Datasheet

LTC1852/LTC1853
14
18523fa
INPUT VOLTAGE (V)
0 FS – 1LBS
OUTPUT CODE
1111...1111
1111...1110
1111...1101
1000...0001
1000...0000
0111...1111
0111...1110
0000...0010
0000...0001
0000...0000
18523 F01A
FS = V
REFCOMP
INPUT VOLTAGE (V)
–FS –1LBS 0 1LBS FS – 1LBS
OUTPUT CODE
0111...1111
0111...1110
0111...1101
0000...0001
0000...0000
1111...1111
1111...1110
1000...0010
1000...0001
1000...0000
18523 F01B
BIPOLAR
ZERO
FS =
V
REFCOMP
2
SINGLE-ENDED/
DIFFERENTIAL BIT
UNIPOLAR/
BIPOLAR BIT
S6 S5
A2 A0
END OF
SEQUENCE BIT
PGA BIT
18523 F01
A1
MUX ADDRESS
S4 S3 S2 S1 S0
adjusted until the output code fl ickers between 1111 1111
1110 and 1111 1111 1111 for the LTC1853 and between
11 1111 1110 and 11 1111 1111 for the LTC1852.
For bipolar inputs, an input voltage of FS – 1.5LSBs should
be applied to the “+” input and the appropriate reference
adjusted until the output code fl ickers between 0111 1111
1110 and 0111 1111 1111 for the LTC1853 and between
01 1111 1110 and 01 1111 1111 for the LTC1852.
These adjustments as well as the factory trims affect all
channels. The channel-to-channel offset and gain error
matching are guaranteed by design to meet the specifi ca-
tions in the Converter Characteristics table.
OUTPUT DATA FORMAT
The LTC1852/LTC1853 have a 14 bit/16-bit parallel out-
put. The output word normally consists of a 10-bit/12-bit
conversion result data word and a 4-bit address (three
address bits A2
OUT
, A1
OUT
, A0
OUT
and the DIFF
OUT
bit).
The output drivers are enabled when RD is low provided
the chip is selected (CS is low). All 14/16 data output pins
and BUSY are supplied by OV
DD
and OGND to allow easy
interface to 3V or 5V digital logic.
The data format of the conversion result is automatically
selected and determined by the UNI/BIP input pin. If
the UNI/BIP pin is low indicating a unipolar input span
(0 – REFCOMP assuming PGA = 1), the format for the
data is straight binary with 1 LSB = FS/4096 (1mV for
REFCOMP = 4.096V). For the LTC1853 and 1LSB = FS/1024
(4mV for REFCOMP = 4.096V) for the LTC1852.
If the UNI/BIP pin is high indicating a bipolar input span
(± REFCOMP/2 for PGA = 1), the format for the data is two’s
complement binary with 1 LSB = [(+FS) – (–FS)]/4096
(1mV for REFCOMP = 4.096V). For the LTC1853 and 1LSB
= [(+FS) – (–FS)]/1024 (4mV for REFCOMP = 4.096V) for
the LTC1852.
In both cases, the code transitions occur midway be-
tween successive integer LSB values (i.e., –FS + 0.5LSB,
–FS + 1.5LSB, ... –1.5LSB, –0.5LSB, 0.5LSB, 1.5LSB, ...
FS – 1.5LSB, FS – 0.5LSB).
The three most signifi cant bits of the data word (D11, D10
and D9 for the LTC1853; D9, D8 and D7 for the LTC1852)
also function as output bits when reading the contents of
the programmable sequencer. During readback, a 7-bit
status word (S6-S0) containing the contents of the cur-
rent sequencer location is available when RD is low. The
individual bits of the status word are outlined in Figure 1.
During readback, the D8 to D0 pins (LTC1853) or D6 to
D0 pins (LTC1852) remain high impedance irrespective
of the state of RD.
Figure 1. Readback Status Word
Unipolar Transfer Characteristic
(UNI/BIP = 0)
Bipolar Transfer Characteristic
(UNI/BIP = 1)
APPLICATIONS INFORMATION