TLC5628C, TLC5628I

OCTAL 8-BIT DIGITAL-TO-ANALOG CONVERTERS

SLAS089E – NOVEMBER 1994 – REVISED APRIL 1997

3

POST OFFICE BOX 655303

detailed description

The TLC5628 is implemented using eight resistor-string DACs. The core of each DAC is a single resistor with

256 taps, corresponding to the 256 possible codes listed in Table 1. One end of each resistor string is connected

to GND and the other end is fed from the output of the reference input buffer. Monotonicity is maintained by use

of the resistor strings. Linearity depends upon the matching of the resistor segments and upon the performance

of the output buffer. Since the inputs are buffered, the DACs always present a high-impedance load to the

reference sources. There are two input reference terminals; REF1 is used for DACA through DACD and REF2

is used by DACE through DACH.

Each DAC output is buffered by a configurable-gain output amplifier, that can be programmed to times 1 or times

2 gain.

On power up, the DACs are reset to CODE 0.

Each output voltage is given by:

V

O

(DACA|B|C|D|E|F|G|H)

+ REF

CODE

256

(1

) RNG bit value)

where CODE is in the range 0 to 255 and the range (RNG) bit is a 0 or 1 within the serial control word.

Table 1. Ideal Output Transfer

D7

D6

D5

D4

D3

D2

D1

D0

OUTPUT VOLTAGE

0

0

0

0

0

0

0

0

GND

0

0000001

(1/256)

× REF (1+RNG)

•

•••••••

•

•

•••••••

•

0

1111111

(127/256)

× REF (1+RNG)

1

0000000

(128/256)

× REF (1+RNG)

•

•••••••

•

•

•••••••

•

1

1

1

1

1

1

1

1

(255/256)

× REF (1+RNG)

data interface

With LOAD high, data is clocked into the DATA terminal on each falling edge of CLK. Once all data bits have

been clocked in, LOAD is pulsed low to transfer the data from the serial input register to the selected DAC as

shown in Figure 1. When LDAC is low, the selected DAC output voltage is updated when LOAD goes low. When

LDAC is high during serial programming, the new value is stored within the device and can be transferred to

the DAC output at a later time by pulsing LDAC low as shown in Figure 2. Data is entered most significant bit

(MSB) first. Data transfers using two 8-clock cycle periods are shown in Figures 3 and 4.

A2

A1

A0

RNG

D7

D6

D5

D4

D2

D1

D0

DAC Update

CLK

DATA

LOAD

tsu(DATA-CLK)

tv(DATA-CLK)

tsu(CLK-LOAD)

tw(LOAD)

tsu(LOAD-CLK)

Figure 1. LOAD-Controlled Update (LDAC = Low)