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PDF ( 数据手册 , 数据表 ) AN-SY8368A

零件编号 AN-SY8368A
描述 Synchronous Step Down Regulator
制造商 Silergy
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AN-SY8368A 数据手册, 描述, 功能
Application Notes: AN_SY8368A
High Efficiency Fast Response
8A Continuous, 16A Peak, 28V Input
Synchronous Step Down Regulator
General Description
The SY8368A develops a high efficiency synchronous
step-down DC-DC regulator capable of delivering 8A
continuous, 16A peak current. The SY8368A operates
over a wide input voltage range from 4.0V to 28V and
integrates main switch and synchronous switch with
very low RDS(ON) to minimize the conduction loss.
The SY8368A adopts the instant PWM architecture to
achieve fast transient responses for high step down
applications and high efficiency at light loads. In
addition, it operates at pseudo-constant frequency of
800kHz under continuous conduction mode to
minimize the size of inductor and capacitor.
Ordering Information
SY8368 (□□)
Tempera ture Code
Packa ge Code
Optional Spec Code
Ordering Number Package type
SY8368AQQC QFN3x3-12
Note
--
Features
4.0-28V wide input voltage range
Low RDS(ON) for internal switches: 20/10m
Instant PWM architecture to achieve fast transient
response
Internal 600us soft-start limits the inrush current
Pseudo-constant frequency: 800kHz
8A continuous, 16A peak output current capability
+/-1% 0.6V reference voltage
Hiccup mode SCP, OVP
Thermal shutdown with auto recovery
Applications
LCD-TV/Net-TV/3DTV
Set Top Box
Notebook
High Power AP
Typical Applications
VIN
CIN
High/Floating/Low
ON/OFF
CVCC
IN
GND
ILMT
EN
VCC
PG
BS
LX
FB
PG (Open Drain Output)
CBS
L
CFF
RFF
R1
R2
VOUT
COUT
Figure 1 Schematic
Figure 2. Efficiency
AN_SY8368A Rev. 0.9B Silergy Corp. Confidential- Prepared for Customer Use Only 1







AN-SY8368A pdf, 数据表
AN_SY8368A
Operation
The SY8368A develops a high efficiency synchronous
step-down DC-DC regulator capable of delivering 8A
continuous, 16A peak current. The SY8368A operates
over a wide input voltage range from 4V to 28V and
integrates main switch and synchronous switch with
very low RDS(ON) to minimize the conduction loss.
The SY8368A adopts the instant PWM architecture to
achieve fast transient responses for high step down
applications and high efficiency at light loads. In
addition, it operates at pseudo-constant frequency of
800kHz under continuous conduction mode to
minimize the size of inductor and capacitor.
Applications Information
Because of the high integration in the SY8368A IC, the
application circuit based on this regulator IC is rather
simple. Only input capacitor CIN, output capacitor COUT,
output inductor L and feedback resistors (R1 and R2)
need to be selected for the targeted applications
specifications.
Feedback resistor dividers R1 and R2:
Choose R1 and R2 to program the proper output voltage.
To minimize the power consumption under light loads,
it is desirable to choose large resistance values for both
R1 and R2. A value of between 10kand 1Mis
highly recommended for both resistors. If Vout is 3.3V,
R1=100k is chosen, then using following equation, R2
can be calculated to be 22.1k:
VOUT
R2
=
0.6V
VOUT 0.6V
R1 .
0.6VFB
GND
R1
R2
Input capacitor CIN:
The ripple current through input capacitor is calculated
as
I = I CIN _ RMS
OUT
D(1D) .
To minimize the potential noise problem, place a
typical X5R or better grade ceramic capacitor really
close to the IN and GND pins. Care should be taken to
minimize the loop area formed by CIN, and IN/GND
pins. In this case, a 10uF low ESR ceramic capacitor is
recommended.
Output capacitor COUT:
The output capacitor is selected to handle the output
ripple noise requirements. Both steady state ripple and
transient requirements must be taken into consideration
when selecting this capacitor. For most applications,
an X5R or better grade ceramic capacitor greater than
66uF capacitance can work well. The capacitance
derating with DC voltage must be considered.
Output inductor L:
There are several considerations in choosing this
inductor.
1) Choose the inductance to provide the desired
ripple current. It is suggested to choose the ripple
current to be about 40% of the maximum output
current. The inductance is calculated as:
L = VOUT (1 VOUT /VIN,MAX )
FSW × IOUT,MAX × 40%
where Fsw is the switching frequency and IOUT,MAX is
the maximum load current.
The SY8368A regulator IC is quite tolerant of different
ripple current amplitude. Consequently, the final choice
of inductance can be slightly off the calculation value
without significantly impacting the performance.
2) The saturation current rating of the inductor must
be selected to be greater than the peak inductor
current under full load conditions.
ISAT, MIN > IOUT, MAX + VOUT(1-VOUT/VIN,MAX)
2 FSW L
3) The DCR of the inductor and the core loss at the
switching frequency must be low enough to
achieve the desired efficiency requirement. It is
desirable to choose an inductor with DCR<10m
to achieve a good overall efficiency.
Current limit setting
The current limit is set to 8A, 12A or 16A when ILMT
pin is pull low, floating or pull high respectively.
Soft-start
The SY8368A has a built-in soft-start to control the
rise rate of the output voltage and limit the input
current surge during IC start-up. The typical soft-start
time is 600us.
Enable Operation
AN_SY8368A Rev. 0.9B Silergy Corp. Confidential- Prepared for Customer Use Only 8














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