LTC2664 datasheet(20/28 Pages) LINER

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LTC2664

2664fa

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operation

Figure 6. Toggle Select Syntax

Figure 7. Global Toggle Syntax

Toggle Operations

SomesystemsrequirethatDACoutputsswitchrepetitively

between two voltage levels. Examples include introducing

a small AC bias, or independently switching between ‘on’

and ‘off’ states. The LTC2664 toggle function facilitates

these kinds of operations by providing two input registers

(A and B) per DAC channel.

Toggling between A and B is controlled by three signals.

The first of these is the toggle select command, which acts

on a data field of 4 bits, each of which controls a single

channel (see Figure 6). The second is the global toggle

command, which controls all selected channels using the

global toggle bit TGB (see Figure 7). Finally, the TGP pin

allows the use of an external clock or logic signal to toggle

the DAC outputs between A and B. The signals from these

controls are combined as shown in Figure 8.

If the toggle function is not needed, tie TGP (Pin 17) to

ground and leave the toggle select register in its power-on

resetstate(clearedtozero).InputregistersAthenfunction

as the sole input registers, and registers B are not used.

Toggle Select Register (TSR)

The Toggle Select command (1100b) syntax is shown in

Figure 6. Each bit in the 4-bit TSR data field controls the

DAC channel of the same name: T0 controls channel 0,

T1 channel 1,…, and Tx controls channel x.

The toggle select bits (T0, T1, T2, T3) have a dual function.

First, each toggle select bit controls which input register

(A or B) receives data from a write-code operation. When

the toggle select bit of a given channel is high, write-code

operationsaredirectedtoinputregisterBoftheaddressed

channel. When the bit is low, write-code operations are

directed to input register A.

Secondly,eachtoggleselectbitenablesthecorresponding

channel for a toggle operation.

Writing to Input Registers A and B

Having chosen channels to toggle, write the desired codes

to Input registers A for the chosen channels; then set

the channels’ toggle select bits using the toggle select

command; and finally, write the desired codes to input

registers B. Once these steps are completed, the channels

are ready to toggle. For example, to set up channel 3 to

toggle between codes 4096 and 4200:

1) Write code channel 3 (code = 4096) to register A

00000011 00010000 00000000

2) Toggle Select (set bit T3)

11000000 00000000 00001000

3) Write code channel 3 (code = 4200) to register B

00000011 00010000 01101000

The Write code of step (3) is directed to register B because

in step (2), bit T3 was set to 1. Channel 3 now has Input

registers A and B holding the two desired codes, and is

prepared for the toggle operation.

Toggling Between Registers A and B

Once Input registers A and B have been written to for all

desired channels and the corresponding toggle select bits

are set high, as in the previous example, the channels are

ready for toggling.

2664 F06

TOGGLE SELECT BITS

(ONE FOR EACH CHANNEL)

DON’T CARE

TOGGLE SELECT

2664 F07

TGB

GLOBAL

TOGGLE

BIT

DON’T CARE

GLOBAL

TOGGLE COMMAND

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