Detailed Description
USB OTG is an emerging USB standard that enables
devices to talk in a peer-to-peer manner on a USB bus.
OTG allows peripherals and mobile devices such as
PDAs, cellular phones, and digital cameras to be
attached directly to one another without requiring a
PC host.
The MAX3355E integrates a charge pump and compara-
tors to enable a system with an integrated USB OTG
dual-role transceiver to function as a USB OTG dual-role
device. The MAX3355E’s internal charge pump supplies
V
BUS
power and signaling as defined in On-the-Go
Supplement: USB 2.0, Revision 1.0. The MAX3355E’s
internal level-detection comparators monitor important
V
BUS
voltages needed to support SRP and HNP.
Charge Pump
The MAX3355E provides power for the V
BUS
line using
an internal charge pump. The charge pump provides
an OTG-compliant output on V
BUS
while sourcing 8mA
load current. The charge pump can be powered from
voltages between +2.6V and +5.5V. A 0.1µF flying
capacitor, connected between C+ and C-, and a 1µF
(min) decoupling reservoir capacitor on V
BUS
are
required for proper operation.
The charge pump is active if OFFVBUS is connected to
V
L
and the MAX3355E is configured as device A (ID_IN
connected to GND). To minimize V
BUS
ripple, select a
reservoir capacitor value between 1µF and 6.8µF. The
charge-pump output is protected from short-circuit con-
ditions on V
BUS
by an internal current clamp that limits
the V
BUS
current to 200mA.
Current Generator
An internal current generator injects up to 600µA of cur-
rent onto the V
BUS
line. The current generator is stable
over the supply voltage variation. The current generator
is connected to V
BUS
when OFFVBUS and SHDN are 1
and ID_IN is open. It remains connected for t
VBUSCHRG
or until the V
BUS
line voltage exceeds the lower of V
CC
and 4.82V.
Comparators
The MAX3355E contains internal comparators for moni-
toring the V
BUS
voltage. The status of V
BUS
is summa-
rized in two status outputs: STATUS1 and STATUS2.
The status outputs can be used to negotiate for the
USB OTG bus. The V
BUS
status is conveyed according
to Table 1. While in shutdown mode, the STATUS2 out-
put can be used to indicate V
BUS
voltage (Table 2).
Device ID
Configure the MAX3355E as device A by connecting
ID_IN to GND and as device B by leaving ID_IN open
(Table 3). ID_IN is level translated to V
L
and provided
as an output at ID_OUT. V
L
sets the logic output high
level. ID_IN is internally pulled up to V
CC
.
MAX3355E
±15kV ESD-Protected USB On-the-Go
Charge Pump and Comparators in UCSP
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