LTC1278-4IN Linear Technology, LTC1278-4IN Datasheet - Page 11

• Manufacturer Part Number: LTC1278-4IN
• Description: IC A/DCONV SAMPLNG W/SHTDN 24DIP
• Manufacturer: Linear Technology

Specifications of LTC1278-4IN

• Number Of Bits: 12
• Sampling Rate (per Second): 400k
• Data Interface: Parallel
• Number Of Converters: 1
• Power Dissipation (max): 150mW
• Voltage Supply Source: Dual ±
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Through Hole
• Package / Case: 24-DIP (0.300", 7.62mm)
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

A
conversion starts. Any op amp that settles in 200ns to
small current transients will allow maximum speed opera-
tion. If slower op amps are used, more settling time can be
provided by increasing the time between conversions.
Suitable devices capable of driving the ADC’s A
include the LT1360, LT1220, LT1223 and LT1224 op
amps.
Internal Reference
The LTC1278 has an on-chip, temperature compensated,
curvature corrected, bandgap reference, which is factory
trimmed to 2.42V. It is internally connected to the DAC and
is available at Pin 2 to provide up to 1mA 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 (10 F tantalum in parallel with a
0.1 F ceramic).
The V
provide input span adjustment in bipolar mode. The V
pin must be driven to at least 2.45V to prevent conflict with
the internal reference. The reference should be driven to
no more than 4.8V to keep the input span within the 5V
supplies.
Figure 6 shows an LT1006 op amp driving the reference
pin. (In the unipolar mode, the input span is already 0V to
5V with the internal reference so driving the reference is
not recommended, since the input span will exceed the
supply and codes will be lost at the full scale.) Figure 7
shows a typical reference, the LT1019A-2.5 connected to
the LTC1278. This will provide an improved drift (equal to
the maximum 5ppm/ C of the LT1019A-2.5) and a 2.582V
full scale.
PPLICATI
1.033V
INPUT RANGE
REF
Figure 6. Driving the V
REF(OUT)
pin can be driven with a DAC or other means to
O
+
–
LT1006
U
S
REF
I FOR ATIO
U
V
REF(OUT)
with the LT1006 Op Amp
2.45V
W
3
10 F
A
V
AGND
LTC1278
IN
REF
U
–5V
5V
IN
LTC1278 F6
input
REF
UNIPOLAR/BIPOLAR OPERATION AND ADJUSTMENT
Figure 8a shows the ideal input/output characteristics for
the LTC1278. 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 naturally
binary with 1LSB = FS/4096 = 5V/4096 = 1.22mV. Figure
8b shows the input/output transfer characteristics for the
bipolar mode in two’s complement format.
Figure 7. Supplying a 2.5V Reference Voltage to the LTC1278
(= 1.033
INPUT RANGE
Figure 8a. LTC1278 Unipolar Transfer Characteristics
Figure 8b. LTC1278 Bipolar Transfer Characteristics
111...111
111...110
111...101
111...100
000...011
000...010
000...001
000...000
011...111
011...110
000...001
000...000
111...111
111...110
100...001
100...000
2.58V
V
REF
)
0V
LT1019A-2.5
–FS/2
UNIPOLAR
ZERO
1LSB = FS
LSB
GND
1
V
5V
IN
V
with the LT1019A-2.5
OUT
4096
INPUT VOLTAGE (V)
INPUT VOLTAGE (V)
=
4096
BIPOLAR
5V
LSB
–1
ZERO
0V
LSB
FS = 5V
1LSB = FS/4096
1
3
10 F
FS/2 – 1LSB
FS – 1LSB
LTC1278 • F8b
LTC1278 F8a
LTC1278
A
V
AGND
LTC1278
IN
REF
–5V
5V
11
LTC1278 F7