ltc1867l Linear Technology Corporation, ltc1867l Datasheet - Page 12

• Manufacturer Part Number: ltc1867l
• Description: Ltc1863l - Micropower, 3v, 12-bit, 8-channel 175ksps Adcs
• Manufacturer: Linear Technology Corporation

LTC1863L/LTC1867L
APPLICATIO S I FOR ATIO
band between DC and half the sampling frequency. THD is
expressed as:
where V
quency and V
second through Nth harmonics.
Internal Reference
The LTC1863L and LTC1867L have an on-chip, tempera-
ture compensated, curvature corrected, bandgap refer-
ence that is factory trimmed to 1.25V. It is internally
connected to a reference amplifier and is available at V
(Pin 10). A 3k resistor is in series with the output so that
it can be easily overdriven by an external reference if
better drift and/or accuracy are required as shown in
Figure 4. The reference amplifier gains the V
2x to 2.5V at REFCOMP (Pin 9). This reference amplifier
12
1.25V
Figure 4b. Using the LT1790A-1.25 as an External Reference
THD
2.5V
=
1
is the RMS amplitude of the fundamental fre-
20
2.2µF
10µF
LT1790A-1.25
Figure 4a. LTC1867L Reference Circuit
10
15
log
9
V
2
3V
IN
V
REFCOMP
GND
V
through V
REF
OUT
V
+
U
2
2
+
10µF
V
U
R3
3
2
N
REFERENCE
V
+
R2
are the amplitudes of the
AMP
1
2.2µF
0.1µF
V
4
10
15
2
9
...
W
V
REFCOMP
GND
REF
+
V
LTC1863L/LTC1867L
LTC1863L/
LTC1867L
R1
3k
N
2
REF
REFERENCE
1863L7L F04b
BANDGAP
U
voltage by
1863L7L F04a
REF
compensation pin, REFCOMP, must be bypassed with a
10µF ceramic or tantalum in parallel with a 0.1µF ceramic
for best noise performance.
Digital Interface
The LTC1863L and LTC1867L have a very simple digital
interface that is enabled by the control input, CS/CONV. A
logic rising edge applied to the CS/CONV input will initiate
a conversion. After the conversion, taking CS/CONV low
will enable the serial port and the ADC will present digital
data in two’s complement format in bipolar mode or
straight binary format in unipolar mode, through the SCK/
SDO serial port.
Internal Clock
The internal clock is factory trimmed to achieve a typical
conversion time of 3.2µs and a maximum conversion
time, 3.7µs, over the full operating temperature range. The
typical acquisition time is 1.68µs, and a throughput sam-
pling rate of 175ksps is tested and guaranteed.
Automatic Nap Mode
The LTC1863L and LTC1867L go into automatic nap mode
when CS/CONV is held high after the conversion is com-
plete. With a typical operating current of 750µA and auto-
matic 170µA nap mode between conversions, the power
dissipation drops with reduced sample rate. The ADC only
keeps the V
is in the automatic nap mode. The slower the sample rate
allows the power dissipation to be lower (see Figure 5).
800
700
600
500
400
300
200
100
REF
Figure 5. Supply Current vs f
1
V
and REFCOMP voltages active when the part
DD
= 2.7V
10
f
SAMPLE
(ksps)
100
1863L7L G09
SAMPLE
1000
1863l7lfa