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5
Application Information
The HA-5340 has the uncommitted differential inputs of an op
amp, allowing the Sample and Hold function to be combined
with many conventional op amp circuits. See the Intersil
Application Note AN517 for a collection of circuit ideas.
Layout
A printed circuit board with ground plane is recommended
for best performance. Bypass capacitors (0.01
μ
F to 0.1
μ
F,
ceramic) should be provided from each power supply
terminal to the Supply Ground terminal on pin 13.
The ideal ground connections are pin 6 (SIG. GND) directly
to the system Signal Ground, and pin 13 (Supply Ground)
directly to the system Supply Common.
Hold Capacitor
The HA-5340 includes a 135pF MOS hold capacitor,
sufficient for most high speed applications (the Electrical
Specifications section is based on this internal capacitor).
Additional capacitance may be added between pins 7 and
11. This external hold capacitance will reduce droop rate at
the expense of acquisition time, and provide other trade-offs
as shown in the Performance Curves.
The hold capacitor C
H
should have high insulation
resistance and low dielectric absorption, to minimize droop
errors. Teflon, polystyrene and polypropylene dielectric
capacitor types offer good performance over the specified
operating temperature range.
The hold capacitor terminal (pin 11) remains at virtual
ground potential. Any PC connection to this terminal should
be kept short and “guarded” by the ground plane, since
nearby signal lines or power supply voltages will introduce
errors due to drift current.
Teflon is a registered Trademark of Dupont Corporation.
Typical Application
Figure 5 shows the HA-5340 connected as a unity gain
noninverting amplifier - its most widely used configuration.
As an input device for a fast successive - approximation A/D
converter, it offers very high throughput rate for a monolithic
IC sample/hold amplifier. Also, the HA-5340’s hold step error
is adjustable to zero using the Offset Adjust potentiometer,
to deliver a 12-bit accurate output from the converter.
The HA-5340 output circuit does not include short circuit
protection, and consequently its output impedance remains
low at high frequencies. Thus, the step changes in load
current which occur during an A/D conversion are absorbed
at the S/H output with minimum voltage error. A momentary
short circuit to ground is permissible, but the output is not
designed to tolerate a short of indefinite duration.
+15V
V
IN
C
H
50k
3
4
9
5
7
1
2
14
15pF
13
6
SYSTEM
POWER
GROUND
5
9
CONVERT
13
INPUT
DIGITAL
OUTPUT
H
S
S/H CONTROL
-15V
HA 5340
-
HI 774
-
OFFSET
ADJUST
≈
±
15mV
ANALOG
COMMON
R/C
SYSTEM
SIGNAL
GROUND
11
NOTE: Pin Numbers Refer to
DIP Package Only.
120pF
FIGURE 5. TYPICAL HA-5340 CONNECTIONS; NONINVERTING UNITY GAIN MODE
HA-5340