rt8288a Richtek Technology Corporation, rt8288a Datasheet - Page 11

• Manufacturer Part Number: rt8288a
• Description: 4a, 21v 500khz Synchronous Step-down Converter
• Manufacturer: Richtek Technology Corporation

This formula has a maximum at V
I
used for design because even significant deviations do
not offer much relief.
The selection of C
to minimize voltage ripple.
Moreover, the amount of bulk capacitance is also a key
for C
Loop stability can be checked by viewing the load transient
response.
The output ripple, ΔV
Higher values, lower cost ceramic capacitors are now
becoming available in smaller case sizes. Their high ripple
current, high voltage rating and low ESR make them ideal
for switching
be taken when these capacitors are used at input and
output. When a ceramic capacitor is used at the input
and the power is supplied by a wall adapter through long
wires, a load step at the output can induce ringing at the
input, V
and be mistaken as loop instability. At worst, a sudden
inrush of current through the long wires can potentially
cause a voltage spike at V
part.
DS8288A-01 August 2011
I
Δ
OUT
RMS
V
OUT
OUT
/ 2. This simple worst case condition is commonly
= I
Location
IN
≤ Δ
OUT(MAX)
selection to ensure that the control loop is stable.
. At best, this ringing can couple to the output
C
C
C
C
C
C
OUT
OUT
OUT
OUT
I ESR
L
IN
IN
regulator applications. However, care must
⎡
⎢
⎣
OUT
V
V
+
OUT
Component Supplier
IN
OUT
8fC
is determined by the required ESR
, is determined by :
1
OUT
V
IN
MURATA
MURATA
MURATA
V
OUT
large enough to damage the
IN
TDK
TDK
TDK
⎤
⎥
⎦
−
IN
Table 3. Suggested Capacitors for C
1
= 2V
OUT
, where I
GRM32ER71C226M
GRM32ER71C226M
GRM31CR60J476M
C3225X5R1C226M
C3225X5R1C226M
C3225X5R0J476M
RMS
Part No.
=
Choose a capacitor rated at a higher temperature than
required. Several capacitors may also be paralleled to
meet size or height requirements in the design.
For the input
capacitors are recommended. For the recommended
capacitor, please refer
EMI Consideration
Since parasitic inductance and capacitance effects in PCB
circuitry would cause a spike voltage on SW pin when
high side MOSFET is turned-on/off, this spike voltage on
SW may impact on EMI performance in the system. In
order to enhance EMI performance, there are two methods
to suppress the spike voltage. One way is by placing an
R-C snubber (R
them as close as possible to the SW pin, as shown in
Figure 5. Another method is by adding a resistor in series
with the bootstrap capacitor, C
decrease the driving capability to the high side MOSFET.
It is strongly recommended to reserve the R-C snubber
during PCB layout for EMI improvement. Moreover,
reducing the SW trace area and keeping the main power
in a small loop will be helpful on EMI performance. For
detailed PCB layout guide, please refer to the section
Layout Considerations.
IN
Capacitance (μF)
and C
capacitor, one 22μF low
S
*, C
S
OUT
*) between SW and GND and locating
22
22
47
47
22
22
to Table 3 for more
BOOT
, but this method will
RT8288A
Case Size
1210
1210
1206
1210
1210
1210
www.richtek.com
detail.
ESR ceramic
11