MAX3450E/MAX3451E/MAX3452E
BD (MAX3452E)
The push-pull bus detect (BD) output monitors VBUS
and asserts high if VBUS is greater than +4.0V. BD
asserts low if VBUS is less than +3.6V and the
MAX3452E enters sharing mode (Table 2).
V
TRM
An internal linear regulator generates the VTRM voltage
(+3.3V typ). VTRM derives power from VBUS (see the
Power-Supply Configurations
section). VTRM powers the
internal portions of the USB circuitry and provides the
pullup voltage for an external USB pullup resistor
MAX3450E/MAX3452E. Bypass VTRM to GND with a 1µF
ceramic capacitor as close to the device as possible.
Do not use VTRM to provide power to external circuitry.
D+ and D-
D+ and D- serve as bidirectional bus connections and
are ESD protected to ±15kV (Human Body Model). For
OE = low, D+ and D- serve as transmitter outputs. For
OE = high, D+ and D- serve as receiver inputs.
V
BUS
For most applications, VBUS connects to the VBUS ter-
minal on the USB connector. VBUS can also connect to
an external supply as low as +3.1V (MAX3450E and
MAX3451E). See the
Power-Supply Configurations
sec-
tion. Drive VBUS low to enable sharing mode. Bypass
VBUS to GND with a 0.1µF ceramic capacitor as close
to the device as possible.
External Components
External Resistors
Proper USB operation requires two external resistors,
each 24.3Ω±1%, 1/8W (or greater). Install one resistor
in series between D+ of the MAX3450E/MAX3451E/
MAX3452E and D+ on the USB connector. Install the
other resistor in series between D- of the MAX3450E/
MAX3451E/MAX3452E and D- on the USB connector
(see the
Typical Operating Circuit
).
The MAX3450E/MAX3452E requires an external 1.5kΩ
pullup resistor between VTRM and D+ or D- to set the
bus speed.
External Capacitors
The MAX3450E/MAX3451E/MAX3452E require three
external capacitors for proper operation. Bypass VLto
GND with a 0.1µF ceramic capacitor. Bypass VBUS to
GND with a 0.1µF ceramic capacitor. Bypass VTRM to
GND with a 1µF (min) ceramic capacitor. Install all capac-
itors as close to the device as possible.
Data Transfer
Transmitting Data to the USB
The MAX3450E/MAX3451E/MAX3452E transmit data to
the USB differentially on D+ and D-. VP and VM serve as
differential input signals to the driver (Tables 3a and 3b).
Receiving Data from the USB
To receive data from the USB, drive OE high and SUS
low. Differential data received by D+ and D- appears
as a differential logic signal at RCV. Single-ended
receivers on D+ and D- drive VP and VM, respectively
(Tables 4a and 4b).
±15kV ESD-Protected USB Transceivers
10 ______________________________________________________________________________________
Figure 2. Timing of VP and VM to D+ and D-