Datasheet

®
ACF2101
9
MODES OF OPERATION
The three basic modes of operation of each integrator are
controlled by the Hold and Reset switches. In Integrate
mode, the output voltage integrates negatively toward –10V.
In Hold mode, the output voltage remains at the present
value, except for output droop. In Reset mode, the integra-
tion capacitor is discharged and the output voltage is driven
to analog common. See Figure 4.
SWITCHES
Each integrator includes four switches: a Hold switch, a
Reset switch, and two output Select switches. See Figure 3.
Hold and Reset Switches
To use the Hold switch, connect the input current to the “Sw
In” pin. The Hold switch disconnects the input current, and
holds the output voltage at a fixed level. For direct input,
connect the input current to the “In” pin that bypasses the
Hold switch and connects directly to the input summing
junction. If the Hold switch is not used, the switch should be
in the off mode and the “Sw In” pin should be connected to
analog common.
The Reset switch is used to discharge the integration capaci-
tor before the start of a new integration period. See Typical
Performance Curve showing Reset Time vs C
INTEGRATION
.
Select Switches
The two Select switches can be used to multiplex the outputs
when multiple integrators are connected to a common bus.
Figure 5 shows a number of ACF2101s multiplexed together
into an A/D converter. The output settling time is deter-
mined by the Select switch “on” resistance of 250Ω and
the total output capacitance. The total output capacitance
includes the ACF2101 output capacitances plus the capaci-
tance of the interconnections to the A/D converter.
FIGURE 3. Switch Control Lines on One Channel of Two
in ACF2101.
MODE OF OPERATION
SWITCH Integrate Hold Reset
Hold Switch ON OFF ON/OFF
Reset Switch OFF OFF ON
ON: Switch shorted; Logic 0 input. OFF: Switch open; Logic 1 input.
FIGURE 4. Modes of Operation.
FIGURE 5. ACF2101s in Multiplexed Operation.
To
ADC
Instrumentation
Amplifier
Hold
Sw In
Reset
Hold Reset Select
Cap
In
Com Sw Com
Sw Out
Out
100pF
C
INTERNAL
MODES OF OPERATION
OUTPUT (V)
0
–10
OFF
ON
OFF
ON
HOLD
RESET
INTEGRATE HOLD RST HOLD
INTEGRATEHOLD