MIC2004 Micrel, MIC2004 Datasheet - Page 14

• Manufacturer Part Number: MIC2004
• Description: Fixed Current Limit Power Distribution Switch
• Manufacturer: Micrel

August 2005
Micrel
Kickstart (MIC2014)
Kickstart allows brief current surges to pass to the load
before the onset of normal current limiting, which
permits dynamic loads to draw bursts of energy without
sacrificing system safety.
Functionally, Kickstart is a forced override of the normal
current limiting function provided by MIC2014. The
Kickstart period is governed by an internal timer which
allows current to pass unimpeded to the load for 128ms
and then normal (primary) current limiting goes into
action.
During Kickstart a secondary current limiting circuit is
monitoring output current to prevent damage to the
MIC2014, as a hard short combined with a robust power
supply can result in currents of many tens of amperes.
This secondary current limit is nominally set at 4 Amps
and reacts immediately and independently of the
Kickstart period. Once the Kickstart timer has finished its
count the primary current limiting circuit takes over and
holds I
excessive load persists.
Once MIC2014 drops out of current limiting the Kickstart
timer initiates a lock-out period of 128ms such that no
further bursts of current above the primary current limit,
will be allowed until the lock-out period has expired.
Kickstart may be over-ridden by the thermal protection
circuit and if sufficient internal heating occurs, Kickstart
will be terminated and I
load is still present I
OUT
1.2
1.0
0.8
0.6
0.4
0.2
to its programmed limit for as long as the
0
0
Normalized Output Current
vs. Output Voltage (2.5V)
0.5
OUTPUT VOLTAGE (V)
OUT
Figure 7.
1.0
OUT
I
LIMIT
1.5
, not I
0. Upon cooling, if the
2.0
KICKSTART
2.5
3.0
.
14
ENABLE
Supply Filtering
A 0.1µF to 1µF bypass capacitor positioned close to the
V
practice
MIC2004/2014. This will control supply transients and
ringing. Without a bypass capacitor, large current surges
or an output short may cause sufficient ringing on V
(from supply lead inductance) to cause erratic operation
of MIC2004/2014’s control circuitry. Good quality, low
ESR capacitors, such as Panasonic’s TE or ECJ series,
are suggested.
When bypassing with capacitors of 10µF and up, it is
good practice to place a smaller value capacitor in
parallel with the larger to handle the high frequency
components of any line transients. Values in the range
of 0.01µF to 0.1µF are recommended. Again, good
quality, low ESR capacitors should be chosen.
Power Dissipation
Power dissipation depends on several factors such as
the load, PCB layout, ambient temperature, and supply
voltage. Calculation of power dissipation can be
accomplished by the following equation:
To relate this to junction temperature, the following
equation can be used:
Where: T
FAULT/
IN
V
I
and GND pins of MIC2004/2014 is both good design
OUT
OUT
P
T
D
J
0
=
=
J
P
R
Kickstart
and
= junction temperature,
D
DS(ON)
×
100
R
θ
required
(J
Current Limiting
Figure 9. Kickstart
×
-
A)
(
I
200
OUT
+
T
A
)
2
Time (ms)
for
Load Removed
300
proper
400
MIC2004/MIC2014
www.DataSheet4U.com
[phone]
operation
M9999-080305
500
600
of
IN