TC2576
3.0A Step-Down Switching Regulator
FEATURES
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3.3V, 5.0V, 12V and Adjustable Output Versions
Adjustable Version Output Voltage Range:
1.23 to 37V
±
4% Max. Over Line and Load Conditions
Guaranteed 3.0A Output Current
Wide Input Voltage Range
Requires Only 4 External Components
52kHz Fixed Frequency Internal Oscillator
TTL Shutdown Capability, Low Power Standby Mode
High Efficiency
Uses Readily Available Standard Inductors
Thermal Shutdown and Current Limit Protection
GENERAL DESCRIPTION
The TC2576 series of regulators are monolithic inte-
grated circuits ideally suited for easy and convenient design
of a step–down switching regulator (buck converter). All
circuits of this series are capable of driving a 3.0A load with
excellent line and load regulation. These devices are avail-
able in fixed output voltages of 3.3V, 5.0V, 12.0V and
an adjustable output version.
These regulators were designed to minimize the num-
ber of external components to simplify the power supply
design. Standard series of inductors optimized for use with
the TC2576 are offered by several different inductor manu-
facturers.
Since the TC2576 converter is a switch-mode power
supply, its efficiency is significantly higher in comparison
with popular three-terminal linear regulators, especially with
higher input voltages. In many cases, the power dissipated
is so low, that no heatsinking is required or its size can be
reduced dramatically.
A standard series of inductors optimized for use with the
TC2576 are available from several different manufacturers.
This feature greatly simplifies the design of switch-mode
power supplies.
The TC2576 features include a guaranteed
±4%
toler-
ance on output voltage within specified input voltages and
output load conditions, and
±10%
on the oscillator fre-
quency (±2% over 0°C to +125°C). External shutdown is
included, featuring 80µA (typical) standby current. The
output switch includes cycle-by-cycle current limiting, as
well as thermal shutdown for full protection under fault
conditions.
APPLICATIONS
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Simple and High-Efficiency Step-Down (Buck)
Regulator
Efficient Pre–Regulator for Linear Regulators
On–Card Switching Regulators
Positive to Negative Converters (Buck–Boost)
Negative Step-Up Converters
Power Supply for Battery Chargers
PIN CONFIGURATIONS
5-Pin TO-220
TC2576
ORDERING INFORMATION
1 2 3 4 5
Part
Number
TC2576-3.3VAT
TC2576-5.0VAT
TC2576-12.0VAT
TC2576VAT*
Package
5-Pin TO-220
5-Pin TO-220
5-Pin TO-220
5-Pin TO-220
Temperature
Range
–40 to +125°C
–40 to +125°C
–40 to +125°C
–40 to +125°C
OUTPUT
GND
FEEDBACK
ON/OFF
V
IN
Note: *ADJ = 1.23 To 37V.
© 2001 Microchip Technology Inc.
DS21399A
TC2576-2 12/04/00
3.0A Step-Down Switching Regulator
TC2576
ABSOLUTE MAXIMUM RATINGS*
Maximum Supply Voltage ................................ V
IN
= 45V
ON/OFF Pin Input Voltage ..................... –0.3V
≤
V
≤
+V
IN
Output Voltage to Ground (Steady State) ............... –1.0 V
Max Power Dissipation (TO-220) ........ (Internally Limited)
Thermal Resistance, Junction-to-Ambient ..... 65°C/W
Thermal Resistance, Junction-to-Case ........ 5.0°C/W
Storage Temperature Range ................. –65°C to +150°C
Minimum ESD Rating .................................................. 2.0
(Human Body Model: C = 100 pF, R = 1.5 kΩ)
Lead Temperature (Soldering, 10 seconds) .......... 260
°C
Maximum Junction Temperature............................. 150°C
Operating Junction Temperature Range .... –40 to +125*C
Supply Voltage ............................................................40V
*This is a stress rating only, and functional operation of the device at these
or any other conditions beyond those indicated in the operation section of
the specifications is not implied. Exposure to absolute maximum ratings
conditions for extended periods of time may affect device reliability.
ELECTRICAL CHARACTERISTICS:
Unless otherwise specified, V
IN
= 12V for the 3.3V, 5.0V, and Adjustable
version,V
IN
= 25V for the 12V version. I
LOAD
= 500mA. For typical values T
J
= 25°C, for min/max values T
J
is the operating
junction temperature range that applies [Note 2], unless otherwise noted.
Symbol
V
OUT
Parameter
Output Voltage
Test Conditions
V
IN
= 12V, I
LOAD
= 0.5A, T
J
= 25°C
6.0V
≤
V
IN
≤
40V, 0.5A
≤
I
LOAD
≤
3.0A
T
J
= 25°C
T
J
= –40°C to +125°
V
IN
= 12V, I
LOAD
= 3.0 A
V
IN
= 12V, I
LOAD
= 0.5A, T
J
= 25°C
8.0V
≤
V
IN
≤
40V, 0.5A
≤
I
LOAD
≤
3.0A
T
J
= 25°C
T
J
= –40°C to +125°C
V
IN
= 12V, I
LOAD
= 3.0 A
V
IN
= 25V, I
LOAD
= 0.5A, T
J
= 25°C
15V
≤
V
IN
≤
40V, 0.5A
≤
I
LOAD
≤
3.0A
T
J
= 25°C
T
J
= –40°C to +125°C
V
IN
= 15V, I
LOAD
= 3.0A
V
IN
= 12V, I
LOAD
= 0.5A, V
OUT
= 5.0V,
T
J
= 25°C
8.0V
≤
V
IN
≤
40V, 0.5A
≤
I
LOAD
≤
3.0A
V
OUT
= 5.0V
T
J
= 25°C
T
J
= –40°C to +125°C
V
IN
= 12V, I
LOAD
= 3.0A, V
OUT
= 5.0V
Min
3.234
3.168
3.135
—
4.9
4.8
4.75
—
11.76
11.52
11.4
—
1.217
Typ
3.3
3.3
—
75
5.0
5.0
—
77
10
12
—
88
1.23
Max
3.366
3.432
3.465
—
5.1
5.2
5.25
—
12.24
12.48
12.6
—
1.243
Units
V
TC2576-3.3 [(Note 1) Test Circuit Figure 2]
η
V
OUT
Efficiency
Output Voltage
%
V
TC2576-5 [(Note 1)Test Circuit Figure 2]
η
V
OUT
Efficiency
Output Voltage
%
V
TC2576-12 [(Note 1) Test Circuit Figure 2]
η
V
OUT
V
FBT
Efficiency
Feedback Voltage
Feedback Voltage
%
V
TC2576-Adjustable Version [(Note 1) Test Circuit Figure 2]
η
Efficiency
1.193
1.18
—
1.23
—
77
1.267
1.28
—
%
NOTES:
1. External components such as the catch diode, inductor, input and output capacitors can affect the switching regulator system
performance. When the TC2576 is used as shown in the Figure 2 test circuit, the system performance will be as
shown in the system parameters section of the Electrical Characteristics.
2. Tested junction temperature range for the TC2576: T
LOW
= –40°C T
HIGH
= +125°C
TC2576-2 12/04/00
2
© 2001 Microchip Technology Inc.
DS21399A
3.0A Step-Down Switching Regulator
TC2576
ELECTRICAL CHARACTERISTICS:
Unless otherwise specified, V
IN
= 12V for the 3.3V, 5.0V, and Adjustable
version,V
IN
= 25V for the 12V version. I
LOAD
= 500mA. For typical values T
J
= 25°C, for min/max values T
J
is the operat-
ing junction temperature range that applies [Note 2], unless otherwise noted.
Symbol
I
b
Parameter
Feedback Bias Current
Test Conditions
Min
Typ
Max
Units
nA
TC2576-ALL OUTPUT VOLTAGE VERSIONS
V
OUT
= 5.0V (Adjustable Version Only)
T
J
= 25°C
T
J
= –40°C to +125°C
Oscillator Frequency (Note 3)
T
J
= 25°C
T
J
= 0 to +125°C
T
J
= –40 to +125°C
Saturation Voltage
I
OUT
= 0.5 A, (Note 4)
T
J
= 25°C
T
J
= –40 to +125°C
Max Duty Cycle (“on”) [Note 5]
Current Limit Peak Current
(Notes 3 and 4)
T
J
= 25°C
T
J
= –40 to +125°C
Output Leakage Current
(Notes 6 and 7), T
J
= 25°C
Output = 0 V
Output = – 1.0 V
Quiescent Current (Note 6)
T
J
= 25°C
T
J
= –40 to +125°C
Standby Quiescent Current,
ON/OFF Pin = 5.0V (“off”)
T
J
= 25°C
T
J
= –40 to +125°C
ON/OFF Pin Logic Input Level
(Test Figure 2)
V
OUT
= 0V
T
J
= 25°C
T
J
= –40 to +125°C
Nominal Output Voltage
T
J
= 25°C
T
J
= –40 to +125°C
ON/OFF Pin Input Current
(Test Figure 2)
ON/OFF Pin = 5.0V (“off”),
T
J
= 25°C
ON/OFF Pin Input Current
ON/OFF Pin = 0V (“on”),
T
J
= 25°C
—
—
—
47
42
—
—
94
4.2
3.5
—
—
—
—
—
—
25
—
52
52
–
1.5
—
98
5.8
—
0.8
6.0
5.0
—
80
—
100
200
—
58
63
1.8
2.0
—
6.9
7.5
mA
2.0
20
mA
9.0
11
µA
200
400
V
2.2
2.4
—
—
—
—
1.4
—
1.2
—
15
0
—
—
V
1.0
0.8
µA
30
5.0
µA
f
OSC
kHz
V
SAT
V
DC
I
CL
%
A
I
L
I
Q
I
STBY
V
IH
V
IL
I
IH
I
IL
NOTES:
3. The oscillator frequency reduces to approximately 18kHz in the event of an output short or an overload which causes the regulated
output voltage to drop approximately 40% from the nominal output voltage. This self protection feature lowers the average power
dissipation of the IC by lowering the minimum duty cycle from 5% down to approximately 2%.
4. Output (Pin 2) sourcing current. No diode, inductor or capacitor connected to the output pin.
5. Feedback (Pin 4) removed from output and connected to 0V.
6. Feedback (Pin 4) removed from output and connected to +12V for the Adjustable, 3.3V, and 5.0V versions, and 25V for the 12V
versions, to force the output transistor "OFF".
7. V
IN
= 40 V.
© 2001 Microchip Technology Inc.
DS21399A
3
TC2576-2 12/04/00
3.0A Step-Down Switching Regulator
TC2576
PIN DESCRIPTION
Pin No.
5-Pin TO-220
1
Symbol
V
IN
Description
This pin is the positive input supply for the TC2576 step-down switching
regulator. In order to minimize voltage transients and to supply the
switching currents needed by the regulator, a suitable input bypass
capacitor must be present (C
IN
in Figure 1).
This is the emitter of the internal switch. The saturation voltage V
SAT
of
this output switch is typically 1.5V. It should be kept in mind that the PCB
area connected to this pin should be kept to a minimum in order to
minimize coupling to sensitive circuitry.
Circuit ground pin. See the information about the printed circuit board
layout.
This pin senses regulated output voltage to complete the feedback loop.
The signal is divided by the internal resistor divider network R2, R1 and
applied to the non-inverting input of the internal error amplifier. In the
adjustable version of the TC2576 switching regulator this pin is the direct
input of the error amplifier and the resistor network R2, R1 is connected
externally to allow programming of the output voltage.
It allows the switching regulator circuit to be shut down using logic level
signals, thus dropping the total input supply current toapproximately 80µA.
The threshold voltage is typically 1.4V. Applying a voltage above this
value (up to +V
IN
) shuts theregulator off. If the voltage applied to this pin is
lower than 1.4V or if this pin is left open, the regulator will be in the "on"
condition.
2
Output
3
4
GND
Feedback
5
ON/OFF
REPRESENTATIVE BLOCK DIAGRAM AND TYPICAL APPLICATION
+VIN
Unregulated
DC Input
CIN
+
1
TC2576
4
3.1V Internal
Regulator
ON/OFF
ON/OFF
5
Output
Voltage Versions
Fixed gain
Error Amplifier
Current
Limit
Comparator
R2 (Ω)
Feedback
R2
+
–
Driver
+
R1
1.0k
–
Freq.
Shift
18kHz
1.235V
Band-Gap
Reference
+
–
Latch
3.3V
1.7k
5.0V
3.1k
12V
8.84k
For Adjustable version
R1 = open, R2 = 0Ω
Regulated
Output
VOUT
Output
1.0 Amp
Switch
52kHz
Oscillator
Reset
Thermal
Shutdown
2
GND
3
L1
D1
+
COUT
Load
TC2576-2 12/04/00
4
© 2001 Microchip Technology Inc.
DS21399A
3.0A Step-Down Switching Regulator
TC2576
Feedback
7.0 – 40V
Unregulated
DC Input
+VIN
CIN
100µF
4
TC2576
3 GND
Output
2
5 ON/OFF
L1
100µH
5.0V Regulated
Output 3.0A Load
D1
1N5822
COUT
1000µF
+
1
Figure 1. Block Diagram and Typical Application: Fixed Output Voltage Versions
Fixed Output Voltage Versions
Feedback
VIN
1
7.0 – 40V
Unregulated
DC Input
+
CIN
100µF
3
4
TC2576
Fixed Output
GND
5
Output
2
ON/OFF
L1
100µH
COUT +
D1
MBR360 1000µF
VOUT
Load
CIN
COUT
D1
L1
R1
R2
- 100µF, 75V, Aluminum Electrolytic
- 1000µF, 25V, Aluminum Electrolytic
- Schottky, MBR360
- 100µH, Pulse Eng. PE-92108
- 2.0k, 0.1%
- 6.12k, 0.1%
Adjustable Output Voltage Versions
Feedback
VIN
1
4
TC2576
Adjustable
3
GND
5
Output
2
ON/OFF
D1
MBR360
L1
100µH
R2
+
CIN
100µF
Load
R1
VOUT
5,000V
7.0 – 40V
Unregulated
DC Input
+ C
IN
100µF
VOUT = VREF
R1= R2
(
1.0 + R2
R1
)
(
VOUT - 1.0
)
VREF
Where VREF = 1.23V, R1
between 1.0k and 5.0k
Figure 2. Typical Test Circuit
© 2001 Microchip Technology Inc.
DS21399A
5
TC2576-2 12/04/00
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