ic-wd iC-Haus, ic-wd Datasheet - Page 6

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

Fig. 1 illustrates the operating principle of the switching
converter in simplified form. When the switch S closes
in steady-state condition, a linearly increasing charg-
ing current for the capacitor C
L
from the supply VB is stored in the coil’s magnetic field.
When the switch opens, the current flows via the diode
through the coil; its energy content is supplied to ca-
pacitor and load.
The block diagram on page 1 shows the iC-WD with
typical wiring. The internally generated clock pulse
closes the switch between VBR and VHL and the cur-
rent in the coil rises (charging phase). A control vari-
able,
teristic in Fig. 2, is obtained from the voltage VH and
the internal reference voltage and is compared to the
voltage at shunt R
current runs free via the integrated power diode (dis-
charge phase). When the next clock signal occurs, this
charging and discharging process is repeated. Fig. 6
shows the resulting current and voltage characteristics.
The current rise (t
voltage VH at the inductor. The following approxima-
tion applies:
V
V
The current dependencies of the saturation and diode
forward voltage (Fig. 3 and 4) are ignored here, as are
the losses due to the internal resistance of the coil.
The regulator operates at a constant frequency under
load. To prevent VH from rising without load, the os-
DESCRIPTION OF FUNCTIONS
iC-WD
SWITCHED-MODE DUAL VOLTAGE REGULATOR
VH
VB
sat
D
V
: Forward voltage of the free-wheeling diode
R
t
r
in addition to the load current in R
= VB
= L
transistor plus voltage drop at R
R
S
VB
V
VH
VD
R
Vsat
is reached, the switch opens and the coil
VB
Figure 1: Principle of operation
in accordance with the regulating charac-
VHL: Saturation voltage of the switching
A/B/C
V
I
off
sat
r
VB
) and fall times (t
. When the cut-off current I
LVH
V(LVH)
VH
VH
t
f
flows through the coil
= L
CVH
VH
f
VB
) depend on the
VH + V
L
. The energy
I
off
D
RL
VH
off
(1)
=
cillator frequency is reduced as the level of voltage VH
rises (Fig. 5).
Figure 3: Saturation voltage of switching transistor
1.5V
1.0V
0.5V
1.5V
1.0V
0.5V
Figure 4: Forward voltage of free-wheeling diode
Figure 2: Regulating characteristic
0V
500mV
400mV
300mV
200mV
100mV
0V
0A
0A
0V
5.5V
100mA
100mA
6.0V
200mA
200mA
max.
6.5V
300mA
300mA
typ.
Rev D1, Page 6/12
typ.
7.0V
V
400mA
400mA
R
= f (VH)
I(VHL)
I(VHL)
max.
typ.
VH
500mA
500mA
7.5V