ic-wd iC-Haus, ic-wd Datasheet - Page 10

• Manufacturer Part Number: ic-wd
• Description: Switched-mode Dual Voltage Regulator
• Manufacturer: iC-Haus

this internal resistance can determine the maximum
available output current (equation 4).
The EMI (electromagnetic interference) caused by the
coil should be taken into account. Toroidal core coils
have little noise radiation but are expensive and difficult
to install. Bar cores are reasonably priced and easy
to handle but emit higher radiation. Reasonably priced
RF chokes in the range of a few tens to a few hundreds
µH are suitable for modest EMI requirements.
Additional interference may be caused by decaying of
the voltage at VHL when the coil current drops to zero
(Fig. 6). Parasitic capacitances at VHL form an oscil-
lating circuit with the coil. This undesirable oscillating
circuit can be damped to an uncritical magnitude by
installing a resistor (
The selection of the backup capacitor C
lematic. Due to the series regulators, the ripple of
the intermediate voltage VH does not affect the out-
put voltages VCC and VCCA. Therefore a low capac-
itance level without special demands on the internal
resistance is sufficient. A combination of electrolytic
and ceramic capacitor (e.g. 4.7 µF/100 nF) is recom-
mended. Tantalum capacitors are also possible when
they are allowed to operate at AC amplitudes like the
residual ripple of voltage VH.
The stability of the series regulators is guaranteed for
the entire load range when the values for C
C
lected. The suppression of interference voltage is im-
proved by small capacitor series resistors. The combi-
nation of tantalum and ceramic capacitors is also rec-
ommended in this case. If one of the two outputs re-
mains open, its capacitor can be omitted.
iC-WD
SWITCHED-MODE DUAL VOLTAGE REGULATOR
VCCA
e.g.: Siemens Matsushita B78108-S1224-J (220 µH/250 mA, axial leads), TDK series NLC565050T-. . . (SMD),
TOKO series 10RF459-. . . (SMD shielded)
given in the electrical characteristics are se-
A/B/C
10 k ) parallel to the coil.
VH
is unprob-
VCC
and
To avoid feedback of interference from supply volt-
age VB onto output voltages VCC and VCCA, provide
blocking directly at pin VB. A combination of tantalum
and ceramic capacitors is also recommended in this
case (several µF/100 nF).
PRINTED CIRCUIT BOARD LAYOUT
The GND path from the switching regulator and from
each series regulator should be strictly separated to
avoid cross couplings. The neutral point of all GND
conductors is the GND connection at the iC-WD. It is
possible and not critical, however, to route the GND of
the supply VB and the base point of capacitor C
gether to the neutral point. The capacitor C
be very close to the pin VH however. To keep down the
decay at the open end of the coil (pin VHL), the capac-
itance of this connection should be low, that means the
connection should be short.
The blocking capacitors of supply voltage VB are to be
placed as close as possible to pins VB and GND. The
capacitors for the outputs VCC and VCCA should be
placed directly by the load and not directly by the iC
to also block interferences which are coupled via the
wiring to the load. A ground plane should be cut out
underneath the wiring of C
circuit conductor between VB, the shunt RVB, and VBR
should have a low impedance, since voltage drops in
the supply path change the effective size of the shunt
and reduce the maximum cut-off current.
The Thermal Pad (optional with the SO8) should be
connected to an appropriate copper area on the PCB.
It has proven to be advantageous to use thermal vias
directly underneath the iC to transfer the power dissi-
pation to a different layer, e.g. a ground plane.
VCC
and C
Rev D1, Page 10/12
VCCA
. The printed
VH
should
VH
to-