DAC34SH84_15 Datasheet, PDF (47/93 Pages) Texas Instruments – DAC34SH84 Quad-Channel, 16-Bit, 1.5 GSPS Digital-to-Analog Converter (DAC)

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DAC34SH84
SLAS808E – FEBRUARY 2012 – REVISED SEPTEMBER 2015
V_A
V_COM = (V_A + V_B)/2
V_{A, B}
V_B
100 Ω
DAC34SH84
LVDS
Receiver
V_A
V_B
V_{A, B}
GND
Logical Bit
Equivalent
Figure 80. LVDS Data Input Levels
Example
1.4 V
1V
400 mV
0V
–400 mV
1
0
B0459-04
Table 9. Example LVDS Data Input Levels
APPLIED VOLTAGES
V_A
1.4 V
1.0 V
1.2 V
0.8 V
V_B
1.0 V
1.4 V
0.8 V
1.2 V
RESULTING
DIFFERENTIAL
VOLTAGE
V_A,B
400 mV
–400 mV
400 mV
–400 mV
RESULTING COMMON-
MODE VOLTAGE
V_COM
1.2 V
1.0 V
LOGICAL BIT
BINARY
EQUIVALENT
1
0
1
0
7.3.16 CMOS Digital Inputs
Figure 81 shows a schematic of the equivalent CMOS digital inputs of the DAC34SH84. SDIO, SCLK, SLEEP
and TXENA have pull-down resistors while SDENB and RESETB have pull-up resistors internal to the
DAC34SH84. All the CMOS digital inputs and outputs are referred to the IOVDD2 supply, which can vary from
1.8 V to 3.3 V. This facilitates the I/O interface and eliminates the need of level translation. See Electrical
Characteristics – Digital Specifications for logic thresholds. The pull-up and pull-down circuitry is approximately
equivalent to 100 kΩ.
IOVDD2
IOVDD2
SDIO
SCLK
SLEEP
TXENA
100 kΩ
400 Ω
Internal
Digital In
100 kΩ
SDENB
RESETB
400 Ω
Internal
Digital In
GND
Figure 81. CMOS Digital Equivalent Input
GND
S0027-04
7.3.17 Reference Operation
The DAC34SH84 uses a bandgap reference and control amplifier for biasing the full-scale output current. The
full-scale output current is set by applying an external resistor R_BIAS to pin BIASJ. The bias current I_BIAS through
resistor R_BIAS is defined by the on-chip bandgap reference voltage and control amplifier. The default full-scale
output current equals 64 times this bias current and can thus be expressed as:
IOUT_FS = 64 × I_BIAS = 64 × (V_EXTIO / R_BIAS ) / 2
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