Datasheet

June 2010 11 MIC2025/2075
MIC2025/2075 Micrel, Inc.
Applications Information
Supply Filtering
A 0.1µF to 1µF bypass capacitor positioned close to V
IN
and
GND of the device is strongly recommended to control sup-
ply transients. Without a bypass capacitor, an output short
may cause sufcient ringing on the input (from supply lead
inductance) to damage internal control circuitry.
Printed Circuit Board Hot-Plug
The MIC2025/75 are ideal inrush current-limiters suitable for
hot-plug applications. Due to the integrated charge pump,
the MIC2025/75 presents a high impedance when off and
slowly becomes a low impedance as it turns on. This “soft-
start” feature effectively isolates power supplies from highly
capacitive loads by reducing inrush current during hot-plug
events. Figure 3 shows how the MIC2075 may be used in a
hot-plug application.
In cases of extremely large capacitive loads (>400µF), the
length of the transient due to inrush current may exceed the
delay provided by the integrated lter. Since this inrush cur-
rent exceeds the current-limit delay specication, FLG will
be asserted during this time. To prevent the logic controller
from responding to FLG being asserted, an external RC lter,
as shown in Figure 4, can be used to lter out transient FLG
assertion. The value of the RC time constant will be selected
to match the length of the transient.
Universal Serial Bus (USB) Power Distribution
The MIC2025/75 is ideally suited for USB (Universal Serial
Bus) power distribution applications. The USB specication
denes power distribution for USB host systems such as
PCs and USB hubs. Hubs can either be self-powered or
bus-powered (that is, powered from the bus). Figure 5 below
shows a typical USB Host application that may be suited for
mobile PC applications employing USB. The requirements
for USB host systems is that the port must supply a minimum
of 500mA at an output voltage of 5V ±5%. In addition, the
output power delivered must be limited to below 25VA. Upon
an overcurrent condition, the host must also be notied. To
support hot-plug events, the hub must have a minimum of
120µF of bulk capacitance, preferably low-ESR electrolytic
or tantulum. Refer to Application Note 17 for more details on
designing compliant USB hub and host systems.
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 addition, to reduce voltage droop on
the upstream V
BUS
, soft-start is necessary. Although the hub
can consume up to 500mA from 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 6 shows a bus-powered hub.
MIC2025-2
EN OUT
FLG
GND OUT
NC
IN
1 8
2 7
3 6
5
NC
4
Adaptor Card
to "Hot"
Receptacle
C
BULK
GND
V
CC
0.1
µF
Backend
Function
Figure 3. Hot Plug Application
10k
V+
MIC2025
EN OUT
FLG
GND OUT
NC NC
IN
1 8
2 7
3 6
4 5
OVERCURRENT
Logic Controller
R
C
Figure 4. Transient Filter