LTC1290BI LINER [Linear Technology], LTC1290BI Datasheet - Page 23

• Manufacturer Part Number: LTC1290BI
• Description: Single Chip 12-Bit Data Acquisition System
• Manufacturer: LINER [Linear Technology]

fundamentals. This is classically referred to as
intermodulation distortion (IMD).
8. Overvoltage Protection
Applying signals to the analog MUX that exceed the
positive or negative supply of the device 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 MUX before power is applied to the LTC1290.
Another example is the input source is operating from
different supplies of larger value than the LTC1290. These
conditions should be prevented either with proper supply
sequencing or by use of external circuitry to clamp or
current limit the input source. As shown in Figure 20, a 1k
resistor is enough to stand off 15V (15mA for one only
channel). If more than one channel exceeds the supplies
A
PPLICATI
Figure 18. LTC1290 ENOB vs Input Frequency
–100
–120
–140
11.6
11.2
10.8
10.4
–20
–40
–60
–80
9.6
9.2
8.8
12
10
0
0
0
Figure 17a. LTC1290 FFT Plot
O
4
20
U
S
8
FREQUENCY (kHz)
FREQUENCY (kHz)
40
I FOR ATIO
12
U
f
SNR = 73.25dB
f
f
IN
SAMPLE
60
SAMPLE
16
= 1kHz
20
= 50.6kHz
= 50.6kHz
W
80
1290 • F17a
1290 F18
24
100
U
then the following guidelines can be used. Limit the
current to 7mA per channel and 28mA for all channels.
This means four channels can handle 7mA of input current
each. Reducing the ACLK and SCLK frequencies from the
maximum of 4MHz and 2MHz, respectively, (see Typical
Peformance Characteristics curves Maximum ACLK Fre-
quency vs Source Resistance and Sample-and-Hold
Acquisition Time vs Source Resistance) allows the use of
V
IN
–100
–120
–140
–100
–120
–20
–40
–60
–80
Figure 20. Overvoltage Protection for MUX
–20
–40
–60
–80
0
0
0
0
f
SNR = 72.54dB
1k
f
IN
SAMPLE
Figure 17b. LTC1290 FFT Plot
Figure 19. LTC1290 FFT Plot
= 25kHz
4
4
= 50.6kHz
CH0
DGND
8
8
FREQUENCY (kHz)
FREQUENCY (kHz)
LTC1290
12
12
AGND
V
f
f
f
V
CC
IN1
IN2
SAMPLE
16
16
–
= 5.1kHz
= 5.6kHz
20
20
= 50.6kHz
22 F
1290 • F17b
5V
1290 • F19
24
24
LTC1290
0.1 F
1290 F20
–5V
23