TLC3574IDW Datasheet, PDF (37/49 Pages) Texas Instruments – 5-V ANALOG,3-/5-V DIGITAL, 14-/12-BIT, 200-KSPS, 4-/8-CHANNEL SERIAL ANALOG-TO-DIGITAL CONVERTERS WITH 10-V INPUTS

TLC3574, TLC3578, TLC2574, TLC2578
5ĆV ANALOG, 3Ć/5ĆV DIGITAL, 14Ć/12ĆBIT, 200ĆKSPS, 4Ć/8ĆCHANNEL
SERIAL ANALOGĆTOĆDIGITAL CONVERTERS WITH ±10ĆV INPUTS
SLAS262C − OCTOBER 2000 − REVISED MAY 2003
APPLICATION INFORMATION
interface with host
Figure 32 shows the examples of the interface between a single converter and host DSP (TMS320C54x DSP)
or microprocessor. The C54x is set as FWID=1 (active pulse width=1CLK); (R/X) DATDLY=1 (1 bit data delay);
CLK(X/R)P=0 (transmit data are clocked out at rising edge of CLK, receive data are sampled on falling edge
of CLK); and FS(X/R)P=1 (FS is active high). If multiple converters connect to the same C54x, use CS as chip
select.
The host microprocessor is set as the SPI master, CPOL=0 (active high clock), and CPHA=1 (transmit data is
clock out at rising edge of CLK, receive data are sampled at falling edge of CLK). 16 bits (or more) per transfer
is required.
VDD
VDD
TMS320C54X
FSR
FSX
DX
DR
CLKR
CLKX
IRQ
10 kΩ
10 kΩ
10 kΩ
Converter
CS
FS
SDI
SDO
Host
Microprocessor
SS
Ain
MOSI
MISO
Converter
CS
FS
Ain
SDI
SDO
SCLK
INT/EOC
SCK
IRQ
SCLK
INT/EOC
Single Converter Connects to DSP
Converter Connects to Microprocessor
Figure 32. Typical Interface to Host DSP and Microprocessor
sampling time analysis
Figure 33 shows the equivalent circuit to evaluate the required sampling time. Req is the Thevenin equivalent
resistor (Req = 3.5 K). The C_(sampling) is sampling capacitor (30 pF maximum).
To get 1/4 LSB accuracy, the sampling capacitor, C_sampling, has to be charged to
V_C = V_S ± voltage of 1/4 LSB = V_S ± (V_S/65532) for 14 bit converter (TLC3574 and TLC3578)
= V_S ± (V_S/16384) for 12 bit converter (TLC2574 and TLC2578)
During the sampling time t_(sampling), C_(sampling) is charge to
ȧȱȲ ^{ǒ Ǔȳȴȧ V}_C ^{+ V}_S ^1–exp
–t_(sampling)
Req C_(sampling)
Therefore, the required sampling time is
t_(sampling) = Req × C_(sampling) × In (65532) for 14-bit (TLC3574 and TLC3578)
t_(sampling) = Req × C_(sampling) × In (16384) for 12-bit (TLC2574 and TLC2578).
TMS320C54x is a trademark of Texas Instruments.
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