ETC TD7580

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Datasheet
4A 240KHZ 23V PWM Buck DC/DC Converter
TD7580
汪工 TEL:13828719410 QQ:1929794238
General Description
Features
The TD7580 is a 240 KHz fixed frequency
monolithic step down switch mode regulator
with a built in internal Power MOSFET. It
achieves 4A continuous output current over a
wide input supply range with excellent load
and line regulation.
The device includes a voltage reference,
oscillation circuit, error amplifier, internal
PMOS and etc.


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4A Constant Output Current
80mΩ RDSON Internal Power PMOSFET
Switch
Up to 95% Efficiency
Fixed 240KHz Frequency
Wide 3.6V to 23V Input Voltage Range
Output Adjustable from 1.222V to 21V
Built in Frequency Compensation
Built in Thermal Shutdown Function
Built in Current Limit Function
SOP-8 Package is Available
The minimum dropout up to 0.3V

Applications
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
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Portable DVD
LCD Monitor / TV
Battery Charger
ADSL Modem
Telecom / Networking Equipment







The PWM control circuit is able to adjust the
duty ratio linearly from 0 to 100%. An enable
function, an over current protection function
and a short circuit protection function are
built inside. An internal compensation block
is built in to minimize external component
count.

The TD7580 serves as ideal power supply
units for portable devices.
Figure 1 Package Type of TD7580
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Datasheet
4A 240KHZ 23V PWM Buck DC/DC Converter
TD7580
Pin Configurations
Figure 2 Pin Configuration of TD7580 (Top View)
Pin Description
Pin Number
Pin Name
Description
1,6, 8
NC
Not Connect.
2
Vin
3
SW
4
GND
5
FB
7
EN
Supply Voltage Input Pin. TD7580 operates from a 3.6V to 23V
DC voltage. Bypass Vin to GND with a suitably large capacitor
to eliminate noise on the input.
Power Switch Output Pin. SW is the switch node that supplies
power to the output.
Ground Pin. Care must be taken in layout. This pin should be
placed outside of the Schottky Diode to output capacitor ground
path to prevent switching current spikes from inducing voltage
noise into TD7580.
Feedback Pin. Through an external resistor divider network, FB
senses the output voltage and regulates it. The feedback
threshold voltage is 1.222V.
Enable Pin. EN is a digital input that turns the regulator on or
off .Drive EN pin high to turn on the regulator, drive it low to
turn it off.
Ordering Information
TD7580
X
X
Packing
Blank: Tube
R:
Type and Reel
Circuit Type
Package
P:
SOP8
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Datasheet
4A 240KHZ 23V PWM Buck DC/DC Converter
TD7580
Function Block
Figure 3 Function Block Diagram of TD7580
Absolute Maximum Ratings
Parameter
Symbol
Input Voltage
Feedback Pin Voltage
Enable Pin Voltage
Switch Pin Voltage
Output Power Limited
Operating Junction Temperature
Storage Temperature
Lead Temperature (Soldering, 10 sec)
ESD (HBM)
Thermal Resistance-Junction to Ambient
Thermal Resistance-Junction to Case
VIN
VFB
VEN
VSW
Pout
TJ
TSTG
TLEAD
RθJA
RθJC
Value
-0.3 to 23
-0.3 to Vin
-0.3 to 12
-0.3 to Vin
24
150
-65 to 150
260
2000
85
45
Unit
V
V
V
V
W
ºC
ºC
ºC
V
ºC / W
ºC / W
Note1: Stresses greater than those listed under Maximum Ratings may cause permanent damage
to the device. This is a stress rating only and functional operation of the device at these or any
other conditions above those indicated in the operation is not implied. Exposure to absolute
maximum rating conditions for extended periods may affect reliability.
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Datasheet
4A 240KHZ 23V PWM Buck DC/DC Converter
TD7580
Recommended Operating Conditions
Parameter
Symbol
Min.
Max.
Unit
Input Voltage
VIN
3.6
23
V
Operating Junction Temperature
TJ
-40
125
ºC
Operating Ambient Temperature
TA
-40
85
ºC
Electrical Characteristics
VCC = 12V, Ta = 25℃ unless otherwise specified.
Parameters
Input voltage
Shutdown Supply Current
Symbol
Test Condition
VIN
Min.
Typ.
3.6
Max.
Unit
23
V
ISTBY
VEN=0V
30
90
uA
Supply Current
ICC
VEN=2V, VFB=1.3V
3.6
4
mA
Feedback Voltage
VFB
VIN = 3.6V to 23V
1.26
V
Feedback Bias Current
IFB
VFB=1.3V
0.1
0.5
uA
Switch Current Limit
ILIM
5
5.6
A
Oscillator Frequency
FOSC
240
280
KHz
Frequency of Current
Limit or Short Circuit
Protection
FOSC1
EN Pin Threshold
VEN
1.185 1.222
200
VFB=0V
42
0.7
KHz
1.2
1.7
V
IH
VEN=2.5V
-0.1
-1
uA
IL
VEN=0.5V
-3
-10
uA
Internal PMOS RDSON
RDSON
VIN =12V, VFB=0V
VEN=12V, Iout=4A
80
mΩ
Max. Duty Cycle
DMAX
VFB=0V, ISW=0.1A
100
%
η
VIN=12V ,Vout=5V
Iout=4A
EN Pin Input Leakage
Current
Efficiency
Thermal Shutdown
TOTSD
-
92
165
September, 2006
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%
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Datasheet
4A 240KHZ 23V PWM Buck DC/DC Converter
TD7580
Typical Performance Characteristics
Figure 4. Switching Frequency vs. Temperature
Figure 6. Icc vs. Temperature
Figure 5. Vfb vs. Temperature
Figure 7. Efficiency vs. Load (Vin=10V)
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Datasheet
4A 240KHZ 23V PWM Buck DC/DC Converter
TD7580
Typical Application Circuit
R2=2K
R1=6.2K
15uh/4A
TD7580
5.5V~23V
DC INPUT
5V4A
D1
SB540
330uF
35V
Fig8. TD7580 Typical Application Circuit @ 5V/4A
Note:In PCB layout. Reserved an area for CFF
R2=3.6K
R1=6.2K
15uh/4A
TD7580
4.5V~23V
DC INPUT
3.3V4A
D1
SB540
330uF
35V
Fig9. TD7580 Typical Application Circuit @ 3.3V/4A
Note:In PCB layout. Reserved an area for CFF
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Datasheet
4A 240KHZ 23V PWM Buck DC/DC Converter
TD7580
R1=6.2K
R2=2K
15uh/4A
TD7580
D1
SB540
330uF
35V
5.5V~23V
DC INPUT
5V4A
Fig10. TD7580 Typical Application Circuit (with ceramic output capacitor) @ 5V/4A
Note:In PCB layout. Reserved an area for CFF
R2=3.6K
R1=6.2K
15uh/4A
TD7580
4.5V~23V
DC INPUT
3.3V4A
D1
SB540
330uF
35V
Fig11. TD7580 Typical Application Circuit (with ceramic output capacitor) @ 3.3V/4A
Note:In PCB layout. Reserved an area for CFF
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Datasheet
4A 240KHZ 23V PWM Buck DC/DC Converter
TD7580
Schottky Rectifier Selection Guide
4A Load Current
Part Number
Vendor
SB540
2
SR540
6
NA05QSA035
1
Vin (Max)
23V
Table 1 lists some rectifier manufacturers.
No.
1
2
3
4
5
6
Vendor
Nihon Inter
Fairchild Semiconductor
General Semiconductor
International Rectifier
On Semiconductor
Pan Jit International
Web Site
www.niec.co.jp
www.fairchildsemi.com
www.gensemi.com
www.irf.com
www.onsemi.com
www.panjit.com.tw
Table 2 Schottky Diode manufacturers.
Output Voltage VS R1, R2 Resistor Selection Guide
Vout = (1+R1/R2)*1.222V
Vout
1.8V
2.5V
3.3V
5V
9V
12V
R2
8.2K
3K
3.6K
2K
2K
1.8K
R1
3.9K
3.2K
6.2K
6.2K
13K
16K
Table 3. Vout VS. R1, R2 Select Table
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Datasheet
4A 240KHZ 23V PWM Buck DC/DC Converter
TD7580
temperatures require more heat sinking.
Function Description
For the best thermal performance, wide copper
traces and generous amounts of printed circuit
board copper should be used in the board layout.
(Once exception to this is the output (switch) pin,
which should not have large areas of copper.)
Large areas of copper provide the best transfer of
heat (lower thermal resistance) to the surrounding
air, and moving air lowers the thermal resistance
even further.
Pin Functions
VIN
This is the positive input supply for the IC
switching regulator. A suitable input bypass
capacitor must be present at this pin to minimize
voltage transients and to supply the switching
currents needed by the regulator
Gnd
Package thermal resistance and junction
temperature rise numbers are all approximate,
and there are many factors that will affect these
numbers. Some of these factors include board
size, shape, thickness, position, location, and
even board temperature. Other factors are, trace
width, total printed circuit copper area, copper
thickness, single or double-sided, multi-layer
board and the amount of solder on the board.
Circuit ground.
SW
Internal switch. The voltage at this pin switches
between (VIN – VSAT) and approximately – 0.5V,
with a duty cycle of approximately VOUT / VIN. To
minimize coupling to sensitive circuitry, the PC
board copper area connected to this pin should
be kept a minimum.
The effectiveness of the PC board to dissipate
heat also depends on the size, quantity and
spacing of other components on the board, as
well as whether the surrounding air is still or
moving. Furthermore, some of these components
such as the catch diode will add heat to the PC
board and the heat can vary as the input voltage
changes. For the inductor, depending on the
physical size, type of core material and the DC
resistance, it could either act as a heat sink taking
heat away from the board, or it could add heat to
the board.
FB
Senses the regulated output voltage to complete
the feedback loop.
EN
Allows the switching regulator circuit to be
shutdown using logic level signals thus dropping
the total input supply current to approximately
30uA. Pulling this pin below a threshold voltage of
approximately 0.7 V turns the regulator down, and
pulling this pin above 1.3V (up to a maximum of
12V) shuts the regulator on. For automatic starup
condition , can be implemented by the addition of
a resistive voltage divider from VIN to GND.
Setting the Output Voltage
The output voltage is set using a resistive
voltage divider from the output voltage to FB. The
voltage divider divides the
output voltage down by the ratio:
VFB = VOUT * R2 / (R1 + R2)
Thus the output voltage is:
VOUT = 1.222 * (R1 + R2) / R2
R2 can be as high as 100KΩ, but a typical
value is 10KΩ. Using that value, R1 is
determined by:
R1 ~= 8.18 * (VOUT – 1.222) (KΩ)
For example, for a 3.3V output voltage, R2 is
10KΩ, and R1 is 17KΩ.
Thermal Considerations
The TD7580 is available in SOP8 package.
The SOP8 package needs a heat sink under most
conditions. The size of the heat sink depends on
the input voltage, the output voltage, the load
current and the ambient temperature. The
TD7580 junction temperature rises above
ambient temperature for a 4A load and different
input and output voltages. The data for these
curves was taken with the TD7580 (SOP8
package) operating as a buck-switching regulator
in an ambient temperature of 25oC (still air).
These temperature rise numbers are all
approximate and there are many factors that can
affect these temperatures. Higher ambient
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Datasheet
4A 240KHZ 23V PWM Buck DC/DC Converter
Inductor
TD7580
The output capacitor is required to maintain
the DC output voltage. Low ESR capacitors
are preferred to keep the output voltage ripple
low. The characteristics of the output
capacitor also affect the stability of the
regulation control system. Ceramic, tantalum,
or low ESR electrolytic capacitors are
recommended. In the case of ceramic
capacitors, the impedance at the switching
frequency is dominated by the capacitance,
and so the output voltage ripple is mostly
independent of the ESR. The output voltage
ripple is estimated to be:
VRIPPLE ~= 1.4 * VIN * (fLC/fSW)^2
Where VRIPPLE is the output ripple voltage, VIN
is the input voltage, fLC is the resonant
frequency of the LC filter, fSW is the switching
frequency. In the case of tanatalum or lowESR electrolytic capacitors, the ESR
dominates the impedance at the switching
frequency, and so the output ripple is
calculated as:
VRIPPLE ~= ΔI * RESR
Where VRIPPLE is the output voltage ripple, ΔI is
the inductor ripple current, and RESR is the
equivalent series resistance of the output
capacitors.
The inductor is required to supply constant
current to the output load while being driven by
the switched input voltage. A larger value
inductor results in less ripple current that in
turn results in lower output ripple voltage.
However, the larger value inductor has a larger
physical size, higher series resistance, and/or
lower saturation current. Choose an inductor
that does not saturate under the worst-case
load conditions. A good rule for determining
the inductance is to allow the peak-to-peak
ripple current in the inductor to be approximately
30% of the maximum load
current. Also, make sure that the peak
inductor current (the load current plus half the
peak-to-peak inductor ripple current) is below
the TBDA minimum current limit. The
inductance value can be calculated by the
equation:
L = (VOUT) * (VIN-VOUT) / VIN * f * ΔI
Where VOUT is the output voltage, VIN is the
input voltage, f is the switching frequency, and
ΔI is the peak-to-peak inductor ripple current.
Input Capacitor
The input current to the step-down converter is
discontinuous, and so a capacitor is required
to supply the AC current to the step-down
converter while maintaining the DC input
voltage. A low ESR capacitor is required to
keep the noise at the IC to a minimum.
Ceramic capacitors are preferred, but tantalum
or low-ESR electrolytic capacitors may also
suffice.
The input capacitor value should be greater
than 10μF. The capacitor can be electrolytic,
tantalum or ceramic. However since it absorbs
the input switching current it requires an
adequate ripple current rating. Its RMS current
rating should be greater than approximately
1/2 of the DC load current.
For insuring stable operation should be
placed as close to the IC as possible.
Alternately a smaller high quality ceramic
0.1μF capacitor may be placed closer to the IC
and a larger capacitor placed further away. If
using this technique, it is recommended that
the larger capacitor be a tantalum or
electrolytic type. All ceramic capacitors should
be places close to the TD7580.
Output Rectifier Diode
The output rectifier diode supplies the current
to the inductor when the high-side switch is off.
To reduce losses due to the diode forward
voltage and recovery times, use a Schottky
rectifier.
Table 1 provides the Schottky rectifier part
numbers based on the maximum input voltage
and current rating.
Choose a rectifier who’s maximum reverse
voltage rating is greater than the maximum
input voltage, and who’s current rating is
greater than the maximum load current.
Feedforward Capacitor (CFF)
For output voltages greater than approximately
8V, an additional capacitor is required. The
compensation capacitor is typically between 100
pF and 33 nF, and is wired in parallel
with the output voltage setting resistor, R1. It
provides additional stability for high output
voltages, low input-output voltages, and/or very
low ESR output capacitors, such as solid
tantalum capacitors.
Output Capacitor
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Datasheet
4A 240KHZ 23V PWM Buck DC/DC Converter
This capacitor type can be ceramic, plastic, silver
mica, etc.(Because of the unstable characteristics
of ceramic capacitors made with Z5U material,
they are not recommended.)
Note:In PCB layout. Reserved an area for CFF.
TD7580
by input power minus output power.
Ptotal _loss = V IN × IIN – V O × IO
The power dissipation of inductor can be
approximately calculated by output current and
DCR of inductor.
Pinductor _loss= IO 2 × Rinductor × 1.1
The junction to ambient temperature can be got
from power dissipation in the TD7580 and thermal
impedance from junction to ambient.
T (jun-amb) =(Ptotalloss–Pinductorloss)× ΘJA
The maximum junction temperature of TD7580 is
145°C, which limits the maximum load current
capability. Please see the thermal de-rating
curves for the maximum load current of the
TD7580 under different ambient temperatures.
The thermal performance of the TD7580 is trongly
affected by the PCB layout. Extra care should be
taken by users during the design process to nsure
that the IC will operate under the recommended
environmental conditions.
Several layout tips are listed below for the best
electric and thermal performance.
1. Do not use thermal relief connection to the VIN
and the GND pin. Pour a maximized copper area
to the GND pin and the VIN pin to help thermal
dissipation.
2. Input capacitor should be connected to the VIN
pin and the GND pin as close as possible.
3. Make the current trace from VOUT pins to L to
the GND as short as possible.
4. Pour copper plane on all unused board area
and connect it to stable DC nodes, like VIN, GND,
or VOUT.
5. Keep sensitive signal traces such as trace
connecting FB pin away from the VOUT pins.
Over Current Protection (OCP)
The cycle by cycle current limit threshold is set
between 5A and 5.6A. When the load current
reaches the current limit threshold, the cycle by
cycle current limit circuit turns off the high side
switch immediately to terminate the current duty
cycle. The inductor current stops rising. The cycle
by cycle current limit protection directly limits
inductor peak current. The average inductor
current is also limited due to the limitation on peak
inductor current. When the cycle by cycle current
limit circuit is triggered, the output voltage drops
as the duty cycle is decreasing.
Thermal Management and Layout
Consideration
In the TD7580 buck regulator circuit, high pulsing
current flows through two circuit loops. The first
loop starts from the input capacitors, to the VIN
pin, to the VOUT pins, to the filter inductor, to the
output capacitor and load, and then returns to the
input capacitor through ground.
Current flows in the first loop when the high side
switch is on. The second loop starts from the
inductor, to the output capacitors and load, to the
GND pin of the TD7580, and to the VOUT pins of
the TD7580. Current flows in the second loop
when the low side diode is on.
In PCB layout, minimizing the two loops area
reduces the noise of this circuit and improves
efficiency. A ground plane is recommended to
connect input capacitor, output capacitor, and
GND pin of the TD7580.
In the TD7580 buck regulator circuit, the two
major power dissipating components are the
TD7580 and output inductor. The total power
dissipation of converter circuit can be measured
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Datasheet
4A 240KHZ 23V PWM Buck DC/DC Converter
TD7580
Package Information
SOP8 Package Outline Dimensions
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Datasheet
4A 240KHZ 23V PWM Buck DC/DC Converter
TD7580
Design Notes
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