Not Recommended

Not Recommended
TS3553
3A/350kHz Synchronous Buck DC/DC Converter
SOP-8EP
Pin Definition:
1. BS
8. SS
2. VIN
7. EN
3. SW
6. COMP
4. GND
5. FB
General Description
The TS3553 is a synchronous step-down DC/DC converter that provides wide 4.5V to 23V input voltage range
and 3A continuous load current capability. 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 that provides fast transient response. In
shutdown mode, the regulator draws 1µA or less of supply current.
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Ordering Information
Package
SOP-8EP
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Part No.
TS3553CS RLG
Packing
2.5Kpcs / 13” Reel
Note: “G” denote for Halogen Free Product
Application
mm
Operating Voltage Range 4.75V~23V
Output load current up to 3A
High Efficiency: Up to 95%
Fixed Switching Frequency 350kHz
100mΩ Internal Power MOSFET
Adjustable Output Voltage from 0.925~20V
Stable with Low ESR Output Ceramic Capacitors
Current Mode Operation
Input Under Voltage Lockout
Over Temperature Protection
Cycle-by Cycle Current limit
<1µA Shutdown Current
Set-Top-Box
DVD, LCD Displays
Netbook
Distributed Power System
DSL Modems
No
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Typical Application Circuit
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Features
3.3V Output Application Circuit
1/11
Version: B11
TS3553
3A/350kHz Synchronous Buck DC/DC Converter
Absolute Maximum Rating
Characteristics
Symbol
Rating
Unit
V
V
V
V
V
W
ºC
ºC
ºC
ºC/W
ºC/W
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Maximum Supply Voltage
VIN
-0.3 ~ +24
Switching Pin Input Voltage
VSW
-1 ~ (VIN +0.3)
Boost Voltage
VBS
(VSW -0.3) ~ (VSW +6)
All Other Pins
-0.3 to +6
Output Voltage
VOUT
0.925 ~ 20
Power Dissipation
PD
Internal Limited
Operating Temperature Range
TOPR
-40 to +85
Storage Temperature Range
TST
-65 to +150
Operating Junction Temperature Range
TJ
+150
Thermal Resistance Junction to case
15
θJC
40
Thermal Resistance Junction to ambient
θJA
Note: Stresses exceed those rating may damage the device
2
Note: θJA is measured with the PCB copper area of approximately 1 in (multi-layer)
Parameter
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Electrical Specifications (TA=25oC, VIN=12V unless otherwise noted)
Symbol
Min
Typ
Max
Unit
4.75
--
23
V
--
1
3
µA
0.9
0.925
0.95
V
REGLOAD
-2
--
+2
%
RDSON
--
100
--
mΩ
RDSON
--
100
--
mΩ
--
--
10
µA
3.8
--
--
A
280
350
430
KHz
VIN
mm
Operating Voltage
Shutdown Supply Current
Feedback Voltage
Low-Side MOSFET On-Resistance
ISD
VEN =0V
VFB
4.75V ≤ VIN ≤ 23V
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Load Regulation
High-Side MOSFET On-Resistance
Conditions
IL(HIGH-SIDE)
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High-Side MOSFET Leakage Current
High-Side MOSFET Current Limit
ILIMIT
Oscillator Frequency
FOSC
VEN = 0V, VSW = 0V
Minimum Duty
FSC
VFB =0V
--
90
--
KHz
Maximum Duty Cycle
DC
VFB =0.8V
--
90
--
%
Soft-Start Current
ISS
VSS=0V
--
6
--
µA
CSS=0.1µF
--
15
--
mS
VEN Rising
1.1
1.5
2.0
V
--
160
--
°C
Soft-Start Period
No
Short Circuit Oscillator Frequency
EN Shutdown Threshold Voltage
VENSD
Thermal Shutdown
OTP
Thermal Shutdown Hysteresis
OTPHYSTERSIS
-35
-°C
Note 1: Specifications are production tested at TA=25°C. Specifications over the -40°C to 85°C operat ing
temperature range are assured by design, characterization and correlation with Statistical Quality Controls
(SQC).
Note 2: It is recommended to use duty ratio above 10% for minimizing resultant duty cycle jitter.
Note 3: It is recommended to connect a soft start capacitor to soft start pin. Leave the soft start pin open may
cause large inrush current and output overshooting
2/11
Version: B11
TS3553
3A/350kHz Synchronous Buck DC/DC Converter
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Block Diagram
Pin Function Description
Pin NO. Pin Name
VIN
3
SW
4
GND
5
FB
6
COMP
7
EN
8
SS
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2
High-Side Gate Drive Boost Input. BS supplies the drive for the high-side N-Channel
MOSFET switch. Connect a 0.01µF or greater capacitor from SW to BS to power the
high side switch.
Power Input. IN supplies the power to the IC, as well as the step-down converter
switches. Drive IN with a 4.75V to 23V power source. Bypass IN to GND with a suitably
large capacitor to eliminate noise on the input to the IC. See Input Capacitor.
Power Switching Output. SW is the switching node that supplies power to the output.
Connect the output LC filter from SW to the output load. Note that a capacitor is
required from SW to BS to power the high-side switch.
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BS
No
1
Pin Description
Ground.
Feedback Input. FB senses the output voltage to regulate that voltage. Drive FB with a
resistive voltage divider from the output voltage. The feedback threshold is 0.925V. See
Setting the Output Voltage.
Compensation Node. COMP is used to compensate the regulation control loop.
Connect a series RC network from COMP to GND to compensate the regulation control
loop. In some cases, an additional capacitor from COMP to GND is required. See
Compensation Components.
Enable Input. EN is a digital input that turns the regulator on or off. Drive EN high to turn
on the regulator, drive it low to turn it off. Pull up with 100kΩ resistor for automatic
startup.
Soft-Start Control Input. SS controls the soft start period. Connect a capacitor from SS
to GND to set the soft-start period. A 0.1µF capacitor sets the soft-start period to 15ms.
To disable the soft-start feature, leave SS unconnected.
3/11
Version: B11
TS3553
3A/350kHz Synchronous Buck DC/DC Converter
Function Description
The TS3553 is a constant frequency current mode step-down synchronous DC/DC converter. It regulates input
voltage from 4.75V to 23V, down to an output voltage as low as 0.925V, and can provide 3A of continuous load
current.
Control Loop
During normal operation, the output voltage is sensed at FB pin through 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
controls the RS latch. At each cycle, the high side NMOS would be turned on when the oscillator sets the RS latch
and would be turned off when current comparator resets the RS latch. When the load current increases, the FB pin
voltage drops below 0.925V, it causes the COMP voltage increase until average inductor current arrive at new load
current.
Enable
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The TS3553 EN pin provides digital control to turn on/turn off the regulator. When the voltage of EN exceeds the
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threshold voltage, the regulator starts the soft start function. If the EN pin voltage is below than the threshold
regulator will be disable and into the shutdown mode.
Maximum Load Current
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voltage, only the bandgap voltage is alive. If the EN pin voltage is below than the shutdown threshold voltage, the
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The maximum load current decreases at lower input voltage because of large IR drop on the high side switch and
low side switch. The slope compensation signal reduces the peak inductor current as a function of the duty cycle to
prevent sub-harmonic oscillations at duty cycles greater than 50%.
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Output Over Voltage Protection
When the FB pin voltage exceeds 20% of the regulation voltage, the output over voltage protection function will
discharge the COMP pin and the SS pin to GND, turning the high side MOSFET off.
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Input Under Voltage Lockout
When the TS3553 power on, the internal circuits are held inactive until VIN exceeds the input UVLO threshold
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voltage. And the regulator will be disabled when VIN below the input UVLO threshold voltage. The hysteretic of the
UVLO comparator is 400 mV.
Short Circuit Protection
The TS3553 provides short circuit protection function to prevent the device damage from short condition. When the
output short to ground, the oscillator frequency is reduced to prevent the inductor current increasing beyond the
current limit. In the meantime, the current limit is also 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 TS3553 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.
Compensation
The stability of the feedback circuit is controlled through COMP pin. The compensation value of the application
circuit is optimized for particular requirements. If different conversions are requires, some of the components may
need to be changes to ensure stability.
4/11
Version: B11
TS3553
3A/350kHz Synchronous Buck DC/DC Converter
Application Information
Setting Output Voltage
The output voltage is set using a resistive divider from the output to FB. The FB pin regulated voltage is 0.925V.
Thus the output voltage is:
R2 recommended value is 10KΩ~30KΩ, so R1 is determined by: R1 = 10.81 x (VOUT – 0.925) KΩ
Recommended Component Selection
R1 (KΩ)
44.1
25.7
9.5
3
0.81
R2 (KΩ)
10
10
10
10
10
R3 (KΩ)
2.2
2.2
2.2
2.2
2.2
L1 (µH)
15
10
4.7
3.3
2.2
COUT (µF)
10 X 2
10 X 2
10 X 2
10 X 2
10 X 2
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Selecting Inductor
C3 (nF)
3.3
3.3
3.3
3.3
3.3
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VOUT (V)
5
3.3
1.8
1.2
1
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VIN (V)
12
5 or 12
5 or 12
5 or 12
5 or 12
mm
The inductor selection depends on the current ripple of inductor, the input voltage and the output voltage.
Accepting a large current ripple of inductor allows the use of a smaller inductance. However, higher current ripple
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of inductor can cause higher output ripple voltage and large core loss. By setting an acceptable current ripple of
inductor, a suitable inductance can be obtained from above formula.
In addition, it is important to ensure the inductor saturation current exceeds the peak value of inductor current in
Soft-Start
No
following formula.
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application to prevent core saturation. The peak value of inductor current can be calculated according to the
The TS3553 provides the soft-start function. Initially, the voltage at SS pin is 0V. Then an internal current source of
6A (typ.) charges an external soft-start capacitor. During the soft-start period, the voltage at SS pin will limit the
feedback threshold voltage at FB pin. When the voltage at SS pin is higher than 0.925V, the feedback threshold
voltage at FB pin reaches the desired value. The soft-start time can be calculated in accordance with the following
formula:
The soft-start capacitor is discharged to GND when the EN pin is connected to GND
5/11
Version: B11
TS3553
3A/350kHz Synchronous Buck DC/DC Converter
Application Information (Continue)
Optional Schottky Diode
A Schottky diode with low forward drop voltage and fast reverse recovery is the ideal choice for better efficiency.
The forward drop voltage of a Schottky diode will result in the conduction losses in the diode, and the diode
capacitance (CT or CD) will cause the switching losses. Therefore, it is necessary to consider both forward voltage
drop and diode capacitance for diode selection. In addition, the rating of selected Schottky diode should be able to
handle the input voltage and the maximum peak diode current.
Input Capacitor the Output Capacitor
To prevent the high input voltage ripple and noise resulted from high frequency switching, the use of low ESR
ceramic capacitor for the maximum RMS current is recommended. The approximated RMS current of the input
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capacitor can be calculated according to the following formula.
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The selection of output capacitor depends on the required output voltage ripple. The output voltage ripple can be
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expressed as:
For lower output voltage ripple, the use of low ESR ceramic capacitor is recommended. The tantalum capacitor can
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also be used well, but its ERS is larger than that of ceramic capacitor.
When choosing the input and output ceramic capacitors, X5R and X7R types are recommended because they
Loop Compensation
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retain their capacitance over wider ranges of voltage and temperature than other types.
In order to avoid the poor output voltage ripple and low efficiency caused by instability, TS3553 requires a proper
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external compensation network to compensate its feedback loop. In this external compensation network, the
compensation resistor, RC, and the compensation capacitor, CC, are used to set the high-frequency integrator gain
and the integrator zero. C7 is used to cancel the zero caused by the output capacitor and it’s ESR. While using the
ceramic capacitor as the output capacitor, C7 can be omitted due to the small ESR.
The system has one pole of importance, due to the output capacitor, C3//C4 and the load resistor. This poles is
located at:
6/11
Version: B11
TS3553
3A/350kHz Synchronous Buck DC/DC Converter
Application Information (Continue)
Loop Compensation
The system has one zero of importance, due to the compensation capacitor, Cc and the compensation resistor, Rc.
This zero is located at:
The system may have another zero of importance, if the output capacitor has a large capacitance and/or a high
ESR value. The zero, due to the ESR and capacitance of the output capacitor, is located at:
In this case, a third pole set by the compensation capacitor, C7 and the compensation resistor, Rc is used to
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compensate the effect of the ESR zero on the loop gain. This pole is located at:
The values of the compensation components given in this data sheet yield a stable control loop for the given output
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voltage and capacitor. If different conversions and output capacitors are requires, some values of the
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compensation components may need to be adjusted to ensure stability.
7/11
Version: B11
TS3553
3A/350kHz Synchronous Buck DC/DC Converter
Electrical Characteristics Curve
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(TA=25ºC, C1=10µF, C2=22µF, C3=0.1µF, L1=10µH unless otherwise noted)
Figure 1. Efficiency vs. Load Current at VIN=12V
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Figure 2. Start-Up Waveform at IOUT=0A
Figure 3. Start-Up Waveform at IOUT=3A
Figure 4. Shutdown Waveform at IOUT=0A
Figure 5. Shutdown Waveform at IOUT=3A
Figure 6. Load Transient
8/11
Version: B11
TS3553
3A/350kHz Synchronous Buck DC/DC Converter
Electrical Characteristics Curve
Figure 8. Short Circuit Recovery Waveforms
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Figure 7. Short Circuit Waveforms
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(TA=25ºC, C1=10µF, C2=22µF, C3=0.1µF, L1=10µH unless otherwise noted)
Figure 9. Stability Waveform at IOUT=0A
Figure 10. Stability Waveform at IOUT=3A
9/11
Version: B11
TS3553
3A/350kHz Synchronous Buck DC/DC Converter
SOP-8EP Mechanical Drawing
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Marking Diagram
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mm
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A
B
C
D
E
E1
F
G
K
M
P
R
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DIM
SOP-8EP DIMENSION
MILLIMETERS
INCHES
MIN
MAX
MIN
MAX.
4.80
5.00
0.189
0.196
3.80
4.00
0.150
0.157
1.35
1.75
0.054
0.068
0.35
0.49
0.014
0.019
2.05
2.41
0.081
0.095
2.82
3.30
0.111
0.130
0.40
1.25
0.016
0.049
1.27BSC
0.05BSC
0.10
0.25
0.004
0.009
0º
7º
0º
7º
5.80
6.20
0.229
0.244
0.25
0.50
0.010
0.019
Y = Year Code
M = Month Code for Halogen Free Product
(O=Jan, P=Feb, Q=Mar, R=Apl, S=May, T=Jun, U=Jul, V=Aug,
W=Sep, X=Oct, Y=Nov, Z=Dec)
L = Lot Code
10/11
Version: B11
TS3553
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3A/350kHz Synchronous Buck DC/DC Converter
Notice
Specifications of the products displayed herein are subject to change without notice. TSC or anyone on its behalf,
assumes no responsibility or liability for any errors or inaccuracies.
Information contained herein is intended to provide a product description only. No license, express or implied, to
any intellectual property rights is granted by this document. Except as provided in TSC’s terms and conditions of
sale for such products, TSC assumes no liability whatsoever, and disclaims any express or implied warranty,
relating to sale and/or use of TSC products including liability or warranties relating to fitness for a particular purpose,
merchantability, or infringement of any patent, copyright, or other intellectual property right.
The products shown herein are not designed for use in medical, life-saving, or life-sustaining applications.
Customers using or selling these products for use in such applications do so at their own risk and agree to fully
indemnify TSC for any damages resulting from such improper use or sale.
11/11
Version: B11
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