006-109
4
current is approximately 4.0mA. This relationship
will remain regardless of the reference voltage
polarity.
Connections for a positive reference voltage are
shown in Figure 7a. For negative reference voltage
inputs, or for bipolar reference voltage inputs in the
multiplying mode., R15 can be tied to a negative
voltage corresponding to the minimum input level.
For a negative reference input, R16 should be
grounded (Figure 7b). In addition, the negative
voltage reference must be at least 3V above the V
EE
supply voltage for best operation. Bipolar input
Figure 6 3410 equivalent circuit
The reference amplifier is internally compensated
with a 10pF feed-forward capacitor, which gives it
its high slew rate and fast settling time. Proper
phase margin is maintained with all possible
values of R16 and reference voltages which supply
2.0mA reference current into Pin 16. The reference
current can also be supplied by a high impedance
current source of 2.0mA. As R16 increases, the
bandwidth of the amplifier decreases slightly and
settling time increases. For a current source with a
dynamic output impedance of 1.0M
Ω, the band-
width of the reference amplifier is approximately
half what it is in the case of R16 = 1.0k
Ω, and
settling time is
≈ 10µs. The reference amplifier
phase margin decreases as the current source
value decreases in the case of a current source
reference, so that the minimum reference current
supplied from a current source is 0.5mA for stability.
Output voltage compliance
The output voltage compliance ranges from -2.5 to
+0.2V. As shown in Figure 2, this compliance range is
nearly constant over temperature. At the temperature
extremes, however, the compliance voltage may be
reduced if V
EE > -15V.
signals may be handled by connecting R16 to a
positive voltage equal to the peak positive input level
at Pin 15.
When a dc reference voltage is used, capacitive
bypass to ground is recommended. The 5V logic
supply is not recommended as a reference voltage.
If a well regulated 5.0V supply, which drives logic,
is to be used as the reference, R16 should be
decoupled by connecting it to the +5.0V logic
supply through another resistor and bypassing the
junction of the two resistors with a 0.1µF capacitor
to ground.
Accuracy
Absolute accuracy is a measure of each output current
level with respect to its intended value. It is dependent
upon relative accuracy and full scale current drift.
Relative accuracy, or linearity, is the measure of each
output current with respect to its intended fraction of
the full scale current. The relative accuracy of the 3410
is fairly constant over temperature due to the excellent
temperature tracking, of the implanted resistors. The
full scale current from the reference amplifier may drift
with temperature causing a change in the absolute
accuracy. However, the 3410 has a low full scale cur-
rent drift with temperature.
The 3410 is accurate to within ±.05% at 25°C with a ref-
erence current of 2.0mA on Pin 16.
Monotonicity
The 3410 is guaranteed monotonic over temperature.
This means that for every increase in the input digital
code, the output current either remains the same or
increases but never decreases. In the multiplying
mode, where reference input current will vary,
monotonicity can be assured if the reference input
current remains above 0.5mA.
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