fitipower integrated technology lnc.
FR9888
85T
23V, 3.5A, 340KHz Synchronous Step-Down
DC/DC Converter
Description
The FR9888 is a synchronous step-down DC/DC
converter that provides wide 4.5V to 23V input
voltage range and 3.5A continuous load current
capability.
The FR9888 fault protection includes cycle-by-cycle
current limit, input UVLO, output over voltage
protection and thermal shutdown. Besides,
adjustable 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
less than 1μA.
The FR9888 is available in an 8-pin SOIC package,
provides a very compact system solution and good
thermal conductance.
Features
● High Efficiency up to 96%
● Low Rds(on) Integrated Power MOSFET
● Internal Compensation Function
● Wide Input Voltage Range: 4.5V to 23V
● Adjustable Output Voltage Range: 0.925V to 20V
● 3.5A Output Current
● Fixed 340KHz Switching Frequency
● Current Mode Operation
● Adjustable Soft-Start
● Cycle-by-Cycle current limit
● Input Under Voltage Lockout
● Over-Temperature Protection with Auto Recovery
● <1μA Shutdown Current
● SOP-8 Exposed Pad Package
Applications
● Set-Top-Box (STB)
● Television
● Distributed Power System
● XDSL Modem
Pin Assignments
SP Package (SOP-8 Exposed Pad )
Ordering Information
FR9888
□□□
TR: Tape/Reel
BOOST
VIN
LX
GND
1
2
3
4
8
7
6
5
SS
SHDN
NC
FB
G: Green
Package Type
SP: SOP-8 (Exposed Pad)
Fig
ure 1. Pin Assignment of FR9888
FR9888- 1.0-JUL-2011
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fitipower integrated technology lnc.
FR9888
85T
Typical Application Circuit
R3
100kΩ
C4
0.1μF
7
2
C1
10μF/25V
CERAMIC x 2
1
LX 3
L1
4.7μH
VOUT
1.2V
R1
3kΩ
(optional)
SHDN BOOST
VIN
4.5V to 23V
VIN
FR9888
6 NC
GND
4
FB
SS
5
C6
C2
22μF/6.3V
CERAMIC x 2
8
C3
0.1μF
R2
10kΩ
Figure 2. C
IN
/C
OUT
use Ceramic Capacitors Application Circuit
C4
0.1μF
R3
100kΩ
7
VIN
4.5V to 23V
C1
100μF/25V
EC x 1
C5
0.1μF/25V
CERAMIC x 1
1
LX
3
L1
4.7μH
VOUT
1.2V
R1
3kΩ
(optional)
SHDN BOOST
2
VIN
FR9888
6
NC
GND
4
FB
SS
5
C6
C2
100μF/6.3V
EC x 1
8
C3
0.1μF
R2
10kΩ
Figure 3. C
IN
/C
OUT
use Electrolytic Capacitors Application Circuit
V
OUT
1.2V
1.8V
2. V
3.3V
5V
1.2V
1.8V
2.5V
3.3V
5V
R1
3kΩ
9.53kΩ
16.9kΩ
26.1kΩ
44.2kΩ
3kΩ
9.53kΩ
16.9kΩ
26.1kΩ
44.2kΩ
R2
10kΩ
10kΩ
10kΩ
10kΩ
10kΩ
10kΩ
10kΩ
10kΩ
10kΩ
10kΩ
C6
200pF~1nF
200pF~1nF
200pF~1nF
200pF~1nF
200pF~1nF
--
--
--
--
--
L1
4.7μH
4.7μH
10μH
10μH
10μH
4.7μH
4.7μH
10μH
10μH
10μH
C
OUT
22μF MLCC x2
22μF MLCC x2
22μF MLCC x2
22μF MLCC x2
22μF MLCC x2
100μF EC x1
100μF EC x1
100μF EC x1
100μF EC x1
100μF EC x1
Table 1. Recommended Component Values
FR9888- 1.0-JUL-2011
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fitipower integrated technology lnc.
FR9888
85T
Functional Pin Description
I/O
I
I
I
I
O
O
O
O
GND
LX
SS
BOOST
NC
Pin Name
FB
VIN
Pin No.
5
2
7
4
3
8
1
6
Pin Function
Voltage Feedback Input Pin. Connect FB and V
OUT
with a resistive voltage divider.
senses feedback voltage via FB and regulates it at 0.925V.
Power Supply Input Pin. Drive this pin by 4.5V to 23V voltage to power on the chip.
Enable Input Pin. This pin provides a digital control to turn the converter on or off.
with a 100KΩ resistor for self-startup.
Ground Pin. Connect this pin to exposed pad.
Power Switching Output.
supply power.
It is the output pin of internal high side NMOS which is the switching to
Connect VIN
This IC
Soft-Start Pin. This pin controls the soft-start period. Connect a capacitor from SS to GND to
set the soft start period.
High Side Gate Drive Boost Pin. A 10nF or greater capacitor must be connected from this pin to
LX. It can boost the gate drive to fully turn on the internal high side NMOS.
No connection. Keeps this pin floating.
Block Diagram
VIN
ISEN
SHDN
1M
UVLO
&
POR
Internal
Regulator
VCC
OTP
VCC
OVP
Oscillator
BOOST
6µA
FB
SS
Current
Comp
S
R
OTP
OVP
UVLO
PWM
Control
Driver
Logic
High-Side
MOSFET
LX
0.925V
Current
Limit
Low-Side
MOSFET
GND
Figure 4. Block Diagram of FR9888
FR9888- 1.0-JUL-2011
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fitipower integrated technology lnc.
FR9888
85T
Absolute Maximum Ratings
(Note1)
● Supply Voltage V
IN
------------------------------------------------------------------------------------------- -0.3V to +25V
● Enable Voltage V
SH
N
------------------------------------------------------------------------------------- -0.3V to +25V
● LX Voltage V
LX
(50ns) --------------------------------------------------------------------------------------- -1V to V
IN
+0.3V
● Boost Trap Voltage V
BOOST
--------------------------------------------------------------------------------- V
LX
-0.3V to V
LX
+6V
● All Other Pins Voltage --------------------------------------------------------------------------------------- -0.3V to +6V
● Maximum Junction Temperature (T
J
) -------------------------------------------------------------------- +150°C
● Storage Temperature (T
S
) ---------------------------------------------------------------------------------- -65°C to +150°C
● Lead Temperature (Soldering, 10sec.) ------------------------------------------------------------------ +260°C
● Power Dissipation @T
A
=25°C, (P
D
)
(Note2)
SOP-8 (Exposed Pad) -------------------------------------------------------------------------- 2.08W
● Package Thermal Resistance, (θ
JA
):
SOP-8 (Exposed Pad) -------------------------------------------------------------------------- 60°C/W
● Package Thermal Resistance, (θ
JC
):
SOP-8 (Exposed Pad) -------------------------------------------------------------------------- 15°C/W
Note 1：Stresses beyond this listed under “Absolute Maximum Ratings" may cause permanent damage to the device.
2
Note 2：PCB heat sink copper area = 10mm .
Recommended Operating Conditions
● Supply Voltage V
IN
------------------------------------------------------------------------------------------ +4.5V to +23V
● Enable Voltage V
SH
N
------------------------------------------------------------------------------------ 0V to V
IN
● Operation Temperature Range -------------------------------------------------------------------------- -40°C to + 85°C
FR9888- 1.0-JUL-2011
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fitipower integrated technology lnc.
FR9888
85T
Electrical Characteristics
(V
IN
=12V, T
A
=25
°C
, unless otherwise specified.)
Parameter
V
IN
Input Supply Voltage
V
IN
Quiescent Current
V
IN
Shutdown Supply Current
Feedback Voltage
Feedback OVP Threshold Voltage
High-Side MOSFET R
DS
(ON)
Low-Side MOSFET R
DS
(ON)
(Note3)
(Note3)
Symbol
V
IN
I
DDQ
I
SD
V
FB
V
OVP
R
DS(ON)
R
DS(ON)
I
LX(leak)
I
LIMIT(HS)
I
LIMIT(LS)
V
SH
N
Conditions
Min
4.5
Typ
Max
23
Unit
V
mA
V
SH
V
SH
N
N
=1.8V, V
FB
=1.0V
=0V
0.9
2.5
1
0.925
1.5
110
80
0.95
μA
V
V
mΩ
mΩ
4.5V≦V
IN
≦23V
High-Side MOSFET Leakage Current
High-Side MOSFET Current Limit
Low-Side MOSFET Current Limit
(Note3)
(Note3)
=0V, V
LX
=0V
4
5
10
μA
A
A
V/V
Minimum Duty
From Drain to Source
1.5
400
Error Amplifier Voltage Gain (Note3)
Oscillation frequency
Short Circuit Oscillation Frequency
Maximum Duty Cycle
Minimum On Time
(Note3)
F
OSC
F
OSC(short)
D
MAX
T
MIN
V
UVLO(Vth)
Threshold
V
UVLO(HYS)
I
SS
T
SS
V
SH
V
SH
I
SH
(Note3)
N(L)
N(H)
N
290
V
FB
=0V
V
FB
=0.8V
340
110
90
100
420
KHz
KHz
%
ns
V
mV
μA
ms
Input UVLO Threshold
Under
Voltage
Hysteresis
Soft-Start Current
Soft-Start Period
SH N Input Low Voltage
SH N Input High Voltage
SH N Input Current
Thermal Shutdown Threshold
Note 3：Not production tested.
Lockout
V
IN
Rising
4.3
250
V
SS
=0V
C
SS
=0.1μF
6
15
0.4
2
V
V
V
SH
N
=2V
2
170
μA
T
SD
°C
FR9888- 1.0-JUL-2011
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