9
Notes on Operation
The HI3276 is a high-speed A/D converter which is capable
of TTL, ECL and PECL level clock input. Characteristic
impedance should be properly matched to ensure optimum
performance during high-speed operation.
The power supply and grounding have a profound influence
on converter performance. The power supply and
grounding method are particularly important during high-
speed operation. General points for caution are as follows:
- The ground pattern should be as large as possible. It is
recommended to make the power supply and ground
patterns wider at an inner layer using a multi-layer
board.
- To prevent interference between AGND and DGND
and between AV
CC
and DV
CC
, make sure the
respective patterns are separated. To prevent a DC
offset in the power supply pattern, connect the AV
CC
and DV
CC
lines at one point each, via a ferrite-bead
filter. Shorting the AGND and DGND patterns in one
place immediately under the A/D converter improves
A/D converter performance.
- Ground the power supply pins (AV
CC
, DV
CC1
, DV
CC2
,
DV
EE3
) as close to each pin as possible with a 0.1
μ
F
or larger ceramic chip capacitor. (Connect the AV
CC
pin to the AGND pattern and the DV
CC1
, DV
CC2
,
DV
EE3
pins to the DGND pattern).
- The digital output wiring should be as short as
possible. If the digital output wiring is long, the wiring
capacitance will increase, deteriorating the output slew
rate and resulting in reflection to the output waveform
since the original output slew rate is quite fast.
The analog input pin V
IN
has an input capacitance of
approximately 10pF. To drive the A/D converter with proper
frequency response, it is necessary to prevent performance
deterioration due to parasitic capacitance or parasitic
inductance by using a large capacity drive circuit; keeping
wiring as short as possible, and using chip parts for
resistors and capacitors, etc.
The V
RT
and V
RB
pins must have adequate bypass to
protect them from high-frequency noise. Bypass them to
AGND with approximately 1
μ
F tantal capacitor and, 0.1
μ
F
capacitor. At this time, approximately DGND3 - 1.2V voltage
is generated. However, this is not recommended for use as
threshold voltage V
BB
as it is too weak.
When the digital input level is PECL level, ***/E pins should
be used and ***/T pins left open. When the digital input level
is TTL, ***/T pins should be used and III/E pins left open.
TABLE 1. A/D CODE
V
IN
STEP
INV
1
0
D7
D0
D7
D0
V
RT
255
1 1 1 1 1 1 1 1 0 0 0 0 0 0 0 0
254
1 1 1 1 1 1 1 0 0 0 0 0 0 0 0 1
V
RM2
128
1 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1
127
0 1 1 1 1 1 1 1 1 0 0 0 0 0 0 0
1
0 0 0 0 0 0 0 1 1 1 1 1 1 1 1 0
V
RB
0
0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1
Test Circuits
FIGURE 4. CURRENT CONSUMPTION MEASUREMENT
CIRCUIT
FIGURE 5. INTEGRAL LINEARITY ERROR/DIFFERENTIAL
LINEARITY ERROR MEASUREMENT CIRCUIT
V
RT
V
IN
V
RB
AV
CC
DV
CC1
DV
CC2
DGND2
DGND1
AGND
DGND3
CLK/E
DV
EE3
4V
1.95V
2V
5MHz PECL
A
A
5V
5V
I
CC
I
EE
A < B A > B
COMPARATOR
A8
TO
A1
B8
TO
B1
B0
A0
HI3276
BUFFER
CONTROLLER
DVM
000...00
TO
111..10
V
IN
8
“0”
8
“1”
-V
+V
S2
S1: ON WHEN A < B
S2: ON WHEN A > B
S1
-
+
HI3276