MIC2536
Micrel
Enable Input
Applications Information
EN must be driven logic high or logic low for a clearly defined
input. Floating the input may cause unpredictable operation.
ENshouldnotbeallowedtogonegativewithrespecttoGND.
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.
Printed Circuit Board Hot-Plug
The MIC2536 is an ideal inrush current-limiter for hot-plug
applications.Duetotheintegratedchargepump, theMIC2536
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.
Input or output transients must not exceed the absolute
maximum supply voltage (V
duration.
= 6V) even for a short
IN(max)
VIN
2.7V to 5.5V
Overcurrent Transients
MIC2536
ENA OUTA
The MIC2536 incorporates an internal circuit designed to
prevent FLG from being asserted due to transient inrush
current. Overcurrentevents<12ms(typ.)willnotassertFLG.
0.1µF to 1µF
FLGA
FLGB
ENB
IN
GND
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
OUTB
Figure 1. Supply Bypassing
selected to match the length of the transient, minus flag t .
D
MIC2536-2
1
2
3
4
8
OUTA
VCC
EN
7
6
FLGA
FLGB
ENB
IN
GND
0.1
µF
Backend
Function
to "Hot"
Receptacle
5
OUTB
CBULK
GND
Adaptor Card
Figure 2. Hot-Plug Card Application
V+
MIC2536
10k
R
Logic Controller
1
2
3
4
8
EN
OUTA
IN
7
OVERCURRENT
FLGA
FLGB
ENB
6
C
GND
OUTB
5
Figure 3. Transient Filter
March 2000
9
MIC2536
MICREL [ MICREL SEMICONDUCTOR ]
