MAX4820 Maxim, MAX4820 Datasheet - Page 7

• Manufacturer Part Number: MAX4820
• Description: The MAX4820/MAX4821 8-channel relay drivers offer built-in kickback protection and drive +3
• Manufacturer: Maxim

The serial interface consists of an 8-bit shift register
and parallel latch controlled by SCLK and CS. The
input to the shift register is an 8-bit word. Each data bit
controls one of the eight outputs, with the most signifi-
cant bit (D7) corresponding to OUT8 and the least sig-
nificant bit (D0) corresponding to OUT1 (see Table 1).
When CS is low (device is selected), data at DIN is
clocked into the shift register synchronously with
SCLK’s rising edge. Driving CS from low to high latches
the data in the shift register to the parallel latch.
DOUT is the output of the shift register. Data appears
on DOUT synchronously with SCLK’s falling edge and
is identical to the data at DIN delayed by eight clock
cycles. When shifting the input data, D7 is the first bit in
and out of the shift register.
While CS is low, the switches always remain in their pre-
vious state. Drive CS high after 8 bits of data have been
shifted in to update the output state and inhibit further
data from entering the shift register. When CS is high,
transitions at DIN and SCLK have no effect on the out-
Figure 1. 3-Wire Serial-Interface Timing Diagram (MAX4820 only)
Table 1. Serial Input Address Map (MAX4820 Only)
DIN
OUT_
3.3V/+5V, 8-Channel, Cascadable Relay Drivers
DOUT
SCLK
OUT_
DIN
CS
OUT1
_______________________________________________________________________________________
D0
t
CSS
t
DS
Serial Interface (MAX4820)
D7
t
DH
OUT2
D1
Digital Interface
t
CL
OUT3
D6
D2
t
CH
with Serial/Parallel Interface
OUT4
D3
put, and the first input bit (D7) is present at DOUT.
If the number of data bits entered while CS is low is
greater or less than 8, the shift register contains only
the last 8 data bits, regardless of when they were
entered.
The 3-wire serial interface is compatible with SPI, QSPI,
and MICROWIRE standards. The latch that drives the
analog switch is updated on the rising edge of CS,
regardless of SCLK’s state.
The parallel interface consists of three address bits
(A0, A1, A2) and one level selector bit (LVL). The
address bits determine which output is updated, and
the level bit determines whether the addressed output
is switched on (LVL = high) or off (LVL = low). When CS
is high, the address and level bits have no effect on the
state of the outputs. Driving CS from low to high latches
the address and level data to the parallel register and
updates the state of the outputs. Address data entered
after CS is pulled low is not reflected in the state of the
outputs following the next low-to-high transition on CS
(Figure 2).
D1
OUT5
D4
t
DO
D0
OUT6
D5
t
CSH
Parallel Interface (MAX4821)
t
t
ON
OFF
,
t
CSW
OUT7
D6
t
CSO
OUT8
D7
7