LTM4602 データシートの表示（PDF） - Linear Technology
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LTM4602 Datasheet PDF : 24 Pages
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LTM4602
APPLICATIONS INFORMATION
7
6
5
4
3
2
1
0LFM
200LFM
400LFM
0
50
60
70
80
90 100
TEMPERATURE (°C)
4602 F16
Figure 16. 12V to 3.3V, No Heat Sink
7
6
5
4
3
2
1
0LFM
200LFM
400LFM
0
50
60
70
80
90 100
TEMPERATURE (°C)
4602 F16
Figure 17. 12V to 3.3V, BGA Heat Sink
Table 3. 1.5V Output
AIR FLOW (LFM)
0
200
400
0
200
400
HEAT SINK
None
None
None
BGA Heat Sink
BGA Heat Sink
BGA Heat Sink
θJA (°C/W)
15.2
14
12
13.9
11.3
10.25
Table 4. 3.3V Output
AIR FLOW (LFM)
0
200
400
0
200
400
HEAT SINK
None
None
None
BGA Heat Sink
BGA Heat Sink
BGA Heat Sink
θJA (°C/W)
15.2
14.6
13.4
13.9
11.1
10.5
Layout Checklist/Example
The high integration of the LTM4602 makes the PCB board
layout very simple and easy. However, to optimize its electri-
cal and thermal performance, some layout considerations
are still necessary.
• Use large PCB copper areas for high current path,
including VIN, PGND and VOUT. It helps to minimize the
PCB conduction loss and thermal stress.
• Place high frequency ceramic input and output capaci-
tors next to the VIN, PGND and VOUT pins to minimize
high frequency noise.
• Place a dedicated power ground layer underneath
the unit.
• To minimize the via conduction loss and reduce module
thermal stress, use multiple vias for interconnection
between top layer and other power layers.
• Do not put vias directly on pads unless they are capped.
16
• Use a separated SGND ground copper area for com-
ponents connected to signal pins. Connect the SGND
to PGND underneath the unit.
Figure 18 gives a good example of the recommended
layout.
LTM4602 Frequency Adjustment
The LTM4602 is designed to typically operate at 850kHz
across most input and output conditions. The control ar-
chitecture is constant on time valley mode current control.
The fADJ pin is typically left open or decoupled with an
optional 1000pF capacitor. The switching frequency has
been optimized to maintain constant output ripple over the
operating conditions. The equations for setting the operat-
ing frequency are set around a programmable constant on
time. This on time is developed by a programmable current
into an on board 10pF capacitor that establishes a ramp
that is compared to a voltage threshold equal to the output
voltage up to a 2.4V clamp. This ION current is equal to:
ION = (VIN – 0.7V)/110k, with the 110k onboard resistor
4602fa
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