RT8057 데이터 시트보기 (PDF) - Richtek Technology
부품명
상세내역
일치하는 목록
RT8057 Datasheet PDF : 11 Pages
| |||
RT8057
Application Information
The basic RT8057 application circuit is shown in Typical
Application Circuit. External component selection is
determined by the maximum load current and begins with
the selection of the inductor value and operating frequency
followed by CIN and COUT.
Output Voltage Setting
The output voltage is set by an external resistive divider
according to the following equation :
VOUT
=
VREF
x
(1+ R1 )
R2
where VREF equals to 0.6V typical. The resistive divider
allows the FB pin to sense a fraction of the output voltage
as shown in Figure 1.
VOUT
R1
FB
RT8057
R2
GND
Figure 1. Setting the Output Voltage
Soft-Start
The RT8057 contains an internal soft-start clamp that
gradually raises the clamp on the FB pin.
100% Duty Cycle Operation
When the input supply voltage decreases toward the output
voltage, the duty cycle increases toward the maximum
on-time. Further reduction of the supply voltage forces
the main switch to remain on for more than one cycle,
eventually reaching 100% duty cycle.
The output voltage will then be determined by the input
voltage minus the voltage drop across the internal
P-MOSFET and the inductor.
Low Supply Operation
The RT8057 is designed to operate down to an input supply
voltage of 2.7V. One important consideration at low input
supply voltages is that the RDS(ON) of the P-Channel and
N-Channel power switches increases. The user should
calculate the power dissipation when the RT8057 is used
at 100% duty cycle with low input voltages to ensure that
thermal limits are not exceeded.
Under Voltage Protection (UVP)
The output voltage can be continuously monitored for under
voltage protection. When the output voltage is less than
33% of its set voltage threshold after OCP occurs, the
under voltage protection circuit will be triggered to auto
re-softstart.
Input Voltage Over Voltage protection (VIN OVP)
When the input voltage (VIN) is higher than 6V, VIN OVP
will be triggered and the IC stops switching. Once the
input voltage drops below 6V, the IC will return to normal
operation.
Output Over Voltage Protection (VOUT OVP)
When the output voltage exceeds more than 5% of the
nominal reference voltage, the feedback loop forces the
internal switches off within 50µs. Therefore, the output
over voltage protection is automatically triggered by the
loop.
Short Circuit Protection
When the output is shorted to ground, the inductor current
decays very slowly during a single switching cycle. A
current runaway detector is used to monitor inductor
current. As current increases beyond the control of current
loop, switching cycles will be skipped to prevent current
runaway from occurring.
Component
Suppl ier
TAIYO YUDEN
Series
NR 4018
T2 R2M
Table 1. Inductors
Inductance (µH) DCR (mΩ) Current Rating (mA)
Dimensions (mm)
2.2µH
60
27 00
4 X 4 X 1.8
www.richtek.com
8
DS8057-03 November 2011
Share Link: 