Datasheet

MAX3353E
The MAX3353E also has a special feature that allows it
to control the timing of the V
BUS
pulse.
Since an OTG device could be plugged into a PC, the
V
BUS
pulse must be particularly well controlled to prevent
damage to a PC host. For this reason, V
BUS
pulsing is
done by turning on and off a current source. The V
BUS
pulse must be timed so it drives a 13µF load (when it is
connected to the A Device) to a voltage greater than
2.1V, and it drives a >96µF load (when it is connected to
a standard PC) to a voltage less than 2.0V.
Firmware can control the current source and the timing
of the V
BUS
pulse through the V
BUS_CHG2
control bit.
The MAX3353E also has the capability to time the pulse
itself. Firmware initiates the self-timed V
BUS
pulse by
setting the V
BUS_CHG1
control bit to 1.
The internal timer and current generator guarantee that
the V
BUS
voltage goes above 2.1V if C
VBUS
< 13µF
within 90ms and stands below 2.0V if C
VBUS
>
96µF.
Once the time has elapsed, if another V
BUS
pulse is
required, it is necessary to clear the V
BUS_CHG1
bit and
then set it again.
Note: SRP V
BUS
pulsing and its associated current gen-
erator work only if the MAX3353E is not in shutdown.
Data-Line Pullup and Pulldown Resistance
For OTG operation, D+ and D- are connected to switch-
able pulldown resistors (host) and switchable pullup
resistors (peripheral). Data-line pullup/pulldown resistors
are individually controlled through data bits 4 through 7 in
control register 1. Two 15kΩ pulldown resistors allow the
device to be set as a host and are asserted by bits 6 and
7. The 1.5kΩ pullup resistor is applied to the data lines
through SW1 and SW2, which are controlled by bits 4 and
5. D+ pullup has higher priority to avoid direct connection
of D+ and D-. Each of the control bits controls a designat-
ed switch; therefore, pullup and pulldown switches can
be asserted at the same time. A simplified schematic of
the switching network is shown in Figure 3.
The bidirectional D+ and D- lines are ESD protected to
±15kV, reducing external components in many applications.
Applications Information
2-Wire I
2
C-Compatible Serial Interface
A register file that interfaces to the control logic uses a
simple 2-wire interface operating up to 400kHz to con-
trol the various switches and modes.
Serial Addressing
The MAX3353E operates as a slave that sends and
receives control and status signals through an I
2
C-
compatible 2-wire interface. The interface uses a serial
data line (SDA) and a serial clock line (SCL) to achieve
USB On-the-Go Charge Pump with Switchable
Pullup/Pulldown Resistors
10 ______________________________________________________________________________________
76543210
0000
CONTROL REGISTER 1
0000
15kΩ
1.5kΩ
V
TRM
SW4
15kΩ
SW3
SW2 SW1
D+
D-
GND
NOTE: SWITCHES ARE SHOWN IN THEIR DEFAULT
(POWER-ON) POSITIONS. A "1" CLOSES A SWITCH.
BIT 4
0
0
1
BIT 5
0
1
0
SW1
OPEN
OPEN
CLOSED
SW2
OPEN
CLOSED
OPEN
1 1 CLOSED OPEN
DEFAULT
(POWER ON)
VALUES
Figure 3. Pullup and Pulldown Resistors Network
SCL
SDA
t
F
t
LOW
t
SU:DAT
t
HD:STA
t
HD:DAT
t
SU:STO
t
BUF
t
HIGH
t
R
Figure 4. 2-Wire Serial Interface Timing Details