Rainbow Electronics MAX5499 - Manual (Page 13)

MAX5494–MAX5499
10-Bit, Dual, Nonvolatile, Linear-Taper
Digital Potentiometers
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resistance is equal to the nominal end-to-end resis-
tance divided by 1024 (10-bit resolution). For example,
the programmable resolution is 9.8
Ω and 48.8Ω for the
MAX5496/MAX5498 and the MAX5497/MAX5499,
respectively.
The 10-bit data in the 10-bit latch register selects the
wiper position from the 1024 possible positions, result-
ing in 1024 values for the resistance from W_ to L_.
Calculate the resistance from W_ to L_ (R
WL
) from the
formula below:
where D is decimal equivalent of the 10 data bits writ-
ten, R
W-L is the nominal end-to-end resistance, and R Z
is the zero-scale error. Table 1 shows R WL at selected
codes.
SPI-Compatible Serial Interface
The MAX5494–MAX5499 use a 3-wire, SPI-compatible,
serial data interface (Figure 6). This write-only interface
contains three inputs: chip-select (CS), data input
(DIN), and data clock (SCLK). Drive CS low to enable
the serial interface and clock data synchronously into
the shift register on each SCLK rising edge.
The WRITE commands (C1, C0 = 00 or 01) require 24
clock cycles to transfer the command and data (Figure
7a). The COPY commands (C1, C0 = 10 or 11) use
either eight clock cycles to transfer the command bits
(Figure 7b) or 24 clock cycles with 16 bits disregarded
by the device (Figure 7a).
After the loading of data into the shift register, drive CS
high to latch the data into the appropriate control regis-
ter (specified by RA1 and RA0) and disable the serial
interface. Keep CS low during the entire serial data
stream to avoid corruption of the data. Table 2 shows
the register map.
Write Wiper Register
The “write wiper register” command (C1, C0 = 00) con-
trols the wiper positions. The 10 data bits (D9–D0) indi-
cate the position of the wiper. For example, if DIN =
000000 0000, the wiper moves to the position closest to
L_. If DIN = 11 1111 1111, the wiper moves closest to H_.
R D
D
R R
WL W L Z
( )
= × +
−
1023
END-TO-END RESISTANCE VALUE
10k Ω 50k Ω CODE (DECIMAL)
R WL ( Ω) R WL ( Ω)
0 70 110
1 80 160
512 5,070 25,110
1023 10,070 50,110
Table 1. R
WL
at Selected Codes
CS
t CSO
t CSS
t CL t CH
t DH t DS
t CP t CSH
t CSW
t CS1
SCLK
DIN
Figure 6. SPI-Interface Timing Diagram