LTC1093CN#PBF Linear Technology, LTC1093CN#PBF Datasheet - Page 25

• Manufacturer Part Number: LTC1093CN#PBF
• Description: IC DATA ACQ SYS 10BIT 6CH 16-DIP
• Manufacturer: Linear Technology
• Type: Data Acquisition System (DAS), ADCr

Specifications of LTC1093CN#PBF

• Resolution (bits): 10 b
• Data Interface: Serial
• Voltage Supply Source: Dual ±
• Voltage - Supply: 4.5 V ~ 10 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Through Hole
• Package / Case: 16-DIP (0.300", 7.62mm)
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Sampling Rate (per Second): -

6. Reduced Reference Operation
The minimum reference voltage of the LTC1091 is limited
to 4.5V because the V
tied together. However, the LTC1092/LTC1093/LTC1094
can operate with reference voltages below 1V.
The effective resolution of the LTC1092/LTC1093/LTC1094
can be increased by reducing the input span of the con-
verter. The parts exhibit good linearity and gain over a wide
range of reference voltages (see typical curves of Linearity
and Full-Scale Error vs Reference Voltage). However, care
must be taken when operating at low values of V
because of the reduced LSB step size and the resulting
higher accuracy requirement placed on the converter. The
following factors must be considered when operating at
low V
1. Offset
2. Noise
3. Conversion speed (CLK frequency)
Offset with Reduced V
The offset of the LTC1092/LTC1093/LTC1094 has a larger
effect on the output code when the A/D is operated with
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 curve of Unadjusted
Offset Error vs Reference Voltage shows how offset in
LSBs is related to reference voltage for a typical value of
V
A
OS
PPLICATI
0.5mV/DIV
Figure 14. Poor Reference Settling Can Cause A/D Errors
. For example, a V
REF
values:
O
U
CC
REF
OS
S
supply and reference are internally
of 0.5mV which is 0.1LSB with a
I FOR ATIO
1 s/DIV
U
W
1091-4 F14
U
REF
5V reference becomes 0.5LSB with a 1V reference and
2.5LSBs with a 0.2V reference. If this offset is unaccept-
able, it can be corrected digitally by the receiving system
or by offsetting the “–” input to the LTC1092/LTC1093/
LTC1094.
Noise with Reduced V
The total input-referred noise of the LTC1092/LTC1093/
LTC1094 can be reduced to approximately 200 V 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 but will
become a larger fraction of an LSB as the size of the LSB
is reduced. The typical curve of Noise Error vs Reference
Voltage shows the LSB contribution of this 200 V of
noise.
For operation with a 5V reference, the 200 V noise is only
0.04LSB peak-to-peak. In this case, the LTC1092/LTC1093/
LTC1094 noise will contribute virtually no uncertainty to
the output code. However, 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 1V reference, this same 200 V noise is 0.2LSB
peak-to-peak. This will reduce the range of input voltages
over which a stable output code can be achieved by
0.2LSB. If the reference is further reduced to 200mV, the
200 V noise becomes equal to one LSB and a stable code
may be difficult to achieve. In this case averaging readings
may be necessary.
This noise data was taken in a very clean setup. Any setup-
induced noise (noise or ripple on V
add to the internal noise. The lower the reference voltage
to be used, the more critical it becomes to have a clean,
noise-free setup.
Conversion Speed with Reduced V
With reduced reference voltages, the LSB step size is
reduced and the LTC1092/LTC1093/LTC1094 internal
comparator overdrive is reduced. Therefore, it may be
necessary to reduce the maximum CLK frequency when
low values of V
REF
are used.
REF
LTC1093/LTC1094
LTC1091/LTC1092
CC
REF
, V
REF
, V
IN
or V
25
–
) will