MAX15020
2A, 40V Step-Down DC-DC Converter with
Dynamic Output-Voltage Programming
16 ______________________________________________________________________________________
Power Dissipation
The MAX15020 is available in a thermally enhanced
package and can dissipate up to 2.7W at T
A
= +70°C.
When the die temperature reaches +160°C, the part
shuts down and is allowed to cool. After the parts cool
by 20°C, the device restarts with a soft-start.
The power dissipated in the device is the sum of the
power dissipated from supply current (P
Q
), transition
losses due to switching the internal power MOSFET
(P
SW
), and the power dissipated due to the RMS cur-
rent through the internal power MOSFET (P
MOSFET
).
The total power dissipated in the package must be lim-
ited such that the junction temperature does not
exceed its absolute maximum rating of +150°C at maxi-
mum ambient temperature. Calculate the power lost in
the MAX15020 using the following equations:
The power loss through the switch:
R
ON
is the on-resistance of the internal power MOSFET
(see the
Electrical Characteristics
table).
The power loss due to switching the internal MOSFET:
where t
R
and t
F
are the rise and fall times of the internal
power MOSFET measured at LX.
The power loss due to the switching supply current
(I
SW
):
P
Q
= V
IN
x I
SW
The total power dissipated in the device is:
P
TOTAL
= P
MOSFET
+ P
SW
+ P
Q
PCB Layout and Routing
Use the following guidelines to layout the switching
voltage regulator:
1) Place the IN and DVREG bypass capacitors close
to the MAX15020 PGND pin. Place the REG
bypass capacitor close to the GND pin.
2) Minimize the area and length of the high-current
loops from the input capacitor, switching MOSFET,
inductor, and output capacitor back to the input
capacitor negative terminal.
3) Keep short the current loop formed by the switch-
ing MOSFET, Schottky diode, and input capaci-
tor.
4) Keep GND and PGND isolated and connect them
at one single point close to the negative terminal
of the input filter capacitor.
5) Place the bank of output capacitors close to the
load.
6) Distribute the power components evenly across
the board for proper heat dissipation.
7) Provide enough copper area at and around the
MAX15020 and the inductor to aid in thermal dis-
sipation.
8) Use 2oz copper to keep the trace inductance and
resistance to a minimum. Thin copper PCBs can
compromise efficiency since high currents are
involved in the application. Also, thicker copper
conducts heat more effectively, thereby reducing
thermal impedance.
9) Place enough vias in the pad for the EP of the
MAX15020 so that the heat generated inside can
be effectively dissipated by PCB copper.
