Datasheet

MAX14978
SuperSpeed USB Passive Switch
(Low/Full/Hi/SuperSpeed)
12
Detailed Description
The MAX14978 is ideal for SuperSpeed USB and low/
full/Hi-Speed (1.5/12/480Mbps) USB switching applica-
tions. The low V
IH
threshold of the device permits it to
be used with logic levels as low as 1.4V. The device’s
Hi-Speed USB analog switches are based on a charge-
pump-assisted n-channel architecture and operate with
36FA (typ) quiescent current. The device features dual
digital control inputs (SEL_) to switch Hi-Speed USB and
SuperSpeed USB signal paths separately.
Digital Control Inputs (SEL1, SEL2)
The device’s provides dual digital control inputs (SEL1,
SEL2) to select the signal path between the COM_ and
NO_ or NC_ channels. Drive SEL1 and SEL2 rail-to-rail
to minimize power consumption. See the Functional
Diagram/Truth Table.
Analog-Signal Levels
The device’s switches are bidirectional, allowing NO_,
NC_, and COM_ to be configured as either inputs or
outputs.
The Hi-Speed USB switches are equipped with a charge-
pump-assisted n-channel architecture that allows the
switch to pass analog signals that exceed V
CC
up to the
overvoltage fault-protection threshold. This allows USB
signals that exceed V
CC
to pass, allowing compliance
with USB requirements for voltage levels.
The SuperSpeed USB switches accept signals on the
COM_, NO_, and NC_ channels within a range of -0.1V
to (V
DD
- 1.2V). Signals on the COM_+ channels are
routed to either the NO_+ or NC_+ channels, and signals
on the COM_- channels are routed to either the NO_- or
NC_- channels.
Overvoltage Fault Protection
The device features overvoltage fault protection on
COMD_. Fault protection prevents these switches from
being damaged due to shorts to the USB VBUS voltage
rail. Fault protection protects the switch and USB trans-
ceiver from damaging voltage levels. When voltages
on COMD_ exceed the fault-protection threshold (V
FP
),
COMD_, NCD_ and NOD_ are high impedance.
Enable Input
The device features a shutdown mode for the Hi-Speed
USB analog switches that reduces the V
CC
quiescent
current to 0.1FA (typ) and places COMD+ and COMD-
in high impedance. Drive EN high to place the Hi-Speed
USB analog switches in shutdown mode, and drive EN
low for normal operation.
Applications Information
USB Switching
The device’s analog switches are fully compliant with the
USB 2.0 and USB 3.0 specifications. The low on-resis-
tance and low on-capacitance of these switches make
them ideal for high-performance switching applications.
The device is ideal for routing USB data lines and for
applications that require switching between multiple
USB hosts or devices. The device’s Hi-Speed USB ana-
log switches also feature overvoltage fault protection to
guard systems against shorts to the USB VBUS voltage
rail that is required for all Hi-Speed USB applications.
Extended ESD Protection
As with all Maxim devices, ESD protection structures are
incorporated on all pins to protect against electrostatic
discharges encountered during handling and assembly.
COMD+ and COMD- are further protected against static
electricity. Maxim’s engineers have developed state-of-
the-art structures to protect these pins against ESD up
to Q15kV without damage. The ESD structures withstand
high ESD in normal operation and when the device is
powered down. After an ESD event, the device continues
to function without latchup.
The device is characterized for protection to the follow-
ing limits:
• Q15kV using Human Body Model
• Q15kV using IEC 61000-4-2 Air Gap Discharge method
• Q8kV using IEC 61000-4-2 Contact Discharge method
Note: High ESD performance is only applicable to the
Hi-Speed USB section of the switch. The SuperSpeed
USB section is rated to Q6kV HBM.