TC2574
0.5A Step-Down Switching Regulator
FEATURES
s
s
s
s
s
s
s
s
s
s
3.3V, 5.0V, 12V and Adjustable Output Versions
Adjustable Version Output Voltage Range,
1.23 to 37 V
±
4% Max Over Line and Load Conditions
Guaranteed 0.5 A Output Current
Wide Input Voltage Range: 4.75 to 40V
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 TC2574 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 0.5A load with
excellent line and load regulation. These devices are avail-
able in fixed output voltages of 3.3V, 5.0V, 12V 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 TC2574 are offered by several different inductor manu-
facturers.
Since the TC2574 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 most cases, the power dissipated
by the TC2574 regulator is so low, that the copper traces on
the printed circuit board are normally the only heatsink
needed and no additional heatsinking is required.
The TC2574 features include a guaranteed
±4%
toler-
ance on output voltage within specified input voltages and
output load conditions, and
±10%
on the oscillator frequency
(±2% over 0°C to +125°C). External shutdown is included,
featuring 60µA (typical) standby current. The output switch
includes cycle–by–cycle current limiting, as well as thermal
shutdown for full protection under fault conditions.
APPLICATIONS
s
s
s
s
s
s
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
16-Pin SOIC (Wide)
NC 1
NC 2
FB 3
SIG GND 4
ON/OFF
5
16 NC
15 NC
14 OUTPUT
ORDERING INFORMATION
Part
Number
TC2574-3.3VPA
TC2574-5.0VPA
TC2574-12.0VPA
TC2574-VPA*
TC2574-VOE*
Package
8-Pin PDIP (Narrow)
8-Pin PDIP (Narrow)
8-Pin PDIP (Narrow)
8-Pin PDIP (Narrow)
16-Pin SOIC (Wide)
Temperature
Range
–40 to +125°C
–40 to +125°C
–40 to +125°C
–40 to +125°C
–40 to +125°C
TC2574
13 NC
12 VIN
11 NC
10 NC
9 NC
PWR GND 6
NC 7
NC 8
Note: *ADJ = 1.23 To 37V.
8-Pin PDIP (Narrow)
FB 1
SIG GND 2
ON/OFF 3
PWR GND 4
8 NC
7 OUTPUT
TC2574
6 NC
5 VIN
© 2001 Microchip Technology Inc.
DS21397A
TC2574-2 12/22/00
0.5A Step-Down Switching Regulator
TC2574
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 (SOIC) ........... (Internally Limited)
Thermal Resistance, Junction-to-Ambient ..... 145°C/W
Max Power Dissipation (PDIP) ............ (Internally Limited)
Thermal Resistance, Junction-to-Ambient ... 100°C/W
Thermal Resistance, Junction-to-Case ........ 5.0°C/W
Storage Temperature Range ................. –65°C to +150°C
Minimum ESD Rating .............................................. 2.0kV
(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
= 100mA. 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
= 100mA, T
J
= 25°C
4.75V
≤
V
IN
≤
40V, 0.1A
≤
I
LOAD
≤
0.5AV
T
J
= 25°C
T
J
= –40°C to +125°
V
IN
= 12V, I
LOAD
= 0.5 A
V
IN
= 12V, I
LOAD
= 100mA, T
J
= 25°C
7.0V
≤
V
IN
≤
40V, 0.1A
≤
I
LOAD
≤
0.5A
T
J
= 25°C
T
J
= –40°C to +125°C
V
IN
= 12V, I
LOAD
= 0.5 A
V
IN
= 25V, I
LOAD
= 100mA, T
J
= 25°C
15V
≤
V
IN
≤
40V, 0.1A
≤
I
LOAD
≤
0.5A
T
J
= 25°C
T
J
= –40°C to +125°C
V
IN
= 15V, I
LOAD
= 0.5 A
V
IN
= 12V, I
LOAD
= 100mA, V
OUT
= 5.0V,
T
J
= 25*C
7.0V
≤
V
IN
≤
40V, 0.1A
≤
I
LOAD
≤
0.5A
V
OUT
= 5.0V
T
J
= 25°C
T
J
= –40°C to +125°C
V
IN
= 12V, I
LOAD
= 0.5A, 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
—
72
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
TC2574-3.3 [( Note 1) Test Circuit Figure 2]
η
V
OUT
Efficiency
Output Voltage
%
V
TC2574-5 [( Note 1) Test Circuit Figure 2]
η
V
OUT
Efficiency
Output Voltage
%
V
TC2574-12 [( Note 1) Test Circuit Figure 2]
η
V
FB
V
FBT
Efficiency
Feedback Voltage
Feedback Voltage
%
V
TC2574-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 TC2574 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 TC2574: T
LOW
= –40°C T
HIGH
= +125°C
TC2574-2 12/22/00
2
© 2001 Microchip Technology Inc.
DS21397A
0.5A Step-Down Switching Regulator
TC2574
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
= 100mA. 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
TC2574-ADJUSTABLE VERSION [(Note 1) Test Circuit Figure 2]
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 = 5.0 V (“off”)
T
J
= 25°C
T
J
= –40 to +125°C
ON/OFF Pin Logic Input Level
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 mA
ON/OFF Pin = 5.0V (“off”), T
J
= 25°C
ON/OFF Pin Input Current mA
ON/OFF Pin = 0 (“on”), T
J
= 25°C
—
—
—
47
42
—
—
93
0.7
0.65
—
—
—
—
—
—
25
—
52
52
–
1.0
—
98
1.0
—
0.6
10
5.0
—
60
—
100
200
—
58
63
1.2
1.4
—
1.6
1.8
mA
2.0
30
mA
9.0
11
µA
200
400
V
2.2
2.4
—
—
—
—
1.4
—
1.2
—
15
0
—
—
1.0
0.8
µA
30
µA
5.0
f
O
kHz
V
SAT
V
DC
I
CL
%
A
I
L
I
Q
I
STBY
V
IH
V
IL
I
IH
I
IL
NOTES:
1. External components such as the catch diode, inductor, input and output capacitors can affect the switching regulator system
performance. When the TC2574 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 TC2574: T
LOW
= –40°C T high = +125°C
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 0 V.
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
version, to force the output transistor OFF.
7. V
IN
= 40 V.
© 2001 Microchip Technology Inc.
DS21397A
3
TC2574-2 12/22/00
0.5A Step-Down Switching Regulator
TC2574
PIN DESCRIPTION
Pin No.
8-Pin PDIP
5
Pin No
16-Pin SOIC
12
Symbol
V
IN
Description
This pin is the positive input supply for the TC2574 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 1.0V. 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 signal ground pin. See the information about the printed circuit board
layout.
Circuit power 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 TC2574 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 to approximately 80µA.
The input threshold voltage is typically 1.5V. Applying a voltage above this
value (up to +V
IN
) shuts the regulator off. If the voltage applied to this pin is
ower than 1.5 V or if this pin is left open, the regulator will be in the “on”
condition.
7
14
Output
2
4
1
4
6
3
SIG Gnd
PWR GND
FB
3
5
ON/OFF
REPRESENTATIVE BLOCK DIAGRAM AND TYPICAL APPLICATION
Unregulated
DC Input
CIN
+VIN
+
5
TC2574
1
3.1V Internal
Regulator
ON/OFF
ON/OFF
3
Output
Voltage Versions
Fixed gain
Error Amplifier
Current
Limit
Comparator
R2 (Ω)
Feedback
R1
+
–
Driver
3.3V
5.0V
12V
1.7k
3.1k
8.84k
+
R2
1.0k
–
Freq.
Shift
18kHz
1.235V
Band-Gap
Reference
+
–
Latch
For Adjustable version
R1 = open, R2 = 0Ω
Output
1.0 Amp
Switch
7
PWR GND
4
D1
L1
VOUT
SIG GND
2
52kHz
Oscillator
Reset
Thermal
Shutdown
+
COUT
Load
TC2574-2 12/22/00
4
© 2001 Microchip Technology Inc.
DS21397A
0.5A Step-Down Switching Regulator
TC2574
Feedback
7.0 – 40V
Unregulated
DC Input
+VIN
CIN
22µF
1
TC2574
2
Sig 4
GND
Output
L1
330µH
5.0V Regulated
Output 0.5A Load
D1 COUT
220µF
+
5
7
PWR 3 ON/OFF
GND
Figure 1. Block Diagram and Typical Application: Fixed Output Versions
Test CIrcuit and Layout Guidelines
1
TC2574
Fixed Output
4
PWR 2
GND
Sig 3
GND
Output
7
ON/OFF
D1
1N5819
L1
330µH
VIN
5
7.0 – 40V
Unregulated
DC Input
+ C
IN
22µF
VOUT
COUT
220µF
+
Load
CIN
COUT
D1
L1
R2
- 22µF, 60V, Aluminum Electrolytic
- 220µF, 25V, Aluminum Electrolytic
- Schottky, 1N5819
- 2.0k,0.1%
- 6.12k, 0.1%
Adjustable Output Voltage Versions
1
TC2574
Adjustable
4
+
CIN
22µF
PWR 2
GND
Sig 3
GND
Output
7
ON/OFF
+
D1
1N5819
COUT
220µF
L1
330µH
VIN
5
7.0 – 40V
Unregulated
DC Input
VOUT
5.0V
R2
6.12k Load
R2
6.12k
VOUT = VREF
R1= R2
(
1.0 + R2
R1
)
(
VOUT - 1.0
)
VREF
Where VREF = 1.23V, R1
between 1.0kΩ and 5.0kΩ
Figure 2. Test Circuit and Layout Guidelines
© 2001 Microchip Technology Inc.
DS21397A
5
TC2574-2 12/22/00
京公网安备 11010802033920号
EEWORLD
