SA9903B
Voltage Sense Input (IVP)
OUTPUT SIGNALS
Figure 8 shows the voltage sense input configuration. The
voltage sense input saturates at an input current of
±17.6μARMS (±25μAPEAK). The current into the voltage sense
input should therefore be set to 14μARMS at nominal mains
voltage (VNOM) to allow for a mains voltage variation of up to
+15% and –50% without saturating the voltage sense input.
Serial Data Out (DO)
The DO pin is the serial data output pin for the SA9903B. The
Serial Clock (SCK) determines the data output rate. Data is
only transferred out on the rising edge of SCK during active
chip select (CS). This output is tri-state when CS is inactive
(low). It is recommended to use an external pull-up or pull-
down resistor on DO to ensure its state is always valid.
For best performance the SA9903B also requires an anti-
alias filter on the voltage sense input. Referring to Figure 8,
the capacitor C1 is used to both implement the anti-alias filter
as well as compensating for any phase shift caused by the
current sensing element. The resistor R4 defines the input
current into the device. The optimum input network is
achieved by setting R4 in the order of 100k. If R4 is made
too large the capacitor C1 will be very small and the accuracy
of the phase compensation could be affected by stray
capacitances.
Mains Voltage Zero Crossover (FMO)
The FMO output generates a signal, which follows the mains
voltage zero crossings, see Figure 9. The microcontroller can
use this signal to extract the mains timing or synchronize to
the mains voltage.
Mains
Voltage
t
R1
R2
R3
R4
VNOM
Voltage In
Neutral
IVP
14µARMS
FMO
GND
R5 << R4 << (R1 + R2 + R3)
C1
R5
GND
GND
Figure 9: Mains voltage zero crossover
Figure 8: Voltage sense input configuration
SPI INTERFACE
Description
A serial peripheral interface bus (SPI) is a synchronous bus
used for data transfers between a microcontroller and the
SA9903B. The pins DO (Serial Data Out), DI (Serial Data In),
CS (Chip Select), and SCK (Serial Clock) are used in the bus
implementation. The SA9903B is the slave device with the
microcontroller being the bus master. The CS input initiates
and terminates data transfers. A SCK signal (generated by
the microcontroller) strobes data between the microcontroller
and the SA9903B. The DI and DO pins are the serial data
input and output pins for the SA9903B respectively.
Serial Clock (SCK)
The SCK pin is used to synchronize data interchange
between the microcontroller and the SA9903B. The clock
signal on this pin is generated by the microcontroller and
determines the data transfer rate of the DO and DI pins.
Serial Data In (DI)
The DI pin is the serial data input pin for the SA9903B. Data
will be input at a rate determined by the Serial Clock (SCK).
Data will be strobed by the SA9903B on the rising edge of
SCK only during an active chip select (CS).
Chip Select (CS)
The CS input is used to address the SA9903B. A high level
on this pin enables the SA9903B to initiate data exchange.
SPEC-0051 (REV. 5)
29-09-2017
10/17
SAMES [ SAMES ]
