MIC2027 Datasheet, PDF (14/16 Pages) Micrel Semiconductor – Quad USB Power Distribution Switch Preliminary Information

MIC2027/2077
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 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 MIC2027/77 are ideal inrush current-limiters for hot-plug
applications. Due to the integrated charge pump, the
MIC2027/77 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.
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 filter. Since this inrush
current exceeds the current-limit flag delay specification,
FLG will be asserted during this time. To prevent the logic
Micrel
controller from responding to FLG being asserted, an exter-
nal RC filter, as shown in Figure 3, 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_D(min) of the MIC2027/77.
Universal Serial Bus (USB) Power Distribution
The MIC2027/77 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). The requirement for
USB self-powered hubs is that the port must supply a mini-
mum 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
120µF 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.
Logic Controller
OVERCURRENT
V+
10k
R
C
MIC2027
1 _{FLGA FLGB} 16
2 _ENA
ENB ¹⁵
3 _{OUTA OUTB} 14
4 _{GND IN(A/B)} 13
5 _{IN(C/D) GND} 12
6 _{OUTC OUTD} 11
7 _ENC
END ¹⁰
8 _{FLGC FLGD} 9
Figure 3. Transient Filter
MIC2027/2077
14
June 2000