FP6381A
/a85T
High Efficiency 1.5MHz 1.2A
Synchronous Step Down Converter
Description
Features
The FP6381A is a high efficiency, high frequency
synchronous DC-DC step-down converter. The
100% duty cycle feature provides low dropout
operation, extending battery life in portable systems.
The internal synchronous switch increases efficiency
and eliminates the need for external Schottky diode.
At shutdown mode, the input supply current is less
than 1µA.
The FP6381A fault protection includes cycle-by-cycle
current limit, short circuit protection, UVLO and
thermal shutdown. The Internal soft-start function
prevents inrush current at turn-on.
The FP6381A is offered in SOT-23-5, TSOT-23-5
and SOT-23-6 Packages
Low RDS(ON) for Internal Switch (Top/Bottom):
300/250mΩ
2.5V~6V Input Voltage Range
0.6V Reference Voltage
1.2A Output Current
1.5MHz Switching Frequency
Internal 1ms Soft-Start Time
Internal Compensation Function
100% Dropout Operation
Power Good Indicator Output (SOT-23-6 only)
RoHS Compliant and Halogen Free
SOT-23-5, TSOT-23-5 and SOT-23-6 Packages
Applications
Set Top Box
LCD TV & Tablet
AP Router & WiFi Dongle
3.5G & 4G Dongle
USB3.0 & SSD storage
Pin Assignments
Ordering Information
S5 Package (SOT-23-5)
FP6381A□□□
FB
VIN
5
4
1
2
TR: Tape/Reel
C: Green
3
Package Type
S5: SOT-23-5
S6: SOT-23-6
S8: TSOT-23-5
EN GND LX
S6 Package (SOT-23-6)
FB
PG VIN
6
5
4
1
2
3
EN GND LX
S8 Package (TSOT-23-5)
FB
VIN
5
4
1
2
SOT-23-5 Marking
Part Number
Product Code
FP6381AS5CTR
FA2
SOT-23-6 Marking
Part Number
Product Code
FP6381AS6CTR
FC4
TSOT-23-5 Marking
Part Number
Product Code
FP6381AS8CTR
FF5
3
EN GND LX
Figure 1. Pin Assignment of FP6381A
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Typical Application Circuit
OFF ON
EN
L1
VIN
VIN
C1
C4
PG
LX
VOUT
FP6381A
R3
PG
R1
C3
C2
(opt.)
FB
GND
R2
Figure 2. Schematic Diagram
VIN=5V, the recommended BOM list is as below.
VOUT
3.3V
2.5V
1.8V
1.5V
1.2V
1.05V
C1
4.7μF MLCC
4.7μF MLCC
4.7μF MLCC
4.7μF MLCC
4.7μF MLCC
4.7μF MLCC
C4
0.1μF MLCC
0.1μF MLCC
0.1μF MLCC
0.1μF MLCC
0.1μF MLCC
0.1μF MLCC
R1
453kΩ
316kΩ
200kΩ
150kΩ
100kΩ
75kΩ
R2
100kΩ
100kΩ
100kΩ
100kΩ
100kΩ
100kΩ
L1
2.2μH
2.2μH
2.2μH
1.8μH
1.8μH
1.5μH
C2
10μF MLCC
10μF MLCC
10μF MLCC
10μF MLCC
10μF MLCC
10μF MLCC
Table 1. Recommended Component Values
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Functional Pin Description
Pin Name
Pin No.
(SOT-23-5)
(TSOT-23-5)
Pin No.
(SOT-23-6)
VIN
4
4
Power Supply Input Pin.
to avoid noise influence.
GND
2
2
Ground Pin.
EN
1
1
Enable Control Pin. Pull high to turn the IC on, and pull low to disable the IC. Don’t
leave this pin floating.
FB
5
6
Voltage Feedback Input Pin. Connect FB and VOUT with a resistive voltage divider.
This IC senses feedback voltage via FB and regulates it at 0.6V.
PG
--
5
Open Drain Power Good Output Pin.
LX
3
3
Power Switching Output.
Pin Function
Placed input capacitors as close as possible from VIN to GND
Connect an external inductor to this switching node.
Block Diagram
PG
(SOT-23-6)
Power Good
EN
VIN
1M
Undervoltage
Lockout
Bias Supply
Enable
Control
Slope Compensation
90%
VREF
FB
COMP
EA
Control Logic
Current Limit
Logic
Control
and
Driver
Logic
1
X
LX
Compensation
VREF
Soft
Start
Oscillator
COMP
GND
Figure 3. Block Diagram of FP6381A
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Absolute Maximum Ratings (Note 1)
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● VIN to GND -------------------------------------------------------------------------------------------------- -0.3V to +6.5V
● LX to GND --------------------------------------------------------------------------------------------------- -0.3V to VIN+0.3V
● EN, FB, PG to GND --------------------------------------------------------------------------------------- -0.3V to VIN
● Package Thermal Resistance, (θJA)
SOT-23-5 ---------------------------------------------------------------------------------------- +250°C/W
TSOT-23-5 -------------------------------------------------------------------------------------- +250°C/W
SOT-23-6 ---------------------------------------------------------------------------------------- +250°C/W
● Package Thermal Resistance, (θJC)
SOT-23-5 ---------------------------------------------------------------------------------------- +130°C/W
TSOT-23-5 -------------------------------------------------------------------------------------- +130°C/W
SOT-23-6 ---------------------------------------------------------------------------------------- +110ºC/W
● Maximum Junction Temperature (TJ) ----------------------------------------------------------------- +150°C
● Lead Temperature (Soldering, 10sec.) --------------------------------------------------------------- +260°C
● Storage Temperature (TS) ------------------------------------------------------------------------------- -65°C to +150°C
Note 1:Stresses beyond those listed under “Absolute Maximum Ratings" may cause permanent damage to the device.
Recommended Operating Conditions (Note 2)
● Supply Voltage (VIN) ------------------------------------------------------------------------------------------- +2.5V to +6V
● Operation Temperature Range (TOPR) -------------------------------------------------------------------- -40°C to +85°C
Note 2:The device is not guaranteed to function outside its operating conditions.
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Electrical Characteristics
(VIN=5V, VOUT=2.5V, TA=25°C, unless otherwise specified.)
Parameter
Symbol
Shutdown Current
ISHDN
Quiescent Current
Iq
Reference Voltage
VREF
FB Input Leakage Current
P-Channel MOSFET On-Resistance
(Note 3)
N-Channel MOSFET On-Resistance
(Note 3)
IFB
Conditions
Min
Typ
Max
Unit
EN=0V
0.1
1
μA
VFB=0.65V, IOUT=0A
80
0.588
VFB=VIN
μA
0.6
0.612
V
0.01
1
µA
RDS(ON)
300
mΩ
RDS(ON)
250
mΩ
P-Channel Current Limit (Note 3)
ILIM
1.6
A
EN High-Level Input Voltage
VIH
1.5
V
EN Low-Level Input Voltage
VIL
Under Voltage Lockout Voltage
0.4
V
UVLO
2.4
V
UVLO Hysteresis
VHYS
0.2
V
Oscillation Frequency
FOSC
IOUT=200mA
1.2
Minimum On Time
50
Maximum Duty Cycle
Internal Soft Start Time
PG Rising Threshold
PG Sink Current
100
TSS
1.8
MHz
ns
%
1
ms
VPG (H)
VFB Rising
90
%
IPG
VPG=0.1V
1
mA
100
Ω
150
°C
LX Discharge Resistance
Thermal Shutdown Temperature
(Note 3)
1.5
TSD
Note 3:Guarantee by design.
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Typical Performance Curves
VIN=5V, C1=4.7μF//0.1μF, C2=10μF, C3=22pF, L1=1.8μH, TA=+25°C, unless otherwise noted.
VOUT=3.3V
VOUT=1.2V
Figure 5. Efficiency vs. Load Current
1.8
0.604
0.602
0.6
0.598
0.596
0.594
0.592
0.59
0.588
0.586
0.584
0.582
0.58
1.7
Frequency (KHz)
Feedback Voltage (V)
Figure 4. Efficiency vs. Load Current
VIN=5V
IOUT=0.2A
1.6
1.5
1.4
VIN=5V, VOUT=1.2V
IOUT=0.4A
1.3
1.2
-40 -30 -20 -10 0
10 20 30 40 50 60 70 80 90
-40 -30 -20 -10
Temperature (°C)
10 20 30 40 50 60 70 80
Temperature (°C)
Figure 6. Feedback Voltage vs. Temperature
IOUT=0A
0
Figure 7. Frequency vs. Temperature
IOUT=1.2A
VIN
2V/div.
VOUT
20mV/div.
VLX
2V/div.
IL
100mA/div.
2V/div.
VOUT
20mV/div.
VLX
2V/div.
IL
4ms/div.
Figure 8. Steady State Waveform
FP6381A-0.5-SEP-2015
VIN
500mA/div.
400ns/div.
Figure 9. Steady State Waveform
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Typical Performance Curves (Continued)
VIN=5V, VOUT=1.2V, C1=4.7μF//0.1μF, C2=10μF, C3=22pF, L1=1.8μH, TA=+25°C, unless otherwise noted.
IOUT=1.2A
IOUT=0A
VIN
2V/div.
VIN
2V/div.
VOUT
500mV/div.
VOUT
500mV/div.
VLX
2V/div.
VLX
2V/div.
IL
200mA/div.
IL
1A/div.
400μs/div.
400μs/div.
Figure 10. Power On through VIN Waveform
IOUT=0A
Figure 11. Power On through VIN Waveform
IOUT=1.2A
VIN
2V/div.
VIN
2V/div.
VOUT
500mV/div.
VOUT
500mV/div.
VLX
2V/div.
IL
VLX
IL
1A/div.
2V/div.
1A/div.
20ms/div.
1ms/div.
Figure 12. Power Off through VIN Waveform
Figure 13. Power Off through VIN Waveform
IOUT=0A
IOUT=1.2A
VEN
VEN
5V/div.
VOUT
500mV/div.
VLX
IL
5V/div.
VOUT
500mV/div.
VLX
5V/div.
5V/div.
500mA/div.
IL
1A/div.
200μs/div.
200μs/div.
Figure 14. Power On through EN Waveform
Figure 15. Power On through EN Waveform
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Typical Performance Curves (Continued)
VIN=5V, VOUT=1.2V, C1=4.7μF//0.1μF, C2=10μF, C3=22pF, L1=1.8μH, TA=+25°C, unless otherwise noted.
IOUT=0A
IOUT=1.2A
VEN
5V/div.
VEN
5V/div.
VOUT
500mV/div.
VOUT
500mV/div.
VLX
2V/div.
VLX
2V/div.
IL
100mA/div.
IL
1A/div.
2ms/div.
40μs/div.
Figure 16. Power Off through EN Waveform
Figure 17. Power Off through EN Waveform
IOUT=0.3A to 1.2A
VOUT
IL
100mV/div.
500mA/div.
200μs/div.
Figure 18. Load Transient Waveform
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Function Description
The FP6381A is a high efficiency, internal
compensation and constant frequency current mode
step-down synchronous DC/DC converter. It has
integrated high-side (300mΩ, typ.) and low-side
(250mΩ, typ.) power switches, and provides 1.2A
continuous load current. It regulates input voltage
from 2.5V to 6V, and down to an output voltage as
low as 0.6V.
Control Loop
Slope compensated current mode PWM control
provides stable switching and cycle-by-cycle current
limit for superior load, line response, protection of the
internal main switch and synchronous rectifier. The
FP6381A switches at a constant frequency (1.5MHz)
and regulates the output voltage. During each cycle,
the PWM comparator modulates the power
transferred to the load by changing the inductor peak
current based on the feedback error voltage. During
normal operation, the main switch is turned on for a
certain time to ramp the inductor current at each
rising edge of the internal oscillator, and switched off
when the peak inductor current is above the error
voltage.
When the main switch is off, the
synchronous rectifier will be turned on immediately
and stay on until next cycle starts.
Enable
The FP6381A EN pin provides digital control to turn
on/off the regulator. When the voltage of EN
exceeds the threshold voltage, the regulator will start
the soft start function. If the EN 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 EN to VIN.
Soft Start
The FP6381A employs internal soft start function to
reduce input inrush current during start up. The
internal soft start time will be 1ms.
Over Current Protection
The FP6381A 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.
Short Circuit Protection
The FP6381A 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
regulation level, the oscillator frequency will be
reduced 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 Temperature Protection
The FP6381A 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 30°C (typ).
PG Signal Output
PG pin is an open-drain output and requires a pull
up resistor. PG is actively held low in soft-start,
standby and shutdown. It is released when the
output voltage rises above 90% of nominal
regulation point.
Under Voltage Lockout
When the FP6381A is power on, the internal circuits
will be held inactive until VIN voltage exceeds the
UVLO threshold voltage. And the regulator will be
disabled when VIN is below the UVLO threshold
voltage. The hysteretic of the UVLO comparator is
200mV (typ).
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Application Information
Output Voltage Setting
The output voltage VOUT is set by using a resistive
divider from the output to FB. The FB pin regulated
voltage is 0.6V. Thus the output voltage is:
T= .
1+
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.
Output Capacitor Selection
R1
R2
Table 2 lists recommended values of R1 and R2 for
most used output voltage.
Table 2 Recommended Resistance Values
VOUT
R1
R2
3.3V
453kΩ
100kΩ
2.5V
316kΩ
100kΩ
1.8V
200kΩ
100kΩ
1.5V
150kΩ
100kΩ
1.2V
100kΩ
100kΩ
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:
R PPL
t =
R PPL
+
C
t +
R PPL ( SL
R PPL
SR
t
t +
S
t
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.
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:
(RMS
=
=
1
T
T
+
VRIPPLE(ESL) (t)
(t)
+
VRIPPLE(C) (t)
(t)
+
VNOISE (t)
(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)
0.6
1.2A
IIN(RMS) (A)
0.5
(t)
0.4
0.3
0.5A
0.2
0.1
0
10 20 30 40 50 60 70 80 90
D (%)
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Application Information (Continued)
R PPL ( SR
=
R PPL ( SL
=
R PPL
(C =
T
F
SC
T
1
L
SR
SL
L+ SL
L=
T
F
SC2
That will lower ripple current and result in lower
output ripple voltage.
The Δ L is inductor
peak-to-peak ripple current:
L C
1
T
F
SC
T
T
The following diagram is an example to graphically
represent Δ L 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.
Probe Ground
0.45
L=1.5μH
0.4
ΔIL (A)
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.
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.
0.35
L=1.8μH
0.3
L=2.2μH
0.25
0.2
0.15
2.5
3
3.5
4.5
6
.
T(MA
T
F
T
SC
L
To guarantee sufficient output current, peak inductor
current must be lower than the FP6381A high-side
MOSFET current limit. The peak inductor current
is shown as below:
P A
=
Load Current
Inductor Selection
FP6381A-0.5-SEP-2015
5.5
A good compromise value between size and
efficiency is to set the peak-to-peak inductor ripple
current Δ L equal to 30% of the maximum load
current. But setting the peak-to-peak inductor
ripple current Δ L between 20%~50% of the
maximum load current is also acceptable. Then
the inductance can be calculated with the following
equation:
Ceramic Capacitor
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.
5
VOUT=1.2V, FOSC=1.5MHz
L=
GND
4
VIN (V)
L=
VOUT
T
1
L
T(MA
+
L
2
IPEAK
IOUT(MAX)
∆IL
Time
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FP6381A
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Application Information (Continued)
Feedforward Capacitor Selection
PCB Layout Recommendation
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 transient response or
higher phase margin.
The device’s performance and stability are
dramatically affected by PCB layout.
It is
recommended to follow these general guidelines
shown as below:
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.
FB
R2
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:
C =
2
1
FCR
SS
1
R1
1
1
+
R1 R2
2. Place feedback resistors close to the FB pin.
3. Keep the sensitive signal (FB) away from the
switching signal (LX).
4. Multi-layer PCB design is recommended.
GND
C1
VOUT
L1
VIN
VIN
4
3
LX
PG
5
2
GND
FB
6
1
EN
R1
C3
C3
R1
FP6381A
R3
VOUT
C2
GND
R2
Figure 19. Recommended Layout Diagram
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 330pF.
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Outline Information
SOT-23-5 Package (Unit: mm)
SYMBOLS
UNIT
DIMENSION IN MILLIMETER
MIN
MAX
A
0.90
1.45
A1
0.00
0.15
A2
0.90
1.30
B
0.30
0.50
D
2.80
3.00
E
2.60
3.00
E1
1.50
1.70
e
0.90
1.00
e1
1.80
2.00
L
0.30
0.60
Note:Followed From JEDEC MO-178-C.
Carrier Dimensions
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Outline Information (Continued)
TSOT-23-5 Package (Unit: mm)
SYMBOLS
UNIT
DIMENSION IN MILLIMETER
MIN
MAX
A
0.70
0.90
A1
0.00
0.10
A2
0.70
1.00
B
0.30
0.50
D
2.80
3.00
E
2.60
3.00
E1
1.50
1.70
e
0.90
1.00
e1
1.80
2.00
L
0.30
0.60
Carrier Dimensions
Tape Size
(W1) mm
Pocket Pitch
(P) mm
8
4
FP6381A-0.5-SEP-2015
Reel Size (A)
in
mm
Reel Width
(W2) mm
7
180
8.4
Empty Cavity
Length mm
Units per Reel
300~1000
3,000
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Outline Information (Continued)
SOT-23-6 Package (Unit: mm)
SYMBOLS
UNIT
DIMENSION IN MILLIMETER
MIN
MAX
A
0.90
1.45
A1
0.00
0.15
A2
0.90
1.30
B
0.30
0.50
D
2.80
3.00
E
2.60
3.00
E1
1.50
1.70
e
0.90
1.00
e1
1.80
2.00
L
0.30
0.60
Note:Followed From JEDEC MO-178-C.
Carrier Dimensions
Life Support Policy
Fitipower’s products are not authorized for use as critical components in life support devices or other medical systems.
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