Datasheet

© 2010 Microchip Technology Inc. DS22187E-page 21
MCP4728
3.0 PIN DESCRIPTIONS
The descriptions of the pins are listed in Table 3-1.
3.1 Supply Voltage Pins (V
DD
, V
SS
)
V
DD
is the power supply pin for the device. The voltage
at the V
DD
pin is used as a power supply input as well
as a DAC external reference. The power supply at the
V
DD
pin should be as clean as possible for a good DAC
performance.
It is recommended to use an appropriate bypass
capacitor of about 0.1 µF (ceramic) to ground. An
additional 10 µF capacitor (tantalum) in parallel is also
recommended to further attenuate high-frequency
noise present in application boards. The supply voltage
(V
DD
) must be maintained in the 2.7V to 5.5V range for
specified operation.
V
SS
is the ground pin and the current return path of the
device. The user must connect the V
SS
pin to a ground
plane through a low-impedance connection. If an
analog ground path is available in the application
printed circuit board (PCB), it is highly recommended
that the V
SS
pin be tied to the analog ground path, or
isolated within an analog ground plane of the circuit
board.
3.2 Serial Clock Pin (SCL)
SCL is the serial clock pin of the I
2
C interface. The
MCP4728 device acts only as a slave and the SCL pin
accepts only external input serial clocks. The input data
from the Master device is shifted into the SDA pin on
the rising edges of the SCL clock, and output from the
MCP4728 occurs at the falling edges of the SCL clock.
The SCL pin is an open-drain N-channel driver.
Therefore, it needs a pull-up resistor from the V
DD
line
to the SCL pin.
Refer to Section 5.0 “I
2
C Serial Interface
Communications” for more details on I
2
C Serial
Interface communication.
Typical range of the pull-up resistor value for SCL and
SDA is from 5 kΩ to 10 kΩ for Standard (100 kHz) and
Fast (400 kHz) modes, and less than 1 kΩ for High
Speed mode (3.4 MHz).
TABLE 3-1: PIN FUNCTION TABLE
Pin No. Name Pin Type Function
1 V
DD
P Supply Voltage
2SCL OI I
2
C Serial Clock Input (Note 1)
3 SDA OI/OO I
2
C Serial Data Input and Output (Note 1)
4LDAC ST This pin is used for two purposes:
(a) Synchronization Input. It is used to transfer the contents of the DAC input
registers to the output registers (V
OUT
).
(b) Select the device for reading and writing I
2
C address bits. (Note 2)
5 RDY/BSY
OO This pin is a status indicator of EEPROM programming activity. An external pull-up
resistor (about 100 kΩ) is needed from RDY/BSY
pin to V
DD
line. (Note 1)
6V
OUT
A AO Buffered analog voltage output of channel A. The output amplifier has rail-to-rail
operation.
7V
OUT
B AO Buffered analog voltage output of channel B. The output amplifier has rail-to-rail
operation.
8V
OUT
C AO Buffered analog voltage output of channel C. The output amplifier has rail-to-rail
operation.
9V
OUT
D AO Buffered analog voltage output of channel D. The output amplifier has rail-to-rail
operation.
10 V
SS
P Ground reference.
Legend: P = Power, OI = Open-Drain Input, OO = Open-Drain Output, ST = Schmitt Trigger Input Buffer,
AO = Analog Output
Note 1: This pin needs an external pull-up resistor from V
DD
line. Leave this pin float if it is not used.
2: This pin can be driven by MCU.