AD5170 Analog Devices, AD5170 Datasheet - Page 14

• Manufacturer Part Number: AD5170
• Description: 256-Position Two-Time Programmable I2C Digital Potentiometer
• Manufacturer: Analog Devices

AD5170
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 34 and Figure 35.
TERMINAL VOLTAGE OPERATING RANGE
The AD5170 V
conditions for proper 3-terminal digital potentiometer opera-
tion. Supply signals present on Terminals A, B, and W that
exceed V
biased diodes (see Figure 36).
POWER-UP SEQUENCE
Because the ESD protection diodes limit the voltage compliance
at Terminals A, B, and W (see Figure 36), it is important to
power V
and W. Otherwise, the diode will be forward biased such that
V
user’s circuit. The ideal power-up sequence is GND, V
digital inputs, and then V
powering V
long as they are powered after V
DD
is powered unintentionally and may affect the rest of the
Figure 36. Maximum Terminal Voltages Set by V
DD
DD
/GND before applying any voltage to Terminals A, B,
or GND will be clamped by the internal forward-
A
, V
Figure 35. ESD Protection of Resistor Terminals
DD
B
Figure 34. ESD Protection of Digital Pins
, V
to GND power supply defines the boundary
W
, and the digital inputs is not important as
A, B, W
GND
GND
340Ω
A
/V
B
/V
LOGIC
DD
W
. The relative order of
/GND.
V
A
W
B
GND
DD
DD
and GND
DD
, the
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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 V
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 operating range
of 2.7 V to 5.5 V. Such dual voltage requirements require
isolation between the supplies. The fuse programming supply
(either an on-board regulator or rack-mount power supply)
must be rated at 6 V and must be able to provide a 100 mA
transient current for 400 ms in order for successful one-time
programming. 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 37 shows the simplest
implementation using a jumper. This approach saves one
voltage supply but draws additional current and requires
manual configuration.
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 38.
Figure 38. Isolate 6 V OTP Supply from 3.5 V to 5.5 V Normal Operating
3.5V–5.5V
Supply. The 6 V supply must be removed once OTP is completed.
6V
R1
R2
DD
6V
50kΩ
250kΩ
terminal of the AD5170. The AD5170 employs
APPLY FOR OTP ONLY
Figure 37. Power Supply Requirement
5V
D1
CONNECT J1 HERE
CONNECT J1 HERE
1µF
1µF
C1
C1
AFTER OTP
FOR OTP
1nF
1nF
C2
C2
V
V
DD
DD
AD5170
AD5170