IC-DC_17 Datasheet, PDF (12/19 Pages) IC-Haus GmbH – 2-CHANNEL BUCK/BOOST DC/DC CONVERTER

iC-DC
2-CHANNEL BUCK/BOOST DC/DC CONVERTER
Rev B1, Page 12/19
Intermittent flow / continuous flow
If the inductor is recharged in the next cycle before the
coil current has run free, there is no gap in the current.
This continuous flow occurs when the supply voltage is
low or the load current high.
If the charge and discharge processes are concluded
within one clock cycle and the coil current drops to zero
each time, intermittent flow prevails. This is the case
when the supply voltage is sufficiently high or the load
current sufficiently low.
When no more current flows through the coil, after fly-
back in intermittent operation both ends of the inductor
are switched to ground. This prevents the oscillations
in no-load operation that are typical of many converters
(RLC resonating circuit). This helps to achieve better
EMC behavior.
As three output voltages are generated with this switch-
ing converter topology using just one single inductor,
the sequence must allow that all three converter outputs
are respectively supplied with the required current. The
core of the converter consists of three independent con-
verters. Each converter has its own regulated cut-off
and restart current and its own voltage monitor. Dur-
ing the startup phase the VH converter ramps up until
a voltage of approximately 7 V is obtained. Here, the
cut-off current is initially limited to lower values so that
a soft start with a low startup current ripple is achieved.
When a high enough VH voltage is available, the VH1
and VH2 converters are also switched on and the volt-
ages rise to their nominal values. Once in a steady
state, the individual converters are cyclically supplied
by the inductor with precisely the amount of current that
is required at that moment. The maximum load current
can thus be drawn from each of the voltages VH, VH1,
VH2, VCC1, or VCC2.
Startup behavior
During startup and with low supply voltages the coil’s
maximum cut-off current is reduced (soft start) until the
nominal voltage is reached at VH. Figure 3 shows the
startup behavior for VH, VCC1 (5 V), and VCC2 (3.3 V)
with the voltage monitor outputs V1OK and V2OK.
Standby
The converters can be individually activated by pins
ENV1 and ENV2. If neither of the two inputs are trig-
gered, the device is in standby mode and the current
consumption is reduced to a minimum. As soon as one
of the two inputs becomes active, the VH voltage is also
available.
Dual 3.3V/5V BOOST/BUCK SMPS, 08.05.2008 08:51:13
600mA
400mA
200mA
0
I(LVBH)
5V
4V
3V
2V
1V
0
V(V1OK)
8V
V(V2OK)
6V
4V
2V
0
500us
V(VH) V(VCC1) V(VCC2)
550us
Time (linear) [Plot 0]
600us
Figure 3: Startup principle for voltages VH, VCC1, VCC2, V1OK, and V2OK