Rainbow Electronics MAX5515 - Manual (Page 16)

Power Modes
The MAX5512–MAX5515 feature two power modes to
conserve power during idle periods. In normal opera-
tion, the device is fully operational. In shutdown mode,
the device is completely powered down, including the
internal voltage reference in the MAX5513/MAX5515.
The MAX5513/MAX5515 also offer a standby mode in
which all circuitry is powered down except the internal
voltage reference. Standby mode keeps the reference
powered up while the remaining circuitry is shut down,
allowing it to be used as a system reference. It also
helps reduce the wake-up delay by not requiring the ref-
erence to power up when returning to normal operation.
Shutdown Mode
The MAX5512–MAX5515 feature a software-programma-
ble shutdown mode that reduces the supply current and
the reference input current to 0.18µA (max). Writing an
input control word with control bits C[3:0] = 1110 (
Table
2) places the device in shutdown mode. In shutdown,
the MAX5512/MAX5514 reference input and DAC output
buffers go high impedance. Placing the MAX5513/
MAX5515 into shutdown turns off the internal reference
and the DAC output buffers go high impedance. The ser-
ial interface still remains active for all devices.
Table 2 shows several commands that bring the
MAX5512–MAX5515 back to normal operation. The
power-up time from shutdown is required before the
DAC outputs are valid.
Note: For the MAX5513/MAX5515, standby mode can-
not be entered directly from shutdown mode. The
device must be brought into normal operation first
before entering standby mode.
Standby Mode (MAX5513/MAX5515 Only)
The MAX5513/MAX5515 feature a software-program-
mable standby mode that reduces the typical supply
current to 3µA (max). Standby mode powers down all
circuitry except the internal voltage reference. Place
the device in standby mode by writing an input control
word with control bits C[3:0] = 1100 (
Table 2). The
internal reference and serial interface remain active
while the DAC output buffers go high impedance.
For the MAX5513/MAX5515, standby mode cannot be
entered directly from shutdown mode. The device must
be brought into normal operation first before entering
standby mode. To enter standby from shutdown, issue
the command to return to normal operation followed
immediately by the command to go into standby.
Table 2 shows several commands that bring the
MAX5513/MAX5515 back to normal operation. When
transitioning from standby mode to normal operation,
only the DAC power-up time is required before the DAC
outputs are valid.
Reference Input
The MAX5512/MAX5514 accept a reference with a volt-
age range extending from 0 to V
DD
. The output voltage
(V OUT ) is represented by a digitally programmable volt-
age source as:
V OUT = (V REF x N / 256) x gain
where N is the numeric value of the DAC’s binary input
code (0 to 255), V
REF is the reference voltage, gain is the
externally set voltage gain for the MAX5514, and gain is
one for the MAX5512.
In shutdown mode, the reference input enters a high-
impedance state with an input impedance of 2.5GΩ (typ).
Reference Output
The MAX5513/MAX5515 internal voltage reference is
software configurable to one of four voltages. Upon
power-up, the default reference voltage is 1.214V.
Configure the reference voltage using D7 and D6 data
bits (
Table 3) when the control bits are as follows C[3:0]
= 1100, 1101, or 1110 ( Table 2). V DD must be kept at a
minimum of 200mV above V REF for proper operation.
MAX5512–MAX5515
Dual, Ultra-Low-Power,
8-Bit, Voltage-Output DACs
16 ______________________________________________________________________________________
Table 3. Reference Output Voltage
Programming
D7 D6 REFERENCE VOLTAGE (V)
0 0 1.214
0 1 1.940
1 0 2.425
1 1 3.885