IC-DC IC-Haus, IC-DC Datasheet - Page 12

• Manufacturer Part Number: IC-DC
• Description: 2-CHANNEL BUCK/BOOST DC/DC CONVERTER
• Manufacturer: IC-Haus

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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.
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.
As three output voltages are generated with this
switching converter topology using just one single in-
iC-DC
2-CHANNEL BUCK/BOOST DC/DC CONVERTER
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
8V
6V
4V
2V
0
V(V1OK)
V(VH)
V(VCC1)
V(V2OK)
Figure 3: Startup principle for voltages VH, VCC1, VCC2, V1OK, and V2OK
V(VCC2)
500us
550us
Time (linear) [Plot 0]
ductor, the sequence must allow that all three con-
verter outputs are respectively supplied with the re-
quired current. The core of the converter consists of
three independent converters. Each converter has its
own regulated cut-off and restart current and its own
voltage monitor. During the startup phase the VH con-
verter 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 cur-
rent 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.
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.
600us
Rev A3, Page 12/19
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