TLC1514, TLC1518

5-V, 10-BIT, 400 KSPS, 4/8 CHANNEL, LOW POWER,

SERIAL ANALOG-TO-DIGITAL CONVERTERS WITH AUTO POWER DOWN

SLAS252 – DECEMBER 1999

35

POST OFFICE BOX 655303

• DALLAS, TEXAS 75265

PRINCIPLES OF OPERATION

power down calculations

i(AVERAGE) = (fS/fSMAX) × i(ON) + (1–fS/fSMAX) × i(OFF)

CASE 1: If VDD = 5 V, auto power down, and an external reference is used:

f

S +

20

kHz

f

SMAX +

400

kHz

i (ON)

+X 4 mA operating current and i(OFF) +X 5 mA auto power-down current

so

i (AVERAGE)

+ 0.05

4000

mA ) 0.95

5

mA + 0.21 mA

CASE 2: Now if software power down is used, another cycle is needed to shut it down.

f

S +

40

kHz

f

SMAX +

400

kHz

i (ON)

+X 4 mA operating current and i(OFF) +X 5 mA power-down current

so

i (AVERAGE)

+ 0.1

4000

mA ) 0.9

5

mA + 0.41 mA

In reality this will be less since the second conversion never happened. It is only the additional cycle to shut down

the ADC.

CASE 3: Now if the hardware power down is used.

f

S +

20

kHz

f

SMAX +

400

kHz

i (ON)

+X 4 mA operating current and i(OFF) +X 5 mA power-down current

so

i (AVERAGE)

+ 0.05

4000

mA ) 0.95

5

mA + 0.21 mA

difference between modes of conversion

The major difference between sweep mode (mode 10) and repeat sweep mode (mode 11) is that the sweep

sequence ends after the FIFO is filled up to the programmed threshold. The repeat sweep can either dump the

FIFO (by ignoring the FIFO content but simply reconfiguring the device) or read the FIFO and then repeat the

conversions on the the same sequence of the channel as before.

FIFO reads are expected after the FIFO is filled up to the threshold in each case. Mode 10 – the device allows

only FIFO read or CFR read or CFR write to be executed. Any conversion command is ignored. In the case of

mode 11, in addition to the above commands, conversion commands are also executed , i.e. the FIFO is cleared

and the sweep sequence is restarted.

Both single shot and repeat modes require selection of a channel after the device is configured for these modes.

Single shot mode does not use the FIFO, but repeat mode does. When the device is operating in repeat mode,

the FIFO can be dumped (by ignoring the FIFO content and simply reconfiguring the device) or the FIFO can

be read and then the conversions repeated on the same channel as before. However, the channel has to be

selected first before any conversion can be carried out. The devices can be programmed with the following

sequences for operating in the different modes that use a FIFO.