MIC2536 Datasheet, PDF (9/12 Pages) Micrel Semiconductor – Dual USB Power Distribution Switch Preliminary Information

MIC2536
Applications Information
Supply Filtering
A 0.1µF to 1µF bypass capacitor from IN to GND, located at
the device, is strongly recommended to control supply tran-
sients. Without a bypass capacitor, an output short may
cause sufficient ringing on the input (from supply lead induc-
tance) to damage internal control circuitry.
Input or output transients must not exceed the absolute
maximum supply voltage (V_IN(max) = 6V) even for a short
duration.
V_IN
2.7V to 5.5V
MIC2536
ENA OUTA
FLGA
IN
FLGB GND
ENB OUTB
0.1µF to 1µF
Figure 1. Supply Bypassing
Micrel
Enable Input
EN must be driven logic high or logic low for a clearly defined
input. Floating the input may cause unpredictable operation.
EN should not be allowed to go negative with respect to GND.
Printed Circuit Board Hot-Plug
The MIC2536 is an ideal inrush current-limiter for hot-plug
applications. Due to the integrated charge pump, the MIC2536
presents a high impedance when off and slowly becomes a
low impedance as it turns on. This “soft-start” feature effec-
tively isolates power supplies from highly capacitive loads by
reducing inrush current. Figure 2 shows how the MIC2536
may be used in a hot-plug card application.
Overcurrent Transients
The MIC2536 incorporates an internal circuit designed to
prevent FLG from being asserted due to transient inrush
current. Overcurrent events <12ms (typ.) will not assert FLG.
In case of large capacitive loads (i.e., >430µF), 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 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, minus flag t_D.
V_CC
to "Hot"
Receptacle
GND
MIC2536-2
1 _EN
OUTA ⁸
0.1 ^{2 FLGA}
IN ⁷
µF _{3 FLGB GND 6}
4 _{ENB OUTB} 5
Adaptor Card
Backend
Function
C_BULK
Figure 2. Hot-Plug Card Application
Logic Controller
OVERCURRENT
V+
10k
R
C
MIC2536
1 _EN
OUTA ⁸
2 _FLGA
IN ⁷
3 _{FLGB GND} 6
4 _{ENB OUTB} 5
Figure 3. Transient Filter
March 2000
9
MIC2536