MAX15002
Dual-Output Buck Controller with
Tracking/Sequencing
27
Maxim Integrated
PWM Controller
Applications Information
Power Dissipation
The 40-pin TQFN thermally enhanced package can dis-
sipate up to 2.96W. Calculate power dissipation in the
MAX15002 as a product of the input voltage and the
total REG output current (I
REG
). I
REG
includes quies-
cent current (I
Q
) and the total gate drive current
(I
DREG_
):
P
D
= V
IN
x I
REG
I
REG
= I
Q
+ [f
SW
x (Q
G1
+ Q
G2
+ Q
G3
+ Q
G4
)]
where Q
G1
to Q
G4
are the total gate charge of the low-
side and high-side external MOSFETs. f
SW
is the
switching frequency of the converter and I
Q
is the qui-
escent current of the device at the switching frequency.
Use the following equation to calculate the maximum
power dissipation (P
DMAX
) in the chip at a given ambi-
ent temperature (T
A
):
P
DMAX
= 37 x (150 - T
A
)……….mW
PCB Layout Guidelines
Use the following guidelines to layout the switching
voltage regulator.
1) Place the IN, REG, and DREG_ bypass capacitors
close to the MAX15002.
2) Minimize the area and length of the high-current
loops from the input capacitor, upper switching
MOSFET, inductor, and output capacitor back to
the input capacitor negative terminal.
3) Keep the current loop formed by the lower switch-
ing MOSFET, inductor and output capacitor short.
4) Keep SGND and PGND isolated and connect them
at one single point close to the negative terminal of
the input filter capacitor.
5) Run the current-sense lines CSP_ and CSN_ close
to each other to minimize the loop area.
6) Avoid long traces between the REG/DREG_ bypass
capacitors, driver output of the MAX15002, MOS-
FET gates, and PGND. Minimize the loop formed
by the DREG_ bypass capacitors, bootstrap diode,
bootstrap capacitor, high-side driver output of the
MAX15002, and upper MOSFET gates.
7) Place the bank of output capacitors close to the
load.
8) Distribute the power components evenly across the
board for proper heat dissipation.
9) Provide enough copper area at and around the
switching MOSFETs, and inductor to aid in thermal
dissipation.
10) Connect the MAX15002 exposed pad to a large
copper plane to maximize its power dissipation
capability. Connect the exposed pad to SGND. Do
not connect the exposed pad to the SGND pin (pin
35) directly underneath the IC.
11) Use 2oz copper to keep the trace inductance and
resistance to a minimum. Thin copper PCBs com-
promise efficiency because high currents are
involved in the application. Also, thicker copper
conducts heat more effectively, thereby reducing
thermal impedance.
