment. Offset error must be adjusted before fullscale error. Zero offset is achieved by applying 0.5mV (i.e., 0.5LSB) at the input and adjusting the offset trim until the LTC1404 output code flickers between 0000 0000 0000 and 0000 0000 0001. For zero full-scale error, apply an analog input of 4.0945V (FS – 1.5LSB or last code transition) at the input and adjust R5 until the LTC1404 output code flickers between 1111 1111 1110 and 1111 1111 1111.
–5V
13
LTC1404
APPLICATIONS INFORMATION
111...111 111...110 111...101
OUTPUT CODE
1LSB = FS = 4.096 4096 4096
111...100
000...011 000...010 000...001 000...000 0V
UNIPOLAR ZERO
1 LSB INPUT VOLTAGE (V)
FS – 1LSB
1404 F08
Figure 8. LTC1404 Unipolar Transfer Characteristics
011...111 011...110 BIPOLAR ZERO
OUTPUT CODE
000...001 000...000 111...111 111...110
100...001 100...000 –FS/2 –1 0V 1 LSB LSB INPUT VOLTAGE (V) FS/2 – 1LSB
1404 F09
Figure 9. LTC1404 Bipolar Transfer Characteristics
R1 50Ω VIN
+
A1 AIN R4 100Ω LTC1404 R3 10k FULL-SCALE ADJUST GND
–
R2 10k
ADDITIONAL PINS OMITTED FOR CLARITY ± 20LSB TRIM RANGE
1404 F10a
Figure 10a. LTC1404 Full-Scale Adjust Circuit
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ANALOG INPUT 0V TO 4.096V
R1 10k R2 10k R9 20Ω
+
A1 AIN R4 100k LTC1404 R5 4.3k FULL-SCALE ADJUST R3 100k R6 400Ω 5V R8 10k OFFSET ADJUST
10k 5V
–
R7 100k
1404 F10b
Figure 10b. LTC1404 Offset and Full-Scale Adjust Circuit
R1 10k
ANALOG INPUT ± 2.048V
+
R2 10k A1 AIN R4 100k R5 4.3k FULL-SCALE ADJUST R3 R7 100k 100k R6 200Ω LTC1404
–
5V
R8 20k OFFSET ADJUST
1404 F10c
–5V
Figure 10c. LTC1404 Bipolar Offset and Full-Scale Adjust Circuit
Bipolar Offset and Full-Scale Error Adjustments Bipolar offset and full-scale errors are adjusted in a similar fashion to the unipolar case. Bipolar offset error adjustment is achieved by applying an input voltage of – 0.5mV (– 0.5LSB) to the input in Figure 10c and adjusting the op amp until the ADC output code flickers between 0000 0000 0000 and 1111 1111 1111. For full-scale adjustment, an input voltage of 2.0465V (FS – 1.5LSBs) is applied to the input and R5 is adjusted until the output code flickers between 0111 1111 1110 and 0111 1111 1111.
LTC1404
APPLICATIONS INFORMATION
BOARD LAYOUT AND BYPASSING To obtain the best performance from the LTC1404, a printed circuit board is required. Layout for the printed circuit board should ensure that digital and analog signal lines are separated as much as possible. In particular, care should be taken not to run any digital traces alongside an analog signal trace or underneath the ADC. The analog input should be screened by GND. High quality 10µF surface mount AVX capacitor with a 0.1µF ceramic should be used at the VCC, VSS and VREF pins. For better results, another 10µF AVX capacitor can be added to the VCC pin. At 600ksps, the CLK frequency can be as high as 9.6MHz. A poor quality capacitor can lose more than 80% of its capacitance at this frequency range. Therefore, it is important to consult the manufacturer’s data sheet before the capacitor is used. For the LTC1404, at 600ksps, every bit decision must be determined within 104ns (9.6MHz). During this short time interval, the supply disturbance due to a CLK transition needs to settle. The ADC must update its DAC, make a comparator decision based on sub-mV overdrive, latch the new DAC information and output the serial data. This ADC provides one power supply, VCC, which is connected to both the internal analog and digital circuitry. Any ringing due to poor supply or reference bypassing, inductive trace runs, CLK and CONV over- or undershoot, or unnecessary DOUT loading can cause ADC errors. Therefore, the bypass capacitors must be located as close to the pins as possible. The traces connecting the pins and the bypass capacitors must be kept short and should be made as wide as possible. In unipolar mode operation, VSS must be connected to the GND pin directly. Input signal leads to AIN and signal return leads from GND (Pin 4) should be kept as short as possible to minimize noise coupling. In applications where this is not possible, a shielded cable between the analog input signal and the ADC is recommended. Also, any potential difference in grounds between the analog signal and the ADC appears as an error voltage in series with the analog input signal. Attention should be paid to reducing the ground circuit impedance as much as possible. Figure 11 shows the recommended system ground connections. All analog circuitry grounds should be terminated at the LTC1404 GND pin. The ground return from the LTC1404 Pin 4 to the power supply should be low impedance for noise free operation. Digital circuitry grounds must be connected to the digital supply common. As an alternative, instead of a direct short between the digital and analog circuitry, a 10Ω or a ferrite bead jumper helps reduce the digital noise.
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ANALOG SUPPLY –5V GND 5V GND
DIGITAL SUPPLY 5V
+
+
+
VSS
GND LTC1404
VCC
GND
VCC
DIGITAL CIRCUITRY
1404 F11
Figure 11. Power Supply Connection
In applications where the ADC data outputs and control signals are connected to a continuously active microprocessor bus, it is possible to get errors in the conversion results. These errors are due to feedthrough from the microprocessor to the successive approximation comparator. The problem can be eliminated by forcing the microprocessor into a Wait state during conversion or by using three-state buffers to isolate the ADC data bus. Power-Down Mode Upon power-up, the LTC1404 is initialized to the active state and is ready for conversion. However, the chip can be easily placed into Nap or Sleep mode by exercising the right combination of CLK and CONV signals. In Nap mode, all power is off except for the internal reference, which is still active and provides 2.43V output voltage to the other circuitry. In this mode, the ADC draws only 7.5mW of power instead of 75mW (for minimum power, the logic
15
LTC1404
APPLICATIONS INFORMATION
inputs must be within 500mV of the supply rails). In Sleep mode, power consumption is reduced to a minimum by cutting off power to all internal circuitry including the reference. Figure 12 illustrates power-down modes for the LTC1404. The chip enters Nap mode by keeping the CLK signal low and pulsing the CONV signal twice. For Sleep mode operation, the CONV signal should be pulsed four times while CLK is kept low. Nap and Sleep modes are activated on the falling edge of the CONV pulse. The LTC1404 returns to active mode easily. The rising edge of CLK wakes up the LTC1404. From Nap mode, wake-up occurs within 350ns. During the transition from Sleep mode to active mode, the VREF voltage ramp-up time is a function of its loading conditions. With a 10µF bypass capacitor, the wake-up time from Sleep mode is typically 2.5ms. A REFRDY signal is activated once the reference has settled and is ready for an A/D conversion. This REFRDY bit is sent to the DOUT pin as the first bit followed by the 12-bit data word (refer to Figure 13). To save power during wake-up from Sleep mode, the chip is designed to enter Nap mode automatically until the reference is ready. Once REFRDY goes high, the comparator powers up immediately and is ready for a conversion. During the Nap interval, any attempt to perform an analog-to-digital conCLK t1 CONV t1
NAP
SLEEP
VREF
REFRDY REFRDY = 0 Hi-Z DOUT NOTE: NAP AND SLEEP ARE INTERNAL SIGNALS. REFRDY APPEARS AS THE FIRST BIT IN THE DOUT WORD Hi-Z Hi-Z ALL ZERO REFRDY BIT +12-BIT DATA WORD Hi-Z REFRDY = 1 1 11 10 1 0
Figure 12. Nap Mode and Sleep Mode Waveforms
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version will result in an all-zero output code, including the REFRDY bit. If no conversion is attempted, the DOUT pin remains in a high impedance state. If the ADC wakes from Sleep mode, this can be determined by monitoring the state of the REFRDY bit at the DOUT pin. DIGITAL INTERFACE The digital interface requires only three digital lines. CLK and CONV are both inputs, and the DOUT output provides the conversion result in serial form. Figure 13 shows the digital timing diagram of the LTC1404 during the A/D conversion. The CONV rising edge starts the conversion. Once initiated, it can not be restarted until the conversion is completed. If the time from CONV signal to CLK rising edge is less than t2, the digital output will be delayed by one clock cycle. The digital output data is updated on the rising edge of the CLK line. The digital output data consists of a REFRDY bit followed by a valid 12-bit data word. DOUT data should be captured by the receiving system on the rising CLK edge. Data remains valid for a minimum time of t10 after the rising CLK edge to allow capture to occur.
REFRDY BIT +12-BIT DATA WORD
1404 F12
LTC1404
APPLICATIONS INFORMATION
t2 t3 1 CLK t4 CONV t6 INTERNAL S/H STATUS SAMPLE HOLD tACQ SAMPLE t8 DOUT Hi-Z REFRDY D11 D10 D9 D8 D7 D6 D5 D4 D3 D2 D1 D0 Hi-Z REFRDY HOLD t5 2 3 4 5 6 7 8 9 10 11 12 13 14 t7 15 16 1 2
Figure 13. ADC Digital Timing Diagram
CLK
VIH t8 t 10 VOH
D OUT VOL
Figure 14. CLK to DOUT Delay
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REFRDY BIT + 12-BIT DATA WORD tCONV tSAMPLE
1404 F13
CLK
VIH
t9 90% D OUT 10%
1404 F14
17
LTC1404
TYPICAL APPLICATIONS
Hardware Interface to the TMS320C50’s TDM Serial Port (Frame Sync is Generated from TFSX)
7.8MHz EXTERNAL CLOCK 1 6 VCC CLK 2 7 AIN CONV LTC1404 5 3 VREF DOUT VSS 8 GND 4
1404 TA04a
+
10µF
Logic Analyzer Waveforms Show 2.05µs Throughput Rate (Input Voltage = 1.606V, Output Code = 0110 0100 0110 = 160610)
NOTE: THE TMS320C50-40MHz HAS A LIMITED SERIAL PORT CLOCK SPEED OF 7.8MHz. TO ALLOW THE LTC1404 TO RUN AT ITS MAXIMUM SPEED OF 9.6MHz, THE TMS320C50-57 OR TMS320C50-80MHz IS NEEDED
Data from the LTC1404 Loaded into the TMS320C50’s TRCV Register
X RDY D11 D10 D9 D8 D7 D6 D5 D4 D3 D2 D1 D0 X X
1404 TA04c
Data Stored in the TMS320C50’s Memory (in Right Justified Format)
0 0 0 RDY D11 D10 D9 D8 D7 D6 D5 D4 D3 D2 D1 D0
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TMS320C50-40MHZ TCLKX TCLKR TFSX TFSR TDR
5V UNIPOLAR INPUT
0.1µF
+
10µF
0.1µF
1404T A04B
1404 TA04d
LTC1404
TYPICAL APPLICATIONS
TMS320C50 Code for Circuit
THIS PROGRAM DEMONSTRATES THE LTC1404 INTERFACE TO THE TMS320C50. FRAME SYNC PULSE IS GENERATED FROM TFSX. DATA SHIFT CLOCK IS EXTERNALLY GENERATED. *Initialization* .mmregs ;- - Initialized data memory to zero .ds 0F00h DATA0 .word 0 DATA1 .word 0 DATA2 .word 0 DATA3 .word 0 DATA4 .word 0 DATA5 .word 0 ;- - Set up the ISR vector .ps 080Ah rint : B RECEIVE xint : B TRANSMIT trnt : B TREC txnt : B TTRANX ;- - Setup the reset vector .ps 0A00h .entry START: ; Defines global symbolic names ; Initialize data to zero ; Begin sample data location ;. ; Location of data ;. ;. ; End sample data location ; Serial ports interrupts ; 0A; ; 0C; ; 0E; ; 10;
*TMS320C50 Initialization* SETC INTM ; Temporarily disable all interrupts LDP #0 ; Set data page pointer to zero OPL #0834h, PMST ; Set up the PMST status and control register LACC #0 SAMM CWSR ; Set software wait state to 0 SAMM PDWSR ; *Configure Serial Port* SPLK #0028h, TSPC ; Set TDM Serial Port ; TDM = 0 Stand Alone mode ; DLB=0 Not loop back ; FO=0 16 Bits ; FSM=1 Burst Mode ; MCM=0 CLKR is generated externally ; TXM=1 FSX as output pin ; Put serial port into reset ; (XRST=RRST=0) SPLK #00E8h, TSPC ; Take Serial Port out of reset ; (XRST=RRST=1) SPLK #0FFFFh, IFR ; Clear all the pending interrupts
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*Start Serial Communication* SACL TDXR ; Generate frame sync pulse SPLK #040h, IMR ; Turn on TRNT receiver interrupt CLRC INTM ; Enable interrupt CLRC SXM ; For Unipolar input, set for right shift ; with no sign extension MAR *, AR7 ; Load the auxiliary register pointer with seven LAR AR7, #0F00h ; Load the auxiliary register seven with #0F00h ; as the begin address for data storage WAIT: NOP ; Wait for a receive interrupt NOP ; NOP ; SACL TDXR ; !! Regenerate the frame sync pulse B WAIT ; ; - - - - - - - end of main program - - - - - - - - - - ; *Receiver Interrupt Service Routine* TREC: LAMM TRCV ; Load the data received from LTC1404 SFR ; Shift right two times SFR ; AND #1FFFh, 0 ; ANDed with #1FFFh ; For converting the data to right ; justified format ; SACL *+, 0 ; Write to data memory pointed by AR7 and ; increase the memory address by one LACC AR7 ; SUB #0F05h,0 ; Compare to end sample address #0F05h BCND END_TRCV, GEQ ; If the end sample address has exceeded jump to END_TRCV ; SPLK #040h, IMR ; Else Re-enable the TRNT receive interrupt RETE ; Return to main program and enable interrupt *After Obtained the Data from LTC1404, Program Jump to END_TRCV* END_TRCV: SPLK #002h, IMR ; Enable INT2 for program to halt CLRC INTM SUCCESS: B SUCCESS *Fill the Unused Interrupt with RETE, to avoid program get “lost”* TTRANX: RETE RECEIVE: RETE TRANSMIT: RETE INT2: B halt ; Halts the running CPU
19
LTC1404
TYPICAL APPLICATIONS
LTC1404 Interface to the ADSP2181’s SPORT0 (Frame Sync is Generated from RFS0)
9.6MHz EXTERNAL CLOCK 1 0.1µF UNIPOLAR INPUT 2 VCC AIN CLK 6 7 5 ADSP2181 SCLKO RFSO DR0
+
10µF
Logic Analyzer Waveforms Show 1.67µs Throughput Rate (Input Voltage = 1.604V, Output Code = 0110 0100 0100 = 160410)
NOTE: WITHOUT THE EXTERNAL CLOCKING SIGNAL, THE ADSP2181 SCLK0 CAN BE PROGRAMMED TO RUN AT 8.3MHz
X
Data Stored in the ADSP2181’s Memory (Normal Mode, SLEN = D)
0 0 0 RDY D11 D10 D9 D8 D7 D6 D5 D4 D3 D2 D1 D0
1404 TA05d
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5V
CONV LTC1404 3 VREF DOUT VSS 8 GND 4
+
10µF
0.1µF
1404 TA05a
1404 TA05b
Data from the LTC1404 (Normal Mode)
RDY D11 D10 D9 D8 D7 D6 D5 D4 D3 D2 D1 D0 X X
1404 TA05c
LTC1404
TYPICAL APPLICATIONS
ADSP2181 Code for Circuit
THIS PROGRAM DEMONSTRATES THE LTC1404 INTERFACE TO THE ADSP-2181. FRAME SYNC PULSE IS GENERATED FROM RFS. DATA SHIFT CLOCK IS EXTERNALLY GENERATED. /*Section 1: Initialization*/ .module/ram/abs = 0 adspltc; /*define the program module*/ jump start; /*jump over interrupt vectors*/ nop; nop; nop; rti; rti; rti; rti; /*code vectors here upon IRQ2 int*/ rti; rti; rti; rti; /*code vectors here upon IRQL1 int*/ rti; rti; rti; rti; /*code vectors here upon IRQL0 int*/ rti; rti; rti; rti; /*code vectors here upon SPORT0 TX int*/ ax0 = rx0; /*Section 5*/ dm (0x2000) = ax0; /*begin of SPORT0 receive interrupt*/ rti; /* */ /* */ /*end of SPORT0 receive interrupt*/ rti; rti; rti; rti; /*code vectors here upon /IRQE int*/ rti; rti; rti; rti; /*code vectors here upon BDMA interrupt*/ rti; rti; rti; rti; /*code vectors here upon SPORT1 TX (IRQ1) int*/ rti; rti; rti; rti; /*code vectors here upon SPORT1 RX (IRQ0) int*/ rti; rti; rti; rti; /*code vectors here upon TIMER int*/ rti; rti; rti; rti; /*code vectors here upon POWER DOWN int*/ /*Section 2: Configure SPORT0*/ start: /*to configure SPORT0 control reg*/ /*SPORT0 address = 0X3FF6*/ /*RFS is used for frame sync generation*/ /*RFS is internal, TFS is not used*/ /*bit 0-3 = Slen*/ /*F = 15 = 1111*/ /*E = 14 = 1110*/ /*D = 13 = 1101*/ /*bit 4,5 data type right justified zero filled MSB*/ /*bit 6 INVRFS = 0*/ /*bit 7 INVTFS = 0*/ /*bit 8 IRFS=1 receive internal frame sync*/ /*bit 9,10,11 are for TFS (don’t care)*/ /*bit 12 RFSW=0 receive is Normal mode*/ /*bit 13 RTFS=1 receive is framed mode*/ /*bit 14 ISCLK=0 SCLK is external */ /*bit 15 multichannel mode = 0*/ ax0 = 0x2F0D; /*normal mode, bit 12=0*/ /*if alternate mode bit 12=1, ax0=0x3F0E*/ dm (0x3FF6) =ax0;
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/*Section 3: configure CLKDIV and RFSDIV, setup interrupts*/ /*Using an external clock source=9.6MHz*/ /*Does not need to configure CLKDIV*/ /*to Configure RFSDIV*/ ax0 = 15; /*set the RFSDIV reg = 15*/ /*=> the frame sync pulse for every 16 SCLK*/ /*if frame sync pulse in every 15 SCLK, ax0=14*/ dm(0x3FF4) =ax0; /*to setup interrupt*/ ifc= 0x0066; /*clear any extraneous SPORT interrupts*/ icntl= 0; /*IRQXB = level sensitivity*/ /*disable nesting interrupt*/ imask= 0x0020; /*bit 0 = timer int = 0*/ /*bit 1 = SPORT1 or IRQ0B int = 0*/ /*bit 2 = SPORT1 or IRQ1B int = 0*/ /*bit 3 = BDMA int = 0*/ /*bit 4 = IRQEB int = 0*/ /*bit 5 = SPORT0 receive int = 1*/ /*bit 6 = SPORT0 transmit int = 0*/ /*bit 7 = IRQ2B int = 0*/ /*enable SPORT0 receive interrupt*/ /*Section 4: Configure System Control Register and Start Communication*/ /*to configure system control reg*/ ax0 = dm(0x3FFF); /*read the system control reg*/ ay0 = 0xFFF0; ar = ax0 AND ay0; /*set wait state to zero*/ ay0 = 0x1000; ar = ar OR ay0; /*bit 12 = 1, enable SPORT0*/ dm(0x3FFF) = ar; /*frame sync pulse regenerated automatically*/ cntr = 5000; do waitloop until ce; nop; nop; nop; nop; nop; nop; waitloop: nop; rts; .endmod;
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LTC1404
TYPICAL APPLICATIONS U
Quick Look Circuit for Converting Data to Parallel Format
5V 5V 1V CC 10µF 0.1µF 2 3 VSS 8 CONV LTC1404 CONV AIN VREF GND CLK DOUT 7 6 5 12 RCK 10 SRCLR
+
2.43V REFERENCE OUTPUT
ANALOG INPUT (0V TO 4.096V)
+
10µF
0.1µF
4
3-WIRE SERIAL INTERFACE LINK
QA QB 11 QC SRCK 74HC595 QD 14 QE SER QF 13 QG G QH QH' 10 SRCLR
15 1 2 3 4 5 6 7 9
D0 D1 D2 D3 D4 D5 D6 D7
12 CLK
QA QB 11 QC SRCK 74HC595 QD 14 QE SER QF 13 QG G QH QH' RCK
15 1 2 3 4 5 6 7 9
D8 D9 D10 D11 REFRDY
1404 TA03
22
LTC1404
PACKAGE DESCRIPTION U
Dimensions in inches (millimeters) unless otherwise noted.
S8 Package 8-Lead Plastic Small Outline (Narrow 0.150)
(LTC DWG # 05-08-1610)
0.189 – 0.197* (4.801 – 5.004) 8 7 6 5
0.228 – 0.244 (5.791 – 6.197)
0.150 – 0.157** (3.810 – 3.988)
1 0.010 – 0.020 × 45° (0.254 – 0.508) 0.008 – 0.010 (0.203 – 0.254) 0°– 8° TYP 0.053 – 0.069 (1.346 – 1.752)
2
3
4
0.004 – 0.010 (0.101 – 0.254)
0.016 – 0.050 0.406 – 1.270
0.014 – 0.019 (0.355 – 0.483)
0.050 (1.270) TYP
*DIMENSION DOES NOT INCLUDE MOLD FLASH. MOLD FLASH SHALL NOT EXCEED 0.006" (0.152mm) PER SIDE **DIMENSION DOES NOT INCLUDE INTERLEAD FLASH. INTERLEAD FLASH SHALL NOT EXCEED 0.010" (0.254mm) PER SIDE
SO8 0996
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 its circuits as described herein will not infringe on existing patent rights.
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LTC1404
TYPICAL APPLICATIONS
LTC1404 Interface to TMS320C50 Running at 5MHz without External Clock
TMS320C50 5V 1 VCC AIN CLK 6 TCLKX TCLKR TFSX TFSR TDR
+
10µF
LTC1404 Interface to ADSP2181 Running at 8.3MHz without External Clock
5V ADSP2181 1 0.1µF UNIPOLAR INPUT 2 VCC AIN CLK 6 7 5 SCLKO (8.3MHz) RFSO DR0
+
10µF
RELATED PARTS
12-Bit Parallel Output ADCs
PART NUMBER LTC1273/LTC1275/ LTC1276 LTC1274/LTC1277 LTC1278/LTC1279 LTC1282 LTC1409 LTC1410 DESCRIPTION Complete 5V Sampling 12-Bit ADCs with 70dB SINAD at Nyquist Low Power 12-Bit ADCs with Nap and Sleep Mode Shutdown High Speed Sampling 12-Bit ADCs with Shutdown Complete 3V 12-Bit ADCs with 12mW Power Dissipation Low Power 12-Bit, 800ksps Sampling ADC 12-Bit, 1.25Msps Sampling ADC with Shutdown COMMENTS Lower Power and Cost Effective for fSAMPLE ≤ 300ksps Lowest Power (10mW) for fSAMPLE ≤ 100ksps Cost Effective 12-Bit ADCs with Convert Start Input Best for 300ksps < fSAMPLE ≤ 600ksps Fully Specified for 3V Powered Applications, fSAMPLE ≤ 140ksps Best Dynamic Performance fSAMPLE ≤ 800ksps, 80mW Dissipation Best Dynamic Performance, THD = 84 and SINAD = 71 at Nyquist
12-Bit Serial Output ADCs
PART NUMBER LTC1285/LTC1288 LTC1286/LTC1298 LTC1290 LTC1296 LTC1400 LTC1401 VCC 3V 5V 5/± 5V 5/± 5V 5/± 5V 3V SAMPLE RATE 7.5/6.6ksps 12.5/11.1ksps 50ksps 46.5ksps 400ksps 200ksps POWER DISSIPATION 0.48mW 1.25mV 30mW 30mW 75mW 15mW DESCRIPTION 3V, One or Two Input, Micropower, SO-8 One or Two Input, Micropower, SO-8 8 Input, Full-Duplex Serial I/O 8 Input, Half-Duplex Serial I/O, Power Shutdown Output Complete 12-Bit, 400ksps, SO-8 ADC with Shutdown Complete 12-Bit, 200ksps, SO-8 ADC with Shutdown
24
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417q (408)432-1900 FAX: (408) 434-0507q TELEX: 499-3977 q www.linear-tech.com
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0.1µF
UNIPOLAR INPUT
2
7 CONV LTC1404 5 3 VREF DOUT VSS 8 GND 4
+
10µF
0.1µF
1404 TA07
CONV LTC1404 3 VREF DOUT VSS 8 GND 4
+
10µF
0.1µF
1404 TA06
1404f LT/TP 0398 4K • PRINTED IN USA
© LINEAR TECHNOLOGY CORPORATION 1998
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