HA-5320_05 Datasheet, PDF (5/8 Pages) Intersil Corporation – 1 Microsecond Precision Sample and Hold Amplifier

HA-5320
Test Circuits and Waveforms
S/H
CONTROL
INPUT
1
-INPUT
2
+INPUT
14
S/H CONTROL
HA-5320
7
OUTPUT
V_O
8 _NC
11
NC
(C_H = 100pF)
FIGURE 1. CHARGE TRANSFER AND DRIFT CURRENT
S/H CONTROL
HOLD (+3.5V)
SAMPLE (0V)
S/H CONTROL
HOLD (+3.5V)
SAMPLE (0V)
V_O
V_P
NOTES:
13. Observe the “hold step” voltage V_P.
14. Compute charge transfer: Q = V_PC_H.
FIGURE 2. CHARGE TRANSFER TEST
V_O
∆V_O
∆t
NOTES:
15. Observe the voltage “droop”, ∆V_O/∆t.
16. Measure the slope of the output during hold, ∆V_O/∆t, and
compute drift current: I_D = C_H ∆V_O/∆t.
FIGURE 3. DRIFT CURRENT TEST
V _IN
10V_P-P
100kHz
SINE WAVE
S/H CONTROL
INPUT
ANALOG
MUX OR
SWITCH
A_IN
V+
V-
HA-5320
9
5
1 _-IN
2 _+IN
7
OUT
14 ^{S/H CONTROL}
SUPPLY
GND
C_EXT
REF
COM
INT.
COMP.
13
11
6
8
V_OUT
NOTE:
Feedthrough in
dB = 20log ^V-----^O----^U----^T- where:
V_IN
V_OUT = V_P-P, Hold Mode, V_IN = V_P-P.
TO
NC
SUPPLY
COMMON
TO
NC
SIGNAL
GND
FIGURE 4. HOLD MODE FEEDTHROUGH ATTENUATION
Application Information
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 AN517 for a collection of circuit
ideas.
Layout
A printed circuit board with ground plane is recommended
for best performance. Bypass capacitors (0.01µF to 0.1µF,
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. 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,
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.
If an external hold capacitor C_EXT is used, then a noise
bandwidth 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
resistance and low dielectric absorption, to minimize droop
errors. Polystyrene dielectric is a good choice for operating
temperatures up to 85°C. Teflon® and glass dielectrics offer
good performance to 125°C and above.
5
FN2857.7
August 24, 2005