FR9809CPGTR [FITIPOWER]
21V, 5A, 500KHz Synchronous PWM-Buck DC/DC Converter;
| 型号： | FR9809CPGTR |
| 厂家： | 
Fitipower |
| 描述： | 21V, 5A, 500KHz Synchronous PWM-Buck DC/DC Converter |
| 文件： | 总13页 (文件大小：1241K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
fitipower integrated technology lnc.
FR9809
21V, 5A, 500KHz Synchronous PWM-Buck
DC/DC Converter
Description
Features
FR9809 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
range from 4.75V to 21V, and continuous load
current capability is 5A. Control circuit is designed
by a particular current mode which provides fast
transient response and eases loop stabilization.
High Efficiency up to 90%
Internal MOSFET RDS(ON): 110mΩꢄ20mΩ
Internal Compensation
Input Operation Voltage Range: 4.75V to 21V
5A Continuous Output Current
Output Voltage down to 0.805V
500KHz Oscillation Frequency
Sync to External Clock from 300KHz to 800KHz
Cycle-by-Cycle Current Limit
Under Voltage Lockout
This product has a very low standby current less
Over-Temperature Protection with Auto Recovery
<1μA Shutdown Current
Thermal Enhanced SOP-8 (Exposed Pad)
Package
than 1μA in shutdown mode. When the ꢀꢁꢂꢃꢄꢀ
pin voltage is less than 0.4V, FR9809 will turn off.
Fault protection includes over current protection
(OCP), under voltage lockout protection (UVLO) and
over temperature protection (OTP) function.
RoHS Compliant
Applications
Networking Equipment
OLPC, Netbook
This high-efficiency current mode step-down “Green
Power Converter” offers the standard SOP-8
package with an exposed pad.
Distributed Power System
LCD Monitor, TV, STB
External HDD
Security System
Pin Assignments
Ordering Information
FR9809□□□
SP Package (SOP-8 Exposed Pad)
TR: Tape/Reel
G: Green
C: Green
8
7
6
5
1
2
VIN
LX
GND
VCC
9
GND
Package Type
SP: SOP-8 (Exposed Pad)
3
4
FB
LX
SHDN/S
BST
Figure 1. Pin Assignment of FR9809
FR9809-Preliminary 0.4-OCT-2012
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FR9809
Typical Application Circuit
C4
0.1μF
5
4
R3
100KΩ
SHDN/S
BST
L1
1.8μH
2,3
1
VOUT
1.2V
VIN
LX
VIN
4.75V to 18V
R1
4.99KΩ/1%
C6
(optional)
FR9809
C2
47μF/6.3V
CERAMIC
C1
22μF/25V
CERAMIC
6
7
FB
VCC
C3
0.1μF
GND
8,9
R2
10KΩ/1%
Figure 2. Output 1.2V Application Circuit
C4
0.1μF
5
4
R3
100KΩ
L1
1.8μH
BST
SHDN/S
2,3
6
1
VIN
VOUT
1.2V
LX
FB
VIN
18V to 21V
R1
4.99KΩ/1%
C1
22μF/25V
CERAMIC
C5
C6
(optional)
FR9809
330μF/25V
EC x1
C2
47μF/6.3V
CERAMIC
7
VCC
C3
0.1μF
GND
8,9
R2
10KΩ/1%
Figure 3. High Input Voltage Application Circuit
FR9809-Preliminary 0.4-OCT-2012
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FR9809
Functional Pin Description
I/O
Pin Name
Pin No.
Pin Function
Voltage Feedback Input Pin. FB and VOUT are connected by a resistive voltage divider. This
IC senses feedback voltage via FB and regulates it at 805mV.
I
I
FB
6
1
7
Power Supply Input Pin. Drive 4.75V~21V voltage to this pin to power on this chip. A 22µF
ceramic bypass capacitor is connected between VIN and GND to eliminate noise.
VIN
Bias Supply Output Pin. A capacitor rating between 0.001µF~1µF must be connected from this
pin to GND.
O
VCC
This pin provides a digital control to turn the converter on or off. For automatic start-up,
connect the ꢀꢁꢂꢃꢄꢀ pin to VIN pin with a 100KΩ resistor. An external clock from 300KHz to
800KHz can be applied to the ꢀꢁꢂꢃꢄꢀ pin to change oscillation frequency.
I
5
ꢀꢁꢂꢃ
Power Switching Output Pin. This is the output pin that internal high-side NMOS switches to
supply power.
O
O
I
LX
BST
2,3
4
High-Side Gate-Drive BST Input. A capacitor rating between 0.01µF~0.1µF must be connected
from this pin to LX. It can boost the gate drive to fully turn on the internal high-side NMOS.
GND
8
Ground Pin. This pin is connected to the exposed pad with copper.
Ground Pin. The exposed pad must be soldered to a large PCB area and connected to GND
for maximum power dissipation.
I
Exposed Pad
9
Block Diagram
SHDN/S
1M
VIN
SHDN/S
+
Oscillator
+
Current Sense
Amplifier
CLK
150KHz / 500KHz
VCC
Regulator
-
+
VCC
BST
5V
-
Vref2
Current Limit
Comparator
High-Side
MOSFET
Control
Logic
LX
+
Low-Side
MOSFET
-
FB
-
PWM
Comparator
+
+
-
Vref1
Rcomp
Ccomp
Error
Amplifier
Current Limit
Low-Side
GND
Figure 4. Block Diagram of FR9809
FR9809-Preliminary 0.4-OCT-2012
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FR9809
Absolute Maximum Ratings (Note1)
● Input Supply Voltage VIN ---------------------------------------------------------------------------------- -0.3V to +23V
● Enable Voltage ꢅꢀꢁꢂꢃꢄꢀ ---------------------------------------------------------------------------------
-0.3V to +23V
● LX Voltage VLX ---------------------------------------------------------------------------------------------- -0.3V to VIN +1V
● 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
● Package Thermal Resistance (θJA) (Note2)
SOP-8 (Exposed Pad) ------------------------------------------------------------------------ 60°C/W
● Package Thermal Resistance (θJC)
SOP-8 (Exposed Pad) ------------------------------------------------------------------------ 15°C/W
Note 1：Stresses beyond those listed under “Absolute Maximum Ratings" may cause permanent damage to the device.
Note 2：PCB heat sink copper area = 10mm2.
Recommended Operating Conditions
● Input Supply Voltage VIN ---------------------------------------------------------------------------------- +4.75V to +21V
● Operation Temperature Range -------------------------------------------------------------------------- -40°C to +85°C
FR9809-Preliminary 0.4-OCT-2012
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FR9809
Electrical Characteristics
(VIN=12V, TA=25°C, unless otherwise specified.)
Parameter
Symbol
VIN
Conditions
Min
Typ
Max
21
1
Unit
V
Input Supply Voltage
4.75
ꢅꢀꢁꢂꢃ=0V
VIN Shutdown Supply Current
VIN Quiescent Supply Current
Feedback Voltage
ISD
μA
mA
mV
mΩ
mΩ
μA
A
ꢅꢀꢁꢂꢃ=2V, VFB=1V
4.75V≦VIN≦21V
IDDQ
VFB
1.5
805
110
20
780
830
10
High-Side MOSFET RDS(ON) (Note2)
Low-Side MOSFET RDS(ON) (Note2)
MOSFET Leakage Current
HSRDS(ON)
LSRDS(ON)
ILX(Leak)
ILIMIT
ꢅꢀꢁꢂꢃ=0V, VLX=0V
0
High-Side MOSFET Current Limit
(Note2)
8
Maximum Duty Cycle
DMAX
VFB=0.7V
90
%
Oscillation frequency
FLX
350
300
500
150
650
800
KHz
KHz
KHz
V
Short-Circuit Oscillation Frequency
Sync Frequency Range
Input UVLO Threshold
FLX(Short)
FSYNC
VFB=0.3V
VUVLO(Vth) VIN Rising
VUVLO(Hys)
4
Under Voltage Lockout Threshold
Hysteresis
200
mV
V
ꢅꢀꢁꢂꢃ (L)
0.4
ꢀꢁꢂꢃꢄꢀ Input Low Voltage
ꢀꢁꢂꢃꢄꢀ Input High Voltage
ꢀꢁꢂꢃꢄꢀ Input Current
VCC Regulator
ꢅꢀꢁꢂꢃ (H)
2.0
V
ꢆꢀꢁꢂꢃ
VCC
TSS
ꢅꢀꢁꢂꢃ=2V
2
μA
V
4.5
600
170
Soft-Start Time
μs
Thermal Shutdown Threshold (Note 2)
TSD
°C
Note 2：Guarantee by design.
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FR9809
Typical Performance Curves
VIN=12V, VOUT=3.3V, C1=22μF, C2=47μF, L1=1.8μꢁ, TA=+25°C, unless otherwise noted.
100
90
80
70
60
50
40
30
20
10
0
100
90
80
70
60
50
40
30
20
10
0
VIN=5V
VIN=12V
VIN=12V
VIN=21V
VOUT=3.3V
VOUT=1.2V
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
Load Current (A)
Load Current (A)
Figure 5. Efficiency vs. Loading
Figure 6. Efficiency vs. Loading
0.835
0.83
100
90
80
70
60
50
40
30
20
10
0
0.825
0.82
0.815
0.81
0.805
0.8
VIN=12V
VIN=21V
VOUT=5V
0.795
0.79
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
0.785
-40 -30 -20 -10
0
10 20 30 40 50 60 70 80 90
Load Current (A)
Case Temperature ( Degrees C )
Figure 7. Efficiency vs. Loading
Figure 8. Feedback Voltage vs. Temperature
650
625
600
575
550
525
500
475
450
425
400
375
350
8.8
8.7
8.6
8.5
8.4
8.3
8.2
8.1
8.0
-40 -30 -20 -10
0
10 20 30 40 50
60 70 80 90
-50 -40 -30 -20 -10
0
10 20 30 40 50 60 70 80 90 100
Temperature (℃)
Case Temperature ( Degrees C )
Figure 9. Frequency vs. Temperature
Figure 10. Current Limit vs. Temperature
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FR9809
Typical Performance Curves (Continued)
VIN=12V, VOUT=3.3V, C1=22μF, C2=47μF, L1=1.8μꢁ, TA=+25°C, unless otherwise noted.
IOUT=0A
IOUT=5A
VIN
50mV/div. (AC)
VIN
200mV/div. (AC)
VOUT 50mV/div. (AC)
VLX 10V/div.
VOUT 50mV/div. (AC)
VLX 10V/div.
ILX 2A/div.
ILX 5A/div.
2μs/div.
2μs/div.
Figure 11. DC Ripple Waveform
Figure 12. DC Ripple Waveform
IOUT=0A
IOUT=5A
ꢄ
5V/div.
2V/div.
ꢄ
5V/div.
2V/div.
ꢀꢁꢂ
ꢀꢁꢂ
VOUT
VOUT
VLX
10V/div.
5A/div.
VLX
10V/div.
5A/div.
ILX
ILX
200μs/div.
200μs/div.
Figure 13. Startup Through ꢀꢁꢂꢃ Waveform
Figure 14. Startup Through ꢀꢁꢂꢃ Waveform
IOUT=0A
IOUT=5A
ꢄ
5V/div.
2V/div.
10V/div.
ꢄ
5V/div.
2V/div.
ꢀꢁꢂ
ꢀꢁꢂ
VOUT
VOUT
VLX
VLX
10V/div.
ILX
5A/div.
ILX
5A/div.
40ms/div.
80μs/div.
Figure 16. Shutdown Through ꢀꢁꢂꢃ Waveform
Figure 15. Shutdown Through ꢀꢁꢂꢃ Waveform
FR9809-Preliminary 0.4-OCT-2012
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FR9809
Typical Performance Curves (Continued)
VIN=12V, VOUT=3.3V, C1=22μF, C2=47μF, L1=1.8μꢁ, TA=+25°C, unless otherwise noted.
IOUT=0A
IOUT=5A
VIN 5V/div.
VOUT 2V/div.
VIN 5V/div.
VOUT 2V/div.
VLX 10V/div.
ILX 5A/div.
VLX 10V/div.
ILX 5A/div.
2ms/div.
Figure 17. Startup Through VIN Waveform
2ms/div.
Figure 18. Startup Through VIN Waveform
IOUT=5A
IOUT=0A
VIN 5V/div.
VIN
5V/div.
VOUT 2V/div.
VOUT 2V/div.
VLX 10V/div.
VLX 10V/div.
ILX 5A/div.
ILX
5A/div.
200ms/div.
200ms/div.
Figure 19. Shutdown Through VIN Waveform
Figure 20. Shutdown Through VIN Waveform
IOUT = 0A to 5A
VOUT 200mV/div.
VOUT 2V/div.
VLX 10V/div.
ILX 5A/div.
ILX
5A/div.
20μs/div.
400μs/div.
Figure 21. Load Transient Waveform
Figure 22. Short Protect Waveform
FR9809-Preliminary 0.4-OCT-2012
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FR9809
Function Description
Introduction
Device Protection:
1. Input Under Voltage Lockout
FR9809 is
step-down synchronous DC/DC converter.
regulates input voltage from 4.75V to 21V and
provides 5A of continuous load current.
a
constant-frequency current-mode
It
When the power of FR9809 is on, the internal
circuits will be held inactive until VIN exceeds the
input UVLO threshold voltage. The regulator will
be disabled when VIN falls below the input UVLO
threshold voltage. The hysteretic of the UVLO
comparator is 200mV.
To achieve bias power supply, FR9809 contains an
internal voltage regulator to support the internal
circuits. For applications in which VIN is less than
4.5V, output decreases and a 0.1µF ceramic
capacitor are required for decoupling. If VIN is
greater than 4.5V, the output of the regulator will be
in full regulation.
2. Short Circuit Protection
The FR9809 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 40% of the
reference, the oscillator frequency will be reduced
to 150KHz to prevent the inductor current
The error amplifier compares the FB voltage with the
internal 0.805V reference. And the voltage of error
amplifier output is compared to the switch current to
control the RS flip-flop. At the beginning of each
clock cycle, the high-side NMOS turns on when the
oscillator sets the RS flip-flop, and turns off when
current comparator resets the RS flip-flop. Then the
low-side NMOS will turn on until the clock period
ends.
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.
3. Over Current Protection
Internal Soft-Start
The FR9809 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.
The internal soft-start function is used to eliminate
the output voltage overshooting during start-up.
When the chip initiates, the internal reference
voltage will rise slowly to 0.805V and the internal
COMP signal will rise slowly to achieve output
voltage. The soft-start time is approximate 600μs.
ꢀꢁꢂꢃ
VIN
R3
FR9809
4. Over Temperature Protection
SHDN/S
The FR9809 incorporates an over temperature
protection circuit to protect itself from overheating.
When the junction temperature exceeds the thermal
shutdown threshold temperature, the regulator will
shutdown. When the junction temperature is less
than the recovery threshold temperature, the chip
will re-enable.
The FR9809 ꢀꢁꢂꢃꢄꢀ pin provides digital control to
turn on/turn off the regulator.
For automatic
start-up, tie ꢀꢁꢂꢃꢄꢀ and VIN with a resister, as
shown in the figure. The recommended value of R3
is 100KΩ. The FR9809 can be synchronized with
an external clock from 300KHz to 800KHz by using
the ꢀꢁꢂꢃꢄꢀ pin.
FR9809-Preliminary 0.4-OCT-2012
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FR9809
Application Information
Output Voltage Setting
A low ESR capacitor is required to keep the noise
minimum.
Ceramic capacitors are better, but
The output voltage VOUT is set by using a resistive
divider from the output to FB. The FB pin regulated
voltage is 0.805V. Thus the output voltage is:
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.
R1
ꢀ
ꢅ
ꢅꢇꢈT=0.805ꢉ 1+
R2
It is recommended that the input EC capacitor
should be added for applications if the FR9809
suffers high spike input voltage (ex. hot plug test).
It can eliminate the spike voltage and induce the IC
damage from high input voltage stress.
Table 1 lists recommended values of R1 and R2 for
most used output voltage.
Table 1 Recommended Resistance Values
VOUT
R1 (1%)
R2 (1%)
VIN
VIN
5V
30.9kΩ
30.9kΩ
4.99kΩ
4.99kΩ
4.99kΩ
5.76kΩ
9.76kΩ
2.32kΩ
3.92kΩ
10kΩ
18V to 21V
FR9809
C5
330μF/25V 22μF/25V
EC x1 MLCC x1
C1
3.3V
2.5V
1.8V
1.2V
Output Capacitor Selection
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:
Resistors R1 and R2 should be placed close to the
FB pin to prevent stray pickup.
Input Capacitor Selection
The use of the input capacitor is filtering the input
voltage ripple and the MOSFETS switching spike
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 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:
ꢂ ꢃ
ꢂ ꢃ
ꢅRꢆPPLꢌ t =ꢅRꢆPPLꢌ(ꢍꢊ t +ꢅRꢆPPLꢌ(ꢌꢀRꢊ(tꢊ
+ꢅRꢆPPLꢌ(ꢌꢀLꢊ(tꢊ+ꢅꢃꢇꢆꢀꢌ(tꢊ
The following figures show the form of the ripple
contributions.
VRIPPLE(ESR)(t)
ꢂ
ꢃ
ꢁ
ꢆꢆꢃ(RMꢀꢊ=ꢆꢇꢈTꢉ ꢂꢉ 1ꢋꢂ
ꢅꢇꢈT
ꢂ=
(t)
+
ꢅꢆꢃ
VRIPPLE(ESL) (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.
(t)
(t)
+
VRIPPLE(C) (t)
5A
4.5A
4A
3.5A
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FR9809
Application Information (Continued)
+
Inductor Selection
VNOISE (t)
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 ΔꢆL is inductor
peak-to-peak ripple current:
=
VRIPPLE(t)
(t)
ꢅꢇꢈT
ꢅ
ꢇꢈTꢀ
ꢎꢆL=
ꢉ 1ꢋ
ꢅꢇꢈT
ꢅ
FꢇꢀꢍꢉL
ꢅꢆꢃ
ꢇꢈTꢀ
ꢅRꢆPPLꢌ(ꢌꢀR, pꢋpꢊ
=
ꢉ 1ꢋ
ꢉꢌꢀR
ꢅ
FꢇꢀꢍꢉL
ꢅꢆꢃ
The following diagram is an example to graphical
represent ΔꢆL equation.
ꢌꢀL
ꢅRꢆPPLꢌ(ꢌꢀL, pꢋpꢊ
=
ꢉꢅꢆꢃ
L+ꢌꢀL
ꢅꢇꢈT
8ꢉFꢇꢀꢍ2ꢉLꢉꢍꢇꢈT
L=1.8μꢀ
ꢇꢈTꢀ
ꢅRꢆPPLꢌ(ꢍ, pꢋpꢊ
=
ꢉ 1ꢋ
ꢅꢆꢃ
L=2.2μꢀ
L=4.7μꢀ
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.
VIN=12V, FOSC=500KHz
Low ESR capacitors are preferred to use. Ceramic,
tantalum or low ESR electrolytic capacitors can be
used depending on the output ripple requirements.
When using the ceramic capacitors, the ESL
component is usually negligible.
A good compromise value between size and
efficiency is to set the peak-to-peak inductor ripple
current ΔꢆL equal to 30% of the maximum load
current. But setting the peak-to-peak inductor
ripple current ΔꢆL between 20%~50% of the
maximum load current is also acceptable. Then
the inductance can be calculated with the following
equation:
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.
Remove 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 eliminates noise.
ꢎꢆL=0.ꢏꢉꢆꢇꢈT(MAꢐꢊ
ꢂ
ꢃ
ꢅꢆꢃꢋꢅꢇꢈT ꢉꢅꢇꢈT
L=
ꢅꢆꢃꢉFꢇꢀꢍꢉꢎꢆL
To guarantee sufficient output current, peak inductor
current must be lower than the FR9809 high-side
MOSFET current limit. The peak inductor current
is shown as below:
Probe Ground
ꢎꢆL
ꢆPꢌAK=ꢆꢇꢈT(MAꢐꢊ
+
2
VOUT
GND
Ceramic Capacitor
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FR9809
Application Information (Continued)
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
FR9809
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
R1
R2
C3
ꢅ
ꢀ
ꢍꢑ=
ꢉ
ꢉ
+
2 ꢉFꢍRꢇꢀꢀ
R1 R1 R2
8
1
7
6
5
4
Where FCROSS is the cross frequency.
To reduce transient ripple, the feedforward capacitor
value can be increased to push the cross frequency
Exposed
GND
Pad
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
C1
C5
+
C2
2
3
VIN
LX
VOUT
L1
to lower region.
In general, the feedforward
capacitor range is between 10pF to 1nF.
Figure 23. Recommended PCB Layout Diagram
External Diode Selection
For 5V input applications, it is recommended to add
an external bootstrap diode. This helps improving
efficiency. The bootstrap diode can be a low cost
one such as 1N4148.
D1
1N4148
VIN
BST
LX
VIN
5V
FR9809
C4
FR9809-Preliminary 0.4-OCT-2012
12
fitipower integrated technology lnc.
FR9809
Outline Information
SOP-8 (Exposed Pad) Package (Unit: mm)
DIMENSION IN MILLIMETER
SYMBOLS
UNIT
MIN
1.25
0.00
1.25
0.31
4.80
MAX
1.70
0.15
1.55
0.51
5.00
A
A1
A2
B
D
D1
E
3.04
3.80
2.15
1.20
5.80
0.40
3.50
4.00
2.41
1.34
6.20
1.27
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.
FR9809-Preliminary 0.4-OCT-2012
13
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