Datasheet MAX5450, MAX5451, MAX5452, MA5453, MAX5454, MAX5455 (Analog Devices) - 8

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