X9470 datasheet(13/25 Pages) XICOR

13 / 25 page

13 of 25

REV 11.16 3/20/03

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Preliminary Information

X9470

Figure 2. Sense and Scale Block Diagram

The wiper of the digital potentiometer acts like its

mechanical equivalent and does not move beyond the

last position. That is, the counter does not wrap around

when clocked to either extreme. The electronic

switches in the potentiometer operate in a “make

before break” mode when the wiper changes tap posi-

tions. If the wiper is moved several positions, multiple

taps are connected to the wiper for tIW (SCL to

RWBIAS change).

When the device is powered-up, the X9470 will load

the last saved value from the non-volatile memory into

the WCR. Note that the current wiper position can be

saved into non-volatile memory register by using the

SCL and CS pins as shown in Figure 4.

Important note: the factory setting of the wiper counter

the default wiper position.

Bias Adjustment Block Instructions and Program-

ming. The SCL, INC/DEC (internal signal) and CS

inputs control the movement of the wiper along the

resistor array. (See Table 1) With CS set HIGH, the

device is selected and enabled to respond to the INC/

DEC and SCL inputs. HIGH to LOW transitions on SCL

will increment or decrement RBIAS (depending on the

state of the INC/DEC input). The INC/DEC input is

derived from the output of the comparator of the Sense

and Scale Block.

Storing Bias Resistor Values in Memory. Wiper val-

ues are stored to VOLATILE memory automatically

when CS is HIGH and INC/DEC either transitions from

HIGH to LOW or from LOW to HIGH. Wiper values are

stored to NON-VOLATILE memory during Byte Write

or as described in the following section.

Table 1. Mode Selection

* When coming out of shutdown, the CS pin must be cycled once before bias

adjustment is enabled.

INC/DEC

RWREF

RLREF

RHREF

VOUT

VDD

VSENSE+

RSENSE

VSENSE–

10k

Ω

64-tap

VREF

Comparator

INC/DEC

~1kohm

Precision

I-Amp

Cint~2pF ±10%

∆V

IDQ

Out

choke

Vgate

RF PA in

K2 = 20X

K1 = 50X

SDA

CS*

SCL

INC /

DEC

Mode

VBIAS is incremented

one tap position.

VBIAS is decremented

one tap position.

Lock Wiper Position.

Save to volatile

memory. (BiasLock™)

Open Loop.

X9470 Datasheet(PDF) 13 Page - Xicor Inc.

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