Philips Semiconductors

Product data

MC1408-8

8-bit multiplying D/A converter

2001 Aug 03

3

BLOCK DIAGRAM

CURRENT SWITCHES

56

7

8

9

10

11

12

MSB

LSB

REFERENCE

CURRENT

AMPLIFIER

14

2

13

16

GND

COMPEN

NPN CURRENT SOURCE PAIR

A1

A2

A3

A4

A5

A6

A7

A8

4

BIAS

CURRENT

R-2R LADDER

15

(+)

(–)

VREF

VREF

VCC

3

VEE

IO

SL00049

Figure 2. Block Diagram

CIRCUIT DESCRIPTION

The MC1408-8 consists of a reference current amplifier, an R-2R

ladder, and 8 high-speed current switches. For many applications,

only a reference resistor and reference voltage need be added.

The switches are non-inverting in operation; therefore, a high state

on the input turns on the specified output current component.

The switch uses current steering for high speed, and a termination

amplifier consisting of an active load gain stage with unity gain

feedback. The termination amplifier holds the parasitic capacitance

of the ladder at a constant voltage during switching, and provides a

low impedance termination of equal voltage for all legs of the ladder.

The R-2R ladder divides the reference amplifier current into

binary-related components, which are fed to the remainder current

which is equal to the least significant bit. This current is shunted to

ground, and the maximum output current is 255/256 of the reference

amplifier current, or 1.992 mA for a 2.0 mA reference amplifier

current if the NPN current source pair is perfectly matched.

ABSOLUTE MAXIMUM RATINGS

SYMBOL

PARAMETER

RATING

UNIT

Positive power supply voltage

+5.5

V

Negative power supply voltage

–16.5

V

Digital input voltage

V

Applied output voltage

–5.2 to +18

V

Reference current

5.0

mA

Reference amplifier inputs

N package

1450

mW

D package

1080

mW

Operating temperature range

0 to +75

°C

Storage temperature range

–65 to +150

°C

Lead soldering temperature (10 sec)

+230

°C

NOTES:

1. Derate above 25

°C, at the following rates:

N package at 11.6 mW/

°C;

D package at 8.6 mW/

°C