MIC2026 Micrel Semiconductor, MIC2026 Datasheet - Page 12

• Manufacturer Part Number: MIC2026
• Description: Dual-Channel Power Distribution Switch Preliminary Information
• Manufacturer: Micrel Semiconductor

MIC2026/2076
Applications Information
Supply Filtering
A 0.1 F to 1 F bypass capacitor positioned close to V
GND of the device is strongly recommended to control supply
transients. Without a bypass capacitor, an output short may
cause sufficient ringing on the input (from supply lead induc-
tance) to damage internal control circuitry.
Printed Circuit Board Hot-Plug
The MIC2026/76 are ideal inrush current-limiters for hot-plug
applications. Due to the integrated charge pump, the
MIC2026/76 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 ca-
pacitive loads by reducing inrush current. Figure 3 shows how
the MIC2076 may be used in a card hot-plug application.
In cases of extremely large capacitive loads (>400 F), the
length of the transient due to inrush current may exceed the
delay provided by the integrated filter. Since this inrush
current exceeds the current-limit delay specification, FLG will
be asserted during this time. To prevent the logic controller
from responding to FLG being asserted, an external RC filter,
as shown in Figure 4, can be used to filter out transient FLG
assertion. The value of the RC time constant should be
selected to match the length of the transient, less t
MIC2026/76.
MIC2026/2076
to "Hot"
Receptacle
GND
V
BUS
Cable
Logic Controller
OVERCURRENT
Figure 3. Hot-Plug Application
Figure 4. Transient Filter
D(min)
4.7
µF
IN
of the
and
1
2
3
4
USB Peripheral
MIC2026-2BM
ENA
FLGA
FLGB
ENB
12
C
10k
R
Universal Serial Bus (USB) Power Distribution
The MIC2026/76 is ideally suited for USB (Universal Serial
Bus) power distribution applications. The USB specification
defines 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 shows a
typical USB Host application that may be suited for mobile PC
applications employing USB. The requirement 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 notified. To support hot-plug
events, the hub must have a minimum of 120 F of bulk
capacitance, preferably low ESR electrolytic or tantulum.
Please 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
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.
V+
OUTA
OUTB
GND
IN
1
2
3
4
EN
FLGA
FLGB
ENB
8
5
7
6
MIC2026
OUTA
OUTB
GND
C
BULK
IN
BUS
C
BULK
8
5
7
6
, soft-start is necessary. Although the hub
Controller
Function
Function
USB
USB
USB
March 2000
Micrel