FAN5601_05 FAIRCHILD [Fairchild Semiconductor], FAN5601_05 Datasheet - Page 12

• Manufacturer Part Number: FAN5601_05
• Description: Regulated Step-Down Charge Pump DC/DC Converter
• Manufacturer: FAIRCHILD [Fairchild Semiconductor]

FAN5601 Rev. 1.0.5
One of the key benefits of the ScalarPump™ architecture is that
the dynamically scaled on-resistance of the switches effectively
reduces the peak current in the bucket capacitor and therefore
input and output ripple current is also reduced. Nevertheless,
due to the ESR of the input and output bypass capacitors, these
current spikes generate voltage spikes at the input and output
pins. However, these ESR spikes can be easily filtered because
their frequency lie at up to 12 times the clock frequency.
In applications where conductive and radiated EMI/RFI interfer-
ence has to be kept as low as possible, the user may consider
the use of additional input and output filtering. For example,
adding an L-C filter to the standard output bypass configuration
is very effective in reducing both the output ripple and the volt-
age spikes. Figure 2 shows an L-C filter using a 100nH chip
inductor and a 1µF capacitor. The channel 1 of Figure 3 shows
the ripple voltage at the output of the device while Channel 2
shows the ripple voltage at the output of the filter at V
Figure 1. Optional L-C Filter
C
IN
= 10µF
INPUT 2.2V to 5.5V
V
ENABLE GND
IN
C+
C
B
= 1µF
V
C–
OUT
C
OUT
= 10µF
L
F
= 100nH Output 1.0V to 1.8V
C
F
IN
= 1µF
= 3.3V,
12
V
greatly reduce the current spikes at the input. The user should
be mindful of considering resistive voltage drops in the induc-
tors connected serially in the input and output leads.
Figure 2. Effect of L-C Filter on output ripple
While evaluating the FAN5601 (or any other switched capacitor
DC-DC converter) the user should be careful to keep the power
supply source impedance low; use of long wires causing high
lead inductances and resistive losses should be avoided. A
carefully laid out ground plane is essential because current
spikes are generated as the bucket capacitor is charged and
discharged. The input and output bypass capacitors should be
placed as close to the device pins as possible.
OUT
= 1.3V and I
V
V
I
OUT
IN
OUT
= 3.3V
= 100mA
= 1.3V
OUT
Time (10µs/div)
= 100mA. Similar filtering method will
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