13

LTC1410

Power Shutdown

The LTC1410 provides two power shutdown modes, Nap

and Sleep, to save power during inactive periods. The

Nap mode reduces the power by 95% and leaves only the

digital logic and reference powered up. The wake-up time

from Nap to active is 200ns. In Sleep mode all bias

currents are shut down and only leakage current re-

mains –– about 1

µA. Wake-up time from Sleep mode is

NAP/SLP

SHDN

1410 F12a

Figure 12a. NAP/SLP to SHDN Timing

Figure 12b. SHDN to CONVST Wake-Up Timing

much slower since the reference circuit must power up

and settle to 0.01% for full 12-bit accuracy. Sleep mode

wake-up time is dependent on the value of the capacitor

connected to the REFCOMP (Pin 4). The wake-up time is

10ms with the recommended 10

µF capacitor.

Shutdown is controlled by Pin 21 (SHDN), the ADC is in

shutdown when it is low. The shutdown mode is selected

with Pin 20 (NAP/SLP); high selects Nap.

CS

CONVST

RD

1410 F12

SHDN

CONVST

1410 F12b

Figure 13. CS to CONVST Setup Timing

Timing and Control

Conversion start and data read operations are controlled

by three digital inputs: CONVST, CS and RD. A logic “0”

applied to the CONVST pin will start a conversion after the

ADC has been selected (i.e., CS is low). Once initiated, it

cannot be restarted until the conversion is complete.

Converter status is indicated by the BUSY output. BUSY

is low during a conversion.

Figures 14 through 18 show several different modes of

operation. In modes 1a and 1b (Figures 14 and 15) CS

and RD are both tied low. The falling edge of CONVST

starts the conversion. The data outputs are always enabled

and data can be latched with the BUSY rising edge. Mode

1a shows operation with a narrow logic low CONVST

pulse. Mode 1b shows a narrow logic high CONVST pulse.

In mode 2 (Figure 16) CS is tied low. The falling edge of

CONVST signal again starts the conversion. Data outputs

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 17 and 18) 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 and the processor takes RD (= CONVST) back

high and reads the new conversion data.

In ROM mode, the processor takes RD (= CONVST) low,

starting a conversion and reading the previous conversion

result. After the conversion is complete, the processor can

read the new result and initiate another conversion.