Datasheet

MCP4728
DS22187E-page 22 © 2010 Microchip Technology Inc.
3.3 Serial Data Pin (SDA)
SDA is the serial data pin of the I
2
C interface. The SDA
pin is used to write or read the DAC register and
EEPROM data. Except for Start and Stop conditions,
the data on the SDA pin must be stable during the high
duration of the clock pulse. The High or Low state of the
SDA pin can only change when the clock signal on the
SCL pin is Low.
The SDA pin is an open-drain N-channel driver.
Therefore, it needs a pull-up resistor from the V
DD
line
to the SDA pin.
Refer to Section 5.0 “I
2
C Serial Interface
Communications” for more details on the I
2
C Serial
Interface communication.
3.4 LDAC Pin
This pin can be driven by an external control device
such as an MCU I/O pin. This pin is used to:
a) transfer the contents of the input registers to
their corresponding DAC output registers and
b) select a device of interest when reading or writ-
ing I
2
C address bits.
For more details on reading and writing the I
2
C address
bits, see Section 5.4.4 “General Call Read Address
Bits” and Section 5.6.8 “Write Command: Write I2C
Address bits (C2=0, C1=1, C0=1)”.
When the logic status of the LDAC
pin changes from
“High” to “Low”, the contents of all input registers
(Channels A – D) are transferred to their corresponding
output registers, and all analog voltage outputs are
updated simultaneously.
If this pin is permanently tied to “Low”, the content of
the input register is transferred to its output register
(V
OUT
) immediately at the last input data byte’s
acknowledge pulse.
The user can also use the UDAC
bit instead. However,
the UDAC
bit updates a selected channel only. See
Section 4.8 “Output Voltage Update” for more
information on the LDAC
pin and UDAC bit functions.
3.5 RDY/BSY Status Indicator Pin
This pin is a status indicator of EEPROM programming
activity. This pin is “High” when the EEPROM has no
programming activity, and “Low” when the EEPROM is
in programming mode. It goes “High” when the
EEPROM program is completed.
The RDY/BSY
pin is an open-drain N-channel driver.
Therefore, it needs a pull-up resistor (about 100 kΩ)
from the V
DD
line to the RDY/BSY pin. Let this pin float
if it is not used.
3.6 Analog Output Voltage Pins
(V
OUT
A, V
OUT
B, V
OUT
C, V
OUT
D)
The device has four analog voltage output (V
OUT
) pins.
Each output is driven by its own output buffer with a
gain of 1 or 2, depending on the gain and V
REF
selection bit settings. In Normal mode, the DC
impedance of the output pin is about 1Ω. In
Power-Down mode, the output pin is internally
connected to 1 kΩ, 100 kΩ, or 500 kΩ, depending on
the Power-Down selection bit settings.
The V
OUT
pin can drive up to 1000 pF of capacitive
load. It is recommended to use a load with R
L
greater
than 5 kΩ.