TLC5620C, TLC5620I
QUADRUPLE 8-BIT DIGITAL-TO-ANALOG CONVERTERS
SLAS081E – NOVEMBER 1994 – REVISED NOVEMBER 2001
detailed description
The TLC5620 is implemented using four 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 the GND terminal and the other end is fed from the output of the reference input buffer. Monotonicity is
maintainedbyuseoftheresistorstrings. Linearitydependsuponthematchingoftheresistorelementsandupon
the performance of the output buffer. Since the inputs are buffered, the DACs always present a high-impedance
load to the reference source.
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:
CODE
V (DACA|B|C|D)
REF
(1 RNG bit value)
O
256
where CODE is in the range 0 to 255 and the range (RNG) bit is 0 or 1 within the serial control word.
Table 1. Ideal Output Transfer
D7
0
0
•
D6
0
0
•
D5
0
0
•
D4
0
0
•
D3
0
0
•
D2
0
0
•
D1
0
0
•
D0
0
1
•
OUTPUT VOLTAGE
GND
(1/256) × REF (1+RNG)
•
•
•
•
•
•
•
•
•
•
0
1
•
1
0
•
1
0
•
1
0
•
1
0
•
1
0
•
1
0
•
1
0
•
(127/256) × REF (1+RNG)
(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.
CLK
t
su(DATA-CLK)
t
su(LOAD-CLK)
D2 D1
su(CLK-LOAD)
t
v(DATA-CLK)
DATA
LOAD
A1
A0 RNG
D7
D6
D5
D4
D3
D0
t
t
w(LOAD)
DAC Update
Figure 1. LOAD-Controlled Update (LDAC = Low)
3
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