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PDF FR9808 Data sheet ( Hoja de datos )
| Número de pieza | FR9808 | |
| Descripción | 500KHz Synchronous PWM-Buck DC/DC Converter | |
| Fabricantes | Fiti | |
| Logotipo |  |
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fitipower integrated technology lnc.
FR9808
21V, 4A, 500KHz Synchronous PWM-Bu8c5kT
DC/DC Converter
Description
FR9808 is a high-efficiency synchronous step-down
DC/DC converter that employs a special process
technique to obtain very low RDS(ON) for the internal
metal–oxide–semiconductor field-effect transistor
(MOSFET). The input operation voltage is in a wide
4.75V to 21V, and continuous load current capability
is 4A. Control circuit is designed by a particular
current mode which provides fast transient response
and eases loop stabilization.
This product has a very low standby current less
than 1μA in shutdown mode. When the EN/SYNC
pin voltage is less than 0.4V, FR9808 will turn off.
Fault protection includes over current protection
(OCP), under voltage lockout protection (UVLO) and
over temperature protection (OTP) function.
This high-efficiency current mode step-down “Green
Power Converter” offers the standard SOP-8
package with an exposed pad.
Features
● High Efficiency up to 90%
● Internal MOSFET RDS(ON): 120mΩ/20mΩ
● Internal Compensation
● Input Operation Voltage Range: 4.75V to 21V
● 4A Continuous Output Current
● Output Voltage down to 0.805V
● 500KHz Oscillation Frequency
● Sync to External Clock from 300 KHz to 800 KHz
● Cycle-by-Cycle Current Limit
● Under Voltage Lockout
● Over-Temperature Protection with Auto Recovery
● <1μA Shutdown Current
● Thermal Enhanced SOP-8 (Exposed Pad) Package
● RoHS Compliant
Applications
● Networking equipment
● OLPC, Netbook
● Distributed power system
● LCD monitor, TV, STB
● External HDD
● Security System
Pin Assignments
SP Package (SOP-8 Expose pad )
VIN 1
8 GND
SW 2 9 7 VCC
SW 3 GND 6 FB
BS 4
5 EN/SYNC
Ordering Information
FR9808□□□
TR: Tape / Reel
G: Green
Package Type
SP: SOP-8 (Exposed Pad)
Figure 1. Pin Assignment of FR9808
FR9808-1.1-SEP-2011
1
1 page  
fitipower integrated technology lnc.
Electrical Characteristics
(VIN=12V, TA=25°C, unless otherwise specified.)
Parameter
Symbol
Conditions
Input Supply Voltage
VIN Shutdown Supply Current
VIN Quiescent Supply Current
Feedback Voltage
High-Side MOSFET RDS(ON) (Note2)
Low-Side MOSFET RDS(ON) (Note2)
VIN
ISD VEN = 0V
IDDQ
VEN = 2 V, VFB = 1 V
VFB 4.75V≦VIN≦21V
HSRDS(ON)
LSRDS(ON)
MOSFET Leakage Current
ISW(Leak) VEN = 0V, VSW = 0V
High-Side MOSFET Current Limit
(Note2)
Maximum Duty Cycle
ILIMIT
DMAX
VFB = 0.7 V
Oscillation frequency
FSW
Short-Circuit Oscillation Frequency
FSW(Short) VFB = 0.3 V
Sync Frequency Range
FSYNC
Input UVLO Threshold
Under Voltage Lockout Threshold
Hysteresis
EN/SYNC Input Low Voltage
VUVLO(Vth)
VUVLO(Hys)
VEN(L)
VIN Rising
EN/SYNC Input High Voltage
VEN(H)
EN Input Current
IEN VEN = 2 V
VCC Regulator
VCC
Soft-Start Time
TSS
Thermal Shutdown Threshold (Note 2)
Note 2：Guarantee by design.
TSD
FR9808
85T
Min Typ Max Unit
4.75 21 V
1 μA
1.1 mA
780 805 830 mV
120 mΩ
20 mΩ
0 10 μA
6.5 A
90 %
350 500 650 KHz
150 KHz
300 800 KHz
4V
200 mV
0.4 V
2.0
2
V
μA
4.5 V
600 μs
160 °C
FR9808-1.1-SEP-2011
5
5 Page 
fitipower integrated technology lnc.
Application Information (Continued)
FR9808
85T
+
VNOISE (t)
=
VRIPPLE(t)
(t)
VRIPPLE(ESR,
p-p)
VOUT
FOSC L
1
VOUT
VIN
ESR
V RIPPLE(ESL, p-p) ESL VIN
L ESL
VRIPPLE(C,
p-p)
VOUT
8
F2
OSC
L
COUT
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
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 ΔIL is inductor
peak-to-peak ripple current:
IL
VOUT
FOSC L
1
VOUT
VIN
The following diagram is an example to graphical
represent ΔIL equation.
L=1.8μH
L=2.2μH
L=4.7μH
VIN=12V, FOSC=500KHz
A good compromise value between size and
efficiency is to set the peak-to-peak inductor ripple
current ΔIL equal to 30% of the maximum load
current. But setting the peak-to-peak inductor
ripple current ΔIL 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)
VIN - VOUT VOUT
L
VIN FOSC IL
To guarantee sufficient output current, peak
inductor current must be lower than the FR9808
high-side MOSFET current limit. The peak
inductor current is as below:
IPEAK=IOUT(MAX)+ ΔIL
2
Ceramic Capacitor
FR9808-1.1-SEP-2011
11
11 Page | ||
| Páginas | Total 13 Páginas | |
| PDF Descargar | [ Datasheet FR9808.PDF ] | |
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