TD1484A [ETC]
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ETC 
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DATASHEET
Techcode®
3.2A 23V Synchronous Rectified
Step-Down Converter
TD1484A
汪工 TEL:13828719410 QQ1929794238
General Description Features
•
•
3.2A Output Current
The TD1484A is a monolithic synchronous buck
regulator. The device integrates two 90mΩ
MOSFETs, and provides 3.2A of continuous load
current over a wide input voltage of 4.75V to 23V.
Wide 4.75V to 23V Operating Input Range
Integrated 90mΩ Power MOSFET Switches
Output Adjustable from 0.923V to 20V
Up to 93% Efficiency
•
•
•
•
•
•
•
•
Current mode control provides fast
response and cycle-by-cycle current limit.
transient
Programmable Soft-Start
An adjustable soft-start prevents inrush current at
turn-on, and in shutdown mode the supply current
drops to 1µA.
Stable with Low ESR Ceramic Output Capacitors
Fixed 340KHz Frequency
Cycle-by-Cycle Over Current Protection
Input Under Voltage Lockout
This device, availablein an SOP8-PP package,
provides a very compact solution with minimal external
components.
Applications
•
•
Distributed Power Systems
Networking Systems
•
•
•
FPGA, DSP, ASIC Power Supplies
Green Electronics/ Appliances
Notebook Computers
Package Types
Figure 1. Package Types of TD1484A
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DATASHEET
Techcode®
3.2A 23V Synchronous Rectified
Step-Down Converter
TD1484A
Pin Configurations
Figure 2 Pin Configuration of TD1484A(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
MOSFET switch. Connect a 0.01µF or greater capacitor from SW to BS to power the
high side switch.
1
2
3
BS
IN
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.
SW
4
5
GND
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. 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.
6
COMP
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.
7
8
EN
SS
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.
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DATASHEET
Techcode®
3.2A 23V Synchronous Rectified
Step-Down Converter
TD1484A
Ordering Information
TD1484A □ □
Circuit Type
Packing:
Blank：Tube
R:Type and Reel
Package
M:SOP8-PP
Function Block
Figure 3 Function Block Diagram of TD1484A
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DATASHEET
Techcode®
3.2A 23V Synchronous Rectified
Step-Down Converter
TD1484A
Absolute Maximum Ratings
Parameter
Supply Voltage
Symbol
VIN
Value
Unit
V
-0.3 to 23
21
Switch Node Voltage
Boost Voltage
VSW
V
VSW – 0.3V to VSW+6V
0.923V to 20
–0.3V to +6V
150
VBS
V
Output Voltage
VOUT
V
All Other Pins
V
Operating Junction Temperature
Storage Temperature
Lead Temperature (Soldering, 10 sec)
ESD (HBM)
TJ
ºC
ºC
ºC
V
TSTG
TLEAD
-65 to 150
260
2000
MSL
Level3
90
Thermal Resistance-Junction to Ambient
Thermal Resistance-Junction to Case
ºC / W
ºC / W
RθJA
RθJC
45
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DATASHEET
Techcode®
3.2A 23V Synchronous Rectified
Step-Down Converter
TD1484A
Electrical Characteristics
VIN = 12V, Ta = 25℃ unless otherwise specified.
Parameters
Symbol
Test Condition
Min.
Typ.
Max.
Unit
Shutdown Supply Current
VEN = 0V
1
3.0
µA
VEN = 2.0V; VFB =
1.0V
Supply Current
1.3
1.5
mA
Feedback Voltage
VFB
4.75V ≤ VIN ≤ 23V
∆IC = ±10µA
0.900
0.923
1.1
0.946
V
V
Feedback Overvoltage Threshold
Error Amplifier Voltage Gain *
Error Amplifier Transconductance
AEA
GEA
400
800
90
V/V
µA/V
mΩ
mΩ
High-Side Switch On Resistance * RDS(ON)1
Low-Side Switch On Resistance * RDS(ON)2
90
High-Side Switch Leakage
Current
VEN = 0V, VSW = 0V
10
µA
Upper Switch Current Limit
Lower Switch Current Limit
Minimum Duty Cycle
From Drain to Source
4.0
5.8
0.9
A
A
COMP to Current Sense
GCS
Transconductance
4.8
A/V
Oscillation Frequency
Fosc1
Fosc2
DMAX
340
KHz
Short Circuit Oscillation
Frequency
VFB = 0V
100
KHz
Maximum Duty Cycle
Minimum On Time *
VFB = 1.0V
90
220
1.5
%
ns
V
EN Shutdown Threshold Voltage
VEN Rising
1.1
2.2
2.0
2.7
EN Shutdown Threshold Voltage
Hysteresis
210
2.5
mV
V
EN Lockout Threshold Voltage
EN Lockout Hysterisis
210
mV
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DATASHEET
Techcode®
3.2A 23V Synchronous Rectified
Step-Down Converter
TD1484A
Electrical Characteristics(Cont.)
VIN = 12V, Ta = 25℃ unless otherwise specified.
Parameters
Symbol
Test Condition
VIN Rising
Min.
3.80
Typ.
4.10
Max.
Unit
V
Input Under Voltage Lockout
Threshold
4.40
Input Under Voltage Lockout
Threshold Hysteresis
210
6
mV
VSS = 0V
Soft-Start Current
µA
ms
°C
CSS = 0.1µF
Soft-Start Period
15
160
Thermal Shutdown *
Typical Performance Characteristics
Figure 4. Steady State Test
Figure 5. Steady State Test
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Techcode®
3.2A 23V Synchronous Rectified
Step-Down Converter
TD1484A
Figure 6. Startup through Enable
Figure 7. Startup through Enable
Figure 8. Shutdown through Enable
Figure 9. Shutdown through Enable
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DATASHEET
Techcode®
3.2A 23V Synchronous Rectified
Step-Down Converter
TD1484A
Figure 11. Short Circuit Test
Figure 10. Load Transient Test
Figure 12. Short Circuit Recovery
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DATASHEET
Techcode®
3.2A 23V Synchronous Rectified
Step-Down Converter
TD1484A
Typical Application Circuit
Fig13. TD1484A with 3.3V Output, 22µF/6.3V Ceramic Output Capacitor
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Techcode®
3.2A 23V Synchronous Rectified
Step-Down Converter
TD1484A
Function Description
Component Selection
Where VOUT is the output voltage, VIN is the input
voltage, fS is the switching frequency, and ꢁIL is the
peak-to-peak inductor ripple current.
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:
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 100kꢀ, but a typical value is
10kꢀ. Using the typical value for R2, R1 is determined
by:
During the transition between high-side switch and
low-side switch, the body diode of the lowside power
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
GND pin to improve overall efficiency. Table 1 lists
example Schottky diodes and their Manufacturers.
For example, for a 3.3V output voltage, R2 is 10kꢀ,
and R1 is 26.1kꢀ.
Inductor
The inductor is required to supply constant current to
the output load while being driven by the switched
input voltage. A larger value inductor will result in less
ripple current that will result in lower output ripple
voltage. However,the larger value inductor will have a
larger physical size, higher series resistance, and/or
lower saturation current. A good rule for determining
the inductance to use is to allow the peak-to-peak
ripple current in the inductor to be approximately 30%
of the maximum switch current limit. Also, make sure
that the peak inductor current is below the maximum
switch current limit. The inductance value can be
calculated by:
Part Number Voltage/Current Vendor
B130
30V, 1A
30V, 1A
30V, 1A
Diodes, Inc.
SK13
Diodes, Inc.
MBRS130
International Rectifier
Input Capacitor
The input current to the step-down converter is
discontinuous, therefore a capacitor is required to
supply the AC current to the step-down converter
while maintaining the DC input voltage. Use low ESR
capacitors for the best performance. Ceramic
capacitors are preferred, but tantalum or low-ESR
electrolytic capacitors may also suffice. Choose X5R
or X7R dielectrics when using ceramic capacitors.
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Techcode®
3.2A 23V Synchronous Rectified
Step-Down Converter
TD1484A
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
estimated by:
In the case of tantalum or electrolytic capacitors,the
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 characteristics of the output capacitor also affect
the stability of the regulation system. The TD1484A
can be optimized for a wide range of capacitance and
ESR values.
The input capacitor can be electrolytic, tantalum or
ceramic. When using electrolytic or tantalum
capacitors, a small, high quality ceramic capacitor, i.e.
Compensation Components
0.1μF, should be placed as close to the IC as possible. TD1484A employs current mode control for easy
When using ceramic capacitors, make sure that they compensation and fast transient response. The
have enough capacitance to provide sufficient charge system stability and transient response are controlled
to prevent excessive voltage ripple at input. The input through the COMP pin. COMP pin is the output of the
voltage ripple for low ESR capacitors can be
estimated by:
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 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
Where AVEA is the error amplifier voltage gain;GCS is
the current sense transconductance and RLOAD is the
load resistor value.
ripple low. The output voltage ripple can be estimated The system has two poles of importance. One is due
by:
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 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:
Where GEA is the error amplifier transconductance.
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Techcode®
3.2A 23V Synchronous Rectified
Step-Down Converter
TD1484A
The system has one zero of importance, due to the
compensation capacitor (C3) and the compensation
resistor (R3). This zero is located at:
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
The system may have another zero of importance, if
the output capacitor has a large capacitance and/or a output capacitor is located at less than half of the
high ESR value. The zero,due to the ESR and
capacitance of the output capacitor, is located at:
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
compensation resistor (R3) is used to compensate the
effect of the ESR zero on the loop gain. This pole is
located at:
ESR zero. Determine the C6 value by the equation:
External Bootstrap Diode
An external bootstrap diode may enhance the
efficiency of the regulator, the applicable
conditions of external BST diode are:
The goal of compensation design is to shape the
converter transfer function to get a desired loop gain.
The system crossover frequency where the feedback
loop has the unity gain is important. Lower crossover
frequencies result in slower line and load transient
responses,while higher crossover frequencies could
z
z
VOUT=5V or 3.3V; and
Duty cycle is high:
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
switching frequency.
to BST pin, as shown in Fig.14
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:
Figure14.Add Optional External Bootstrap Diode to Enhance
Efficiency
Where fC is the desired crossover frequency which is
typically below one tenth of the switching frequency.
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.
The recommended external BST diode is IN4148, and
the BST cap is 0.1~1μF.
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DATASHEET
Techcode®
3.2A 23V Synchronous Rectified
Step-Down Converter
TD1484A
Package Information
SOP8pp Package Outline Dimensions
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DATASHEET
Techcode®
3.2A 23V Synchronous Rectified
Step-Down Converter
TD1484A
Design Notes
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