MAX5477 データシートの表示（PDF） - Maxim Integrated
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MAX5477 Datasheet PDF : 16 Pages
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Dual, 256-Tap, Nonvolatile, I2C-Interface,
Digital Potentiometers
Table 2. Write-Protect Behavior of VREG and NVREG
COMMAND
WP = 0
WP = 1
Write to VREG
I2C data is written to VREG.
Wiper position updates with I2C data.
No change to NVREG.
Copy NVREG to VREG.
Wiper position updates with NVREG data.
No change to NVREG.
Write to NVREG
No change to VREG or wiper position.
I2C data is written to NVREG.
No change to VREG or wiper position.
No change to NVREG.
Copy NVREG to VREG
Copy NVREG to VREG.
Wiper position updates with NVREG data.
No change to NVREG.
Copy NVREG to VREG.
Wiper position updates with NVREG data.
No change to NVREG.
Copy VREG to NVREG Copy VREG to NVREG.
No change to VREG or wiper position.
No change to VREG or wiper position.
No change to NVREG.
Table 3. Command Byte Summary
SCL CYCLE
NUMBER
ADDRESS BYTE
COMMAND BYTE
DATA BYTE
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27
START
STOP NOTES
(S) A6 A5 A4 A3 A2 A1 A0
ACK
(A)
TX NV V
R3
R2
R1
R0
ACK
(A)
D7
D6
D5 D4 D3
D2
D1
D0
ACK
(A)
(P)
VREG
NVREG
NVREGxVREG
VREGxNVREG
VREG
NVREG
NVREGxVREG
0 1 0 1 A2 A1 A0 0
0 1 0 1 A2 A1 A0 0
0 1 0 1 A2 A1 A0 0
0 1 0 1 A2 A1 A0 0
0 1 0 1 A2 A1 A0 0
0 1 0 1 A2 A1 A0 0
0 1 0 1 A2 A1 A0 0
0001 0001
0010 0001
0110 0001
0101 0001
0001 0010
0010 0010
0110 0010
D7 D6 D5 D4 D3 D2 D1 D0
D7 D6 D5 D4 D3 D2 D1 D0
D7 D6 D5 D4 D3 D2 D1 D0
D7 D6 D5 D4 D3 D2 D1 D0
D7 D6 D5 D4 D3 D2 D1 D0
D7 D6 D5 D4 D3 D2 D1 D0
D7 D6 D5 D4 D3 D2 D1 D0
WIPER A
ONLY
WIPER B
ONLY
VREGxNVREG
VREG
NVREG
NVREGxVREG
VREGxNVREG
0 1 0 1 A2 A1 A0 0
0 1 0 1 A2 A1 A0 0
0 1 0 1 A2 A1 A0 0
0 1 0 1 A2 A1 A0 0
0 1 0 1 A2 A1 A0 0
0101 0010
0001 0011
0010 0011
0110 0011
0101 0011
D7 D6 D5 D4 D3 D2 D1 D0
D7 D6 D5 D4 D3 D2 D1 D0
D7 D6 D5 D4 D3 D2 D1 D0
D7 D6 D5 D4 D3 D2 D1 D0
D7 D6 D5 D4 D3 D2 D1 D0
WIPERS
A AND B
Digital Interface
The MAX5477/MAX5478/MAX5479 feature an internal,
nonvolatile EEPROM that stores the wiper state for ini-
tialization during power-up. The shift register decodes
the command and address bytes, routing the data to
the proper memory registers. Data written to a volatile
memory register immediately updates the wiper posi-
tion, or writes data to a nonvolatile register for storage
(see Table 3).
The volatile register retains data as long as the device
is powered. Removing power clears the volatile regis-
ter. The nonvolatile register retains data even after
power is removed. Upon power-up, the power-on reset
circuitry controls the transfer of data from the non-
volatile register to the volatile register.
Write Protect (WP)
A write-protect feature prevents accidental overwriting of
the EEPROM. Connect WP to VDD or leave unconnected
to prevent any EEPROM write cycles. Writing to the
volatile register (VREG) while WP = 1 updates the wiper
position with the protected data stored in the nonvolatile
register (NVREG). Connect WP to GND to allow write
commands to the EEPROM and to update the wiper
position from either the value in the EEPROM or directly
from the I2C interface (Table 2). Connecting WP to GND
increases the supply current by 19.6µA (max).
To ensure a fail-safe, write-protect feature, write the
data to be protected to both the nonvolatile and volatile
registers before pulling WP high. Releasing WP (WP =
0) and sending partial or invalid I2C commands (such
as single-byte address polling) can load the volatile
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