MIC2551A-2.5_10 Datasheet, PDF (8/10 Pages) Micrel Semiconductor – USB Transceiver

MIC2551A-2.5
Power Supply Configuration
The MIC2551A can be set up for different power supply
configurations which modify the behavior of the device. Both
V_BUS and V_IF have special thresholds that detect when they
are either removed or grounded. Table 1 depicts the behavior
under the different power supply configuration scenarios that
are explained below.
Normal Mode
V_BUS is connected to the 5.0V USB bus voltage and V_IF is
connected to a supply voltage in the range of 1.6V to 3.6V. In
this case V_TRM supplies a 3.3V voltage for powering the speed
select resistor via V_PU depending on the state of CON pin.
Disconnect Mode
V_IF is connected to a supply in a range of 1.6V to 3.6V and
V_BUS is open or grounded. If V_BUS is opened while transmitting,
the data lines (D+, D–) have sharing capability and may be
driven with external devices up to approximately 3.6V if and
only if SUSPEND is enabled (SUS = 1). With V_BUS ground,
D+, D– sharing mode is not permitted.
Disable Mode
V_BUS is connected to the 5.0V USB bus voltage and V_IF is
open. All logic controlled inputs become high impedances,
thus minimal current will be supplied by V_IF if the input pins
are pulled up to an external source.
Alternate Power Supply Configuration Option
I/O Interface Using 3.3V
In systems where the I/O interface utilizes a 3.3V USB con-
troller, an alternate solution is shown in Figure 7. No extra
components are required; however, the load on V_TRM must
not exceed 10mA.
3.3V
MIC2551A
V_DD
VIF
VBUS
USB
Controller
I/O
V_P/V_M/
VTRM
RCV/OE#
VBUS
Micrel, Inc.
Speed
The speed pin (SPD) sets D+/D– output edge rates by in-
creasing or decreasing biasing current sources within the
output drivers. For low speed, SPD = 0. For full speed, SPD
= 1. By setting SPD = 0 during idle periods, in conjunction
with suspend (SUS), the lowest quiescent current can be
obtained. However, designers must provide a 300ns delay
between changing SPD from 0 to 1 and transmission of data
at full speed. This delay ensures the output drivers have ar-
rived at their proper operating conditions. Failure to do so
can result in leading edge distortion on the first few data bits
transmitted.
Non-Multiplexed Bus
In order to save pin count for the USB logic controller interface,
the MIC2551A was designed with V_P and V_M as bi-directional
pins. To interface the MIC2551A with a non-multiplexed data
bus, resistors can be used for low cost isolation, as shown
in Figure 8.
USB Logic
Controller
(SIE)
MIC2551A
V_P
V_P
10k
V_PO
V_M
V_M
10k
V_MO
Figure 8.  MIC2551A Interface to
Non-Multiplexed Data Bus
Figure 7.  I/O Interface Using 3.3V
Signal Amplitude Respective to V_IF
When operating the MIC2551A, it is necessary to provide
input signals which do not exceed V_IF + 0.3V.
Suspend
When the suspend pin (SUS) is high, power consumption is
reduced to a minimum. V_TRM is not disabled. RCV, V_P and
V_M are still functional to enable the device to detect USB
activity. For minimal current consumption in suspend mode,
it is recommended that OE# = 1, and SPD = 0.
M9999-030810
8
March 2010