TL3577
100-kHz CURRENT-MODE SIMPLE STEP-UP/FLYBACK SWITCHING REGULATOR
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SLVS633 – OCTOBER 2006
FEATURES
APPLICATIONS
•
•
•
•
•
•
•
•
•
•
Simple Boost Converter
Flyback Converters, Single/Multiple Outputs
SEPIC Converter With VIN Higher or Lower
Than Output Voltage
Transformer-Coupled Forward Converters
KTT (TO-263) PACKAGE
(TOP VIEW)
GND
•
Few External Components Required (As Few
As Six)
Current Limit, Undervoltage Lockout, and
Thermal Shutdown
Wide Input Voltage Range: 3 V to 40 V
100-kHz Internal Oscillator Allows for Use of
Small Magnetics
Current-Mode Operation for Faster Transient
Response, Line Regulation, and
Cycle-by-Cycle Current Limiting
Soft-Start Capability Provides Controlled
Startup Current
Improved Replacement for LM2577 Series
5
4
3
2
1
VIN
SWITCH
GND
FEEDBACK
COMP
DESCRIPTION/ORDERING INFORMATION
The TL3577 series are easy-to-use devices that incorporate all the active circuitry required to implement either
step-up (boost), flyback, forward converter, or SEPIC converter switching regulators. The internal 3-A 65-V
switch allows the TL3577 to provide an output voltage of up to 60 V as a simple boost regulator; higher output
voltages can be achieved with the TL3577 configured as a flyback or forward converter.
Requiring few external components, The TL3577 features a wide input voltage range of 3 V to 40 V and offers
an adjustable output voltage. Basic protection features include undervoltage lockout, thermal protection, and soft
start, which is provided to reduce input current during startup. Current-mode control provides cycle-by-cycle
current limiting, as well as faster line and load regulation. The internal 100-kHz oscillator allows for use of
smaller magnetics and filter components, when compared with similar regulators running at 52 kHz. A standard
series of inductors and capacitors optimized for use with these regulators is available from several
manufacturers and are listed in this data sheet.
The TL3577 is characterized for operation over the virtual junction temperature range of –40°C to 125°C.
ORDERING INFORMATION
TJ
–40°C to 125°C
(1)
VO
(NOM)
ADJ
PACKAGE (1)
TO-263 – KTT
Reel of 500
ORDERABLE PART NUMBER
TL3577-ADJIKTTR
TOP-SIDE MARKING
TL3577ADJI
Package drawings, standard packing quantities, thermal data, symbolization, and PCB design guidelines are available at
www.ti.com/sc/package.
Please be aware that an important notice concerning availability, standard warranty, and use in critical applications of Texas
Instruments semiconductor products and disclaimers thereto appears at the end of this data sheet.
PRODUCTION DATA information is current as of publication date.
Products conform to specifications per the terms of the Texas
Instruments standard warranty. Production processing does not
necessarily include testing of all parameters.
Copyright © 2006, Texas Instruments Incorporated
TL3577
100-kHz CURRENT-MODE SIMPLE STEP-UP/FLYBACK SWITCHING REGULATOR
www.ti.com
SLVS633 – OCTOBER 2006
FUNCTIONAL BLOCK DIAGRAM
VIN
SWITCH
Current Limit,
Thermal Limit, and
Undervoltage Shutdown
2.5-V
Regulator
3-A 65-V
NPN Switch
Driver
Stage
Logic
100-kHz
Oscillator
Corrective
Ramp
Voltage
+
Comparator
S
+ CurrentSense
Voltage
Amp
FEEDBACK
Soft
Start
Error
Amplifier
1.23-V
Reference
COMP
2
CurrentSense
Resistor
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TL3577
100-kHz CURRENT-MODE SIMPLE STEP-UP/FLYBACK SWITCHING REGULATOR
SLVS633 – OCTOBER 2006
Absolute Maximum Ratings
(1)
over operating free-air temperature range (unless otherwise noted)
MIN
MAX
UNIT
VIN
Supply voltage
45
V
VSW
Output SWITCH voltage
65
V
ISW
Output SWITCH current
TJ
Maximum junction temperature
Tstg
Storage temperature range
TJ
Junction temperature
(1)
–65
6
A
150
°C
150
°C
150
°C
Stresses beyond those listed under "absolute maximum ratings" may cause permanent damage to the device. These are stress ratings
only, and functional operation of the device at these or any other conditions beyond those indicated under "recommended operating
conditions" is not implied. Exposure to absolute-maximum-rated conditions for extended periods may affect device reliability.
Package Thermal Data (1)
(1)
PACKAGE
BOARD
θJA
θJC
θJCB
TO-263 (KTT)
High K, JESD 51-5
31.8
35.0
1.13
Maximum power dissipation is a function of TJ(max), θJA, and TA. The maximum allowable power dissipation at any allowable ambient
temperature is PD = (TJ(max) – TA)/θJA. Operating at the absolute maximum TJ of 150°C can affect reliability.
Recommended Operating Conditions
over operating free-air temperature range (unless otherwise noted)
MIN
MAX
VIN
Supply voltage
3
40
V
VSW
Output SWITCH voltage
0
60
V
ISW
Output SWITCH current
3
A
TJ
Operating virtual junction temperature
–40
125
°C
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UNIT
3
TL3577
100-kHz CURRENT-MODE SIMPLE STEP-UP/FLYBACK SWITCHING REGULATOR
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SLVS633 – OCTOBER 2006
Electrical Characteristics
VIN = 5 V, VFEEDBACK = VREF, ISWITCH = 0 (unless otherwise noted)
PARAMETER
TEST CONDITIONS
TL3577-ADJ
MIN
TYP
MAX
12
12.4
VOUT
Output voltage
VIN = 5 V to 10 V,
ILOAD = 100 mA to 800 mA, See Figure 1
25°C
11.6
Full range
11.4
DVOUT
DVIN
Line regulation
VIN = 3.5 V to 10 V, ILOAD = 200 mA,
See Figure 1
Full range
DVOUT
DILOAD
Load regulation
ILOAD = 100 mA to 800 mA, See Figure 1
η
Efficiency
ILOAD = 800 mA, See Figure 1
VFEEDBACK = 1.5 V (SWITCH Off)
ICC
Input supply current
ISWITCH = 2 A,
VCOMP = 2 V (maximum duty cycle)
VUV
Input supply undervoltage lockout ISWITCH = 100 mA
fO
Oscillator frequency
Measured at SWITCH, ISWITCH = 100 mA
VREF
Reference voltage
Measured at FEEDBACK,
VIN = 3 V to 40 V, VCOMP = 1 V
DVREF
DVIN
Reference voltage line regulation
VIN = 3 V to 40 V
IB
Error amplifier input bias current
VCOMP = 1 V
GM
Error amplifier transconductance
ICOMP = –30 µA to 30 µA, VCOMP = 1 V
AVOL
Error amplifier voltage gain
VCOMP = 1.1 V to 1.9 V, RCOMP = 1 MΩ (1)
Upper limit, VFEEDBACK = 1 V
Error amplifier output swing
Lower limit, VFEEDBACK = 1.5 V
25°C
12.6
20
25°C
20
80
25°C
7.5
Full range
45
Full range
25°C
2.7
85
Full range
80
25°C
1.214
Full range
1.206
100
1.23
25°C
100
Full range
25°C
2400
1600
25°C
500
Full range
250
25°C
2.2
3700
±130
±90
Switch leakage current
VSWITCH = 65 V,
VFEEDBACK = 1.5 V (SWITCH off)
Full range
VSAT
Switch saturation voltage
ISWITCH = 2 A,
VCOMP = 2 V (maximum duty cycle)
Full range
NPN switch current limit
VCOMP = 2 V
25°C
2.5
Full range
1.5
25°C
88
Full range
84
±200
4800
kHz
V
nA
µmho
V/V
0.4
±300
±400
5
7.5
9.5
90
12.5
25°C
10
V
0.5
3
4.3
µA
A/V
300
0.7
0.9
3.7
µA
%
600
25°C
25°C
V
2.4
25°C
Full range
mA
0.55
25°C
IL
300
800
0.3
Full range
Switch transconductance
mV
mV
5800
Full range
DISWITCH
DVCOMP
1.246
2
25°C
VCOMP = 1.5 V, ISWITCH = 100 mA
115
800
Full range
Maximum duty cyle
2.85
1.254
0.5
D
70
120
25°C
VFEEDBACK = 1 V, VCOMP = 0
mV
10
2.95
25°C
Soft-start current
V
85
Full range
ISS
UNIT
%
14
25°C
VFEEDBACK = 1 V to 1.5 V, VCOMP = 1 V
50
100
25°C
Full range
50
100
Full range
Error amplifier output current
(1)
4
TJ
5.3
6
µA
V
A
A 1-MΩ resistor is connected to the compensation pin (which is the error amplifier output) to ensure accuracy in measuring AVOL. In
actual applications, this load resistance should be ≥10 MΩ, resulting in AVOL that is typically twice the specified minimum limit.
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TL3577
100-kHz CURRENT-MODE SIMPLE STEP-UP/FLYBACK SWITCHING REGULATOR
SLVS633 – OCTOBER 2006
Electrical Characteristics (continued)
VIN = 5 V, VFEEDBACK = VREF, ISWITCH = 0 (unless otherwise noted)
PARAMETER
COMP current
TEST CONDITIONS
VCOMP = 0 V
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TJ
25°C
Full range
TL3577-ADJ
MIN
TYP
MAX
25
40
50
UNIT
µA
5
TL3577
100-kHz CURRENT-MODE SIMPLE STEP-UP/FLYBACK SWITCHING REGULATOR
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SLVS633 – OCTOBER 2006
TYPICAL CHARACTERISTICS
∆ REFERENCE VOLTAGE
vs
SUPPLY VOLTAGE
REFERENCE VOLTAGE
vs
TEMPERATURE
1.25
0.5
1.248
∆ Reference Voltage – mV
VREF – Reference Voltage – V
0.4
1.246
1.244
1.242
1.24
1.238
1.236
1.234
0.3
0.2
0.1
0
-0.1
1.232
-0.2
1.23
-40 -25 -10
0
5
5
10
20 35 50 65 80 95 110 125
15
20
25
30
35
40
VIN – Supply Voltage – V
TA – Temperature – °C
ERROR AMPLIFIER VOLTAGE GAIN
vs
TEMPERATURE
5000
1600
4750
1500
AV – Error Amplifier Voltage Gain – V/V
G M – Error Amplifier Transconductance – µmho
ERROR AMPLIFIER TRANSCONDUCTANCE
vs
TEMPERATURE
4500
4250
4000
3750
3500
3250
3000
2750
2500
-40 -25 -10
5
20 35 50 65 80 95 110 125
1400
1300
1200
1100
1000
900
800
700
600
-40 -25 -10
20 35 50 65 80 95 110 125
TA – Temperature – °C
TA – Temperature – °C
6
5
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100-kHz CURRENT-MODE SIMPLE STEP-UP/FLYBACK SWITCHING REGULATOR
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TYPICAL CHARACTERISTICS (continued)
QUIESCENT CURRENT
vs
TEMPERATURE
SWITCH CURRENT LIMIT
vs
TEMPERATURE
6
10.5
5.8
10
5.6
Switch Current Limit – A
IQ – Quiescent Current – mA
11
9.5
9
8.5
8
7.5
5.4
5.2
5
4.8
4.6
4.4
7
4.2
6.5
6
-40 -25 -10
4
-40 -25 -10
5
20 35
50 65 80 95 110 125
5
20
35 50
65 80
95 110 125
TA – Temperature – °C
TA – Temperature – °C
OSCILLATOR FREQUENCY
vs
TEMPERATURE
130
110
120
108
110
106
f O – Oscillator Frequency – kHz
IB – FEEDBACK Bias Current – nA
FEEDBACK BIAS CURRENT
vs
TEMPERATURE
100
90
80
70
60
50
104
102
100
98
96
94
40
92
30
-40 -25 -10
90
-40 -25 -10
5
20
35 50
65 80 95 110 125
5
20
35 50
65 80 95 110 125
TA – Temperature – °C
TA – Temperature – °C
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TL3577
100-kHz CURRENT-MODE SIMPLE STEP-UP/FLYBACK SWITCHING REGULATOR
SLVS633 – OCTOBER 2006
TYPICAL CHARACTERISTICS (continued)
SWITCH SATURATION VOLTAGE
vs
TEMPERATURE
0.9
VSAT – Switch Saturation Voltage – V
0.85
0.8
ISW = 2 A
VCOMP = 2 V
0.75
0.7
0.65
0.6
0.55
0.5
0.45
0.4
0.35
0.3
-40 -25 -10
5
20 35
50 65 80 95 110 125
TA – Temperature – °C
8
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TL3577
100-kHz CURRENT-MODE SIMPLE STEP-UP/FLYBACK SWITCHING REGULATOR
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PARAMETER MEASUREMENT INFORMATION
220 µF
VIN
10 kW
100 µH
VIN
120 W
SWITCH
TL3577-ADJ
0.1 µF
COMP
2 kW
R1
24 W
COUT
680 µF
0.1 µF
LOAD
SW1
FEEDBACK
GND
60 W
SW2
R2
0.33 µF
A.
R1 = 48.7 kΩ in series with 511 Ω
B.
R2 = 5.62 kΩ (1%)
Figure 1. Test Circuit
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TL3577
100-kHz CURRENT-MODE SIMPLE STEP-UP/FLYBACK SWITCHING REGULATOR
SLVS633 – OCTOBER 2006
APPLICATION INFORMATION
Figure 2 shows a typical application of the TL3577 in a boost regulator.
5-V
Input
12 V at £800 mA
Regulated Output
100 µH
680 µF
0.1 µF
VIN
SWITCH
TL3577-ADJ
COMP
2.2 kW
17.4 kW
FEEDBACK
GND
2 kW
0.33 µF
Figure 2. Typical Application – Boost Regulator
Figure 3 shows a typical application of the TL3577 in a flyback regulator.
5V
(4 V to 6 V)
100 µF
12 V at 150 mA
1:2.5
330 µF
47 µH
1 µF
12 V at 150 mA
330 µF
VIN
SWITCH
TL3577-ADJ
17.4 kΩ
COMP
2.4 kΩ
FEEDBACK
GND
2 kΩ
0.47 µF
Figure 3. Typical Application – Flyback Regulator
10
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TL3577
100-kHz CURRENT-MODE SIMPLE STEP-UP/FLYBACK SWITCHING REGULATOR
SLVS633 – OCTOBER 2006
APPLICATION INFORMATION (continued)
Figure 4 shows a typical application of the TL3577 in a SEPIC regulator.
Input
3 V to 12 V
1 µF
(See Note A)
100 µH
VIN
SWITCH
100 µH
TL3577-ADJ
22 µF
20 kΩ
COMP
10 kΩ
Output
3.3 V
FEEDBACK
GND
12.1 kΩ
10 µF
680 pF
A.
Low ESR. Voltage rating must be at least VIN + VOUT.
Figure 4. Typical Application – SEPIC Regulator
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TL3577
100-kHz CURRENT-MODE SIMPLE STEP-UP/FLYBACK SWITCHING REGULATOR
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SLVS633 – OCTOBER 2006
APPLICATION INFORMATION (continued)
Step-Up (Boost) Regulator
Figure 2 shows a step-up switching regulator utilizing the TL3577. The regulator produces an output voltage
higher than the input voltage. The TL3577 turns its switch on and off at a fixed frequency of 100 kHz, thus
storing energy in the inductor (L). When the NPN switch is on, the inductor current is charged at a rate of VIN/L.
When the switch is off, the voltage at the SWITCH terminal of the inductor rises above VIN, discharging the
stored current through the output diode (D) into the output capacitor (COUT) at a rate of (VOUT – VIN)/L. The
energy stored in the inductor is thus transferred to the output. The output voltage is controlled by the amount of
energy transferred, which is controlled by modulating the peak inductor current. This modulation is accomplished
by feeding a portion of the output voltage to an error amplifier that amplifies the difference between the feedback
voltage and an internal 1.23-V precision reference voltage. The output of the error amplifier is compared to a
voltage that is proportional to the switch current or the inductor current during the switch-on time. A comparator
terminates the switch-on time when the two voltages are equal and, thus, controls the peak switch current to
maintain a constant output voltage. Figure 5 shows voltage and current waveforms for the circuit. Formulas for
calculation are shown in Table 1.
Step-Up Regulator Design Procedure
Given:
VIN(min) = Minimum input supply voltage
VOUT = Regulated output voltage
VSW(OFF)
Switch
Voltage
Diode
Voltage
VSAT
0V
VF
0V
VR
Inductor
Current
Switch
Current
IIND(AVG)
∆IIND
0
ISW(PK)
0
Diode
Current
ID(PK)
ID(AVG)
0
Figure 5. Step-Up Regulator Waveforms
12
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100-kHz CURRENT-MODE SIMPLE STEP-UP/FLYBACK SWITCHING REGULATOR
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Table 1. Step-up Regulator Formulas
Duty cycle
Average inductor current
VOUT + VF – VIN
∆IIND
Peak inductor current
IIND(PK)
VOUT – VIN
≈
VOUT + VF – VSAT
VOUT
ILOAD
IIND(AVG)
Inductor current ripple
Peak switch current
1–D
VIN – VSAT
L
•
ILOAD
1–D
ILOAD
ISW(PK)
1–D
D
100,000
+
+
∆IIND
2
∆IIND
2
Switch voltage when off
VSW(OFF)
VOUT + VF
Diode reverse voltage
VR
VOUT – VSAT
Average diode current
ID(AVG)
ILOAD
Peak diode current
ID(PK)
Power dissipation
(1)
D
(1)
PD
ILOAD
1–D
0.25 Ω
(
ILOAD
1–D
(
+
∆IIND
2
D+
2
ILOAD • D • VIN
50 (1 – D)
VF = forward-biased diode voltage, ILOAD = output load
First, determine if the TL3577 can provide these values of VOUT and ILOAD(max) when operating with the minimum
value of VIN. The upper limits for VOUT and ILOAD(max) are given by the following equations.
VOUT ≤ 60 V and
VOUT ≤ 10 × VIN
ILOAD(max) ≤ (2.1 A × VIN(min))/VOUT
These limits must be greater than or equal to the values specified in this application.
1. Output Voltage Section
Resistors R1 and R2 are used to select the desired output voltage. These resistors form a voltage divider and
present a portion of the output voltage to the error amplifier, which compares it to an internal 1.23-V reference.
Select R1 and R2 such that:
R1/R2 = (VOUT/1.23 V) – 1
2. Inductor Selection (L)
A. Preliminary Calculations
To select the inductor, the calculation of the following three parameters is necessary:
Dmax, the maximum switch duty cycle (0 ≤ D ≤ 0.9):
Dmax = VOUT + VF – VIN(min)/VOUT + VF – 0.6 V
where, typically, VF = 0.5 V for Schottky diodes and VF = 0.8 V for fast-recovery diodes.
E • T, the product of volts • time that charges the inductor:
E • T = Dmax × (VIN(min) – 0.6V)106/100,000 Hz (Vµs)
IIND,DC, the average inductor current under full load:
IIND,DC = (1.05 × ILOAD(max))/(1 – Dmax)
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100-kHz CURRENT-MODE SIMPLE STEP-UP/FLYBACK SWITCHING REGULATOR
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B. Identify Inductor Value
1. From Figure 6, identify the inductor code for the region indicated by the intersection of E • T and IIND,DC. This
code gives the inductor value in microhenries. The L or H prefix signifies whether the inductor is rated for a
maximum E • T of 90 Vµs (L) or 250 Vµs (H).
2. If D < 0.85, go to step C. If D ≥ 0.85, calculate the minimum inductance needed to ensure the switching
regulator’s stability:
If Lmin is smaller than the inductor values found in step B1, go on to step C. Otherwise, the inductor value
found in step 1, above, is too low; an appropriate inductor code should be obtained from Figure 6 as follows:
a. Find the lowest-value inductor that is greater than Lmin.
b. Find where E • T intersects this inductor value to determine if it has an L or H prefix. If E • T intersects
both the L and H regions, select the inductor with an H prefix.
C. Inductor Selection
Select an inductor from Table 2 which cross references the inductor codes to the part numbers of the three
different manufacturers. The inductors listed in Table 2 have the following characteristics:
AIE (ferrite, pot-core inductors): Benefits of this type are low electromagnetic interference (EMI), small
physical size, and very low power dissipation (core loss).
Pulse (powdered iron, toroid core inductors): Benefits are low EMI and ability to withstand E • T and peak
current above rated value better than ferrite cores.
Renco (ferrite, bobbin-core inductors): Benefits are low cost and best ability to withstand E • T and peak
current above rated value. Be aware that these inductors generate more EMI than the other types, and this
may interfere with signals sensitive to noise.
200
H2200
150
H1500
H1000
H680
H470
H330
H220
E • T (V • µs)
100
90
H150
80
70
L680
60
50
45
40
L470
L330
L220
L150
L100
L68
35
30
L47
25
20
0.3 0.35 0.4 0.45 0.5 0.6 0.7 0.8 0.9 1.0
1.5
2.0
2.5
3.0
I IND,DC (A)
A.
This chart assumes that the inductor ripple current inductor is approximately 20% to 30% of the average inductor
current (when the regulator is under full load). Greater ripple current causes higher peak switch currents and greater
output ripple voltage. Lower ripple current is achieved with larger value inductors. The factor of 20% to 30% is
chosen as a convenient balance between the two extremes.
Figure 6. Inductor Selection Graph
14
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TL3577
100-kHz CURRENT-MODE SIMPLE STEP-UP/FLYBACK SWITCHING REGULATOR
SLVS633 – OCTOBER 2006
Table 2. Standardized Inductors and Manufacturer’s Part Numbers
Manufacturer’s Part Number
Inductor Code
(1)
(2)
(3)
AIE (1)
Pulse (2)
Renco (3)
L47
415 - 0932
PE - 53112
RL2442
L68
415 - 0931
PE - 92114
RL2443
L100
415 - 0930
PE - 92108
RL2444
L150
415 - 0953
PE - 53113
RL1954
L220
415 - 0922
PE - 52626
RL1953
L330
415 - 0926
PE - 52627
RL1952
L470
415 - 0927
PE - 53114
RL1951
L680
415 - 0928
PE - 52629
RL1950
H150
415 - 0936
PE - 53115
RL2445
H220
430 - 0636
PE - 53116
RL2446
H330
430 - 0635
PE - 53117
RL2447
H470
430 - 0634
PE - 53118
RL1961
H680
415 - 0935
PE - 53119
RL1960
H1000
415 - 0934
PE - 53120
RL1959
H1500
415 - 0933
PE - 53121
RL1958
H2200
415 - 0945
PE - 53122
RL2448
AIE Magnetics, Div. Vernitron Corp., (813) 347-2181 2801 72nd Street North, St. Petersburg, FL 33710
Pulse Engineering, (619) 674-8100 12220 World Trade Drive, San Diego, CA 92128
Renco Electronics, Inc., (516) 586-5566 60 Jeffryn Blvd. East, Deer Park, NY 11729
3. Compensation Network (RC, CC) and Output Capacitor (COUT) Selection
The compensation network consists of resistor RC and capacitor CC, which form a simple pole-zero network and
stabilize the regulator. The values of RC and CC depend upon the voltage gain of the regulator, ILOAD(max), the
inductor L, and output capacitance COUT. A procedure to calculate and select the values for RC, CC, and COUT
that ensures stability is described below. It should be noted, however, that this may not result in optimum
compensation. To guarantee optimum compensation, a standard procedure for testing loop stability is
recommended, such as measuring VOUT transient responses to pulsing ILOAD.
A. Calculate the maximum value for RC.
RC ≤ (750 × ILOAD(max) × VOUT2)/VIN(min)2
Select a resistor less than or equal to this value, not to exceed 3 kΩ.
B. Calculate the minimum value for COUT using the following two equations.
COUT ≥ (0.19 × L × RC × ILOAD(max))/(VIN(min) × VOUT) and
COUT ≥ (VIN(min) × RC × (VIN(min) + (3.74 × 105 × L))/(487,800 × VOUT3)
The larger of these two values is the minimum value that ensures stability.
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100-kHz CURRENT-MODE SIMPLE STEP-UP/FLYBACK SWITCHING REGULATOR
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C. Calculate the minimum value of CC.
CC ≥ 58.5 × VOUT2 × COUT × RC2 × VIN(min)
The compensation capacitor also is used in the soft-start function of the regulator. When the input voltage is
applied to the part, the switch duty cycle is increased slowly at a rate defined by the compensation capacitor and
the soft-start current, thus eliminating high input currents. Without the soft-start circuitry, the switch duty cycle
would instantly rise to about 90% and draw large currents from the input supply. For proper soft starting, the
value for CC should be equal to or greater than 0.22 µF.
Table 3 lists several types of aluminum electrolytic capacitors that could be used for the output filter. Use the
following parameters to select the capacitor:
Working Voltage (WVDC): Choose a capacitor with a working voltage at least 20% higher than the regulator
output voltage.
Ripple Current: This is the maximum RMS value of current that charges the capacitor during each switching
cycle. For step-up and flyback regulators, the formula for ripple current is:
IRIPPLE(rms) = (ILOAD(max) × Dmax)/(1 – Dmax)
Choose a capacitor that is rated at least 50% higher than this value at 100 kHz.
Equivalent Series Resistance (ESR): This is the primary cause of output ripple voltage, and it also affects the
values of RC and CC needed to stabilize the regulator. As a result, the preceding calculations for CC and RC are
only valid if the ESR does not exceed the maximum value specified by the following equations.
ESR ≤ (0.01 × 15 V)/IRIPPLE(P-P) and ≤ (8.7 × 10-3 × VIN)/ILOAD(max) where
IRIPPLE(P-P) = (1.15 × ILOAD(max))/(1 – Dmax)
Select a capacitor with an ESR, at 100 kHz, that is less than or equal to the lower value calculated. Most
electrolytic capacitors specify ESR at 120 kHz, which is 15% to 30% higher than at 100 kHz. Also, note that
ESR increases by a factor of 2 when operating at –20°C.
In general, low values of ESR are achieved by using large-value capacitors (C ≥ 470 µF) and capacitors with
high WVDC, or by paralleling smaller-value capacitors.
4. Input Capacitor Selection (CIN)
To reduce noise on the supply voltage caused by the switching action of a step-up regulator (ripple current
noise), VIN should be bypassed to ground. A good quality 0.1-µF capacitor with low ESR should provide
sufficient decoupling. If the TL3577 is located far from the supply-source filter capacitors, an additional
electrolytic (47 µF, for example) is required.
Table 3. Aluminum Electrolytic Capacitors Recommended for Switching Regulators
Nichicon – Types PF, PX, or PZ
927 East State Parkway, Schaumburg, IL 60173
(708) 843-7500
16
United Chemi-CON – Types LX, SXF, or SXJ
9801West Higgens, Rosemont, IL 60018
(708) 696-2000
Submit Documentation Feedback
www.ti.com
TL3577
100-kHz CURRENT-MODE SIMPLE STEP-UP/FLYBACK SWITCHING REGULATOR
SLVS633 – OCTOBER 2006
5. Output Diode Selection (D)
In the step-up regulator, the switching diode must withstand a reverse voltage and be able to conduct the peak
output current of the TL3577. Therefore, a suitable diode must have a minimum reverse breakdown voltage
greater than the circuit output voltage and should also be rated for average and peak current greater than
ILOAD(max) and ID(pk). Because of their low forward-voltage drop (and higher regulator efficiencies), Schottky
barrier diodes often are used in switching regulators. Refer to Table 4 for recommended part numbers and
voltage ratings of 1-A and 3-A diodes.
Table 4. Diode Selection Chart (1)
VOUT(max)
(V)
Schottky
Fast Recovery
1A
3A
20
1N5817
MBR120P
1N5820
MBR320P
30
1N5818
MBR130P
11DQ03
1N5821
MBR330P
31DQ03
40
1N5819
MBR140P
11DQ04
1N5822
MBR340P
31DQ04
50
MBR150
11DQ05
MBR350
31DQ05
3A
1N4933
MUR105
1N4934
MUR110
10DL1
100
(1)
1A
MR851
30DL1
MR831
MBRxxx and MURxxx are manufactured by Motorola.
1DDxxx, 11Cxx and 31Dxx are manufactured by International Rectifier
Submit Documentation Feedback
17
PACKAGE OPTION ADDENDUM
www.ti.com
21-Nov-2006
PACKAGING INFORMATION
Orderable Device
Status (1)
Package
Type
Package
Drawing
TL3577-ADJIKTTR
ACTIVE
DDPAK/
TO-263
KTT
Pins Package Eco Plan (2)
Qty
5
500
Green (RoHS &
no Sb/Br)
Lead/Ball Finish
CU SN
MSL Peak Temp (3)
Level-3-245C-168 HR
(1)
The marketing status values are defined as follows:
ACTIVE: Product device recommended for new designs.
LIFEBUY: TI has announced that the device will be discontinued, and a lifetime-buy period is in effect.
NRND: Not recommended for new designs. Device is in production to support existing customers, but TI does not recommend using this part in
a new design.
PREVIEW: Device has been announced but is not in production. Samples may or may not be available.
OBSOLETE: TI has discontinued the production of the device.
(2)
Eco Plan - The planned eco-friendly classification: Pb-Free (RoHS), Pb-Free (RoHS Exempt), or Green (RoHS & no Sb/Br) - please check
http://www.ti.com/productcontent for the latest availability information and additional product content details.
TBD: The Pb-Free/Green conversion plan has not been defined.
Pb-Free (RoHS): TI's terms "Lead-Free" or "Pb-Free" mean semiconductor products that are compatible with the current RoHS requirements
for all 6 substances, including the requirement that lead not exceed 0.1% by weight in homogeneous materials. Where designed to be soldered
at high temperatures, TI Pb-Free products are suitable for use in specified lead-free processes.
Pb-Free (RoHS Exempt): This component has a RoHS exemption for either 1) lead-based flip-chip solder bumps used between the die and
package, or 2) lead-based die adhesive used between the die and leadframe. The component is otherwise considered Pb-Free (RoHS
compatible) as defined above.
Green (RoHS & no Sb/Br): TI defines "Green" to mean Pb-Free (RoHS compatible), and free of Bromine (Br) and Antimony (Sb) based flame
retardants (Br or Sb do not exceed 0.1% by weight in homogeneous material)
(3)
MSL, Peak Temp. -- The Moisture Sensitivity Level rating according to the JEDEC industry standard classifications, and peak solder
temperature.
Important Information and Disclaimer:The information provided on this page represents TI's knowledge and belief as of the date that it is
provided. TI bases its knowledge and belief on information provided by third parties, and makes no representation or warranty as to the
accuracy of such information. Efforts are underway to better integrate information from third parties. TI has taken and continues to take
reasonable steps to provide representative and accurate information but may not have conducted destructive testing or chemical analysis on
incoming materials and chemicals. TI and TI suppliers consider certain information to be proprietary, and thus CAS numbers and other limited
information may not be available for release.
In no event shall TI's liability arising out of such information exceed the total purchase price of the TI part(s) at issue in this document sold by TI
to Customer on an annual basis.
Addendum-Page 1
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