Reference Design of a 1-Wire B

Reference Design of a 1-Wire Bidirectional Voltage-Level Translator for 1.8V to 5V

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.