LTC1274CSW Datasheet, PDF (17/20 Pages) Linear Technology – 12-Bit, 10mW, 100ksps ADCs with 1μA Shutdown

LTC1274/LTC1277
APPLICATI S I FOR ATIO
The narrow logic pulse on CONVST ensures that CONVST
doesn’t return high during the conversion (see Note 13
following the Timing Characteristics table).
In Mode 2 (Figure 15) CS is tied low. The falling edge of
CONVST signal again starts the conversion. Data outputs
both are in three-state until read by the MPU with the RD
signal. Mode 2 can be used for operation with a shared
MPU databus.
In slow memory and ROM modes (Figures 16 and 17) CS
is tied low and CONVST and RD are tied together. The MPU
starts the conversion and reads the output with the RD
signal. Conversions are started by the MPU or DSP (no
external sample clock).
In slow memory mode the processor applies a logic low to
RD (= CONVST), starting the conversion. BUSY goes low,
forcing the processor into a Wait state. The previous
conversion result appears on the data outputs. When the
conversion is complete, the new conversion results ap-
pear on the data outputs; BUSY goes high releasing the
processor; the processor applies a logic high to RD
(= CONVST) and reads the new conversion data.
In ROM mode the processor applies a logic low to RD
(= CONVST), starting a conversion and reading the
previous conversion result. After the conversion is com-
plete, the processor can read the new result and initiate
another conversion.
RD
CS
CONVST
NAP
SLEEP
ACTIVE HIGH
ENABLE THREE-STATE OUTPUTS
DB11....DB0
BUSY
D
Q
CONVERSION
START (RISING
EDGE TRIGGER)
FLIP
FLOP
CLEAR
1274/77 • F12
Figure 12. Internal Logic for Control Inputs CS, RD, CONVST, NAP and SLEEP (LTC1277)
CS = RD = 0
HBEN (LTC1277)
CONVST
BUSY
LTC1274 DATA
LTC1277 DATA
t_CONV
t₄
(SAMPLE N)
t₅
t₁₆
t₁₅
(SAMPLE N + 1)
t₇
DATA (N – 1)
DB11 TO DB0
t₆
DATA N
DB11 TO DB0
DATA (N + 1)
DB11 TO DB0
DATA (N – 1)
DB7 TO DB0
DATA N
DB7 TO DB0
DATA N
DB11 TO DB8
DATA N
DB7 TO DB0
DATA (N + 1)
DB7 TO DB0
Figure 13. Mode 1a. CONVST Starts a Conversion. Data Outputs Always Enabled
(CONVST =
)
LTC1274/77 • F13
17