hi5703 Intersil Corporation, hi5703 Datasheet - Page 13

• Manufacturer Part Number: hi5703
• Description: 10-bit, 40 Msps A/d Converter
• Manufacturer: Intersil Corporation

Reference Voltage Inputs, V
The HI5703 requires two reference voltages connected to the
V
V
range of 1.25V. V
voltages as long as the reference common mode voltage,
((V
the limits on V
In order to minimize overall converter noise it is recommended
that adequate high frequency decoupling be provided at the
reference voltage input pins, V
Analog Input, Differential Connection
The analog input to the HI5703 is a differential input that can
be configured in various ways depending on the signal
source and the required level of performance. A fully
differential connection (Figure 16 and Figure 17) will give the
best performance for the converter.
Since the HI5703 is powered by a single +5V analog supply,
the analog input is limited to be between ground and +5V.
For the differential input connection this implies the analog
input common mode voltage can range from 0.625V to
4.375V. The performance of the ADC does not change
significantly with the value of the analog input common
mode voltage.
A DC voltage source, V
available to the user to help simplify circuit design when using
an AC coupled differential input. This low output impedance
voltage source is not designed to be a reference but makes an
excellent bias source and stays within the analog input
common mode voltage range over temperature. It has a
temperature coefficient of approximately +200ppm/
For the AC coupled differential input (Figure 16) assume the
difference between V
typically 2V, is 1.25V. Fullscale is achieved when the V
and V
out of phase with V
fullscale when the V
at V
converter will be at negative full scale when the V
equal to V
V
REF
REF
IN
REF
DC
- = -1.25V).
+ equal to 3.25V for a fully differential input voltage
IN
pins. The HI5703 is tested with V
FIGURE 16. AC COUPLED DIFFERENTIAL INPUT
+ + V
- 0.625V (V
- inputs are 1.25V
V
-V
DC
IN
IN
REF
- 0.625V and V
REF
-)/2), does not exceed 2.625V 50mV and
+ and V
REF
IN
IN
IN
+ - V
REF
+. The converter will be at positive
+ input is at V
+ and V
DC
+, typically 3.25V, and V
REF
, equal to 2.8V (typical), is made
P-P
IN
4-13
- = 1.25V). Conversely, the
IN
, with V
- are not exceeded.
REF
REF
R
R
- is at V
REF
+ and V
- can differ from the above
DC
IN
- and V
REF
DC
- being 180 degrees
+ 0.625V and V
REF
+ 0.625V (V
V
V
- equal to 2V and
V
DC
IN
IN
-
+
-.
HI5703
REF
IN
REF
o
+
+ input is
C.
-,
IN
IN
IN
+
+ -
- is
The analog input can be DC coupled (Figure 17) as long as
the inputs are within the analog input common mode voltage
range (0.625V
The resistors, R, in Figure 17 are not absolutely necessary
but may be used as load setting resistors. A capacitor, C,
connected from V
frequency noise on the inputs, also improving performance.
Values around 20pF are sufficient and can be used on AC
coupled inputs as well. Note, however, that the value of
capacitor C chosen must take into account the highest
frequency component of the analog input signal.
Analog Input, Single-Ended Connection
The configuration shown in Figure 18 may be used with a
single ended AC coupled input.
Again, assume the difference between V
3.25V, and V
sinewave, then V
positive voltage equal to VDC. The converter will be at
positive fullscale when V
negative fullscale when V
Sufficient headroom must be provided such that the input
voltage never goes above +5V or below AGND. In this case,
VDC could range between 1.25V and 3.75V without a
significant change in ADC performance. The simplest way to
produce VDC is to use the V
VDC
VDC
V
FIGURE 18. AC COUPLED SINGLE ENDED INPUT
IN
FIGURE 17. DC COUPLED DIFFERENTIAL INPUT
V
IN
-
V
REF
IN
VDC
VDC
-, typically 2V, is 1.25V. If V
IN
IN
+ is a 2.5V
+ to V
4.375V).
IN
IN
IN
+ is at VDC + 1.25V and will be at
+ is equal to VDC - 1.25V.
- will help filter any high
R
R
DC
P-P
R
output of the HI5703.
sinewave riding on a
C
REF
V
V
V
DC
IN
IN
V
V
-
+
IN
HI5703
IN
IN
+, typically
-
HI5703
+
is a 2.5V
P-P