ML6401CS-3 datasheet(6/10 Pages) MICRO-LINEAR

6 / 10 page

ML6401

Figure 1. AC Coupled Input, External Resistors

Bias the Input.

Figure 2. DC Coupled Input.

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 (VIN–) which affects only bias (code 128). An

internally generated VREFOUT (1 volt) is brought to pin 16

(VRTS of 1175), and an internally generated VIN-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

VDDA 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.

VDDA

GNDD

ADC 1

S & H

VIN+

VIN–

INTERNAL

REFERENCES

1.5V

1.0V

Ω

VIDEO

INPUT

µF

0.01

µF

0.1

µF

VIN-BIAS

VREFOUT

VREFIN

VDDA

GNDD

ADC 1

S & H

VIN+

VIN–

INTERNAL

REFERENCES

1.5V

1.0V

VIDEO

INPUT

VIN-BIAS

VREFOUT

VREFIN

× RA

0.01

µF

0.01

µF

+0.5V to 2.5V

–0.5V to +0.5V

RA = 1k TYP

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