Datasheet

LTC2754
10
2754f
S0 (Pin 33): Span Bit 0. In Manual Span mode (M-SPAN
tied to V
DD
), Pins S0, S1 and S2 are pin-strapped to select
a single fi xed output range for all DACs. These pins should
be tied to either GND or V
DD
even if they are unused.
S1 (Pin 34): Span Bit 1. In Manual Span mode (M-SPAN
tied to V
DD
), Pins S0, S1 and S2 are pin-strapped to select
a single fi xed output range for all DACs. These pins should
be tied to either GND or V
DD
even if they are unused.
S2 (Pin 35): Span Bit 2. In Manual Span mode (M-SPAN
tied to V
DD
), Pins S0, S1 and S2 are pin-strapped to select
a single fi xed output range for all DACs. These pins should
be tied to either GND or V
DD
even if they are unused.
LDAC (Pin 36): Asynchronous DAC Load Input. When
LDAC is a logic low, all DACs are updated (CS/LD must
be high).
GND (Pin 37): Ground; provides shielding for I
OUT2B
. Tie
to ground.
I
OUT2B
(Pin 38): DAC B Current Output Complement. Tie
I
OUT2B
to ground.
R
INB
(Pin 39): Input Resistor for Reference Inverting
Amplifi er. The 20k input resistor is connected internally
from R
INB
to R
COMB
. For normal operation tie R
INB
to the
external reference voltage V
REFB
(see Typical Applica-
tions). Any or all of these precision-matched resistor sets
(Each set comprising R
INX
, R
COMX
and REFX) may be
used to invert one or more positive reference voltages to
the negative voltages needed by the DACs. Typically 5V;
accepts up to ±15V.
GE
ADJB
(Pin 40): Gain Adjust Pin for DAC B. This control
pin can be used to null gain error or to compensate for
reference errors. Nominal adjustment range is ±512 LSB
(LTC2754-16) for a voltage input range of ±V
RINB
(i.e., ±5V
for a 5V reference input). Tie to ground if not used.
R
COMB
(Pin 41): Center Tap Point for Reference Amplifi er
Inverting Resistors. The 20k reference inverting resistors
are connected internally from R
INB
to R
COMB
and from
R
COMB
to REFB, respectively (see Block Diagram). For
normal operation tie R
COMB
to the negative input of external
reference inverting amplifi er (see Typical Applications).
REFB (Pin 42): Inverted Reference Voltage for DAC B, with
internal connection to the reference inverting resistor. The
20k resistor is connected internally from REFB to R
COMB
.
For normal operation tie this pin to the output of reference
inverting amplifi er (see Typical Applications). Typically –5V;
accepts up to ±15V. The impedance looking into this pin
is 10k to ground (R
INB
and R
COMB
fl oating).
R
OFSB
(Pin 43): Bipolar Offset Network for DAC B. This
pin provides the translation of the output voltage range for
bipolar spans. Accepts up to ±15V; for normal operation
tie to the positive reference voltage at R
INB
(Pin 39). The
impedance looking into this pin is 20k to ground.
R
FBB
(Pin 44): DAC B Feedback Resistor. For normal
operation tie to the output of the I/V converter amplifi er
for DAC B (see Typical Applications). The DAC output
current from I
OUT1B
fl ows through the feedback resistor
to the R
FBB
pin. The impedance looking into this pin is
10k to ground.
I
OUT1B
(Pin 45): DAC B Current Output. This pin is a virtual
ground when the DAC is operating and should reside at
0V. For normal operation tie to the negative input of the I/V
converter amplifi er for DAC B (see Typical Applications).
V
OSADJB
(Pin 46): DAC B Offset Adjust Pin. This control
pin can be used to null unipolar offset or bipolar zero error.
The offset-voltage delta is inverted and attenuated such that
a 5V control voltage applied to V
OSADJB
produces ∆V
OS
=
–512 LSB (LTC2754-16) in any output range (assumes a
5V reference voltage at R
INB
). Tie to ground if not used.
V
OSADJA
(Pin 47): DAC A Offset Adjust Pin. This control
pin can be used to null unipolar offset or bipolar zero error.
The offset-voltage delta is inverted and attenuated such that
a 5V control voltage applied to V
OSADJA
produces ∆V
OS
=
–512 LSB (LTC2754-16) in any output range (assumes a
5V reference voltage at R
INA
). Tie to ground if not used.
I
OUT1A
(Pin 48): DAC A Current Output. This pin is a virtual
ground when the DAC is operating and should reside at
0V. For normal operation tie to the negative input of the I/V
converter amplifi er for DAC A (see Typical Applications).
R
FBA
(Pin 49): DAC A Feedback Resistor. For normal
operation tie to the output of the I/V converter amplifi er
for DAC A (see Typical Applications). The DAC output
current from I
OUT1A
fl ows through the feedback resistor
to the R
FBA
pin. The impedance looking into this pin is
10k to ground.
PIN FUNCTIONS