HA-5320883 Datasheet, PDF (8/11 Pages) Intersil Corporation – High Speed Precision Sample and Hold Amplifier

TM
HA-5320
DESIGN INFORMATION
May 2002
High Speed Precision
Sample and Hold Amplifier
The information contained in this section has been developed through characterization by Intersil Semiconductor and is for use as applica-
tion and design information only. No guarantee is implied.
Applying the HA-5320
The HA-5320 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 517 for a collection of circuit ideas.
Layout
A printed circuit board with ground plane is recommended
for best performance. Bypass capacitors (0.01 to 0.1µF,
ceramic) should be provided from each power supply termi-
nal to the Supply Ground terminal on pin 13.
The ideal ground connections are pin 6 (SIG. Ground)
directly to the system Signal Ground, and pin 13 (Supply
Ground) directly to the system Supply Common.
Hold Capacitor
The HA-5320 includes a 100pF MOS hold capacitor, suffi-
cient for most high speed applications (the Electrical Specifi-
cations 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.
If an external hold capacitor C_EXT is used, then a noise
band- width capacitor of value 0.1C_EXT should be connected
from pin 8 to ground. Exact value and type are not critical.
The hold capacitor C_EXT should have high insulation resis-
tance and low dielectric absorption, to minimize droop
errors. Polystyrene dielectric is a good choice for operating
temperatures up to +85^oC. Teflon and glass dielectrics
offer good performance to +125^oC and above.
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.
Applications
Figure 1 shows the HA-5320 connected as a unity gain non-
inverting 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 hold step error is adjust-
able to zero using the Offset Adjust potentiometer, to deliver
a 12-bit accurate output from the converter.
The application may call for an external hold capacitor C_EXT
as shown. As mentioned earlier, 0.1C_EXT is then recom-
mended at pin 8 to reduce output noise in the Hold mode.
The HA-5320 output circuit does not include short circuit pro-
tection, 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 cir-
cuit to ground is permissible, but the output is not designed
to tolerate a short of indefinite duration.
OFFSET
ADJUST
±15mV
-15V +15V
10kΩ
3 4 5 9 11
1
V_IN
2 +^-
C_EXT
100pF
-
7
+
HI-574A
13
INPUT
S/H CONTROL
H
S
14
13
HA-5320
68
CONVERT
SYSTEM
POWER
GROUND
SYSTEM
SIGNAL
GROUND
0.1C_EXT
5 ^R/C
9 _ANALOG
COMMON
DIGITAL
OUTPUT
FIGURE 1. TYPICAL HA-5320/883 CONNECTIONS; NONINVERTING UNITY GAIN MODE
Spec Number 511096-883
8