MAX14934–MAX14936 Four-Channel, 5kVRMS Digital Isolators
www.maximintegrated.com Maxim Integrated
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Detailed Description
The MAX14934–MAX14936 are a family of four-channel
digital isolators. The MAX14934–MAX14936 family transfers
digital signals between circuits with different power
domains. The devices are rated for 5kVRMS isolation voltage
for 60 seconds. This family of digital isolators offers low-
power operation, high electromagnetic interference (EMI)
immunity, and stable temperature performance through
Maxim’s proprietary process technology. The devices
isolate different ground domains and block high-voltage/
high-current transients from sensitive or human interface
circuitry.
The MAX14934–MAX14936 family offers three unidi-
rectional channel configurations for design convenience.
The MAX14934 features four channels transferring digital
signals in one direction for applications such as isolated
digital I/O. The MAX14935 has three channels transmitting
data in one direction and one channel transmitting in the
opposite direction, making it ideal for applications such as
isolated SPI and RS-485 communication. The MAX14936
provides further design flexibility with two channels in each
direction for isolated RS-232 or other applications.
Devices are available with data rates from DC up to 1Mbps
(A/D versions), 25Mbps (B/E versions), or 150Mbps (C/F
versions). Each device can also be ordered with default-
high or default-low outputs. This is the state an output
will go to when the input side of the device is unpowered.
The devices have two supply inputs, VDDA and VDDB,
that independently set the logic levels on either side of
the device. VDDA and VDDB are referenced to GNDA and
GNDB, respectively. The MAX14934–MAX14936 family
also features a refresh circuit to ensure output accuracy
when an input remains in the same state indefinitely.
Digital Isolation
The MAX14934–MAX14936 family provides galvanic
isolation for digital signals that are transmitted between
two ground domains. Up to 1200VPEAK of continuous
isolation is supported, as well as transient differences of
up to 5kVRMS for up to 60 seconds.
Level Shifting
The wide supply voltage range of both VDDA and VDDB
allows the MAX14934–MAX14936 family to be used for
level translation in addition to isolation. VDDA and VDDB
can be independently set to any voltage from 1.71V
to 5.5V. The supply voltage sets the logic level on the
corresponding side of the isolator.
Unidirectional Channels
Each channel of the MAX14934–MAX14936 is
unidirectional; it only passes data in one direction, as
indicated in the functional diagram. Each device features
four unidirectional channels that operate independently
with guaranteed data rates from DC up to 1Mbps (A/D
versions), 25Mbps (B/E versions), or 150Mbps (C/F
versions). The output driver of each channel is push-pull,
eliminating the need for pullup resistors. The outputs are
able to drive both TTL and CMOS logic inputs.
Startup and Undervoltage Lockout
The VDDA and VDDB supplies are both internally
monitored for undervoltage conditions. Undervoltage
events can occur during power-up, power-down, or during
normal operation due to a sagging supply voltage. When
an undervoltage condition is detected on either supply, all
outputs go to their default states regardless of the status
of the inputs (Table 1). Figure 2 through Figure 5 show the
behavior of the outputs during power-up and power-down.
Applications Information
Power-Supply Sequencing
The MAX14934–MAX14936 do not require special power-
supply sequencing. The logic levels are set independently
on either side by VDDA and VDDB. Each supply can be
present over the entire specified range regardless of the
level or presence of the other supply.
Power-Supply Decoupling
To reduce ripple and the chance of introducing data errors,
bypass VDDA and VDDB with 0.1µF ceramic capacitors to
GNDA and GNDB, respectively. Place the bypass capacitors
as close to the power-supply input pins as possible.