MAX5427(2002) Просмотр технического описания (PDF) - Maxim Integrated

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MAX5427
(Rev.:2002)

One-Time Programmable, Linear-Taper Digital Potentiometers

Maxim Integrated 

One-Time Programmable, Linear-Taper

Digital Potentiometers

VDD

tUP

CS

tCU

tCI

tIL

tIH

tIC

U/D

tIW

VW

Figure 2. Increment Mode Serial Interface Timing Diagram

VDD

tUP

CS

tCU

tCI

tIH

tIL

tIC

U/D

tIW

VW

Figure 3. Decrement Mode Serial Interface Timing Diagram

The value of the counter is then stored and the wiper

position is maintained.

The wiper performs a make-before-break transition,

ensuring that there is never an open circuit during a tran-

sition from one resistor tap to another. When the wiper is

at either end (max/min) of the resistor array, additional

transitions in the direction of the endpoint do not change

the counter value (the counter does not wrap around).

One-Time Programming

The factory-set default position of the wiper on power-

up is tap 16. However, the power-up position can be

changed once using the one-time programming fea-

ture. After the wiper is moved to the desired position,

the programming sequence is initiated by setting U/D

high, applying 11V to VPP, and then taking CS low. Five

pulses on CS (consisting of CS starting from low and

going high for tCH and then low for tCL) program the

device (Figure 4). The programming voltage should

then be taken to zero. After the device is programmed,

VPP can be set to zero or be allowed to float. The wiper

position is still adjustable, but always returns to this

programmed position on power-up.

If the intent is to program the device to a specific wiper

position and not to allow further adjustments, then six

programming pulses are required (as opposed to five),

as shown in Figure 4. The sixth pulse locks the wiper

position and disables the serial interface. This also

allows U/D and CS to float without any increase in sup-

ply current. Once the lockout bit is set, no further

adjustment to the potentiometer is possible, effectively

changing the potentiometer into a fixed resistor-divider

(Table 1).

Table 1. One-Time Programming Options

MODE

Factory Default

(Unprogrammed)

POWER-ON

RESET WIPER

POSITION

Tap 16

ADJUSTABLE

WIPER

Yes

Programmed

(5 Programming Pulses)

Programmed

position

Yes

Lock-Bit Set

(6 Programming Pulses)

Programmed

position

No

6 _______________________________________________________________________________________

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