LTC1298CS8 Linear Technology, LTC1298CS8 Datasheet - Page 14

• Manufacturer Part Number: LTC1298CS8
• Description: IC A/D CONV SAMPLING 12BIT 8SOIC
• Manufacturer: Linear Technology

Specifications of LTC1298CS8

• Number Of Bits: 12
• Sampling Rate (per Second): 11.1k
• Data Interface: MICROWIRE™, Serial, SPI™
• Number Of Converters: 1
• Power Dissipation (max): 1.8mW
• 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

LTC1286/LTC1298
APPLICATION INFORMATION
D
Capacitive loading on the digital output can increase power
consumption. A 100pF capacitor on the D
more than 50 A to the supply current at a 200kHz clock
frequency. An extra 50 A or so of current goes into
charging and discharging the load capacitor. The same
goes for digital lines driven at a high frequency by any logic.
The C V f currents must be evaluated and the trouble-
some ones minimized.
OPERATING ON OTHER THAN 5V SUPPLIES (LTC1286)
The LTC1286 operates from 4.5V to 9V supplies and the
LTC1298 operates from a 5V supply. To operate the LTC1286
on other than 5V supplies a few things must be kept in
mind.
Input Logic Levels
The input logic levels of CS, CLK and D
TTL on a 5V supply. When the supply voltage varies, the
input logic levels also change. For the LTC1286 to sample
and convert correctly, the digital inputs have to be in the
proper logical low and high levels relative to the operating
supply voltage (see typical curve of Digital Input Logic
Threshold vs Supply Voltage). If achieving micropower
consumption is desirable, the digital inputs must go rail-to-
rail between supply voltage and ground (see ACHIEVING
MICROPOWER PERFORMANCE section).
14
OUT
Figure 5. Shutdown current with CS high is 1nA typically,
regardless of the clock. Shutdown current with CS = ground
varies from 1 A at 1kHz to 35 A at 200kHz.
Loading
0.002
35
30
25
20
15
10
5
1
0
1
T
V
20
A
CC
= 25°C
= V
40 60
U
REF
CS = V
= 5V
FREQUENCY (kHz)
U
80
CS = 0
(AFTER CONVERSION)
CC
100
120
140
W
160
LT1286/98 G01
IN
180 200
are made to meet
OUT
pin can add
U
COMMON-MODE RANGE
Clock Frequency
The maximum recommended clock frequency is 200kHz
for the LTC1286/LTC1298 running off a 5V supply. With
the supply voltage changing, the maximum clock fre-
quency for the devices also changes (see the typical curve
of Maximum Clock Rate vs Supply Voltage). If the maxi-
mum clock frequency is used, care must be taken to
ensure that the device converts correctly.
Mixed Supplies
It is possible to have a microprocessor running off a 5V
supply and communicate with the LTC1286 operating on
a 9V supply. The requirement to achieve this is that the
outputs of CS and CLK from the MPU have to be able to trip
the equivalent inputs of the LTC1286 and the output of
D
equivalent input of the MPU (see typical curve of Digital
Input Logic Threshold vs Supply Voltage). With the
LTC1286 operating on a 9V supply, the output of D
go between 0V and 9V. The 9V output may damage the
MPU running off a 5V supply. The way to get around this
possibility is to have a resistor divider on D
and connect the center point to the MPU input. It should
be noted that to get full shutdown, the CS input of the
LTC1286 must be driven to the V
input buffer from drawing current. An alternative is to
leave CS low after a conversion, clock data until D
outputs zeros, and then stop the clock low.
DIFFERENTIAL INPUTS
OUT
Figure 6. Interfacing a 9V Powered LTC1286 to a 5V System
from the LTC1286 must be able to toggle the
0V TO 5V
5V
V
+IN
–IN
GND
REF
LTC1286
D
CLK
V
OUT
CS
CC
9V
50k
CC
4.7 F
voltage to keep the CS
50k
P1.4
P1.3
P1.2
OUT
(e.g. 8051)
MPU
(Figure 6)
OUT
LTC1286/98 • F06
may
OUT
5V