LTC1096 Linear Technology, LTC1096 Datasheet - Page 22

• Manufacturer Part Number: LTC1096
• Description: Micropower Sampling 8-Bit Serial I/O A/D Converters
• Manufacturer: Linear Technology

A
Effective Number of Bits
The effective number of bits (ENOBs) is a measurement of
the resolution of an A/D and is directly related to the
S/(N + D) by the equation:
where S/(N + D) is expressed in dB. At the maximum
sampling rate of 33kHz the LTC1096 maintains 7.5 ENOBs
or better to 40kHz. Above 40kHz the ENOBs gradually
decline, as shown in Figure 12, due to increasing second
harmonic distortion. The noise floor remains approxi-
mately 70dB.
LTC1096/LTC1096L
LTC1098/LTC1098L
MICROPROCESSOR INTERFACES
The LTC1096(L)/LTC1098(L) can interface directly (with-
out external hardware to most popular microprocessor
(MPU) synchronous serial formats (see Table 1). If an
MPU without a dedicated serial port is used, then three or
four of the MPU’s parallel port lines can be programmed
to form the serial link to the LTC1096(L)/LTC1098(L).
Included here is one serial interface example and one
example showing a parallel port programmed to form the
serial interface.
Motorola SPI (MC68HC05C4,CM68HC11)
The MC68HC05C4 has been chosen as an example of
an MPU with a dedicated serial port. This MPU transfer
data MSB-first and in 8-bit increments. With two 8-bit
transfers, the A/D result is read into the MPU. The first
8-bit transfer sends the D
and clocks into the processor. The second 8-bit trans-
fer clocks the A/D conversion result, B7 through B0,
into the MPU.
ANDing the first MUP received byte with 00Hex clears the
first byte. Notice how the position of the start bit in the first
MPU transmit word is used to position the A/D result
right-justified in two memory locations.
22
TYPICAL
PPLICATI
ENOB = [S/(N + D) –1.76]/6.02
A
O
PPLICATI
U
S
I FOR ATIO
U
IN
word to the LTC1098(L)
O
U
W
S
U
Table 1. Microprocessor with Hardware Serial Interfaces
Compatible with the LTC1096(L)/LTC1098(L)
*
Requires external hardware
MICROWIRE and MICROWIRE/PLUS are trademarks of
National Semiconductor Corp.
Motorola
RCA
Hitachi
National Semiconductor
Texas Instruments
Figure 12. Dynamic Accuracy Is Maintained Up to an Input
Frequency of 40kHz
MC6805S2,S3
MC68HC11
MC68HC05
CDP68HC05
HD6305
HD63705
HD6301
HD63701
HD6303
HD64180
COP400 Family
COP800 Family
NS8050U
HPC16000 Family
TMS7002
TMS7042
TMS70C02
TMS70C42
TMS32011*
TMS32020
PART NUMBER
7
6
4
3
2
0
8
5
1
0
f
SAMPLE
= 31.25kHz
INPUT FREQUENCY (kHz)
20
SPI
SPI
SPI
SPI
SCI Synchronous
SCI Synchronous
SCI Synchronous
SCI Synchronous
SCI Synchronous
CSI/O
MICROWIRE
MICROWIRE/PLUS
MICROWIRE/PLUS
MICROWIR/PLUS
Serial Port
Serial Port
Serial Port
Serial Port
Serial Port
Serial Port
TYPE OF INTERFACE
TM
40
LTC1096/8 • F12
TM