Techcode®
DATASHEET
2A 20V Synchronous Rectified Step-Down Converte
TD1482A
General Description
Features
The TD1482A is a monolithic pulse-width-modulated (PWM)
synchronous step-down switch mode regulator with two
internal power MOSFETs. It achieves 2A continuous output
current over a wide input supply range with excellent load
and line regulation. Current mode operation provides fast
transient response and eases loop stabilization. Fault
condition protection includes cycle-by-cycle current limit and
thermal shutdown.
This device, available in an SOP8 package, provides a
very compact solution with minimal external components.
•
•
2A Output Current
Wide 4.75V to 20V Operating Input Range
•
Integrated 130mΩ Power MOSFET Switches
•
Output Adjustable from 0.923V to 18V
•
Up to 93% Efficiency
•
Programmable Soft-Start
•
Stable with Low ESR Ceramic Output Capacitors
•
Fixed 340KHz Frequency
•
Cycle-by-Cycle Over Current Protection
•
Input Under Voltage Lockout
Applications
•
•
Distributed Power Systems
Networking Systems
•
FPGA, DSP, ASIC Power Supplies
•
Green Electronics/ Appliances
•
Notebook Computers
Package Types
SOP8
Figure 1. Package Types of TD1482A
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DATASHEET
2A 20V Synchronous Rectified Step-Down Converte
TD1482A
Pin Configurations
Figure 2 Pin Configuration of TD1482A(Top View)
Pin Description
Pin Number
Pin Name
Description
High-Side Gate Drive Boost Input. BS supplies the drive for the high-side N-Channel
1
BS
MOSFET switch. Connect a 0.01µF or greater capacitor from SW to BS to power the
high side switch.
2
IN
Supply Voltage. The TD1482A operates from a +4.75V to +20V unregulated input.
C1 is needed to prevent large voltage spikes from appearing at the input.
Power Switching Output. SW is the switching node that supplies power to the output.
3
SW
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.
4
GND
5
FB
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 0.923V.
Compensation Node. COMP is used to compensate the regulation control loop.
6
COMP
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.
Enable Input. EN is a digital input that turns the regulator on or off. Drive EN high to
7
EN
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
8
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.
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DATASHEET
2A 20V Synchronous Rectified Step-Down Converte
TD1482A
Ordering Information
TD1482A □
□
Circuit Type
Packing:
Blank:Tube
R:Type and Reel
Package
P:SOP8
Function Block
Figure 3 Function Block Diagram of TD1482A
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TD1482A
2A 20V Synchronous Rectified Step-Down Converte
Absolute Maximum Ratings
Parameter
Symbol
Value
Unit
Supply Voltage
VIN
-0.3 to 20
V
Switch Node Voltage
VSW
20
V
Boost Voltage
VBS
VSW – 0.3V to VSW +6V
V
Output Voltage
VOUT
0.923V to 18
V
–0.3V to +6V
V
All Other Pins
Operating Junction Temperature
TJ
150
ºC
Operating Ambient Temperature
TA
-40 to 80
ºC
Storage Temperature
TSTG
-65 to 150
ºC
Lead Temperature (Soldering, 10 sec)
TLEAD
260
ºC
2000
V
ºC / W
ºC / W
ESD (HBM)
MSL
Thermal Resistance-Junction to Ambient
RθJA
Level3
90
Thermal Resistance-Junction to Case
RθJC
45
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TD1482A
2A 20V Synchronous Rectified Step-Down Converte
Electrical Characteristics
VIN = 12V, Ta = 25℃ unless otherwise specified.
Parameters
Symbol
Shutdown Supply Current
Min.
VEN = 0V
VEN = 2.0V; VFB =
Supply Current
Feedback Voltage
Test Condition
1.0V
VFB
4.75V ≤ VIN ≤ 20V
0.900
Feedback Overvoltage Threshold
Typ.
Max.
Unit
1
3.0
µA
1.3
1.5
mA
0.923
0.946
V
1.1
V
400
V/V
800
µA/V
Error Amplifier Voltage Gain *
AEA
Error Amplifier Transconductance
GEA
High-Side Switch On Resistance *
RDS(ON)1
130
mΩ
Low-Side Switch On Resistance *
RDS(ON)2
130
mΩ
High-Side Switch Leakage
∆IC = ±10µA
VEN = 0V, VSW = 0V
Current
Upper Switch Current Limit
Minimum Duty Cycle
Lower Switch Current Limit
From Drain to Source
COMP to Current Sense
Transconductance
Oscillation Frequency
Short Circuit Oscillation
Frequency
Maximum Duty Cycle
10
2.4
GCS
Fosc1
3.4
A
1.1
A
3.5
A/V
340
KHz
Fosc2
VFB = 0V
100
KHz
DMAX
VFB = 1.0V
90
%
220
ns
Minimum On Time *
EN Shutdown Threshold Voltage
µA
VEN Rising
1.1
1.5
2.0
V
EN Shutdown Threshold Voltage
Hysteresis
210
EN Lockout Threshold Voltage
2.2
EN Lockout Hysterisis
October, 20, 2010.
2.5
210
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mV
2.7
V
mV
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TD1482A
2A 20V Synchronous Rectified Step-Down Converte
Electrical Characteristics(Cont.)
VIN = 12V, Ta = 25℃ unless otherwise specified.
Parameters
Symbol
Input Under Voltage Lockout
Threshold
Test Condition
VIN Rising
Min.
3.80
Input Under Voltage Lockout
Typ.
4.10
Max.
4.40
Unit
V
210
mV
Threshold Hysteresis
Soft-Start Current
VSS = 0V
6
µA
Soft-Start Period
CSS = 0.1µF
1
ms
5
Thermal Shutdown
*
160
°C
Typical Performance Characteristics
VIN=12V,Vo=3.3V,L=10uH,C1=10uF,C2=22uF,TA=+25℃
Figure 4.
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Efficiency vs Load Current
Figure 5. OSC Frequency vs Temperature
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2A 20V Synchronous Rectified Step-Down Converte
TD1482A
Typical Performance Characteristics(Cont.)
Figure 6. Output Voltage vs Temperature
Figure 7. Line Regulation
Figure 8.Load Regulation
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2A 20V Synchronous Rectified Step-Down Converte
TD1482A
Operating Waveforms
VIN=12V,VOUT=3.3V,IOUT=1A(Resistance Load)
VIN=12V,VOUT=3.3V,IOUT=1A(Resistance Load)
Figure 9. Startup through Enable
Figure 10. Shutdown through Enable
VIN=12V,VOUT=3.3V,IOUT=0A
VIN=12V,VOUT=3.3V,IOUT=1A
Figure11 Light Load Operation
Figure12 Medium Load Operation
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2A 20V Synchronous Rectified Step-Down Converte
TD1482A
Operating Waveforms(Cont.)
VIN=12V,VOUT=3.3V,IOUT=2A
VIN=12V,VOUT=3.3V,IOUT=0A to 2A
Figure 13. Heavy Load Operation
Figure 14.Load Transient
Figure15 Short Circuit Protection
Figure16 Short Circuit Recovery
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2A 20V Synchronous Rectified Step-Down Converte
TD1482A
Typical Application Circuit
Fig17. TD1482A with 3.3V Output, 22µF/6.3V Ceramic Output Capacitor
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2A 20V Synchronous Rectified Step-Down Converte
TD1482A
Function Description
Component Selection
Setting the Output Voltage
The output voltage is set using a resistive voltage
divider from the output voltage to FB pin.The voltage
divider divides the output voltage down to the
feedback voltage by the ratio:
Where VOUT is the output voltage, VIN is the input
voltage, fS is the switching frequency, and ΔIL is the
peak-to-peak inductor ripple current.
Choose an inductor that will not saturate under the
maximum inductor peak current. The peak inductor
current can be calculated by:
Where VFB is the feedback voltage and VOUT is the
output voltage.Thus the output voltage is:
Where ILOAD is the load current.
The choice of which style inductor to use mainly
depends on the price vs. size requirements and any
EMI requirements.
Optional Schottky Diode
R2 can be as high as 100kΩ, but a typical value is
During the transition between high-side switch and
10kΩ. Using the typical value for R2, R1 is determined
low-side switch, the body diode of the lowside power
by:
MOSFET conducts the inductor current. The forward
voltage of this body diode is high. An optional Schottky
diode may be paralleled between the SW pin and
For example, for a 3.3V output voltage, R2 is 10kΩ,
GND pin to improve overall efficiency. Table 1 lists
and R1 is 26.1kΩ.
example Schottky diodes and their Manufacturers.
Inductor
The inductor is required to supply constant current to
Part Number Voltage/Current Vendor
the output load while being driven by the switched
B130
30V, 1A
Diodes, Inc.
input voltage. A larger value inductor will result in less
SK13
30V, 1A
Diodes, Inc.
ripple current that will result in lower output ripple
MBRS130
30V, 1A
International Rectifier
voltage. However,the larger value inductor will have a
Input Capacitor
larger physical size, higher series resistance, and/or
The input current to the step-down converter is
lower saturation current. A good rule for determining
discontinuous, therefore a capacitor is required to
the inductance to use is to allow the peak-to-peak
ripple current in the inductor to be approximately 30% supply the AC current to the step-down converter
while maintaining the DC input voltage. Use low ESR
of the maximum switch current limit. Also, make sure
capacitors for the best performance. Ceramic
that the peak inductor current is below the maximum
capacitors are preferred, but tantalum or low-ESR
switch current limit. The inductance value can be
electrolytic capacitors may also suffice. Choose X5R
calculated by:
or X7R dielectrics when using ceramic capacitors.
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2A 20V Synchronous Rectified Step-Down Converte
TD1482A
Since the input capacitor (C1) absorbs the input
switching current it requires an adequate ripple current
rating. The RMS current in the input capacitor can be In the case of tantalum or electrolytic capacitors,the
estimated by:
ESR dominates the impedance at the switching
frequency. For simplification, the output ripple can be
approximated to:
The worst-case condition occurs at VIN = 2VOUT,where
IC1 = ILOAD/2. For simplification, choose the input
capacitor whose RMS current rating greater than half
of the maximum load current.
The input capacitor can be electrolytic, tantalum or
ceramic. When using electrolytic or tantalum
capacitors, a small, high quality ceramic capacitor, i.e.
0.1μF, should be placed as close to the IC as possible.
When using ceramic capacitors, make sure that they
have enough capacitance to provide sufficient charge
to prevent excessive voltage ripple at input. The input
voltage ripple for low ESR capacitors can be
estimated by:
Where C1 is the input capacitance value.
Output Capacitor
The output capacitor is required to maintain the DC
output voltage. Ceramic, tantalum, or low ESR
electrolytic capacitors are recommended. Low ESR
capacitors are preferred to keep the output voltage
ripple low. The output voltage ripple can be estimated
by:
Where C2 is the output capacitance value and RESR is
the equivalent series resistance (ESR) value of the
output capacitor.
In the case of ceramic capacitors, the impedance at
the switching frequency is dominated by the
capacitance. The output voltage ripple is mainly
caused by the capacitance. For simplification, the
output voltage ripple can be estimated by:
October, 20, 2010.
The characteristics of the output capacitor also affect
the stability of the regulation system. The TD1482A
can be optimized for a wide range of capacitance and
ESR values.
Compensation Components
TD1482A employs current mode control for easy
compensation and fast transient response. The
system stability and transient response are controlled
through the COMP pin. COMP pin is the output of the
internal transconductance error amplifier. A series
capacitor-resistor combination sets a pole-zero
combination to control the characteristics of the control
system.
The DC gain of the voltage feedback loop is given by:
Where AVEA is the error amplifier voltage gain;GCS is
the current sense transconductance and RLOAD is the
load resistor value.
The system has two poles of importance. One is due
to the compensation capacitor (C3) and the output
resistor of the error amplifier, and the other is due to
the output capacitor and the load resistor. These poles
are located at:
Where GEA is the error amplifier transconductance.
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2A 20V Synchronous Rectified Step-Down Converte
The system has one zero of importance, due to the
compensation capacitor (C3) and the compensation
resistor (R3). 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:
TD1482A
Determine the C3 value by the following equation:
Where R3 is the compensation resistor.
3. Determine if the second compensation capacitor
(C6) is required. It is required if the ESR zero of the
output capacitor is located at less than half of the
switching frequency, or the following relationship is
valid:
If this is the case, then add the second compensation
In this case (as shown in Figure 14), a third pole set by capacitor (C6) to set the pole fP3 at the location of the
the compensation capacitor (C6) and the
ESR zero. Determine the C6 value by the equation:
compensation resistor (R3) is used to compensate the
effect of the ESR zero on the loop gain. This pole is
located at:
External Bootstrap Diode
An external bootstrap diode may enhance the
efficiency of the regulator, the applicable
The goal of compensation design is to shape the
conditions of external BST diode are:
converter transfer function to get a desired loop gain.
VOUT=5V or 3.3V; and
The system crossover frequency where the feedback
Duty cycle is high:
loop has the unity gain is important. Lower crossover
frequencies result in slower line and load transient
responses,while higher crossover frequencies could
In these cases, an external BST diode is
cause system instability. A good rule of thumb is to set recommended from the output of the voltage regulator
the crossover frequency below one-tenth of the
to BST pin, as shown in Fig.14
switching frequency.
To optimize the compensation components, the
following procedure can be used.
1. Choose the compensation resistor (R3) to set the
desired crossover frequency.
Determine the R3 value by the following equation:
Figure18.Add Optional External Bootstrap Diode to Enhance
Efficiency
Where fC is the desired crossover frequency which is
The recommended external BST diode is IN4148, and
typically below one tenth of the switching frequency.
the BST cap is 0.1~1μF.
2. Choose the compensation capacitor (C3) to achieve
the desired phase margin. For applications with typical
inductor values, setting the compensation zero, fZ1,
below one-forth of the crossover frequency provides
sufficient phase margin.
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2A 20V Synchronous Rectified Step-Down Converte
TD1482A
Package Information
SOP8 Package Outline Dimensions
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DATASHEET
2A 20V Synchronous Rectified Step-Down Converte
TD1482A
Design Notes
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