ML6401
INPUT COUPLING
The following two figures illustrate two simple means
of connecting AC and DC coupled signals into the
ML6401-1.
CXD1175 REPLACEMENT
The 24-pin ML6401-1 is pin compatible with the Sony
CXD1175 since all features common to both A/D’s share
common pins. The 24-pin ML6401-1 is not, however, a
direct replacement for the CXD1175. The architectural
differences between the two parts result in slightly
different application circuits only in the area of the
reference pins.
The 1175 brings the top and bottom of the reference
ladder to external pins (denoted VRT and VRB
respectively), and provides two additional pins (VRTS and
VRBS) which can be used to bias the ladder. There are
three major differences in the use of the 24-pin ML6401-
1. First, there is no single resistor ladder which can be
brought out to users in order to vary gain and offset.
Second, the 24-pin ML6401 cannot handle full scale
ranges of VDDA volts. And third, where the 1175
architecture has two voltages (VRT and VRB) which fix the
two endpoints of the conversion range (code 255 and
code 0), the 24-pin ML6401 has one voltage (VREF) which
affects only full scale range (code 255 – code 0) and one
voltage (V
IN
–) which affects only bias (code 128). An
internally generated VREF
OUT
(1 volt) is brought to pin 16
(VRTS of 1175), and an internally generated V
IN-BIAS
(1.5
volts) is brought to pin 22 (VRBS of 1175). This allows the
following four modes of operation:
1.
CXD1175
— See Figure 3. Connect VRTS to VRT and
VRBS to VRB. The ladder will have 2 volts across it
(equal to the full scale range), which varies with supply.
ML6401
— With pin 16 connected to pin 17, and pin
22 connected to pin 23, the A/D will supply internally
generated bandgap biases, making full scale range 2
volts and bias (code 128) 1.5 volts. This is a virtual
drop in for an 1175 with pins 16 and 17 shorted, and
pins 22 and 23 shorted (0.1 volt bias difference).
2.
CXD1175
— See Figure 4. Leave VRTS and VRBS open,
and drive VRT and VRB with external voltages. The
1175 spec allows VRT-VRB to equal from 1.8 volts to
VDD
A
volts. This allows users the flexibility to supply
higher quality references (higher precision, lower
noise), and change the full scale range of the A/D (these
voltages can be varied to effectively implement a VGA).
Also, the offset of the A/D can be varied.
ML6401
— Leave pin 16 and pin 22 open, and drive
pin 17 and pin 23 with external voltages. The full scale
range will be 2
×
pin 17 volts, and the bias (code 128)
will occur at pin 23
±2%
volts. The full scale range of
the A/D must be kept below 4 volts, but the part is only
specified for full scale range of 2 volts.
VIDEO
INPUT
+
47µF
V
IN
–
0.1µF
R
L
75Ω
0.01µF
R
B
1kΩ
R
B
1kΩ
V
IN
+
S&H
VIDEO
INPUT
VDD
A
–0.5V to +0.5V
R
A
ADC 1
+
VDD
A
V
IN
+
S&H
3
×
R
A
V
IN
–
ADC 1
+0.5V to 2.5V
R
A
R
A
10µF
+
V
IN-BIAS
1.5V
VREF
OUT
VREF
IN
INTERNAL
1.0V REFERENCES
R
A
= 1k TYP
0.01µF
V
IN-BIAS
1.5V
VREF
OUT
VREF
IN
0.01µF
GND
D
INTERNAL
1.0V REFERENCES
GND
D
Figure 1. AC Coupled Input, External Resistors
Bias the Input.
Figure 2. DC Coupled Input.
6
MICRO-LINEAR [ MICRO LINEAR CORPORATION ]
