Datasheet

 2010 Microchip Technology Inc. DS22250A-page 17
MCP4902/4912/4922
3.0 PIN DESCRIPTIONS
The descriptions of the pins are listed in Table 3- 1.
TABLE 3-1: PIN FUNCTION TABLE
3.1 Supply Voltage Pins (V
DD,
V
SS
)
V
DD
is the positive supply voltage input pin. The input
supply voltage is relative to V
SS
and can range from
2.7V to 5.5V. 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.
V
SS
is the analog 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 Chip Select (CS)
CS is the Chip Select input, which requires an active
low signal to enable serial clock and data functions.
3.3 Serial Clock Input (SCK)
SCK is the SPI compatible serial clock input pin.
3.4 Serial Data Input (SDI)
SDI is the SPI compatible serial data input pin.
3.5 Latch DAC Input (LDAC)
LDAC (latch DAC synchronization input) pin is used to
transfer the input latch registers to their corresponding
DAC registers (output latches, V
OUT
). When this pin is
low, both V
OUTA
and V
OUTB
are updated at the same
time with their input register contents. This pin can be
tied to low (V
SS
) if the V
OUT
update is desired at the
rising edge of the CS
pin. This pin can be driven by an
external control device such as an MCU I/O pin.
3.6 Hardware Shutdown Input (SHDN)
SHDN is the hardware shutdown input pin. When this
pin is low, both DAC channels are shut down. DAC
output is not available during the shutdown.
3.7 Analog Outputs (V
OUTA
, V
OUTB
)
V
OUTA
is the DAC A output pin, and V
OUTB
is the DAC
B output pin. Each output has its own output amplifier.
The DAC output amplifier of each channel can drive the
output pin with a range of V
SS
to V
DD
.
3.8 Voltage Reference Inputs
(V
REFA
, V
REFB
)
V
REFA
is the voltage reference input for DAC channel
A, and V
REFB
is the reference input for DAC channel B.
The reference on these pins is utilized to set the
reference voltage on the string DAC. The input signal
can range from V
SS
to V
DD
. These pins can be tied to
V
DD
.
Pin No. Symbol Function
1V
DD
Supply Voltage Input (2.7V to 5.5V)
2 NC No Connection
3CS
Chip Select Input
4 SCK Serial Clock Input
5 SDI Serial Data Input
6 NC No Connection
7 NC No Connection
8LDAC
Synchronization Input. This pin is used to transfer DAC settings (Input Registers)
to the output registers (V
OUT
)
9SHDN
Hardware Shutdown Input
10 V
OUTB
DAC
B
Output
11 V
REFB
DAC
B
Reference Voltage Input (V
SS
to V
DD
)
12 V
SS
Ground reference point for all circuitry on the device
13 V
REFA
DAC
A
Reference Voltage Input (V
SS
to V
DD
)
14 V
OUTA
DAC
A
Output