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PDF FR9885 Data sheet ( Hoja de datos )

Número de pieza FR9885
Descripción Synchronous Step-Down DC/DC Converter
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No Preview Available ! FR9885 Hoja de datos, Descripción, Manual

Lily 0755-83234073
159 153 736 32
Q Q 100 754 5980
fitipower integrated technology lnc.
FR9885
18V, 2A, 500KHz Synchronous Step-Down
DC/DC Converter
Description
The FR9885 is a synchronous step-down DC/DC
converter that provides wide 4.5V to 18V input
voltage range and 2A peak load current capability.
At light load condition, the FR9885 can operate at
PSM mode to support high efficiency and reduce
power loss.
The FR9885 fault protection includes cycle-by-cycle
current limit, UVLO, output overvoltage protection
and thermal shutdown.The internal soft-start function
prevents inrush current at turn-on. This device uses
current mode control scheme which provides fast
transient response. Internal compensation function
reduces external compensation components and
simplifies the design process.
In shutdown
mode, the supply current is about 1µA.
The FR9885 is offered in SOT-23-6 package and
provides good thermal conductance.
Pin Assignments
S6 Package (SOT-23-6)
Features
Low Rds(on) Integrated Power MOSFET
(170m/135m)
Internal Compensation Function
Wide Input Voltage Range: 4.5V to 18V
Adjustable Output Voltage Down to 0.6V
2A Peak Output Current
500kHz Switching Frequency
Internal 0.8ms Soft-Start
Cycle-by-Cycle Current Limit
Hiccup Short Circuit Protection
Over-Temperature Protection with Auto
Recovery
OVP and UVLO
SOT-23-6 Package
Applications
STB (Set-Top-Box)
LCD Display, TV
Distributed Power System
Networking, XDSL Modem
Ordering Information
FR9885□□□
TR: Tape/Reel
C: Green
Package Type
S6: SOT-23-6
Figure 1. Pin Assignment of FR9885
SOT-23-6 Marking
Part Number
FR9885S6CTR
Product Code
A9A
FR9885-Preliminary 0.3-MAY-2014
1

1 page




FR9885 pdf
fitipower integrated technology lnc.
Electrical Characteristics
(VIN=12V, TA=25°C, unless otherwise specified.)
Parameter
Symbol
Conditions
VIN Input Supply Voltage
VIN Quiescent Current
VIN Shutdown Supply Current
Feedback Voltage
High-Side MOSFET RDS(ON) (Note2)
Low-Side MOSFET RDS(ON) (Note2)
High-Side MOSFET Leakage Current
High-Side MOSFET Current Limit (Note2)
Oscillation Frequency
Short Circuit Oscillation Frequency
Maximum Duty Cycle
VIN
IDDQ
ISD
VFB
RDS(ON)
RDS(ON)
ILX(leak)
ILIMIT(HS)
FOSC
FOSC(short)
DMAX
VSHDN=2V, VFB=1.0V
VSHDN=0V
4.5VVIN18V
VSHDN=0V, VLX=0V
Minimum Duty
VFB=0V
VFB=0.4V
Minimum On Time (Note2)
TMIN
Input Supply Voltage UVLO Threshold
Input Supply Voltage UVLO Threshold
Hysteresis
Internal Soft-Start Period
SHDN Input Low Voltage
SHDN Input High Voltage
SHDN Input Current
Thermal Shutdown Threshold (Note2)
Note 2Not production tested.
VUVLO(Vth) VIN Rising
VUVLO(HYS)
TSS
VSHDN(L)
VSHDN(H)
ISHDN
TSD
VSHDN=2V
FR9885
Min Typ Max Unit
4.5 18 V
2 mA
1 10 µA
0.585 0.6 0.615 V
170 m
135 m
10 µA
3.2 A
400 500 600 kHz
150 kHz
90 %
100 ns
4.3 V
400 mV
0.8 ms
0.4 V
2V
2 µA
160 °C
FR9885-Preliminary 0.3-MAY-2014
5

5 Page





FR9885 arduino
fitipower integrated technology lnc.
FR9885
Application Information (Continued)
VRIPPLE(ESR) =
VOUT
FOSCL
1
VOUT
VIN
ESR
ESL
VRIPPLE(ESL)= L+ESL VIN
VRIPPLE(C)
=
VOUT
8FOSC2 LCOUT
1
VOUT
VIN
Where FOSC is the switching frequency, L is the
inductance value, VIN is the input voltage, ESR is the
equivalent series resistance value of the output
capacitor, ESL is the equivalent series inductance
value of the output capacitor and the COUT is the
output capacitor.
Low ESR capacitors are preferred to use. Ceramic,
tantalum or low ESR electrolytic capacitors can be
used depending on the output ripple requirement.
When using the ceramic capacitors, the ESL
component is usually negligible.
It is important to use the proper method to eliminate
high frequency noise when measuring the output
ripple. The figure shows how to locate the probe
across the capacitor when measuring output ripple.
Removing the scope probe plastic jacket in order to
expose the ground at the tip of the probe. It gives a
very short connection from the probe ground to the
capacitor and eliminating noise.
Probe Ground
VOUT
GND
Ceramic Capacitor
Inductor Selection
The output inductor is used for storing energy and
filtering output ripple current. But the trade-off
condition often happens between maximum energy
storage and the physical size of the inductor. The
first consideration for selecting the output inductor is
to make sure that the inductance is large enough to
keep the converter in the continuous current mode.
That will lower ripple current and result in lower
output ripple voltage. The IL is inductor
peak-to-peak ripple current:
∆IL=
VOUT
FOSCL
1
VOUT
VIN
The following diagram is an example to graphical
represent IL equation.
2.2
2
1.8 L=2.2µH
1.6
1.4 L=3.3µH
1.2
1 L=4.7µH
0.8
0.6
0.4
0.2
5 6 7 8 9 10 11 12 13 14 15 16 17 18
VIN (V)
VOUT=3.3V, FOSC=500kHz
A good compromise value between size and
efficiency is to set the peak-to-peak inductor ripple
current IL equal to 30% of the maximum load
current. But setting the peak-to-peak inductor
ripple current IL between 20%~50% of the
maximum load current is also acceptable. Then the
inductance can be calculated with the following
equation:
∆IL=0.3×IOUT(MAX)
L=
VIN VOUT ሻൈVOUT
VIN FOSC ∆IL
To guarantee sufficient output current, peak inductor
current must be lower than the FR9885 high-side
MOSFET current limit. The peak inductor current is
as below:
IPEAK =IOUT(MAX) +
∆IL
2
FR9885-Preliminary 0.3-MAY-2014
11

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