and Lookup Table

_____________________________________________________________________

7

Detailed Description

The DS3501 operates in one of three operating modes:

Default Mode, LUT Mode, or LUT Adder Mode. In

Default Mode, the DS3501 is pin and software compati-

ble with the ISL95311. The potentiometer’s wiper posi-

tion is controlled by the Wiper Register (WR) and the

LUT Mode and LUT Adder Mode, the potentiometer’s

wiper position is calculated/controlled as a function of

the current temperature measured by the DS3501’s

internal temperature sensor. The difference between

the two LUT modes is the way the potentiometer wiper

position is calculated. A detailed description of the

three modes as well as additional features of the

DS3501 follow below.

Digital Potentiometer Output

The potentiometer consists of 127 resistors in series

connected between the RH and RL pins. Between each

resistance and at the two end points, RH and RL, solid-

state switches enable RW to be connected within the

resistive network. The wiper position and the output on

RW are decoded based on the value in WR. If RH, RL,

and RW are externally connected in a voltage-divider

configuration, then the voltage on RW can be easily

calculated using the following equation:

where WR is the wiper position in decimal (0–127).

Temperature Conversion and

Supply Voltage Monitoring

Temperature Conversion

The DS3501 features an internal 8-bit temperature sen-

sor that is capable of driving the LUT and providing a

reading address 0Ch. The sensor is functional over the

entire operating temperature range and is in signed

two’s complement format with a resolution of 1°C/bit.

See below for the temperature sensor’s bit weights.

To calculate the temperature, treat the two’s comple-

ment binary value as an unsigned binary number, then

convert it to decimal. If the result is greater than or

equal to 128, subtract 256 from the result.

Supply Voltage Monitoring

The DS3501 also features an internal 8-bit supply volt-

To calculate the supply voltage, simply convert the

hexadecimal result into decimal and then multiply it by

the LSB as shown in the

Analog Voltage Monitoring

Characteristics electrical table.

Mode Selection

The DS3501 mode of operation is determined by two

bits located in Control Register 1 (CR1), which is non-

volatile. In particular, the mode is determined by the

Update Mode bit (CR1.0) and the Adder Mode bit

(CR1.1). Table 1 illustrates how the two control bits are

used to select the operating mode. When shipped from

the factory, the DS3501 is programmed with the CR1.0

bit = 0, hence configuring the DS3501 in Default Mode.

Default Mode

Default Mode of the DS3501 is the simplest mode of the

three. As shown in the Default Mode Block Diagram,

the potentiometer is controlled by the Wiper Register/

Initial Value Register (WR/IVR). Upon power-up of the

DS3501, the value stored in the NV Initial Value

Register (IVR) is recalled into the volatile Wiper

Register (WR). The wiper can then be changed any

time after by writing the desired value to the WR/IVR

Register. The WR/IVR Register is located at memory

address 00h and is implemented as EEPROM shad-

owed SRAM. This register can be visualized as an

SRAM byte (the WR portion) in parallel with a EEPROM

byte (the IVR portion). The operation of the register is

controlled by the Shadow EEPROM (SEE) bit, CR0.7.

When the SEE bit = 0 (default), data written to memory

(WR) and EEPROM (IVR). Conversely, when SEE = 1,

only the SRAM (WR) is written to the new value. The

EEPROM byte (IVR) continues to store the last value

written to it when SEE was 0. Reading memory address

00h reads the value stored in WR. As shown in the

Default Mode memory map (see Table 2), the SEE bit is

volatile and its power-up default state is 0.

VV

WR

VV

RW

RL

RH

RL

=+

−

()

127

S2

6

2

5

2

4

2

3

2

2

2

1

2

0

UPDATE MODE

BIT (CR1.0)

ADDER MODE

BIT (CR1.1)

MODE

0

X

Default Mode (default)

1

0

LUT Mode

1

1

LUT Adder Mode

Table 1. DS3501 Operating Modes