AD5172BRM2.5-RL7(RevA) View Datasheet(PDF) - Analog Devices

Part Name

Description

Manufacturer

AD5172BRM2.5-RL7
(Rev.:RevA)

256-Position One-Time Programmable Dual-Channel I2C Digital Potentiometers

Analog Devices 

AD5172/AD5173

ESD PROTECTION

All digital inputs—SDA, SCL, AD0, and AD1— are protected

with a series input resistor and parallel Zener ESD structures, as

shown in Figure 39 and Figure 40.

340Ω

LOGIC

GND

Figure 39. ESD Protection of Digital Pins

A,B,W

GND

Figure 40. ESD Protection of Resistor Terminals

TERMINAL VOLTAGE OPERATING RANGE

The AD5172/AD5173 VDD to GND power supply defines the

boundary conditions for proper 3-terminal digital potentiom-

eter operation. Supply signals present on terminals A, B, and W

that exceed VDD or GND are clamped by the internal forward-

biased diodes (see Figure 41).

VDD

A

W

B

GND

Figure 41. Maximum Terminal Voltages Set by VDD and GND

POWER-UP SEQUENCE

Because the ESD protection diodes limit the voltage compliance

at terminals A, B, and W (see Figure 41), it is important to

power VDD/GND before applying any voltage to terminals A, B,

and W. Otherwise, the diode will be forward biased such that

VDD is powered unintentionally and may affect the rest of the

user’s circuit. The ideal power-up sequence is GND, VDD, the

digital inputs, and then VA/VB/VW. The relative order of

powering VA, VB, VW, and the digital inputs is not important as

long as they are powered after VDD/GND.

POWER SUPPLY CONSIDERATIONS

To minimize the package pin count, both the one-time pro-

gramming and normal operating voltage supplies are applied to

the same VDD terminal of the AD5172/AD5173. The AD5172/

AD5173 employ fuse link technology that requires 6 V to blow

the internal fuses to achieve a given setting. The user is allowed

only one attempt at blowing the fuses. Once programming is

completed, power supply voltage must be reduced to the normal

2.7 V to 5.5 V operating range. Such dual voltage requirements

require isolation between the supplies. The fuse programming

supply (either an on-board regulator or rack-mount power sup-

ply) must be rated at 6 V and must be able to provide a 100 mA

transient current for 400 ms for successful one-time program-

ming. Once programming is complete, the 6 V supply must be

removed to allow normal operation at 2.7 V to 5.5 V at regular

microamp current levels. Figure 42 shows the simplest imple-

mentation using a jumper. This approach saves one voltage

supply, but draws additional current and requires manual

configuration.

6V

R1 50kΩ

CONNECT J1 HERE

FOR OTP

C1

C2

5V 1µF 1nF

R2 250kΩ

CONNECT J1 HERE

AFTER OTP

VDD

AD5172/

AD5173

Figure 42. Power Supply Requirement

An alternate approach in 3.5 V to 5.5 V systems adds a signal

diode between the system supply and the OTP supply for

isolation, as shown in Figure 43.

6V

3.5V–5.5V

APPLY FOR OTP ONLY

D1

C1

C2

1µF 1nF

VDD

AD5172/

AD5173

Figure 43. Isolate 6 V OTP Supply from 3.5 V to 5.5 V Normal Operating

Supply. The 6 V supply must be removed once OTP is completed.

Rev. A | Page 14 of 24

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