Datasheet

AD5751 Data Sheet
Rev. B | Page 24 of 32
DEFAULT REGISTERS AT POWER-ON
The AD5751 power-on-reset circuit ensures that all registers are
loaded with zero code.
In software SPI mode, the part powers up with all outputs
disabled (OUTEN bit = 0). The user must set the OUTEN bit in
the control register to enable the output and, in the same write,
set the output range configuration using the R3 to R0 bits.
If hardware mode is selected, the part powers up to the
conditions defined by the R3 to R0 bits and the status of the
OUTEN pin. It is recommended to keep the output disabled
when powering up the part in hardware mode.
RESET FUNCTION
In software mode, the part can be reset using the
RESET
pin
(active low) or the reset bit (reset = 1). A reset disables both the
current and voltage outputs to their power-on condition. The
user must write to the OUTEN bit to enable the output and, in
the same write, set the output range configuration. The
RESET
pin is a level sensitive input; the part stays in reset mode as long
as the
RESET
pin is low. The reset bit clears to 0 following a
reset command to the control register.
In hardware mode, there is no reset. If using the part in
hardware mode, the
RESET
pin should be tied high.
OUTEN
In software mode, the output can be enabled or disabled using
the OUTEN bit in the control register. When the output is
disabled, both the current and voltage channels go into tristate.
The user must set the OUTEN bit to enable the output and
simultaneously set the output range configuration.
In hardware mode, the output can be enabled or disabled using
the OUTEN pin. When the output is disabled, both the current
and voltage channels go into tristate. The user must write to the
OUTEN pin to enable the output. It is recommended that the
output be disabled when changing the ranges.
SOFTWARE CONTROL
Software control is enabled by connecting the HW SELECT pin
to ground. In software mode, the AD5751 is controlled over a
versatile 3-wire serial interface that operates at clock rates up to
50 MHz. It is compatible with SPI, QSPI™, MICROWIRE, and
DSP standards.
Input Shift Register
The input shift register is 16 bits wide. Data is loaded into the
device MSB first as a 16-bit word under the control of a serial
clock input, SCLK. Data is clocked in on the falling edge of SCLK.
The input shift register consists of 16 control bits, as shown in
Table 7. The timing diagram for this write operation is shown in
Figure 2. The first three bits of the input shift register are used to set
the hardware address of the AD5751 device on the printed circuit
board (PCB). Up to eight devices can be addressed per board.
Bit D11, Bit D1, and Bit D0 must always be set to 0 during any
write sequence.
Table 7. Input Shift Register Contents for a Write Operation—Control Register
MSB LSB
D15 D14 D13 D12 D11 D10 D9 D8 D7 D6 D5 D4 D3 D2 D1 D0
A2 A1 A0 R/
W
0 R3 R2 R1 R0 CLRSEL OUTEN Clear RSET Reset 0 0
Table 8. Input Shift Register Descriptions for Control Register
Bit Description
A2, A1, A0 Used in association with the AD2, AD1, and AD0 external pins to determine which part is being addressed by the system
controller.
A2 A1 A0 Function
0 0 0 Addresses part with Pin AD2 = 0, Pin AD1 = 0, Pin AD0 = 0.
0 0 1 Addresses part with Pin AD2 = 0, Pin AD1 = 0, Pin AD0 = 1.
0 1 0 Addresses part with Pin AD2 = 0, Pin AD1 = 1, Pin AD0 = 0.
0 1 1 Addresses part with Pin AD2 = 0, Pin AD1 = 1, Pin AD0 = 1.
1 0 0 Addresses part with Pin AD2 = 1, Pin AD1 = 0, Pin AD0 = 0.
1 0 1 Addresses part with Pin AD2 = 1, Pin AD1 = 0, Pin AD0 = 1.
1 1 0 Addresses part with Pin AD2 = 1, Pin AD1 = 1, Pin AD0 = 0.
1 1 1 Addresses part with Pin AD2 = 1, Pin AD1 = 1, Pin AD0 = 1.
R/
W
Indicates a read from or a write to the addressed register.