Data Sheet
AD5749
Rev. B | Page 21 of 28
Status Bit Read Operation
A read of the status bits can be initiated as part of a normal write
operation. The read is activated by selecting the correct device
address (A2, A1, A0) and then setting the R/W bit to 1. By
default, the SDO pin is disabled. After having addressed the
AD5749 and setting R/W to 1 the SDO pin is enabled and data
is clocked out on the 5th rising edge of SCLK. After all the data
has been clocked out on SDO, a rising edge on SYNC disables
(tristates) the SDO pin again. Status register data (se
e Table 9)and control register data are both available during the same
read cycle. Data contained in Bit D10 to Bit D0 of the write
operation are still valid and can be used to change the operating
The status bits comprise three read-only bits. They are used to
notify the user of specific fault conditions that occur, such as
an open circuit on the output, over-temperature error or an
interface error. If any of these fault conditions occur, a hardware
FAULT is also asserted low, which can be used as a hardware
interrupt to the controller.
explanation of fault conditions.
HARDWARE CONTROL
Hardware control is enabled by connecting the HW SELECT
pin to DVCC. In this mode, the R3, R2, R1, and R0 pins, in
conjunction with the RSET pin, are used to configure the
In hardware mode, there is no status register. The fault conditions
(open circuit, and overtemperature) are available on Pin IFAULT
and Pin TEMP. If any one of these fault conditions is set, a low is
asserted on the specific fault pin. IFAULT and TEMP are open-
drain outputs and, therefore, can be connected together to allow the
user to generate one interrupt to the system controller to commun-
icate a fault. If hardwired in this way, it is not possible to isolate
which fault occurred in the system.
TRANSFER FUNCTION
The
AD5749 consists of an internal signal conditioning block
that maps the analog input voltage to a programmed output
range. The available analog input range is 0 V to 4.096 V.
For all ranges, the
AD5749 implements a straight linear
mapping function, where 0 V maps to the lower end of the
selected range and 4.096 V maps to the upper end of the
selected range.
Table 9. Input Shift Register Contents for a Read Operation—Status Register
MSB
LSB
D15
D14
D13
D12
D11
D10
D9
D8
D7
D6
D5
D4
D3
D2
D1
D0
A2
A1
A0
1
0
R3
R2
R1
R0
CLRSEL
OUTEN
RSET
PEC Error
OVER TEMP
IOUT Fault
Unused
Table 10. Status Bit Options
Bit
Description
PEC Error
OVER TEMP
This bit is set if th
e AD5749 core temperature exceeds approximately 150°C.
IOUT Fault
This bit is set if there is an open circuit on the IOUT pin.