Micrel

MIC2003/MIC20013

October 2005

14

M9999-102605

0

0.2

0.4

0.6

0.8

1.0

1.2

0

0.5 1.0 1.5

2.0 2.5 3.0

OUTPUT VOLTAGE (V)

Normalized Output Current

vs. Output Voltage (2.5V)

Figure 7.

Kickstart (MIC2013)

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 MIC2013. 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

MIC2013, 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

excessive load persists.

Once MIC2013 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

0. Upon cooling, if the

0

Time (ms)

100

200

300

400

500

600

Kickstart

Current Limiting

Load Removed

Figure 9. Kickstart

Supply Filtering

A 0.1µF to 1µF bypass capacitor positioned close to the

practice

and

required

for

proper

operation

of

MIC2003/2013. This will control supply transients and

ringing. Without a bypass capacitor, large current surges

(from supply lead inductance) to cause erratic operation

of MIC2003/2013’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:

(

OUT

DS(ON)

D

I

R

P

×

=

To relate this to junction temperature, the following

equation can be used:

A

A)

-

(J

D

J

T

R

P

T

+

×

=

θ