LTC1290BIJ Linear Technology, LTC1290BIJ Datasheet - Page 29

• Manufacturer Part Number: LTC1290BIJ
• Description: 12-BIT SERIAL I/O ADC W/8 CH MUX
• Manufacturer: Linear Technology
• Type: Data Acquisition System (DAS), ADCr

Specifications of LTC1290BIJ

• Resolution (bits): 12 b
• Sampling Rate (per Second): 50k
• Data Interface: Serial, Parallel
• Voltage Supply Source: Dual ±
• Voltage - Supply: ±5V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Through Hole
• Package / Case: *
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

TYPICAL
Power Shutdown
For battery-powered applications it is desirable to keep
power dissipation at a minimum. The LTC1290 can be
powered down when not in use reducing the supply
current from a nominal value of 5mA to typically 5µA (with
ACLK turned off). See the curve for Supply Current (Power
Shutdown) vs ACLK if ACLK cannot be turned off when the
LTC1290 is powered down. In this case the supply current
is proportional to the ACLK frequency and is independent
of temperature until it reaches the magnitude of the supply
current attained with ACLK turned off.
As an example of how to use this feature let’s add this to
the previous application, SNEAK-A-BIT. After the CHK
SIGN subroutine call insert the following:
JSR CHK SIGN
JSR SHUTDOWN
The actual subroutine is:
SHUTDOWN: LDA #$3D
SCLK
SCLK
SCLK
CS
CS
CS
A
JSR TRANSFER Read LTC1290 routine
RTS
PPLICATI
Determines which reading has valid
data, converts to 2’s complement
and stores in RAM
LTC1290 power shutdown routine
1
1
•
•
1
O
Load D
LTC1290 into ACC
Return
U
S
Figure 23. Power Shutdown Timing Problem
IN
word for
DUMMY CONVERSION FINISHES AFTER 52 ACLK PERIODS
Figure 25. Power Shutdown Timing
Figure 24. Power Shutdown Timing
DUMMY CONVERSION FINISHES AFTER 52 ACLK PERIODS
DUMMY CONVERSION FINISHES AFTER 52 ACLK PERIODS
POWER SHUTDOWN STARTS
POWER SHUTDOWN STARTS
POWER SHUTDOWN STARTS
To place the device in power shutdown the word length
bits are set to WL1 = 0 and WL0 = 1. The LTC1290 is
powered up on the next request for a conversion and it’s
ready to digitize an input signal immediately.
Power Shutdown Timing Considerations
After power shutdown has been requested, the LTC1290
is powered up on the next request for a conversion. This
request can be initiated either by bringing CS low or by
starting the next cycle of SCLKs if CS is kept low (see
Figures 3 and 4). When the SCLK frequency is much
slower than the ACLK frequency a situation can arise
where the LTC1290 could power down and then prema-
turely power back up. Power shutdown begins at the
negative going edge of the 10th SCLK once it has been
requested. A dummy conversion is executed and the
LTC1290 waits for the next request for conversion. If the
SCLKs have not finished once the LTC1290 has finished its
dummy conversion, it will recognize the next remaining
SCLKs as a request to start a conversion and power up the
LTC1290 (see Figure 23). To prevent this, bring either CS
high at the 10th SCLK (Figure 24) or clock out only 10
SCLKs (Figure 25) when power shutdown is requested.
10
10
10
POWER UP
1290 TAF23
1290 TAF25
POWER UP
LTC1290
1290 TAF24
POWER UP
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