Datasheet

MAX5450–MAX5455
Detailed Description
The MAX5450–MAX5455 contain two independent
resistor arrays each with 255-resistive elements. 256-
tap points are accessible to the wiper along the resistor
arrays between H and L (Figure 2). Power-on reset cir-
cuitry sets the wiper to midscale (position 127) at
power-up.
Logic inputs CS, U/D, and INC determine the wiper
position of the MAX5450–MAX5455. With CS low and
U/D high, a high-to-low (falling edge) transition on INC,
increments the internal counter, which increases the
resistance between W and L. When both CS and U/D
are low, a high-to-low INC transition decrements the
internal counter, decreasing the resistance between W
and L (Figure 1). The wiper performs a make-before-
break transition ensuring that there is never an open
circuit during a transition from one resistor tap to anoth-
er. When the wiper is at either end (max/min) of the
resistor array, additional transitions in the direction of
the endpoint will not change the counter value (the
counter will not wrap around).
The MAX5450/MAX5452/MAX5454 are similar to the
MAX5451/MAX5453/MAX5455 except for internal con-
nections. The MAX5450/MAX5452/MAX5454 internally
connect INC1 to INC2, U/D1 to U/D2, W1 to H1, and
W2 to H2 (Figures 3 and 4). The internal connections
configure the MAX5450/MAX5452/MAX5454 to be vari-
able resistors.
Applications Information
The MAX5450–MAX5455 are ideal for adjustable volt-
age or adjustable gain circuits where accurate
adjustable resistances are required.
Adjustable Current to Voltage Converter
Figure 5 shows the MAX5450/MAX5452/MAX5454 with
a MAX4250 low-noise op amp to fine-tune a current to
voltage converter. The physical sizes of both devices
minimize circuit space.
Adjustable Gain Amplifier
Figures 6a and 6b shows the MAX5450–MAX5455 digi-
tally adjusting the gain of the MAX4493 general-pur-
pose, dual supply op amp. Figure 6a shows the
MAX5450/MAX5452/MAX5454 variable resistor in
series with a resistor to ground to form the adjustable
gain control. Figure 6b shows the MAX5451/MAX5453/
MAX5455 as a 3-terminal potentiometer. In these appli-
cations the low 5ppm/°C ratiometric tempco allows for
a very stable adjustable gain over temperature.
Adjustable Linear Regulator
In Figure 7, the MAX5450/MAX5452/MAX5454 is shown
digitally adjusting the output voltage of the MAX8866
dual linear regulator. In this circuit, the MAX5450/
MAX5452/MAX5454 is connected in series with a resis-
tor to ground to form the adjustable feedback stage.
The 8-bit MAX5450/MAX5452/MAX5454 allows precise
tuning of the output voltage.
Dual, 256-Tap, Up/Down Interface,
Digital Potentiometers
8 _______________________________________________________________________________________
Figure 1. Digital Interface and Timing diagram
t
ID
t
IW
t
DI
t
CI
t
IL
t
IH
t
IC
CS_
W_
U/D_
INC_