iC-DC
2-CHANNEL BUCK/BOOST DC/DC CONVERTER
Rev A3, Page 12/19
Intermittent flow / continuous flow
ductor, the sequence must allow that all three con-
If the inductor is recharged in the next cycle before the verter outputs are respectively supplied with the re-
coil current has run free, there is no gap in the current. quired current. The core of the converter consists of
This continuous flow occurs when the supply voltage three independent converters. Each converter has its
is low or the load current high.
own regulated cut-off and restart current and its own
voltage monitor. During the startup phase the VH con-
If the charge and discharge processes are concluded verter ramps up until a voltage of approximately 7 V is
within one clock cycle and the coil current drops to zero obtained. Here, the cut-off current is initially limited to
each time, intermittent flow prevails. This is the case lower values so that a soft start with a low startup cur-
when the supply voltage is sufficiently high or the load rent ripple is achieved.
current sufficiently low.
When a high enough VH voltage is available, the VH1
and VH2 converters are also switched on and the volt-
When no more current flows through the coil, after fly- ages rise to their nominal values. Once in a steady
back in intermittent operation both ends of the inductor state, the individual converters are cyclically supplied
are switched to ground. This prevents the oscillations by the inductor with precisely the amount of current
in no-load operation that are typical of many converters that is required at that moment. The maximum load
(RLC resonating circuit). This helps to achieve better current can thus be drawn from each of the voltages
EMC behavior.
VH, VH1, VH2, VCC1, or VCC2.
Startup behavior
Standby
During startup and with low supply voltages the coil’s The converters can be individually activated by pins
maximum cut-off current is reduced (soft start) until the ENV1 and ENV2. If neither of the two inputs are trig-
nominal voltage is reached at VH. Figure 3 shows the gered, the device is in standby mode and the current
startup behavior for VH, VCC1 (5 V), and VCC2 (3.3 V) consumption is reduced to a minimum. As soon as
with the voltage monitor outputs V1OK and V2OK.
one of the two inputs becomes active, the VH voltage
is also available.
As three output voltages are generated with this
switching converter topology using just one single in-
600mA
400mA
200mA
0
I(LVBH)
5V
4V
3V
2V
1V
0
V(V1OK)
8V
V(V2OK)
6V
4V
2V
0
500us
550us
Time (linear) [Plot 0]
600us
V(VH)
V(VCC1)
V(VCC2)
Figure 3: Startup principle for voltages VH, VCC1, VCC2, V1OK, and V2OK
ICHAUS [ IC-HAUS GMBH ]
