ISL54226
8
FN7614.1
September 12, 2013
Detailed Description
The ISL54226 device is a dual single pole/single throw (SPST)
analog switch configured as a DPST that operates from a single
DC power supply in the range of 2.7V to 5.25V.
It was designed for switching a USB high-speed or full-speed
source in portable battery powered products. It is offered in small
TQFN and TDFN packages for use in MP3 players, cameras,
PDAs, cellphones, and other personal media players.
The part consists of two 3.5 high-speed SPST switches. These
switches have high bandwidth and low capacitance to pass USB
high-speed (480Mbps) differential data signals with minimal
edge and phase distortion. They can also swing from 0V to 3.6V
to pass USB full speed (12Mbps) differential data signals with
minimal distortion.
The part contains special overvoltage detection and protection
(OVP) circuitry on the COM+ and COM- pins. This circuitry acts to
open the USB in-line switches when the part senses a voltage on
the COM pins that is >3.8V (typ) or < -0.45V (typ). It isolates
voltages up to 5.25V and down to -5V from getting through to the
other side of the switch to protect the USB transceiver connected
at the D+ and D- pins.
The device has an open drain OE/ALM pin that can be driven
“Low” to open all switches. The OE/ALM pin gets internally pulled
“Low” whenever the part senses an overvoltage condition. The
pin must be externally pulled “High” with a 100k pull-up resistor
and monitored for a “Low” to determine when an overvoltage
condition has occurred.
The part has charger port interrupt detection circuitry (CP) on the
COM pins that outputs a Low on the INT pin to inform the
Controller or power management circuitry when entering a
dedicated charging port mode of operation. The charger mode
operation is initiated by driving the OE/ALM pin Low and
externally connecting the COM pins together which pulls the COM
lines High, triggering the INT pin to go Low and the SPST switches
to open.
The ISL54226 was designed for MP3 players, cameras,
cellphones, and other personal media player applications that
need to switch a high-speed or full-speed transceiver source. A
“Typical Application Block Diagram” of this functionality is shown
A detailed description of the SPST switches is provided in the
following section.
High-Speed (Dx) SPST Switches
The Dx switches are bi-directional switches that can pass USB
high-speed and USB full-speed signals when VDD is in the range
of 2.7V to 5.25V.
When powered with a 2.7V supply, these switches have a
nominal rON of 3.5 over the signal range of 0V to 400mV with a
rON flatness of 0.26. The rON matching between the switches
over this signal range is only 0.2
, ensuring minimal impact by
the switches to USB high-speed signal transitions. As the signal
level increases, the rON switch resistance increases. At signal
level of 3.3V, the switch resistance is nominally 9.8.
The Dx switches were specifically designed to pass USB 2.0
high-speed (480Mbps) differential signals in the range of 0V to
400mV. They have low capacitance and high bandwidth to pass
the USB high-speed signals with minimum edge and phase
distortion to meet USB 2.0 high-speed signal quality
specifications. See Figure
17 in the “Typical Performance Curves”
on
page 12 for USB High-speed Eye Pattern taken with switch in
the signal path.
The Dx switches can also pass USB full-speed signals (12Mbps) in
the range of 0V to 3.6V with minimal distortion and meet all the
USB requirements for USB 2.0 full-speed signaling. See Figure
18in the “Typical Performance Curves” on
page 13 for USB
Full-speed Eye Pattern taken with switch in the signal path.
The switches are active (turned ON) whenever the OE/ALM
voltage is logic “1” (High) and OFF when the OE/ALM voltage is
logic “0” (Low).
Overvoltage Protection (OVP)
The maximum normal operating signal range for the Dx switches
is from 0V to 3.6V. For normal operation the signal voltage
should not be allow to exceed these voltage levels or go below
ground by more than -0.3V.
However, in the event that a positive voltage >3.8V (typ) to 5.25V,
such as the USB 5V VBUS voltage, gets shorted to one or both of
the COM+ and COM- pins or a negative voltage < -0.45V (typ) to
-5V gets shorted to one or both of the COM pins, the ISL54226
has OVP circuitry to detect the over voltage condition and open
the SPST switches to prevent damage to the USB down-stream
transceiver connected at the signal pins (D-, D+).
The OVP and power-off circuitry allows the COM pins (COM-,
COM+) to be driven up to 5.25V while the VDD supply voltage is in
the range of 0V to 5.25V. In this condition the part draws <100A
of ICOMx and IDD current and causes no stress to the IC. In
addition the SPST switches are OFF and the fault voltage is
isolated from the other side of the switch.
The OE/ALM pin gets internally pulled low whenever the part
senses an overvoltage condition. The pin must be externally
pulled “High” with a 100k pull-up resistor and monitored for a
“Low” to determine when an overvoltage condition has occurred.
This output can be monitored by a Controller to indicate a fault
condition to the system.