FR9888CSECTR [FITIPOWER]
23V, 3.5A, 340KHz Synchronous Step-Down DC/DC Converter;
| 型号： | FR9888CSECTR |
| 厂家： | 
Fitipower |
| 描述： | 23V, 3.5A, 340KHz Synchronous Step-Down DC/DC Converter |
| 文件： | 总13页 (文件大小：1392K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
fitipower integrated technology lnc.
FR9888C
23V, 3.5A, 340KHz Synchronous Step-Down
DC/DC Converter
Description
Features
The FR9888C 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.
High Efficiency up to 96%
Low Rds(on) Integrated Power MOSFET
(110mΩ/80mΩ)
Wide Input Voltage Range: 4.5V to 23V
Adjustable Output Voltage Range: 0.925V to 20V
3.5A Output Current
The
FR9888C
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.
In shutdown mode, the supply current is less than
1μA.
Fixed 340kHz Switching Frequency
Current Mode Operation
External Compensation Function
Adjustable Soft-Start
Cycle-by-Cycle Current Limit
Input Under Voltage Lockout
Over-Temperature Protection with Auto Recovery
<1μA Shutdown Current
The FR9888C is available in SOP-8 exposed pad
package, provides a very compact system solution
and good thermal conductance.
SOP-8 Exposed Pad Package
Applications
Set-Top-Box (STB)
LCD Displays, TV
Distributed Power System
XDSL Modem
Pin Assignments
Ordering Information
SP Package (SOP-8 Exposed Pad)
FR9888C□□□
TR: Tape/Reel
8
7
6
5
BST
VIN
1
2
SS
C: Green
9
PAD
SHDN
COMP
FB
Package Type
SP: SOP-8 (Exposed Pad)
SE: SOP-8 (Exposed Pad) (Note 1)
3
4
LX
GND
SE Package (SOP-8 Exposed Pad)
8
7
6
5
BST
VIN
1
2
SS
SHDN
COMP
FB
9
PAD
3
4
LX
GND
Note 1: Exposed pad is small pad.
Figure 1. Pin Assignment of FR9888C
FR9888C-0.3-MAR-2014
1
fitipower integrated technology lnc.
FR9888C
Typical Application Circuit
C4
0.1μF
R3
100kΩ
7
1
L1
10μH
SHDN
BST
LX
2
6
3
5
VIN
VOUT
3.3V
VIN
4.5V to 23V
C1
10μF
CERAMIC x 2
C6
(optional)
C2
22μF
R1
FR9888C
30.9kΩ
CERAMIC x 2
FB
COMP
C5
4.7nF
SS
8
GND
4
C7
(optional)
R2
12kΩ
R4
8.2kΩ
C3
0.1μF
Figure 2. CIN /COUT use Ceramic Capacitors Application Circuit
C4
0.1μF
R3
100kΩ
7
1
L1
10μH
SHDN
BST
2
3
5
VIN
VOUT
3.3V
LX
VIN
4.5V to 23V
C6
(optional)
C2
100μF
EC x 1
FR9888C
R1
30.9kΩ
C1
100μF
EC x 1
C8
0.1μF
CERAMIC x 1
6
COMP
FB
C5
4.7nF
SS
8
GND
4
C7
(optional)
R2
12kΩ
R4
8.2kΩ
C3
0.1μF
Figure 3. CIN /COUT use Electrolytic Capacitors Application Circuit
VIN=12V, the recommended BOM list is as below.
VOUT
1.2V
1.8V
3.3V
5V
R1
R2
R4
C5
L1
4.7μH
6.8μH
10μH
10μH
4.99kΩ
4.99kΩ
30.9kΩ
30.9kΩ
16.5kΩ
5.23kΩ
12kΩ
3.3kΩ
5.6kΩ
8.2kΩ
10kΩ
4.7nF
4.7nF
4.7nF
4.7nF
6.98kΩ
Table 1. Recommended Component Values
FR9888C-0.3-MAR-2014
2
fitipower integrated technology lnc.
FR9888C
Functional Pin Description
Pin Name
Pin No.
Pin Function
High Side Gate Drive Boost Pin. A capacitance between 10nF~100nF must be connected from this pin
to LX. It can boost the gate drive to fully turn on the internal high side NMOS.
BST
1
2
3
Power Supply Input Pin. Placed input capacitors as close as possible from VIN to GND to avoid noise
influence.
VIN
LX
Power Switching Node. Connect an external inductor to this switching node.
Ground Pin. Connect this pin to exposed pad.
GND
4
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.
FB
5
6
7
Compensation Pin. This pin is used to compensate the regulation control loop. Connect a series RC
network from COMP pin to GND.
COMP
ꢀꢁꢂ
Enable input pin. Pull high to turn on IC, and pull low to turn off IC. Connect VIN with a 100kΩ resistor
for self-startup.
Soft-Start Pin. This pin controls the soft-start period. Connect a capacitor from SS to GND to set the
soft start period.
SS
8
9
Exposed
Pad
Ground pin. The exposed pad must be soldered to a large PCB area and connected to GND for
maximum power dissipation
Block Diagram
VIN
ISEN
Internal
Regulator
OTP
OVP
VCC
UVLO
&
POR
VCC
SHDN
1M
Oscillator
BST
High-Side
MOSFET
6µA
FB
S
R
Driver
Logic
PWM
Control
Current
Comp
LX
OTP
OVP
SS
UVLO
Low-Side
MOSFET
0.925V
Current
Limit
COMP
GND
Figure 4. Block Diagram of FR9888C
FR9888C-0.3-MAR-2014
3
fitipower integrated technology lnc.
FR9888C
Absolute Maximum Ratings (Note 2)
● Supply Voltage VIN ------------------------------------------------------------------------------------------- -0.3V to +25V
● Enable Voltage ꢀꢁHꢂꢃ -------------------------------------------------------------------------------------
-0.3V to +25V
● LX Voltage VLX ------------------------------------------------------------------------------------------------ -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) (Note 3)
SOP-8 (Exposed Pad) -------------------------------------------------------------------------- 2.08W
● Package Thermal Resistance, (θJA)
SOP-8 (Exposed Pad) -------------------------------------------------------------------------- 60°C/W
● Package Thermal Resistance, (θJC)
SOP-8 (Exposed Pad) -------------------------------------------------------------------------- 15°C/W
Note 2: Stresses beyond this listed under “Absolute Maximum Ratings" may cause permanent damage to the device.
Note 3: PCB heat sink copper area=10mm2.
Recommended Operating Conditions
● Supply Voltage VIN ------------------------------------------------------------------------------------------ +4.5V to +23V
● Operation Temperature Range -------------------------------------------------------------------------- -40°C to + 85°C
FR9888C-0.3-MAR-2014
4
fitipower integrated technology lnc.
FR9888C
Electrical Characteristics
(VIN=12V, TA=25°C, unless otherwise specified.)
Parameter
Symbol
Conditions
Min
Typ
Max
Unit
VIN Input Supply Voltage
VIN
IDDQ
4.5
23
V
mA
μA
V
ꢀꢁHꢂꢃ=2V, VFB=1.0V
ꢀꢁHꢂꢃ=0V
VIN Quiescent Current
2.5
VIN Shutdown Supply Current
ISD
1
Feedback Voltage
VFB
4.5V≦VIN≦23V
0.9
0.925
1.5
0.95
Feedback OVP Threshold Voltage
High-Side MOSFET RDS(ON) (Note 4)
Low-Side MOSFET RDS(ON) (Note 4)
High-Side MOSFET Leakage Current
High-Side MOSFET Current Limit (Note 4)
Low-Side MOSFET Current Limit (Note 4)
VOVP
V
RDS(ON)
RDS(ON)
ILX(leak)
ILIMIT(HS)
ILIMIT(LS)
110
80
mΩ
mΩ
μA
A
ꢀꢁHꢂꢃ=0V, VLX=0V
Minimum Duty
10
4
5
From Drain to Source
A
1.5
3.5
Current sense to COMP Transconductance
(Note 4)
A/V
μA/V
V/V
kHz
kHz
%
Δ ICOMP = ±10μA
Error Amplifier Transconductance (Note 4)
Error Amplifier Voltage Gain (Note 4)
Oscillation frequency
1600
400
340
110
90
FOSC
290
420
Short Circuit Oscillation Frequency
Maximum Duty Cycle
FOSC(short) VFB=0V
DMAX
TMIN
VFB=0.8V
Minimum On Time (Note 4)
Input UVLO Threshold
100
4.3
ns
VUVLO(Vth) VIN Rising
VUVLO(HYS)
V
Under Voltage Lockout Threshold
Hysteresis
400
mV
Soft-Start Current
Soft-Start Period
ISS
VSS=0V
6
μA
ms
V
TSS
CSS=0.1μF
15
ꢀꢁHꢂꢃ(ꢄꢅ
0.4
ꢁHꢂꢃ Input Low Voltage
ꢁHꢂꢃ Input High Voltage
ꢀꢁHꢂꢃ(Hꢅ
ꢆꢁHꢂꢃ
TSD
2
V
ꢀꢁHꢂꢃ=2V
2
μA
°C
ꢁHꢂꢃ Input Current
Thermal Shutdown Threshold (Note 4)
Note 4: Not production tested.
170
FR9888C-0.3-MAR-2014
5
fitipower integrated technology lnc.
FR9888C
Typical Performance Curves
VIN=12V, VOUT=3.3ꢀ, C1=10μF× 2, C2=22μF×2, ꢄ1=10μH, TA=+25°C, unless otherwise noted.
VOUT = 3.3V
VOUT = 1.2V
Figure 5. Efficiency vs. Load Current
Figure 6. Efficiency vs. Load Current
VOUT = 5V
Figure 7. Efficiency vs. Load Current
Figure 8. Current Limit vs. Temperature
Figure 9. Feedback Voltage vs. Temperature
Figure 10. Switching Frequency vs. Temperature
FR9888C-0.3-MAR-2014
6
fitipower integrated technology lnc.
FR9888C
Typical Performance Curves (Continued)
VIN=12V, VOUT=3.3ꢀ, C1=10μF×2, C2=22μF×2, ꢄ1=10μH, TA=+25°C, unless otherwise noted.
IOUT=0A
IOUT=3.5A
VIN 10mV/div.
VOUT 20mV/div.
VIN 100mV/div.
IL 1A/div.
VOUT 20mV/div.
IL
1A/div.
VLX 5V/div.
VLX 5V/div.
2μs/div.
Figure 11. Steady State Waveform
2μs/div.
Figure 12. Steady State Waveform
IOUT=0A
IOUT=3.5A
VIN 5V/div.
VOUT 1V/div.
VIN 5V/div.
VOUT 1V/div.
IL
1A/div.
IL
1A/div.
VLX 5V/div.
VLX 5V/div.
40ms/div.
40ms/div.
Figure 13. Power On through VIN Waveform
Figure 14. Power On through VIN Waveform
IOUT=0A
IOUT=3.5A
VIN 10V/div.
VOUT 1V/div.
VIN 10V/div.
VOUT 1V/div.
IL
1A/div.
IL
1A/div.
VLX 5V/div.
VLX 5V/div.
10ms/div.
Figure 16. Power Off through VIN Waveform
20ms/div.
Figure 15. Power Off through VIN Waveform
FR9888C-0.3-MAR-2014
7
fitipower integrated technology lnc.
FR9888C
Typical Performance Curves (Continued)
VIN=12V, VOUT=3.3ꢀ, C1=10μF×2, C2=22μF×2, ꢄ1=10μH, TA=+25°C, unless otherwise noted.
IOUT=3.5A
IOUT=0A
ꢃ
5V/div.
ꢃ
5V/div.
ꢀꢁꢂ
ꢀꢁꢂ
VOUT 1V/div.
VOUT 1V/div.
IL
1A/div.
IL
1A/div.
VLX 5V/div.
VLX 5V/div.
4ms/div.
4ms/div.
Figure 18. Power On through ꢁHꢂꢃ Waveform
Figure 17. Power On through ꢁHꢂꢃ Waveform
IOUT=0A
IOUT=3.5A
ꢃ
5V/div.
ꢀꢁꢂ
ꢃ
5V/div.
ꢀꢁꢂ
VOUT 1V/div.
VOUT 1V/div.
IL 1A/div.
IL
1A/div.
5V/div.
VLX 5V/div.
VLX
80μs/div.
4ms/div.
Figure 19. Power Off through ꢁHꢂꢃ Waveform
Figure 20. Power Off through ꢁHꢂꢃ Waveform
VOUT 200mV/div.
VOUT 1V/div.
IL
2A/div.
IL
1A/div.
400μs/div.
Figure 22. Short Circuit Test
400μs/div.
Figure 21. Load Transient Waveform
FR9888C-0.3-MAR-2014
8
fitipower integrated technology lnc.
FR9888C
Function Description
Input Under Voltage Lockout
The FR9888C is a high efficiency and constant
frequency current mode step-down synchronous
When the FR9888C is power on, the internal
circuits will be 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).
DC/DC converter.
It has integrated high-side
(110mΩ, typ) and low-side (80mΩ, typꢅ power
switches, and provides 3.5A continuous load current.
It regulates input voltage from 4.5V to 23V, and down
to an output voltage as low as 0.925V.
Control Loop
Short Circuit Protection
During normal operation, the output voltage is
sensed at FB pin by a resistive voltage divider and
amplified through the error amplifier. The voltage of
error amplifier output pin -- COMP is compared to
the switch current to control the RS latch. At each
cycle, the high side NMOS will be turned on when
the oscillator sets the RS latch and turned off when
current comparator resets the RS latch. When the
load current increases, the FB pin voltage will drop
below 0.925V, and it will cause the COMP voltage
increasing until average inductor current arrives at
new load current.
The FR9888C provides short circuit protection
function to prevent the device damage 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.
Over Current Protection
The FR9888C over current protection function is
implemented by 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.
Enable
The FR9888C ꢁHꢂꢃ pin provides digital control to
turn on/turn off the regulator. When the voltage of
ꢁHꢂꢃ exceeds the threshold voltage, the regulator
will start the soft start function. If the ꢁHꢂꢃ pin
voltage is below the shutdown threshold voltage, the
regulator will turn into shutdown mode and shutdown
current will be smaller than 1μA. For auto start-up
operation, connect ꢁHꢂꢃ to ꢀꢆꢃ through a 100KΩ
resistor.
Over Temperature Protection
The FR9888C 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).
Soft Start
The FR9888C 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:
Compensation
The stability of the feedback circuit is controlled by
ꢀ
Cꢁꢁ nF ꢇꢀFꢈ
ꢀ
Tꢁꢁ ms =
COMP pin.
application circuit is optimized for particular
requirements. If different conversions are
The compensation value of the
ꢀ
ꢆꢁꢁ μA
The VFB voltage is 0.925V and the ISS current is 6μA.
ꢆf a 0.1μF capacitor is connected from ꢁꢁ pin to
GND, the soft start time will be 15ms.
required, some of the components may need to be
changed to ensure stability.
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.
FR9888C-0.3-MAR-2014
9
fitipower integrated technology lnc.
FR9888C
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 0.925V. 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
ꢁ
ꢂ
ꢀꢉꢊT=0.925ꢀꢇ 1+
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
30.9kΩ
30.9kΩ
4.99kΩ
4.99kΩ
6.98kΩ
12kΩ
ꢀ
ꢀ
ꢀRꢆPPꢄꢌ t =ꢀRꢆPPꢄꢌ(Cꢅ t +ꢀRꢆPPꢄꢌ(ꢌꢁRꢅ(tꢅ
3.3V
1.8V
1.2V
+ꢀRꢆPPꢄꢌ(ꢌꢁꢄꢅ(tꢅ+ꢀꢃꢉꢆꢁꢌ(tꢅ
5.23kΩ
16.5kΩ
The following figures show the form of the ripple
contributions.
Place resistors R1 and R2 close to FB pin to prevent
stray pickup.
VRIPPLE(ESR)(t)
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:
(t)
+
VRIPPLE(ESL) (t)
(t)
(t)
+
VRIPPLE(C) (t)
ꢀ
ꢃ
ꢆꢆꢃ(RMꢁꢅ=ꢆꢉꢊTꢇ ꢂꢇ 1ꢋꢂ
ꢀꢉꢊT
ꢂ=
ꢀꢆꢃ
+
Where D is the duty cycle of the power MOSFET.
VNOISE (t)
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.
2
3.5A
1.75
=
1.5
VRIPPLE(t)
1.25
1
0.75
1A
0.5
0.25
(t)
0
10 20 30 40 50 60 70 80 90
D (%)
FR9888C-0.3-MAR-2014
10
fitipower integrated technology lnc.
FR9888C
Application Information (Continued)
ꢀꢉꢊT
ꢀ
That will lower ripple current and result in lower
ꢁ
ꢉꢊTꢂ
ꢀRꢆPPꢄꢌ(ꢌꢁR, pꢋpꢅ
=
ꢇ 1ꢋ
ꢇꢌꢁR
output ripple voltage.
The ΔꢆL is inductor
FꢉꢁCꢇꢄ
ꢀꢆꢃ
peak-to-peak ripple current:
ꢌꢁꢄ
ꢀRꢆPPꢄꢌ(ꢌꢁꢄ, pꢋpꢅ
=
ꢇꢀꢆꢃ
ꢀꢉꢊT
ꢀ
ꢁ
ꢉꢊTꢂ
ꢄ+ꢌꢁꢄ
ꢀꢉꢊT
8ꢇFꢉꢁC2ꢇꢄꢇCꢉꢊT
ꢍꢆꢄ=
ꢇ 1ꢋ
FꢉꢁCꢇꢄ
ꢀꢆꢃ
ꢀ
ꢉꢊTꢂ
ꢁ
ꢀRꢆPPꢄꢌ(C, pꢋpꢅ
=
ꢇ 1ꢋ
The following diagram is an example to graphical
represent ΔꢆL equation.
ꢀꢆꢃ
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.
2
1.8
1.6
1.4
1.2
1
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 requirements.
When using the ceramic capacitors, the ESL
component is usually negligible.
0.8
0.6
0.4
0.2
5
8
11
14
17
20
23
VIN (V)
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 eliminates noise.
VOUT=3.3V, FOSC=340kHz
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:
Probe Ground
ꢍꢆꢄ=0.3ꢇꢆꢉꢊT(MAꢎꢅ
ꢀ
ꢀꢆꢃꢋꢀꢉꢊT ꢇꢀꢉꢊT
ꢄ=
ꢀꢆꢃꢇFꢉꢁCꢇꢍꢆꢄ
To guarantee sufficient output current, peak
inductor current must be lower than the FR9888C
VOUT
GND
high-side MOSFET current limit.
inductor current is as below:
The peak
Ceramic Capacitor
Inductor Selection
ꢍꢆꢄ
ꢆPꢌAK=ꢆꢉꢊT(MAꢎꢅ
+
2
IPEAK
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.
IOUT(MAX)
∆IL
Time
FR9888C-0.3-MAR-2014
11
fitipower integrated technology lnc.
FR9888C
Application Information (Continued)
Compensation Components 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:
COMP
C5
FR9888C
C7
(optional)
R4
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.
Select the appropriate compensation value by
following procedure:
. Calculate the R4 value with the following equation:
2. Place feedback resistors close to the FB pin.
3. Keep the sensitive signal (FB) away from the
switching signal (LX).
2 ꢇCꢉꢊTꢇ0.1ꢇFꢉꢁCꢇꢀꢉꢊT
R4ꢏ
ꢐꢌAꢇꢐCꢁꢇꢀRꢌF
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.
where GEA is the error amplifier voltage gain, and GCS
is the current sense gain.
. Calculate the C5 value with the following equation:
4
C5ꢑ
2 ꢇR4ꢇ0.1ꢇFꢉꢁC
External Diode Selection
5. Multi-layer PCB design is recommended.
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.
C6
R1
R3
D1
1N4148
R2
8
1
7
6
5
Exposed
VIN
BST
VIN
5V
GND
Pad
FR9888C
C4
C2
C1
4
2
3
LX
VIN
VOUT
LX
L1
C4
Figure 23. Recommended Layout Diagram
FR9888C-0.3-MAR-2014
12
fitipower integrated technology lnc.
FR9888C
Outline Information
SOP-8 (Exposed Pad) Package (Unit: mm)
DIMENSION IN MILLIMETER
SP SE
SYMBOLS
UNIT
MIN
1.25
0.00
MAX
1.70
0.15
MIN
1.25
0.00
MAX
1.70
0.15
A
A1
A2
B
1.25
0.31
4.80
3.04
3.80
2.15
1.20
5.80
0.40
1.55
0.51
5.00
3.50
4.00
2.41
1.34
6.20
1.27
1.25
0.31
4.80
1.80
3.80
1.80
1.20
5.80
0.40
1.55
0.51
5.00
2.40
4.00
2.40
1.34
6.20
1.27
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.
FR9888C-0.3-MAR-2014
13
相关型号：
©2020 ICPDF网 联系我们和版权申明