DAC7744_14 Datasheet, PDF (18/28 Pages) Texas Instruments – 16-Bit, Quad Voltage Output DIGITAL-TO-ANALOG CONVERTER

REFERENCE INPUTS
The reference inputs, V_REFL and V_REFH, can be any voltage
between V_SS + 4V and V_CC – 4V, provided that V_REFH is at
least 1.25V greater than V_REFL. The minimum output of
each DAC is equal to V_REFL plus a small offset voltage
(essentially, the offset of the output op amp). The maximum
output is equal to V_REFH plus a similar offset voltage. Note
that V_SS (the negative power supply) must either be
connected to ground or must be in the range of –14.25V to
–15.75V. The voltage on V_SS sets several bias points within
the converter. If V_SS is not in one of these two configura-
tions, the bias values may be in error and proper operation
of the device is not guaranteed.
The current into the V_REFH input and out of V_REFL depends
on the DAC output voltages and can vary from a few
microamps to approximately 2.0mA. The reference input
appears as a varying load to the reference. If the reference
can sink or source the required current, a reference buffer is
not required. The DAC7744 features a reference drive and
sense connection such that the internal errors caused by the
changing reference current and the circuit impedances can be
minimized. Figures 5 through 12 show different reference
configurations and the effect on the linearity and differential
linearity.
The analog supplies (or the analog supplies and the reference
power supplies) have to come up first. If the power supplies
for the reference come up first, then the V_CC and V_SS
supplies will be “powered from the reference via the ESD
protection diode”, see page 4.
NC 48
NC 47
NC 46
NC 45
V_OUTA Sense 44
DAC7744
V_OUTA 43
V_REFL AB Sense 42
V_REFL AB 41
V_REFH AB 40
V_REFH AB Sense 39
V_OUTB Sense 38
V_OUTB 37
V_OUT
100Ω
1000pF
100Ω
1000pF
2200pF
2200pF
V_OUT
+V
OPA2234
–10V
–V
+V
+10V
FIGURE 5. Dual Supply Configuration-Buffered References, used for Dual Supply Performance Curves (1/2 DAC7744).
NC 48
NC 47
NC 46
NC 45
V_OUTA Sense 44
DAC7744
V_OUTA 43
V_REFL AB Sense 42
V_REFL AB 41
V_REFH AB 40
V_REFH AB Sense 39
V_OUTB Sense 38
V_OUTB 37
V_OUT
100Ω
1000pF
100Ω
1000pF
2200pF
2200pF
V_OUT
+V
OPA350
OPA227
2kΩ
+0.050V
99kΩ
+V
+10V
NOTE: V_REFL has been chosen to be 50mV to allow for current sinking voltage
drops across the 100Ω resistor and the output stage of the buffer op amp.
FIGURE 6. Single-Supply Buffered Reference with a Reference Low of 50mV Used for Single-Supply Performance Curves
(1/2 DAC7744).
®
DAC7744
18