ic-wd iC-Haus, ic-wd Datasheet - Page 9

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

DIMENSIONING
The size of shunt R
I
the inductor L
the timing can be adapted to the application.
Normally the supply voltage range and the maximum
output current for VCC and VCCA is specified. Define
whether or not only intermittent flow is desired. The
maximum inductance L
lowing basis: In the worst situation, charging and dis-
charging process last exactly one period, which is the
case at minimum supply power. The cut-off current ad-
justs to I
that:
EXAMPLE
Specified are: VB = 18...36 V, I
The inductance selected is 150 µH, for example. Consequently, the maximum required cut-off current and the
shunt are found to be:
It is not always possible to dimension the circuit for in-
termittent flow, particularly not when high output cur-
rents are required with a low supply voltage. Permit-
ting continuous flow may prove conducive to higher
efficiency and less interference. The inductance se-
lected is to be higher than in the above formula; the
equations for maximum cut-off current and the shunt
can be used with the selected coil.
It is simplest to ascertain the correct dimensioning
by experiment in a test set-up (Evaluation Board).
The dimensioning shown in the block diagram (L
off
APPLICATIONS INFORMATION
iC-WD
SWITCHED-MODE DUAL VOLTAGE REGULATOR
. By varying this in combination with the value for
L
VH
off
max
= 2
=
2I
VH
L
A/B/C
I
, the power input, the efficiency and
max
L
T
max
min
(VH)
VB
(VH). From equation (1) it follows
VH
determines the cut-off current
I
off
max
can be estimated on the fol-
L
VB
VH
=
min
L
max
max
V
1
2 100 mA
=
sat
= 100 mA; the maximum inductance can be estimated to:
1 125 kHz
1
200 mA
VH
+
VH+V
1 75 kHz
150 H
1
R
VB
D
18 V 1.1 V 7.0 V
=
VH
400 mV
324 mA
30 V 1.1 V 7 V
1
Using equation (3) it is possible to determine the maxi-
mum cut-off current for intermittent flow. The maximum
value for VB must be inserted:
The shunt R
tion.
= 220 µH, R
mance throughout the entire specification range.
SELECTING THE COMPONENTS
Since the coil must not to become saturated, it should
be designed for maximum cut-off current. This can be
checked by testing the coil current with a current probe:
In the event of saturation the current rises much more
sharply than with low currents. A low internal resis-
tance of the coil reduces the losses and increases the
regulator’s efficiency. When the supply voltage is low,
I
off
1
1
max
1.2
+
VR
=
7.0 V +1.1 V
1
max
+
2 I
1
VB
VB
7 V +1.1 V
can be obtained from Fig. 2:
L
max
can be dimensioned with this informa-
= 1
1
= 178 H
(VH)
R
= 324 mA
VB
is suitable for maximum perfor-
T
L
=
max
VH
I
off
V
R
max
VB
max
max
Rev D1, Page 9/12
1
V
sat
1
VH
+
VH+V
1
D