MIC2536-2YM Micrel Inc, MIC2536-2YM Datasheet - Page 11

• Manufacturer Part Number: MIC2536-2YM
• Description: Dual USB Switch -
• Manufacturer: Micrel Inc
• Type: USB Switchr

Specifications of MIC2536-2YM

• Number Of Outputs: 2
• Rds (on): 700 mOhm
• Internal Switch(s): Yes
• Current Limit: 275mA
• Voltage - Input: 2.7 ~ 5.5 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 8-SOIC (3.9mm Width)
• Short Circuit Current Limit: 275mA
• Input Voltage Range: 2.7 to 5.5V
• Number Of Switches: Dual
• Operating Temp Range: -40C to 85C
• Operating Temperature Classification: Industrial
• Mounting: Surface Mount
• Pin Count: 8
• Package Type: SOP
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: 576-2165; MIC2536-2YM

MIC2536
Universal Serial Bus (USB) Power Distribution
Applications
The MIC2536 is ideally suited for USB (Universal Serial Bus)
power distribution applications. For Bus-Powered hubs, USB
requires that each downstream port be switched on or off
under control by the host. Up to four downstream ports each
capable of supplying 100mA at 4.4V minimum are allowed. In
additon, to reduce voltage droop on the upstream bus the hub
must consume only 100mA max at start-up until it enumer-
ates with the host prior to requesting more power. The same
requirements apply for bus-powered peripherals that have no
downstream ports. Figure 4 shows a two-port bus-powered
hub.
Bus-Powered Hub Port Switching
The USB Specification requires that bus-powered hubs imple-
ment port switching on either a ganged or individual basis.
The specific implementation must be reported via the Hub
Descriptor Status Register. Individual port switching has
advantages in that a fault on one port will not prevent the other
ports from operating correctly. In addition, a soft-start circuit
must be included in order to reduce inrush currents when the
switch is enabled. To meet this requirement, the MIC2536
has been designed to slowly ramp its output.
Suspend Current
Universal Serial Bus Specification places a maximum sus-
pend current requirement of 500 A on devices. For hubs,
Universal Serial Bus Specification Revision 1.1 clarifies this
issue. Revision 1.1, section 7.2.3, stipulates that the maxi-
mum suspend current for a configured hub is 2.5mA. This
number is derived by allocating 500 A for up to four down-
stream ports plus 500 A for the hub’s internal functions. A
nonconfigured hub is considered a low-power device and
March 2000
4.50V to 5.25V
Upstream V
100mA max.
V
D+
D–
GND
BUS
BUS
Data
4.7µF
MIC5207-3.3
IN
1.5k
GND
OUT
Figure 4. USB Two-Port Bus-Powered Hub
1µF
3.3V USB Controller
VIN
OVERCURRENT
OVERCURRENT
10k
ON/OFF
ON/OFF
10k
11
may not consume more than 500 A. In a nonconfigured state
all downstream devices will be switched off. In most cases, a
nonconfigured hub is not a practical state for the system.
Therefore, the 2.5mA specification is the applicable target
specification for the suspend state. In a bus-powered hub
with less than 4 ports, the hub may use the additional current
for internal functions.
The 500 A worst case suspend current must be further
divided among the data port termination resistors and internal
functions. The termination resistors will consume
3.6V
internal functions. Assuming 100 A as the maximum USB
controller suspend current, 170 A remains for the rest of the
system. The MIC2536 will consume 100 A maximum, leav-
ing a margin of 70 A.
USB Voltage Regulation
USB specifications require a minimum downstream voltage
supply of 4.40V from a bus-powered hub port (See Applica-
tion Note 17 for details). The USB specification allows for a
100mV drop across the hub, leaving 250mV for PCB, up-
stream cable, and connector resistance. Therefore, the on-
resistance of the switch for each port, not including PCB
resistance, must be <100mV
has a maximum on-resistance of 700m , which easily satis-
fies this requirement.
Overcurrent Indication
The USB Specification does not require bus-powered hubs to
report overcurrent conditions to the host, since the hub is
already current-limited at the upstream port. However, if it is
desired to report overcurrent, the Hub Descriptor Status
Register must be programmed to indicate this. The MIC2536
provides a flag output for this application.
ENA
FLGA
FLGB
ENB
(16.5K – 5%) = 230 A. This leaves only 270 A for
MIC2536-2
OUTA
OUTB
GND
IN
0.1µF
63µF
63µF
(Two Pair)
Controller
to USB
Data
Ferrite
Beads
100mA = 1 . The MIC2536
.01µF
.01µF
GND
GND
V
V
BUS
BUS
D+
D–
D+
D–
Port 1
Port 2
USB
USB
MIC2536
Micrel