FR9886D [FITIPOWER]
23V, 2A/2.5A, 340KHz Synchronous Step-Down DC/DC Converter;
| 型号： | FR9886D |
| 厂家： | 
Fitipower |
| 描述： | 23V, 2A/2.5A, 340KHz Synchronous Step-Down DC/DC Converter |
| 文件： | 总15页 (文件大小：1073K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
fitipower integrated technology lnc.
FR9886D
23V, 2A/2.5A, 340KHz Synchronous Step-Down
DC/DC Converter
Description
Features
The FR9886D is a synchronous step-down DC/DC
converter that provides wide 4.5V to 23V input
● High Efficiency Synchronous Buck Converter with
Low ISD(<1μA)
voltage range.
SOP-8(EP)) to support 2A/2.5A continuous output
current.
There are two packages (SOP-8 &
● Low Rds(on) Integrated Power MOSFET
● Internal Compensation Function
● Wide Input Voltage Range: 4.5V to 23V
● Adjustable Output Voltage from 0.925V to 20V
● 2A Output Current (Package: SOP-8)
● 2.5A Output Current (Package: SOP-8(EP))
● 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
● SOP-8 and SOP-8 Exposed Pad Packages
The
FR9886D
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 FR9886D is available in SOP-8/SOP-8 (Exposed
Pad) packages. It is RoHS compliant and 100%
lead (Pb) free.
Applications
● STB (Set-Top-Box)
● LCD Display, TV
● Distributed Power System
● Networking, XDSL Modem
Pin Assignments
Ordering Information
FR9886D□□□
SO Package (SOP-8)
TR: Tape / Reel
8
7
6
5
SS
BST
VIN
LX
1
2
3
4
C: Green
SHDN
NC
Package Type
SO: SOP-8
SP: SOP-8 (Exposed Pad)
FB
GND
SP Package (SOP-8 Exposed Pad)
1
2
3
4
SS
BST
VIN
LX
8
7
SHDN
NC
6
5
FB
GND
Figure 1. Pin Assignments of FR9886D
FR9886D-1.0-JAN-2012
1
fitipower integrated technology lnc.
FR9886D
Typical Application Circuit
C4
0.1μF
R3
100kΩ
1
7
L1
4.7μH
SHDN
BST
LX
2
6
3
5
VOUT
1.2V
VIN
4.5V to 23V
VIN
C1
C6
(optional)
C2
R1
FR9886D
10μF/25V
CERAMIC x 2
3kΩ 1%
22μF/6.3V
CERAMIC x 2
FB
NC
SS
8
GND
4
R2
10kΩ 1%
C3
0.1μF
Figure 2. CIN /COUT use Ceramic Capacitors Application Circuit
C4
0.1μF
R3
100kΩ
7
1
L1
4.7μH
SHDN
BST
2
6
3
5
VIN
VOUT
1.2V
LX
VIN
4.5V to 23V
R1
3kΩ 1%
C6
C2
C5
0.1μF/25V
CERAMIC x 1
FR9886D
C1
100μF/25V
EC x 1
(optional)
100μF/6.3V
EC x 1
NC
FB
SS
8
GND
4
R2
10kΩ 1%
C3
0.1μF
Figure 3. CIN /COUT use Electrolytic Capacitors Application Circuit
VOUT
R1
R2
C6
L1
C2
1.2V
1.8V
2.5V
3.3V
5V
3kΩ
10kΩ
10kΩ
10kΩ
10kΩ
10kΩ
10kΩ
10kΩ
10kΩ
10kΩ
10kΩ
10pF~1nF
4.7μH
4.7μH
10μH
10μH
10μH
4.7μH
4.7μH
10μH
10μH
10μH
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
9.53kΩ
16.9kΩ
26.1kΩ
44.2kΩ
3kΩ
10pF~1nF
10pF~1nF
10pF~1nF
10pF~1nF
1.2V
1.8V
2.5V
3.3V
5V
--
--
--
--
--
9.53kΩ
16.9kΩ
26.1kΩ
44.2kΩ
Table 1. Recommended Component Values
FR9886D-1.0-JAN-2012
2
fitipower integrated technology lnc.
FR9886D
Functional Pin Description
I/O
Pin Name
Pin No.
Pin Function
Voltage Feedback Input Pin. Connect FB and VOUT with a resistive voltage divider. This IC
senses feedback voltage via FB and regulates it at 0.925V.
I
FB
5
2
7
4
3
8
1
6
I
VIN
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. Connect VIN
with a 100KΩ resistor for self-startup.
I
ꢀꢁꢂ
I
GND
Ground Pin. Connect this pin to exposed pad.
Power Switching Output. It is the output pin of internal high side NMOS which is the switching to
supply power.
O
O
O
O
LX
SS
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.
BST
NC
No connection.
Block Diagram
VIN
ISEN
Internal
Regulator
OTP
OVP
VCC
UVLO
&
POR
VCC
SHDN
2.7M
Oscillator
BST
High- Side
MOSFET
6µA
S
R
FB
Driver
Logic
PWM
Control
Current
Comp
LX
OTP
OVP
SS
UVLO
Low- Side
MOSFET
0.925V
Current
Limit
GND
Figure 4. Block Diagram of FR9886D
FR9886D-1.0-JAN-2012
3
fitipower integrated technology lnc.
FR9886D
Absolute Maximum Ratings (Note1)
● Supply Voltage VIN ------------------------------------------------------------------------------------------- -0.3V to +25V
● Enable Voltage VSHꢀN -------------------------------------------------------------------------------------
-0.3V to +25V
● LX Voltage VLX (50ns) --------------------------------------------------------------------------------------- -1V to VIN+0.3V
● BST Voltage VBST -------------------------------------------------------------------------------------------- VLX-0.3V to VLX+6V
● All Other Pins Voltage -------------------------------------------------------------------------------------- -0.3V to +6V
● Maximum Junction Temperature (TJ) ------------------------------------------------------------------- +150°C
● Storage Temperature (TS) --------------------------------------------------------------------------------- -65°C to +150°C
● Lead Temperature (Soldering, 10sec.) ----------------------------------------------------------------- +260°C
● Power Dissipation @TA=25°C, (PD) (Note2)
SOP-8 ----------------------------------------------------------------------------------------------- 1.39W
SOP-8 (Exposed Pad) -------------------------------------------------------------------------- 2.08W
● Package Thermal Resistance, (θJA):
SOP-8 ----------------------------------------------------------------------------------------------- 90°C/W
SOP-8 (Exposed Pad) -------------------------------------------------------------------------- 60°C/W
● Package Thermal Resistance, (θJC):
SOP-8 ----------------------------------------------------------------------------------------------- 39°C/W
SOP-8 (Exposed Pad) -------------------------------------------------------------------------- 15°C/W
Note 1：Stresses beyond this listed under “Absolute Maximum Ratings" may cause permanent damage to the device.
Note 2：PCB heat sink copper area = 10mm2.
Recommended Operating Conditions
● Supply Voltage VIN ------------------------------------------------------------------------------------------- +4.5V to +23V
● Enable Voltage VSHꢀN -------------------------------------------------------------------------------------
0V to VIN
● Operation Temperature Range --------------------------------------------------------------------------- -40°C to +85°C
FR9886D-1.0-JAN-2012
4
fitipower integrated technology lnc.
FR9886D
Electrical Characteristics
(VIN=12V, TA=25°C, unless otherwise specified.)
Parameter
VIN Input Supply Voltage
VIN Quiescent Current
Symbol
Conditions
Min
Typ
Max
Unit
V
VIN
IDDQ
ISD
4.5
23
VSHꢀN=1.8V, VFB=1.0V
VSHꢀN=0V
2
mA
μA
V
VIN Shutdown Supply Current
Feedback Voltage
1
VFB
VOVP
4.5V≦VIN≦23V
0.9
0.925
1.5
0.95
Feedback OVP Threshold Voltage
V
SOP-8
130
120
110
High-Side MOSFET RDS(ON) (Note3)
RDS(ON)
mΩ
SOP-8(EP)
Low-Side MOSFET RDS(ON) (Note3)
High-Side MOSFET Leakage Current
RDS(ON)
ILX(leak)
mΩ
μA
VSHꢀN=0V, VLX=0V
10
SOP-8
SOP-8(EP)
2.8
3.1
4
High-Side MOSFET Current Limit
(Note3)
Minimum
Duty
ILIMIT(HS)
A
4.5
1.5
400
340
110
90
Low-Side MOSFET Current Limit
(Note3)
ILIMIT(LS)
From Drain to Source
A
V/V
KHz
KHz
%
Error Amplifier Voltage Gain (Note3)
Oscillation frequency
FOSC
290
420
Short Circuit Oscillation Frequency
Maximum Duty Cycle
FOSC(short) VFB=0V
DMAX
TMIN
VFB=0.8V
Minimum On Time (Note3)
Input UVLO Threshold
100
4.3
250
6
ns
VUVLO(Vth) VIN Rising
VUVLO(HYS)
V
Under Voltage Lockout Threshold
Hysteresis
mV
μA
ms
Soft-Start Current
Soft-Start Period
ISS
VSS=0V
TSS
CSS=0.1μF
15
VSHꢀN
(L)
0.4
V
SHꢀN Input Low Voltage
VSHꢀN
2
V
(H)
SHꢀN Input High Voltage
SHꢀN Input Current
I SHꢀN
VSHꢀN=2V
0.75
170
μA
°C
Thermal Shutdown Threshold (Note3)
Note 3：Not production tested.
TSD
FR9886D-1.0-JAN-2012
5
fitipower integrated technology lnc.
FR9886D
Typical Performance Curves
VIN = 12V, VOUT = 3.3V, C1 = 10μF x 2, C2 = 22μF x 2, L1 = 10μH, TA = +25°C, unless otherwise noted.
100
100
95
90
95
90
85
80
85
80
75
70
65
60
55
50
75
70
65
60
55
50
VOUT = 1.2V
VOUT = 1.2V
VIN= 5V
VIN= 12V
VIN= 5V
VIN= 12V
0.1
0.4
0.7
1
1.3
1.6
1.9
2.2
0.1
0.4
0.7
1
1.3
1.6
1.9
2.2
2.5
Load Current (A)
Load Current (A)
Figure 5. Efficiency vs. Loading (SOP-8)
Figure 6. Efficiency vs. Loading (SOP-8 Exposed Pad)
100
95
90
85
80
75
70
65
60
55
50
100
95
90
85
80
75
70
65
VIN= 5V
VIN= 12V
VIN= 23V
VIN= 5V
VIN= 12V
VIN= 23V
60
55
50
VOUT = 3.3V
VOUT = 3.3V
0.1
0.4
0.7
1
1.3
1.6
1.9
2.2
2.5
0.1
0.4
0.7
1
1.3
1.6
1.9
2.2
Load Current (A)
Load Current (A)
Figure 7. Efficiency vs. Loading (SOP-8)
Figure 8. Efficiency vs. Loading (SOP-8 Exposed Pad)
100
95
90
85
80
75
70
65
60
55
50
100
95
90
85
80
75
70
65
60
VIN= 12V
VIN= 23V
VOUT = 5V
VIN= 12V
VIN= 23V
VOUT = 5V
55
50
0.1
0.4
0.7
1
1.3
1.6
1.9
2.2
0.1
0.4
0.7
1
1.3
1.6
1.9
2.2
2.5
Load Current (A)
Load Current (A)
Figure 9. Efficiency vs. Loading (SOP-8)
Figure 10. Efficiency vs. Loading (SOP-8 Exposed Pad)
FR9886D-1.0-JAN-2012
6
fitipower integrated technology lnc.
FR9886D
Typical Performance Curves (Continued)
VIN = 12V, VOUT = 3.3V, C1 = 10μF x 2, C2 = 22μF x 2, L1 = 10μH, TA = +25°C, unless otherwise noted.
0.950
0.945
380
370
0.940
0.935
0.930
0.925
0.920
0.915
0.910
0.905
0.900
360
350
340
330
320
310
300
290
280
-40
-20
0
20
40
60
80
100
-40
-20
0
20
40
60
80
100
Temperature ( Degrees C )
Temperature ( Degrees C )
Figure 11. Feedback Voltage vs. Temperature
IOUT=0A
Figure 12. Frequency vs. Temperature
IOUT=2.5A
VIN 10mV/div. (AC)
VIN 200mV/div. (AC)
VOUT 20mV/div. (AC)
IL 1A/div.
VOUT 20mV/div. (AC)
IL 1A/div.
VLX 5V/div.
VLX 5V/div.
4μs/div.
Figure 13. DC Ripple Waveform
4μs/div.
Figure 14. DC Ripple Waveform
IOUT=2.5A
IOUT=0A
ꢃ
5V/div.
ꢃ
5V/div.
ꢀꢁꢂ
ꢀꢁꢂ
VOUT 0.5V/div.
IL 1A/div.
VOUT 0.5V/div.
IL 1A/div.
VLX 5V/div.
VLX 5V/div.
4ms/div.
4ms/div.
Figure 15. Startup Through SHꢀN Waveform
FR9886D-1.0-JAN-2012
Figure 16. Startup Through SHꢀN Waveform
7
fitipower integrated technology lnc.
FR9886D
Typical Performance Curves (Continued)
VIN = 12V, VOUT = 3.3V, C1 = 10μF x 2, C2 = 22μF x 2, L1 = 10μH, TA = +25°C, unless otherwise noted.
IOUT=0A IOUT=2.5A
ꢃ
5V/div.
ꢃ
5V/div.
ꢀꢁꢂ
ꢀꢁꢂ
VOUT 0.5V/div.
VOUT 0.5V/div.
IL 1A/div.
IL 1A/div.
VLX 5V/div.
VLX 5V/div.
4ms/div.
200μs/div.
Figure 17. Shutdown Through SHꢀN Waveform
Figure 18. Shutdown Through SHꢀN Waveform
IOUT=100mA to 2.5A step
VOUT, 200mV/div. (AC)
IL 1A/div.
VOUT ,, 1V/div.
IL 1A/div.
40μs/div.
400μs/div.
Figure 19. Load Transient Waveform
Figure 20. Short Circuit Test
FR9886D-1.0-JAN-2012
8
fitipower integrated technology lnc.
FR9886D
Function Description
The FR9886D is
a
high efficiency, internal
Input Under Voltage Lockout
compensation and constant frequency current mode
synchronous step-down DC/DC converter. There
are two packages (SOP-8 & SOP-8(EP)) to support
2A/2.5A continuous output current. It regulates
input voltage from 4.5V to 23V and down to output
voltage as low as 0.925V.
When the FR9886D is power on, the internal
circuits will be held inactive until VIN voltage
exceeds the input UVLO threshold voltage. And
the regulator will be disabled when VIN is below the
input UVLO threshold voltage. The hysteretic of
the UVLO comparator is 250mV (typ).
Control Loop
Short Circuit Protection
Under normal operation, the output voltage is sensed
by FB pin through a resistive voltage divider and
amplified through the error amplifier. The voltage of
error amplifier output is compared to the switch
current to control the RS latch. At the beginning of
each clock cycle, the high-side NMOS turns on when
the oscillator sets the RS latch, and turns off when
current comparator resets the RS latch. Then the
low-side NMOS will turn on until the clock period
ends.
The FR9886D provides short circuit protection
function to prevent the device damaged from short
condition. When the short condition occurs and
the feedback voltage drops lower than 0.4V, the
oscillator frequency will be reduced to 110KHz to
prevent the inductor current increasing beyond the
current limit. In the meantime, the current limit will
also be reduced to lower the short current. Once
the short condition is removed, the frequency and
current limit will return to normal.
Enable
Over Current Protection
The FR9886D SHꢀN pin provides digital control to
turn on/off the regulator. When the voltage of
SHꢀN exceeds the threshold voltage, the regulator
will start the soft start function. If the SHꢀN pin
voltage is below the shutdown threshold voltage, the
regulator will turn into the shutdown mode and the
shutdown current will be smaller than 1μA. For
auto start-up operation, connect SHꢀN to VIN
through a 100KΩ resistor.
The FR9886D over current protection function is
implemented using cycle-by-cycle current limit
architecture. The inductor current is monitored by
measuring the high-side MOSFET series sense
resistor voltage. When the load current increases,
the inductor current will also increase. When the
peak inductor current reaches the current limit
threshold, the output voltage will start to drop.
When the over current condition is removed, the
output voltage will return to the regulated value.
Soft Start
Over Temperature Protection
The FR9886D employs adjustable soft start function
to reduce input inrush current during start up.
When the device turns on, a 6μA current will begin to
charge the capacitor which is connected from SS pin
to GND. The equation for the soft start time is
shown as below:
The FR9886D incorporates an over temperature
protection circuit to protect itself from overheating.
When the junction temperature exceeds the
thermal shutdown threshold temperature, the
regulator will be shutdown. And the hysteretic of
the over temperature protection is 60°C (typ).
ꢀ
ꢁ
CSS nF ꢁVFꢂ
ꢀ
ꢁ
TSS ms =
Internal Compensation Function
ꢀ
ꢁ
ISS μA
The stability of the feedback circuit is controlled by
The VFB voltage is 0.925V and the ISS current is 6μA.
If a 0.1μF capacitor is connected from SS pin to
GND, the soft start time will be 15ms.
internal compensation circuits.
This internal
compensation function is optimized for most
applications, and this function can reduce external
R, C components.
Output Over Voltage Protection
When the FB pin voltage exceeds 1.5V, the output
over voltage protection function will be triggered and
turn off the high-side/low-side MOSFET.
FR9886D-1.0-JAN-2012
9
fitipower integrated technology lnc.
FR9886D
Application Information
Output Voltage Setting
A low ESR capacitor is required to keep the noise
minimum. Ceramic capacitors are better, but
tantalum or low ESR electrolytic capacitors may
also suffice. When using tantalum or electrolytic
capacitors, a 0.1μF ceramic capacitor should be
placed as close to the IC as possible.
The output voltage VOUT is set by using a resistive
divider from the output to FB. The FB pin regulated
voltage is 0.925V. Thus the output voltage is:
R1
VOUT=0.925Vꢁ ꢂ1ꢃ
ꢃ
R2
Output Capacitor Selection
Table 2 lists recommended values of R1 and R2 for
most used output voltage.
The output capacitor is used to keep the DC output
voltage and supply the load transient current.
When operating in constant current mode, the
output ripple is determined by four components:
Table 2 Recommended Resistance Values
VOUT
5V
R1
R2
ꢀ ꢁ ꢀ ꢁ
VRIPPLE t =VRIPPLE C t ꢃVRIPPLE ESR t
ꢁ
ꢀ ꢁ
ꢀ
ꢁ
ꢀ
44.2kΩ
26.1kΩ
16.9kΩ
9.53kΩ
3kΩ
10kΩ
10kΩ
10kΩ
10kΩ
10kΩ
ꢀ ꢁ
ꢃVRIPPLE(ESL) t ꢃVNOISE
ꢀ ꢁ
t
3.3V
2.5V
1.8V
1.2V
The following figures show the form of the ripple
contributions.
VRIPPLE(ESR)(t)
Place resistors R1 and R2 close to FB pin to prevent
stray pickup.
(t)
Input Capacitor Selection
+
The use of the input capacitor is filtering the input
voltage ripple and the MOSFETS switching spike
VRIPPLE(ESL) (t)
voltage.
Because the input current to the
step-down converter is discontinuous, the input
capacitor is required to supply the current to the
converter to keep the DC input voltage.
The
(t)
(t)
+
capacitor voltage rating should be 1.25 to 1.5 times
greater than the maximum input voltage. The input
capacitor ripple current RMS value is calculated as:
VRIPPLE(C) (t)
ꢀ
ꢁ
IIN(RMS)=IOUTꢁꢄꢀꢁ 1ꢅꢀ
VOUT
ꢀ=
+
VIN
VNOISE (t)
Where D is the duty cycle of the power MOSFET.
This function reaches the maximum value at D=0.5
and the equivalent RMS current is equal to IOUT/2.
The following diagram is the graphical representation
of above equation.
=
VRIPPLE(t)
IOUT=2.5A
IOUT=2A
IOUT=1.5A
(t)
IOUT=1A
FR9886D-1.0-JAN-2012
10
fitipower integrated technology lnc.
FR9886D
Application Information
VOUT
V
That will lower ripple current and result in lower
VRIPPLE(ESR, pꢅp)
=
ꢆ ꢂ1ꢅ OUTꢃ ꢆESR
output ripple voltage.
The ΔIL is inductor
FOSCꢆL
VIN
peak-to-peak ripple current:
ESL
VRIPPLE(ESL, pꢅp)
=
ꢆVIN
VOUT
V
ꢄIL=
ꢆ ꢂ1ꢅ OUTꢃ
LꢃESL
VOUT
8ꢆFOSC2ꢆLꢆCOUT
FOSCꢆL
VIN
V
ꢆ ꢂ1ꢅ OUTꢃ
VIN
VRIPPLE(C, pꢅp)
=
The following diagram is an example to graphically
represent ΔIL equation.
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.
L=4.7μꢀ
L=6.8μꢀ
L=10μꢀ
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.
VOUT=3.3V, FOSC=340KHz
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:
Probe Ground
ꢄIL=0.3ꢁIOUT(MAX)
ꢀ
ꢁ
VINꢅVOUT ꢆVOUT
L=
VINꢆFOSCꢆꢄIL
To guarantee sufficient output current, peak
inductor current must be lower than the FR9886
VOUT
GND
high-side MOSFET current limit.
inductor current is shown as below:
The peak
Ceramic Capacitor
Inductor Selection
ꢄIL
IPEAK=IOUT(MAX)
ꢃ
2
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.
FR9886D-1.0-JAN-2012
11
fitipower integrated technology lnc.
FR9886D
Application Information
Feedforward Capacitor Selection
PCB Layout Recommendation
The device’s performance and stability are
dramatically affected by PCB layout. It is
recommended to follow these general guidelines
shown as below:
Internal compensation function allows users saving
time in design and saving cost by reducing the
number of external components. The use of a
feedforward capacitor C6 in the feedback network is
recommended to improve the transient response or
higher phase margin.
1. Place the input capacitors and output
capacitors as close to the device as possible.
The traces which connect to these capacitors
should be as short and wide as possible to
minimize parasitic inductance and resistance.
VOUT
R1
R2
C6
FR9886D
2. Place feedback resistors close to the FB pin.
FB
3. Keep the sensitive signal (FB) away from the
switching signal (LX).
4. The exposed pad of the package should be
soldered to an equivalent area of metal on the
PCB. This area should connect to the GND
plane and have multiple via connections to the
back of the PCB as well as connections to
intermediate PCB layers. The GND plane area
connecting to the exposed pad should be
maximized to improve thermal performance.
For optimizing the feedforward capacitor, knowing
the cross frequency is the first thing. The cross
frequency (or the converter bandwidth) can be
determined by using a network analyzer. When
getting the cross frequency with no feedforward
capacitor identified, the value of feedforward
capacitor C6 can be calculated with the following
equation:
5. Multi-layer PCB design is recommended.
1
1
1
1
ꢇ
C6=
ꢁ
ꢁ ꢂ
ꢃ
ꢃ
2 ꢁFCROSS
R1 R1 R2
Where FCROSS is the cross frequency.
To reduce transient ripple, the feedforward capacitor
value can be increased to push the cross frequency
to higher region.
Although this can improve
transient response, it also decreases phase margin
and causes more ringing. In the other hand, if more
phase margin is desired, the feedforward capacitor
value can be decreased to push the cross frequency
to lower region.
In general, the feedforward
capacitor range is between 10pF to 1nF.
External Boost Diode Selection
For 5V input applications, it is recommended to add
an external boost diode. This helps improving the
efficiency. The boost diode can be a low cost one
such as 1N4148.
D1
1N4148
BST
VIN
VIN
5V
C4
FR9886D
LX
FR9886D-1.0-JAN-2012
12
fitipower integrated technology lnc.
FR9886D
Application Information (Continued)
C6
R1
R3
R2
8
1
7
6
5
GND
GND
–
–
C1
+
C5
C2
+
4
2
3
VIN
VOUT
LX
L1
C4
Figure 21. FR9886D SOP-8 package CIN/COUT with EC capacitors Recommended PCB Layout Diagram
C6
R1
R3
R2
8
1
7
6
5
Exposed
Pad
GND
–
–
C1
+
C5
C2
4
2
3
+
VIN
VOUT
LX
L1
C4
Figure 22. FR9886D SOP-8(Exposed Pad) package CIN/COUT with EC capacitors Recommended PCB Layout Diagram
FR9886D-1.0-JAN-2012
13
fitipower integrated technology lnc.
FR9886D
Outline Information
SOP-8 Package (Unit: mm)
DIMENSION IN MILLIMETER
SYMBOLS
UNIT
MIN
1.35
0.10
1.25
0.31
4.80
3.80
1.20
5.80
0.40
MAX
1.75
0.25
1.50
0.51
5.00
4.00
1.34
6.20
1.27
A
A1
A2
B
D
E
e
H
L
Note：Followed From JEDEC MO-012-E.
Carrier dimensions
FR9886D-1.0-JAN-2012
14
fitipower integrated technology lnc.
FR9886D
Outline Information (Continued)
SOP-8 (Exposed Pad) Package (Unit: mm)
DIMENSION IN MILLIMETER
SYMBOLS
UNIT
MIN
1.25
0.00
1.25
0.31
4.80
3.04
3.80
2.15
1.20
5.80
0.40
MAX
1.70
0.15
1.55
0.51
5.00
3.50
4.00
2.41
1.34
6.20
1.27
A
A1
A2
B
D
D1
E
E1
e
H
L
Note：Followed From JEDEC MO-012-E.
Carrier dimensions
Life Support Policy
Fitipower’s products are not authorized for use as critical components in life support devices or other medical systems.
FR9886D-1.0-JAN-2012
15
相关型号：
©2020 ICPDF网 联系我们和版权申明