Reference Design of a 1-Wire® Bidirectional Voltage-Level Translator for 1.8V to 5V
By: Stewart Merkel
Abstract: Designers need open-drain logic to run at 1.8V at the 1-Wire master IO. Most 1-Wire slave devices cannot run at 1.8V. This application note presents an RD (reference design) of a circuit that translates from a 1.8V 1-Wire master to a 5V 1-Wire slave device. The RD is used for driving typical 1-Wire slave devices. The MAX3394E voltage-level translator is featured in the design.
Introduction
Devices such as FPGAs, microprocessors, the DS2482-100, and DS2480B are examples of 1-Wire master devices. The 1-Wire/iButton® slave devices are manufactured by Maxim and comprise an extensive family of parts that typically operate from 2.8V to 5.25V. The 1-Wire masters and slave devices have traditionally been 5V open-drain logic in the past.
Today designers need open-drain logic to run at 1.8V at the 1-Wire master IO. While most 1-Wire slave devices can run safely at 5V, most of those same devices cannot run at 1.8V. A bidirectional voltage-level translator circuit is needed to overcome this limitation. This RD (reference design) features the Maxim® MAX3394E, which is a bidirectional voltage-level translator for these applications.
Voltage-Level Translator
The MAX3394E is a dual-level translator available in an 8-pin, 3mm x 3mm TDFN package. It is ideal for driving high-capacitive loads, thanks to its internal slew-rate enhancement circuitry. 1-Wire slave devices often have capacitive loading greater than 500pF. The MAX3394E's VCC I/O pins are protected to ±15kV HBM (Human Body Model), which protects the 1-Wire master. The 1-Wire bus architectures often interface to the external world, making HBM essential. However, it is recommended that a DS9503P be added as ESD protection for the pullup resistor (R3), the optional strong pullup circuitry, and the 1-Wire slave device.
Application Circuit
The circuit in Figure 1 shows the MAX3394E used to perform bidirectional 1.8V to 5V voltage-level translation in an open-drain system.
Figure 1. Schematic of 1-Wire bidirectional voltage level translation from 1.8V to 5V. Note that the pins I/O VL and I/O VCC have a typical 10kΩ internal pullup.
The BOM (bill of materials) for this reference design is given in Table 1.
Table 1. Bill of Materials
Item
Quantity
Reference
Part
Manufacturer
Part Number
1
1
C1
1.0µF 0402
Panasonic
ECJ-0EB0J105M
2
2
C2, C3
0.1µF 0201
Panasonic
ECJ-ZEB0J104K
3
1
Q1
BSS84-7-F
Diodes, Inc/Zetex
BSS84-7-F
4
1
R1
33Ω 0201
Panasonic
ERJ-1GEJ330C
5
1
R2
10kΩ 0402
Panasonic
ERJ-2RKF1002X
6
1
R3
1kΩ 0402
Panasonic
ERJ-2RKF1001X
7
1
R4
2.2kΩ 0402
Panasonic
ERJ-2RKF2201X
8
2
CH1, CH2
TEST POINT
N/A
N/A
9
1
U1
MAX3394E
Maxim
MAX3394EETA+
Waveform Measurements/Test Results
The test results in Figures 2 through 5 were generated from the board built for evaluating the circuit.
Setup:
VL = 1.8V
VCC = 5.0V
CH1: 1-Wire master (OW_MASTER)
CH2: DS1920 (OW_SLAVE)
OW_SLAVE wire length: 2.4m, max.
Test results did not include the optional strong pullup circuitry in Figure 1.
Room temperature measurements only
Figure 2. The scope plot of a 1-Wire Reset shows the performance of the MAX3394E with presence pulse amplitude of no more than 250mV, lower than a typical 1-Wire master VIL maximum of 0.4V.
Figure 3. The scope plot of a 1-Wire Write, one timeslot with a clean tLOW1 < 15µs.
Figure 4. The scope plot of a 1-Wire Write, zero timeslot with 60µs < tLOW0 < 120µs.
Figure 5. The scope plot of a 1-Wire Read, zero timeslot with an active 1-Wire slave open-drain return and lower than a typical 1-Wire master VIL maximum of 0.4V.
Conclusion
This RD for 1.8V to 5V 1-Wire bidirectional logic-level translation drives typical 1-Wire slave devices. The design was built and then tested. The circuit schematic, BOM, and typical waveforms have been presented.
1-Wire is a registered trademark of Maxim Integrated Products, Inc. iButton is a registered trademark of Maxim Integrated Products, Inc.
Maxim is a registered trademark of Maxim Integrated Products, Inc.
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