
Philips Semiconductors
PIP202-12M
DC to DC converter powertrain
Product data
Rev. 01 — 15 July 2002
11 of 20
9397 750 10031
Koninklijke Philips Electronics N.V. 2002. All rights reserved.
To protect the control circuit from the transient voltages, the following precautions
must be taken. Refer to
Figure 12
.
1. The output stage ground (V
SSO
) must be connected to the decoupling capacitor
(C
in
) before joining the ground plane. Otherwise, the switching noise on V
SSO
will
couple into the control circuit ground (V
SSC
).
2. The control circuit supply must be filtered using a resistor-capacitor (RC) filter.
The values shown in
Figure 12
are suitable for most applications.
3. It is essential that the V
SSC
(signal ground) connection at the device is not
connected in the current return path between the V
SSO
(power ground)
connection at the device and the V
DDO
input capacitor.
4. It is also essential that the input to the V
DDC
(logic power) filter is not connected in
the current path between the V
DDO
(conversion power) connection at the device.
11.4 Switching frequency
A high operating frequency reduces the size and number of capacitors needed to
filter the output current, and also reduces the size of the output inductors. The
disadvantage, however is higher dissipation due to switching and MOSFET driver
losses. For example, doubling the operating frequency of the circuit in
Figure 11
from
500 kHz to 1 MHz would increase the power dissipation in each PIP202-12M from
4 W to 6 W, at an output current of 20 A in each PIP202-12M.
The maximum switching frequency is limited by thermal considerations, the
dissipation in the PIP202-12M device(s) and the thermal resistance from junction to
ambient.
11.5 Thermal design
The PIP202-12M has three pads on its underside. These are designated PAD1, PAD2
and PAD3 (
Figure 2
). PAD1 is connected to V
DDO
, PAD2 is connected to V
SSC
and
PAD3 is connected to VO. In addition to providing low inductance electrical
connections, these pads conduct heat away efficiently from the MOSFETs and
control IC to the printed-circuit board. The thermal resistance from junction to
printed-circuit board is approximately 5 K/W. In order to take full advantage of the low
Fig 12. External connection of power and signal lines.
VI
VDDC
VSSC
VO
VDDO
control circuit
supply (12 V)
output stage supply voltage
VSSO
CB
03ae27
output
100
nF
Lout
Cout
10
1
μ
F
Cin
signal ground
power ground
input voltage
from PWM controller