MIC2009YM6 TX Micrel Inc, MIC2009YM6 TX Datasheet - Page 15

• Manufacturer Part Number: MIC2009YM6 TX
• Manufacturer: Micrel Inc

Specifications of MIC2009YM6 TX

• Short Circuit Current Limit: 0.2 to 2A
• Input Voltage Range: 2.5 to 5.5V
• Operating Temp Range: -40C to 85C
• Operating Temperature Classification: Industrial
• Mounting: Surface Mount
• Pin Count: 6
• Package Type: SOT-23
• Lead Free Status / RoHS Status: Compliant

September 2005
Micrel
circuit takes over and holds I
for as long as the excessive load persists.
Once the MIC2019 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
ENABLE
Supply Filtering
A 0.1µF to 1µF bypass capacitor positioned close to the
V
practice and required for proper operation of the
MIC2009/2019. 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 the MIC2009/2019’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.
FAULT/
IN
V
Figure 9. Kickstart operation with varying load
I
OUT
OUT
and GND pins of MIC2009/2019 is both good design
0
Kickstart
100
Current Limiting
OUT
200
OUT
I
LIMIT
Time (ms)
300
Load Removed
OUT
, not I
0. Upon cooling, if the
to its programmed limit
KICKSTART
400
500
.
600
IN
15
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
In normal operation, the MIC2009/2019’s Ron is low
enough that no significant I
heating is most often caused by a short circuit — or very
heavy load — when a significant portion of the input
supply voltage appears across the MIC2009/2019’s
power MOSFET. Under these conditions, the heat
generated will exceed the package and PCB’s ability to
cool the device and thermal limiting will be invoked.
In Figure 10, die temperature is plotted against I
assuming a constant case temperature of 85°C. The
plots also assume a worst case R
temperature of 135°C. Under these conditions, it is clear
that an SOT-23 packaged device will be on the verge of
thermal shutdown (typically 145°C die temperature)
when operating at a load current of 1.25A. For this
reason, it is recommend that MLF package be used for
any
continuous currents of 1A or more.
Figure 10 assumes no backside contact is made to the
T
R
P
T
A
D
J
θ (J-A)
MIC2009/2019
= ambient temperature
=
160
140
120
100
=
80
60
40
20
J
Figure 10. Die temperature vs. Package
0
P
R
is the thermal resistance of the package
0.20 0.40 0.60 0.80 1.00 1.20 1.40 1.60 1.80 2.00
= junction temperature,
D
DS(ON)
Die Temperature vs. Iout for Tcase = 85°C
×
R
θ
(J
×
-
A)
(
I
OUT
+
designs
T
A
)
Iout - Amps
2
2
R heating occurs. Device
intending
ON
MIC2009/MIC2019
of 140 m Ω at a die
SOT-23
MLF
[phone]
M9999-092305
to
supply
OUT