1
TC2574
0.5A Step-Down Switching Regulator
TC2574-1 1/6/00
0.5A Step-Down Switching Regulator
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 switchmode 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 60
A (typical) standby current. The output switch
includes cyclebycycle current limiting, as well as thermal
shutdown for full protection under fault conditions.
FEATURES
s
3.3V, 5.0V, 12V and Adjustable Output Versions
s
Adjustable Version Output Voltage Range,
1.23 to 37 V
4% Max Over Line and Load Conditions
s
Guaranteed 0.5 A Output Current
s
Wide Input Voltage Range: 4.75 to 40V
s
Requires Only 4 External Components
s
52kHz Fixed Frequency Internal Oscillator
s
TTL Shutdown Capability, Low Power Standby Mode
s
High Efficiency
s
Uses Readily Available Standard Inductors
s
Thermal Shutdown and Current Limit Protection
APPLICATIONS
s
Simple and HighEfficiency StepDown (Buck)
Regulator
s
Efficient Pre-Regulator for Linear Regulators
s
OnCard Switching Regulators
s
Positive to Negative Converters (BuckBoost)
s
Negative Step-Up Converters
s
Power Supply for Battery Chargers
ORDERING INFORMATION
Part
Temperature
Number
Package
Range
TC2574-3.3VPA
8-Pin PDIP (Narrow) 40 to +125
C
TC2574-5.0VPA
8-Pin PDIP (Narrow) 40 to +125
C
TC2574-12.0VPA
8-Pin PDIP (Narrow) 40 to +125
C
TC2574-VPA*
8-Pin PDIP (Narrow) 40 to +125
C
TC2574-VOE*
16-Pin SOIC (Wide) 40 to +125
C
TC2574
TelCom Semiconductor reserves the right to make changes in the circuitry and specifications of its devices.
PIN CONFIGURATIONS
1
2
3
4
16
15
14
13
SIG GND
5
6
7
12
11
10
9
8
FB
NC
NC
OUTPUT
TC2574
NC
NC
NC
NC
NC
NC
NC
NC
PWR GND
ON/OFF
1
8
2
7
3
6
4
5
SIG GND
FB
OUTPUT
VIN
VIN
NC
NC
PWR GND
TC2574
ON/OFF
16-Pin SOIC (Wide)
8-Pin PDIP (Narrow)
Note: *ADJ = 1.23 To 37V.
TC2574
2
TC2574-1 1/6/00
0.5A Step-Down Switching Regulator
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 k
)
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
Parameter
Test Conditions
Min
Typ
Max
Units
TC2574-3.3 [( Note 1) Test Circuit Figure 2]
V
OUT
Output Voltage
V
IN
= 12V, I
LOAD
= 100mA, T
J
= 25
C
3.234
3.3
3.366
V
4.75V
V
IN
40V, 0.1A
I
LOAD
0.5AV
T
J
= 25
C
3.168
3.3
3.432
T
J
= 40
C to +125
3.135
--
3.465
Efficiency
V
IN
= 12V, I
LOAD
= 0.5 A
--
72
--
%
TC2574-5 [( Note 1) Test Circuit Figure 2]
V
OUT
Output Voltage
V
IN
= 12V, I
LOAD
= 100mA, T
J
= 25
C
4.9
5.0
5.1
V
7.0V
V
IN
40V, 0.1A
I
LOAD
0.5A
T
J
= 25
C
4.8
5.0
5.2
T
J
= 40
C to +125
C
4.75
--
5.25
Efficiency
V
IN
= 12V, I
LOAD
= 0.5 A
--
77
--
%
TC2574-12 [( Note 1) Test Circuit Figure 2]
V
OUT
Output Voltage
V
IN
= 25V, I
LOAD
= 100mA, T
J
= 25
C
11.76
10
12.24
V
15V
V
IN
40V, 0.1A
I
LOAD
0.5A
T
J
= 25
C
11.52
12
12.48
T
J
= 40
C to +125
C
11.4
--
12.6
Efficiency
V
IN
= 15V, I
LOAD
= 0.5 A
--
88
--
%
TC2574-Adjustable Version [( Note 1) Test Circuit Figure 2]
V
FB
Feedback Voltage
V
IN
= 12V, I
LOAD
= 100mA, V
OUT
= 5.0V,
1.217
1.23
1.243
V
T
J
= 25*C
V
FBT
Feedback Voltage
7.0V
V
IN
40V, 0.1A
I
LOAD
0.5A
V
OUT
= 5.0V
T
J
= 25
C
1.193
1.23
1.267
T
J
= 40
C to +125
C
1.18
--
1.28
Efficiency
V
IN
= 12V, I
LOAD
= 0.5A, V
OUT
= 5.0V
--
77
--
%
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
TC2574
0.5A Step-Down Switching Regulator
TC2574-1 1/6/00
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
Parameter
Test Conditions
Min
Typ
Max
Units
TC2574-ADJUSTABLE VERSION [(Note 1) Test Circuit Figure 2]
I
b
Feedback Bias Current
V
OUT
= 5.0V (Adjustable Version Only)
nA
T
J
= 25
C
--
25
100
T
J
= 40
C to +125
C
--
--
200
f
O
Oscillator Frequency (Note 3)
T
J
= 25
C
--
52
--
kHz
T
J
= 0 to +125
C
47
52
58
T
J
= 40 to +125
C
42
63
V
SAT
Saturation Voltage
I
OUT
= 0.5 A, (Note 4)
V
T
J
= 25
C
--
1.0
1.2
T
J
= 40 to +125
C
--
--
1.4
DC
Max Duty Cycle ("on") [Note 5]
93
98
--
%
I
CL
Current Limit Peak Current (Notes 3 and 4)
A
T
J
= 25
C
0.7
1.0
1.6
T
J
= 40 to +125
C
0.65
--
1.8
I
L
Output Leakage Current (Notes 6 and 7), T
J
= 25
C
mA
Output = 0 V
--
0.6
2.0
Output = 1.0 V
--
10
30
I
Q
Quiescent Current (Note 6)
mA
T
J
= 25
C
--
5.0
9.0
T
J
= 40 to +125
C
--
--
11
I
STBY
Standby Quiescent Current
ON/OFF Pin = 5.0 V ("off")
A
T
J
= 25
C
--
60
200
T
J
= 40 to +125
C
--
--
400
ON/OFF Pin Logic Input Level
V
V
IH
V
OUT
= 0V
T
J
= 25
C
2.2
1.4
--
T
J
= 40 to +125
C
2.4
--
--
V
IL
Nominal Output Voltage
T
J
= 25
C
--
1.2
1.0
T
J
= 40 to +125
C
--
--
0.8
ON/OFF Pin Input Current mA
A
I
IH
ON/OFF Pin = 5.0V ("off"), T
J
= 25
C
--
15
30
I
IL
ON/OFF Pin Input Current mA
A
ON/OFF Pin = 0 ("on"), T
J
= 25
C
--
0
5.0
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.
TC2574
4
TC2574-1 1/6/00
0.5A Step-Down Switching Regulator
REPRESENTATIVE BLOCK DIAGRAM AND TYPICAL APPLICATION
PIN DESCRIPTION
Pin No.
Pin No
8-Pin PDIP
16-Pin SOIC
Symbol
Description
5
12
V
IN
This pin is the positive input supply for the TC2574 stepdown 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).
7
14
Output
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.
2
4
SIG Gnd
Circuit signal ground pin. See the information about the printed circuit board
layout.
4
6
PWR GND
Circuit power ground pin. See the information about the printed circuit board
layout.
1
3
FB
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 noninverting 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.
3
5
ON/OFF
It allows the switching regulator circuit to be shut down using logic level
signals, thus dropping the total input supply current to approximately 80
A.
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.
TC2574
+
+
3.1V Internal
Regulator
ON/OFF
ON/OFF
Latch
Freq.
Shift
18kHz
Reset
Thermal
Shutdown
3
7
1.0 Amp
Switch
D1
L1
COUT
+VIN
CIN
VOUT
Driver
Output
PWR GND
1
5
2
For Adjustable version
R1 = open, R2 = 0
Load
Feedback
Unregulated
DC Input
SIG GND
R1
R2
1.0k
Current
Limit
Comparator
Fixed gain
Error Amplifier
+
+
+
52kHz
Oscillator
1.235V
Band-Gap
Reference
4
Output
Voltage Versions
3.3V
5.0V
12V
R2 (
)
1.7k
3.1k
8.84k
5
TC2574
0.5A Step-Down Switching Regulator
TC2574-1 1/6/00
CIN
22
F
COUT
220
F
+VIN
5
2
Sig
GND
PWR
GND
4
3
7
1
L1
330
H
Output
D1
Feedback
ON/OFF
7.0 40V
Unregulated
DC Input
5.0V Regulated
Output 0.5A Load
TC2574
+
Figure 1. Block Diagram and Typical Application: Fixed Output Versions
Figure 2. Test Circuit and Layout Guidelines
CIN
22
F
COUT
220
F
VOUT
VIN
5
4
Sig
GND
PWR
GND
2
3
7
1
D1
1N5819
L1
330
H
Output
Test CIrcuit and Layout Guidelines
CIN - 22
F, 60V, Aluminum Electrolytic
COUT - 220
F, 25V, Aluminum Electrolytic
D1 - Schottky, 1N5819
L1 - 2.0k,0.1%
R2 - 6.12k, 0.1%
VOUT = VREF
(
1.0 + R2
)
R1
ON/OFF
7.0 40V
Unregulated
DC Input
TC2574
+
+
Load
Fixed Output
CIN
22
F
R2
6.12k
R2
6.12k
COUT
220
F
VOUT
5.0V
VIN
5
4
Sig
GND
PWR
GND
2
3
7
1
D1
1N5819
L1
330
H
Output
Where VREF = 1.23V, R1
between 1.0k
and 5.0k
Adjustable Output Voltage Versions
ON/OFF
7.0 40V
Unregulated
DC Input
TC2574
+
+
Load
Adjustable
R1= R2
(
VOUT - 1.0
)
VREF
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