Datasheet

© 2010 Microchip Technology Inc. DS22187E-page 51
MCP4728
7.0 TYPICAL APPLICATIONS
The MCP4728 device is a part of Microchip’s latest
DAC family with nonvolatile EEPROM memory. The
device is a general purpose resistor string DAC
intended to be used in applications where a precise
and low power DAC, with moderate bandwidth, is
required.
Since the device includes nonvolatile EEPROM
memory, the user can use this device for applications
that require the output to return to the previous set-up
value on subsequent power-ups.
Applications generally suited for the MCP4728 device
family include:
• Set Point or Offset Trimming
• Sensor Calibration
• Portable Instrumentation (Battery Powered)
• Motor Speed Control
7.1 Connecting to I
2
C BUS Using
Pull-Up Resistors
The SCL, SDA, and RDY/BSY pins of the MCP4728
device are open-drain configurations. These pins
require a pull-up resistor, as shown in Figure 7-1. The
LDAC
pin has a Schmitt trigger input configuration and
it can be driven by an external MCU I/O pin.
The pull-up resistor values (R
1
and R
2
) for SCL and
SDA pins depend on the operating speed (standard,
fast, and high speed) and loading capacitance of the
I
2
C bus line. Higher value of pull-up resistor consumes
less power, but increases the signal transition time
(higher RC time constant) on the bus line. Therefore, it
can limit the bus operating speed. A lower resistor
value, on the other hand, consumes higher power, but
allows for higher operating speed. If the bus line has
higher capacitance due to long metal traces or multiple
device connections to the bus line, a smaller pull-up
resistor is needed to compensate for the long RC time
constant. The pull-up resistor is typically chosen
between 1 kΩ and 10 kΩ range for standard and fast
modes, and less than 1 kΩ for high speed mode.
FIGURE 7-1: Example of the MCP4728 Device Connection.
Analog Outputs
V
DD
1
2
3
4
10
6
7
8
V
DD
SCL
SDA
V
SS
V
OUT
D
V
OUT
C
LDAC
RDY/BSY
9
5
V
OUT
B
V
OUT
A
MCP4728
R
1
R
2
R
3
To MCU
R
1
and R
2
=
Pull-up resistors for I
2
C Serial Communications
=
=
5kΩ - 10 kΩ for f
SCL
= 100 kHz to 400 kHz
~700Ω for f
SCL
= 3.4 MHz
R
3
=
(a) Pull-up resistor to monitor RDY/BSY bit = ~ 100 kΩ
(b) Let this pin float when not used
C
1
=
0.1 µF, Ceramic capacitor
C
2
=
10 µF, Tantalum capacitor
C
2
C
1