LTC2408CG Linear Technology, LTC2408CG Datasheet - Page 12

• Manufacturer Part Number: LTC2408CG
• Description: IC A/D CONV 24BIT 8-CHAN 28-SSOP
• Manufacturer: Linear Technology

Specifications of LTC2408CG

• Number Of Bits: 24
• Sampling Rate (per Second): 7.5
• Data Interface: MICROWIRE™, Serial, SPI™
• Number Of Converters: 1
• Power Dissipation (max): 1mW
• Voltage Supply Source: Single Supply
• Operating Temperature: 0°C ~ 70°C
• Mounting Type: Surface Mount
• Package / Case: 28-SSOP (0.200", 5.30mm Width)
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

APPLICATIONS
LTC2404/LTC2408
Ease of Use
The LTC2404/LTC2408 data output has no latency, filter
settling or redundant data associated with the conversion
cycle. There is a one-to-one correspondence between the
conversion and the output data. Therefore, multiplexing
an analog input voltage is easy.
The LTC2404/LTC2408 perform offset and full-scale cali-
brations every conversion cycle. This calibration is trans-
parent to the user and has no effect on the cyclic operation
described above. The advantage of continuous calibration
is extreme stability of offset and full-scale readings with
respect to time, supply voltage change and temperature
drift.
Power-Up Sequence
The LTC2404/LTC2408 automatically enter an internal
reset state when the power supply voltage V
below approximately 2.2V. When the V
above this critical threshold, the converter creates an
internal power-on-reset (POR) signal with duration of
approximately 0.5ms. The POR signal clears all internal
registers within the ADC and initiates a conversion. At
power-up, the multiplexer channel is disabled and should
be programmed once the device enters the sleep state.
The results of the first conversion following a POR are not
valid since a multiplexer channel was disabled.
Reference Voltage Range
The LTC2404/LTC2408 can accept a reference voltage
from 0V to V
by the thermal noise of the front-end circuits, and as such,
its value in microvolts is nearly constant with reference
voltage. A decrease in reference voltage will not signifi-
cantly improve the converter’s effective resolution. On the
other hand, a reduced reference voltage will improve the
overall converter INL performance. The recommended
range for the LTC2404/LTC2408 voltage reference is
100mV to V
Input Voltage Range
The converter is able to accommodate system level offset
and gain errors as well as system level overrange
situations due to its extended input range, see Figure 2.
12
CC
CC
.
. The converter output noise is determined
U
INFORMATION
U
W
CC
voltage rises
U
CC
drops
The LTC2404/LTC2408 converts input signals within the
extended input range of – 0.125 • V
For large values of V
range of – 0.3V to (V
ESD protection devices begin to turn on and the errors due
to the input leakage current increase rapidly.
Input signals applied to V
– 300mV and above V
current, a resistor of up to 5k may be added in series with
any channel input pin (CH0 to CH7) without affecting the
performance of the device. In the physical layout, it is im-
portant to maintain the parasitic capacitance of the connec-
tion between this series resistance and the channel input
pin as low as possible; therefore, the resistor should be
located as close as practical to the channel input pin. The
effect of the series resistance on the converter accuracy can
be evaluated from the curves presented in the Analog In-
put/Reference Current section. In addition, a series resis-
tor will introduce a temperature dependent offset error due
to the input leakage current. A 1nA input leakage current
will develop a 1ppm offset error on a 5k resistor if V
5V. This error has a very strong temperature dependency.
Output Data Format
The LTC2404/LTC2408 serial output data stream is 32 bits
long. The first 4 bits represent status information indicat-
ing the sign, input range and conversion state. The next 24
bits are the conversion result, MSB first. The remaining 4
bits are sub LSBs beyond the 24-bit level that may be in-
cluded in averaging or discarded without loss of resolution.
V
CC
–1/8V
9/8V
1/2V
+ 0.3V
–0.3V
V
Figure 2. LTC2404/LTC2408 Input Range
REF
REF
REF
REF
0
NORMAL
RANGE
INPUT
CC
REF
CC
+ 0.3V). Beyond this range the input
by 300mV. In order to limit any fault
this range is limited to a voltage
IN
EXTENDED
may extend below ground by
RANGE
INPUT
REF
ABSOLUTE
MAXIMUM
RANGE
INPUT
24048 F02
to 1.125 • V
REF
REF
=
.