MAX5527 Просмотр технического описания (PDF) - Maxim Integrated

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MAX5527

One-Time Programmable, Linear-Taper Digital Potentiometers

Maxim Integrated 

One-Time Programmable, Linear-Taper Digital

Potentiometers

U/D

+11V

PV

0V

CS

tCH

tPC

tCL

6 PULSES RECORD WIPER POSITION

Figure 5. One-Time Program Mode, Serial-Interface Timing Diagram

tCP

tPH

OPTIONAL 7TH

LOCKOUT BIT

Table 1. One-Time Programming Options

MODE

Factory Default

(Unprogrammed)

Programmed by

Six CS Pulses

Programmed by

Seven CS Pulses

POWER-ON RESET ADJUSTABLE

WIPER POSITION

WIPER

Tap 31

Yes

Programmed position

Yes

Programmed position

No

Change the wiper’s power-up position using the PV

one-time programming sequence after power-up (see

Figure 5). After setting the wiper to the desired power-

up position, perform the following six-step sequence:

1) Set U/D and CS high.

2) Connect an external voltage source at PV in the

range of +11V to +11.55V.

3) Pull CS low.

4a) Pulse CS high for six cycles, consisting of CS

starting low and going high for at least tCH, and

then low for at least tCL, to change the wiper

power-up position. The wiper remains adjustable.

4b) Pulse CS high for seven cycles, consisting of CS

starting low and going high for at least tCH and then

low for at least tCL, to change the wiper power-up

position and lock the wiper in that same position.

The seventh CS pulse is labeled the optional lock-

out bit in Figure 5.

5) Connect PV to GND or release the voltage source,

leaving PV floating.

6) Pull CS high.

11V

22μF

TRACE PARASITICS

LPARASITIC

< 250μH

RPARASITIC

< 40Ω

PV

MAX5527

MAX5528

MAX5529

Figure 6. PV Power-Supply Decoupling

Pulse CS high for six cycles to change the wiper power-

up position. The wiper position returns to this pro-

grammed position on power-up, but remains adjustable.

Pulse CS high for seven cycles to lock the MAX5527/

MAX5528/MAX5529 to a specific wiper position with no

further adjustments allowed. This effectively converts

the potentiometer to a fixed resistor-divider. The sev-

enth pulse locks the wiper position and disables the

up/down interface. Once locked, connect U/D and CS

high, low, or leave them floating without increasing the

supply current (see Table 1).

If six clock pulses are used, the interface is enabled

and the device can be put into program mode again.

However, the part uses one-time programmable (OTP)

memory and should be programmed only once. If the

part is programmed more than once, all applied values

are ORed together. Thus, if 010101 is programmed the

first time and 101010 is programmed the second time,

the result will be 111111.

The external PV power supply must source at least 5mA

and have a good transient response. Decouple the PV

power supply with a 22µF capacitor to GND. Ensure that

no more than 250µH of inductance and/or 40Ω of para-

sitic resistance exists between the capacitor and the

device (see Figure 6).

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