RT8282B RICHTEK [Richtek Technology Corporation], RT8282B Datasheet - Page 10

• Manufacturer Part Number: RT8282B
• Description: 2A, 23V, 1.2MHz Synchronous Step-Down Converter
• Manufacturer: RICHTEK [Richtek Technology Corporation]

RT8282B
Hiccup Mode
For the RT8282BH, it provides Hiccup Mode Under Voltage
Protection (UVP). When the FB voltage drops below half
of the feedback reference voltage, V
will be triggered and the RT8282BH will shut down for a
period of time and then recover automatically. The Hiccup
Mode UVP can reduce input current in short-circuit
conditions.
Latch-Off Mode
For the RT8282BL, it provides Latch-Off Mode Under
Voltage Protection (UVP). When the FB voltage drops
below half of the feedback reference voltage, V
will be triggered and the RT8282BL will shut down in Latch-
Off Mode. In shutdown condition, the RT8282BL can be
reset by EN pin or power input VIN.
Inductor Selection
The inductor value and operating frequency determine the
ripple current according to a specific input and output
voltage. The ripple current ΔI
and decreases with higher inductance :
Having a lower ripple current reduces not only the ESR
losses in the output capacitors but also the output voltage
ripple. High frequency with small ripple current can achieve
highest efficiency operation. However, it requires a large
inductor to achieve this goal.
For the ripple current selection, the
will be a reasonable starting point. The
current occurs at the highest V
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10
Δ
12V
I =
V
L
IN
Figure 4. The Resistors can be Selected to Set IC
⎡
⎢
⎣
C
V
R
R
100k
f L
SS
9 (Exposed Pad)
OUT
EN1
EN2
×
⎤ ⎡
⎥ ⎢
⎦ ⎣
×
10µF
C
1
IN
−
Lockout Threshold
4,
2
7
8
V
VIN
EN
SS
GND
V
OUT
IN
RT8282B
⎤
⎥
⎦
COMP
BOOT
L
SW
FB
increases with higher V
IN
. To guarantee that the
1
3
5
6
value of ΔI
FB
C
C
, the UVP function
C
C
P
BOOT
R
L
C
largest ripple
L
= 0.24(I
R1
R2
FB
V
8V
OUT
, UVP
C
MAX
OUT
IN
)
ripple current stays below the specified maximum, the
inductor value should be chosen according to the following
equation :
The inductor's current rating (caused a 40°C temperature
rising from 25°C ambient) should be greater than the
maximum load current and its saturation current should
be greater than the short circuit peak current limit. Please
see Table 2 for the inductor selection reference.
C
The input capacitance, C
trapezoidal current at the source of the high side MOSFET.
To prevent large ripple current, a low ESR input capacitor
sized for the maximum RMS current should be used. The
RMS current is given by :
This formula has a maximum at V
I
commonly used for design because even significant
deviations do not offer much relief.
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 capacitor, one 10μF low ESR ceramic
capacitors are recommended. For the recommended
capacitor, please refer to table 3 for more detail.
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
L =
I
RMS
RMS
IN
Component
⎡
⎢
⎣
and C
OUT
f
Supplier
= I
YUDEN
= I
TAIYO
× Δ
Table 2. Suggested Inductors for Typical
TDK
TDK
V
OUT(MAX)
OUT
selection to ensure that the control loop is stable.
OUT
I
L(MAX)
OUT
/2. This simple worst-case condition is
Selection
⎤ ⎡
⎥ ⎢
⎦ ⎣
×
Application Circuit
V
OUT
V
OUT
1
IN
VLF10045
SLF12565
−
is determined by the required ESR
NR8040
Series
V
IN(MAX)
V
V
OUT
V
OUT
IN,
IN
DS8282B-01 March 2011
is needed to filter the
⎤
⎥
⎦
−
1
12.5 x 12.5 x 6.5
IN
10 x 9.7 x 4.5
Dimensions
= 2V
8 x 8 x 4
(mm)
OUT
, where