LTC1288IS8 Linear Technology, LTC1288IS8 Datasheet - Page 10

• Manufacturer Part Number: LTC1288IS8
• Description: IC A/D CONV SAMPLING 12BIT 8SOIC
• Manufacturer: Linear Technology

Specifications of LTC1288IS8

• Number Of Bits: 12
• Sampling Rate (per Second): 6.6k
• Data Interface: MICROWIRE™, Serial, SPI™
• Number Of Converters: 1
• Power Dissipation (max): 630µW
• Voltage Supply Source: Single Supply
• Operating Temperature: 0°C ~ 70°C
• Mounting Type: Surface Mount
• Package / Case: 8-SOIC (0.154", 3.90mm Width)
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

LTC1285/LTC1288
APPLICATION INFORMATION
OVERVIEW
The LTC1285 and LTC1288 are 3V micropower, 12-bit,
successive approximation sampling A/D converters. The
LTC1285 typically draws 160 A of supply current when
sampling at 7.5kHz while the LTC1288 nominally con-
sumes 210 A of supply current when sampling at 6.6 kHz.
The extra 50 A of supply current on the LTC1288 comes
from the reference input which is intentionally tied to the
supply. Supply current drops linearly as the sample rate is
reduced (see Supply Current vs Sample Rate). The ADCs
automatically power down when not performing conver-
sions, drawing only leakage current. They are packaged in
8-pin SO and DIP packages. The LTC1285 and LTC1288
operate on a single supply from 2.7V to 6V.
Both the LTC1285 and the LTC1288 contain a 12-bit,
switched-capacitor ADC, a sample-and-hold, and a serial
port (see Block Diagram). Although they share the same
10
D
D
CLK
OUT
CLK
OUT
CS
CS
*AFTER COMPLETING THE DATA TRANSFER, IF FURTHER CLOCKS ARE APPLIED WITH CS LOW,
*AFTER COMPLETING THE DATA TRANSFER, IF FURTHER CLOCKS ARE APPLIED WITH CS LOW,
BECOMES A HIGH IMPEDANCE NODE, LEAVING THE CLK RUNNING TO CLOCK OUT LSB-FIRST DATA OR ZEROES.
THE ADC WILL OUTPUT LSB-FIRST DATA THEN FOLLOWED WITH ZEROS INDEFINITELY.
THE ADC WILL OUTPUT ZEROS INDEFINITELY.
t
DATA
t
SMPL
t
HI-Z
SMPL
HI-Z
: DURING THIS TIME, THE BIAS CIRCUIT AND THE COMPARATOR POWER DOWN AND THE REFERENCE INPUT
t
suCS
t
suCS
NULL
NULL
BIT
BIT
(MSB)
(MSB)
U
B11
B11
B10
B10
U
B9
B9
B8
B8
W
B7
B7
t
t
CONV
CONV
t
CYC
B6
B6
Figure 1. LTC1285 Operating Sequence
B5
B5
B4
B4
U
B3
B3
t
CYC
B2
B2
B1
B1
basic design, the LTC1285 and LTC1288 differ in some
respects. The LTC1285 has a differential input and has an
external reference input pin. It can measure signals float-
ing on a DC common-mode voltage and can operate with
reduced spans to 1.5V. Reducing the spans allows it to
achieve 366 V resolution. The LTC1288 has a two-chan-
nel input multiplexer and can convert either channel with
respect to ground or the difference between the two. The
reference input is tied to the supply pin.
SERIAL INTERFACE
The 2-channel LTC1288 communicates with micropro-
cessors and other external circuitry via a synchronous,
half duplex, 4-wire serial interface. The single channel
LTC1285 uses a 3-wire interface (see Operating Sequence
in Figures 1 and 2).
B0*
B0
B1
t
DATA
HI-Z
POWER
DOWN
B2
B3
NULL
BIT
B4
B11
B5
POWER DOWN
B10 B9
B6
t
DATA
B7
B8
B8
B9
B10
B11*
LTC1285/88 • F01
HI-Z