RT8253B View Datasheet(PDF) - Richtek Technology
Part Name
Description
Manufacturer
RT8253B Datasheet PDF : 15 Pages
| |||
RT8253B
To prevent enabling circuit when VIN is smaller than the VOUT target value, a resistive voltage divider can be placed
between the input voltage and ground and connected to the EN pin to adjust IC lockout threshold, as shown in Figure 4.
For example, if an 8V output voltage is regulated from a 12V input voltage, the resistor REN2 can be selected to set input
lockout threshold larger than 8V.
VIN
12V
2 VIN
CIN
BOOT 1
REN1
10µF
RT8253B
100k
SW 3
7 EN
REN2
8 SS
CSS
4,
9 (Exposed Pad)
GND
FB 5
COMP 6
CBOOT L
VOUT
8V
R1
COUT
CC RC
R2
CP
Figure 4. The Resistors can be Selected to Set IC Lockout Threshold
Hiccup Mode
For the RT8253BH, it provides Hiccup Mode Under Voltage
Protection (UVP). When the FB voltage drops below half
of the feedback reference voltage, VFB, the UVP function
will be triggered and the RT8253BH 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 RT8253BL, it provides Latch-Off Mode Under
Voltage Protection (UVP). When the FB voltage drops
below half of the feedback reference voltage, VFB, the UVP
will be triggered and the RT8253BL will shut down in Latch-
Off Mode. In shutdown condition, the RT8253BL 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 ΔIL increases with higher VIN
and decreases with higher inductance.
ΔIL
=
⎡
⎢⎣
VOUT
f ×L
⎤
⎥⎦
×
⎡⎢⎣1−
VOUT
VIN
⎤
⎥⎦
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.
www.richtek.com
10
For the ripple current selection, the value of ΔIL = 0.24(IMAX)
will be a reasonable starting point. The largest ripple
current occurs at the highest VIN. To guarantee that the
ripple current stays below the specified maximum, the
inductor value should be chosen according to the following
equation :
L
=
⎡
⎢⎣
f
×
VOUT
ΔIL(MAX)
⎤
⎥⎦
×
⎡⎢⎣1−
VOUT
VIN(MAX)
⎤
⎥⎦
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.
Table 2. Suggested Inductors for Typical
Application Circuit
C ompo nen t
Supplier
Ser ie s
D ime nsion s
(mm)
TDK
VLF10045 10 x 9.7 x 4.5
TDK
TAIYO
YUDEN
SLF12565
NR8040
12.5 x 12.5 x 6.5
8x8x4
CIN and COUT Selection
The input capacitance, CIN, is needed to filter the
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 :
DS8253B-02 March 2011
Share Link: 