Simple Step-Up Voltage Regulator
•
Requires Few External Components
•
NPN Output Switches 3.0A, 65V(max)
•
Extended Input Voltage Range: 3.0V to 40V
•
Current Mode Operation for Improved
Transient Response, Line Regulation, and
Current Limiting
•
Soft Start Function Provides Controlled
Startup
•
52kHz Internal Oscillator
•
Output Switch Protected by Current Limit,
Undervoltage Lockout and Thermal
Shutdown
•
Improved Replacement for LM2577-ADJ
Series
The UC2577-ADJ device provides all the active functions necessary to impl ement step-up (boost), flyback, and forward converter
switching regulat ors. R equirin g only a few c omponen ts, these simple regula tors efficiently provide up to 60V as a step-up regulator,
and even high er volta ges as a flyback or forwa rd converter regulator.
The UC2577-ADJ features a wide input voltage range of 3.0V to
40V and an adjustable output voltage. An on-chip 3.0A NPN switch
is included with undervoltage lockout, thermal protection circuitry,
and current limiting , as well as soft star t mode operation to reduce
current during startup. Other features include a 52kHz fixed frequency on-chip oscillator with no external components and current
mode control for better line and load regulation.
A standard series of inductors and capacitors are available from
several manufacturers optimized for use with these regulators and
are listed in this data sheet.
UC2577-ADJ
3/97
FEATURES DESCRIPTION
CONNECTION DIAGRAM
BLOCK DIAGRAM
UDG-94034
•
Simple Boost and Flyback Converters
•
SEPIC Topology Permits Input Voltage to
be Higher or Lower than Output Voltage
•
Transformer Coupled Forward Regulators
•
Multiple Output Designs
TYPICAL APPLICATIONS
5-Pin TO-220 (Top View)
T Package
Also available in TO-263 Package (TD).
PARAMETER TEST CONDITIONS MIN TYP MAX UNITS
System Parameters
Circuit Figure 1
(Note 3)
Output Voltage VIN = 5V to 10V, I
LOAD
= 100mA to 800mA 11.40 12.0 12.60 V
T
J
= 25°C 11.60 12.40 V
Line Regulation VIN = 3.0V to 10V, I
LOAD
= 300mA 20 100 mV
T
J
= 25°C50mV
Load Regulation VIN = 5V, I
LOAD
= 100mA to 800mA 20 100 mV
T
J
= 25°C50mV
Efficiency VIN = 5V, I
LOAD
= 800mA 80 %
Device Parameters
Input Supply Current VFB = 1.5V (Switch Off) 7.5 14 mA
T
J
= 25°C10mA
I
SWITCH
= 2.0A, V
COMP
= 2.0V (Max Duty Cycle) 45 85 mA
T
J
= 25°C70mA
Input Supply UVLO I
SWITCH
= 100mA 2.70 2.95 V
T
J
= 25°C2.85V
Oscillator Frequency Measured at SWITCH Pin, I
SWITCH
= 100mA 42 52 62 kHz
T
J
= 25°C4856kHz
Reference Voltage Measured at FB Pin, VIN = 3.0V to 40V, V
COMP
= 1.0V 1.206 1.230 1.254 V
T
J
= 25°C 1.214 1.246 V
Reference Voltage Line Regulation VIN = 3.0V to 40V 0.5 mV
Error Amp Input Bias Current V
COMP
= 1.0V 100 800 nA
T
J
= 25°C 300 nA
Error Amp Transconductance
I
COMP
= −30µA to +30µA, V
COMP
= 1.0V 1600 3700 5800
µ
mho
T
J
= 25°C 2400 4800
µmho
Error Amp Voltage Gain V
COMP
= 0.8V to 1.6V, R
COMP
= 1.0MW (Note 4) 250 800 V/V
T
J
= 25°C 500 V/V
Error Amplifier Output Swing Upper Limit V
FB
= 1.0V 2.0 2.4 V
T
J
= 25°C2.2V
Lower Limit V
FB
= 1.5V 0.3 0.55 V
T
J
= 25°C0.40V
Error Amp Output Current
V
FB
= 1.0V to 1.5V, V
COMP
= 1.0V
±
90±200±400 µA
T
J
= 25°C
±
130
±
300 µA
Soft Start Current
V
FB
= 1.0V, V
COMP
= 0.5V 1.5 5.0 9.5
µA
T
J
= 25°C2.57.5
µA
Maximum Dut y Cycle V
COMP
= 1.5V, I
SWITCH
= 100mA 90 95 %
T
J
= 25°C93%
Unless otherwise stated, these specifications apply for T
A
= −40°C to +125°C, VIN =
5V, VFB = V
REF
, I
SWITCH
= 0, and TA =TJ.
ELECTRICAL CHARACTERISTICS
RECOMMENDED OPERATING RANGE
Supply Voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45V
Output Switch Voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65V
Output Switch Current (Note 2) . . . . . . . . . . . . . . . . . . . . . 6.0A
Power Dissipation. . . . . . . . . . . . . . . . . . . . . . Internally Limited
Storage Temperature Range . . . . . . . . . . . . . −65°C to +150°C
Lead Temperature (Soldering, 10 sec.) . . . . . . . . . . . . . . 260°C
Maximum Junction Temperature . . . . . . . . . . . . . . . . . . . 150°C
Minimum ESD Rating (C = 100pF, R = 15kΩ) . . . . . . . . . . . 2kV
ABSOLUTE MAXIMUM RATINGS
(Note 1)
UC2577-ADJ
Supply Voltage . . . . . . . . . . . . . . . . . . . . . . . . 3.0V ≤ VIN ≤ 40V
Output Switch Voltage . . . . . . . . . . . . . . . 0V ≤ V
SWITCH
≤ 60V
Output Switch Current . . . . . . . . . . . . . . . . . . . . I
SWITCH
≤ 3.0A
Junction Te mperature Range . . . . . . . . . . −40°C ≤ TJ ≤ +125°C
2
UC2577-ADJ
PARAMETER TEST CONDITIONS MIN TYP MAX UNITS
Device Parameters (cont.)
Switch Transconductance 12.5 A/V
Switch Leakage Current
V
SWITCH
= 65V, VFB = 1.5V (Switch Off) 10 600
µA
T
J
= 25°C300
µA
Switch Saturation Voltage I
SWITCH
= 2.0A, V
COMP
= 2.0V (Max Duty Cycle) 0.5 0.9 V
T
J
= 25°C0.7V
NPN Switch Current Limit V
COMP
= 2.0V 3.0 4.3 6.0 A
Thermal Resistance
Junction to Ambient 65
°C/W
Junction to Case 2
°
C/W
COMP Pin Current
V
COMP
= 0 25 50
µ
A
TJ = 25°C40
µA
Unless otherwise stated, these specifications apply for T
A
= −40°C to +125°C, VIN =
5V, VFB = V
REF
, I
SWITCH
= 0, and TA =TJ.
ELECTRICAL CHARACTERISTICS
Note 1: Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Operating ratings
indicate cond it io ns duri ng which the device is intended to be functional, but device pa ram et er sp ec ifications may not be
guaranteed under these conditions. For guaranteed specifications and test conditions, see the Electrical Characteristics.
Note 2: Output current cannot be internally limi ted when the UC2577 is used as a step-up regulator. To prevent damage to
the switch, its current must be externally limit ed to 6.0A. However, output current is internally limited when the UC2577 is
used as a flyback or forward converter regulator.
Note 3. External components such as the diode, inductor, input and output capacitors can affect switching regulator
performance. Wh en the UC2 57 7 is use d as sho w n in the Test Circuit, sys te m pe rfo r ma nc e wil l be as specified by the
system parameters.
Note 4: A 1.0M
Ω
resistor is con nected to the compensation pin (which is the error amplifier’s output) to ensure accuracy in
measuring A
VOL.
In actual applications, this pin’s load resistance should be ≥ 10MΩ, resulting in A
VOL
that is typically twice
the guaranteed mi nimum limit.
Figure 1. Circuit Used to Specify System Parameters
UDG-94035
L = 415-0930 (AIE)
D = any manufacturer
C
OUT
= Sprague Type 673D
Electrolytic 680µF, 20V
R1 = 48.7k in series with 511Ω (1%)
R2 = 5.62k (1%)
3
The Block Dia gram shows a step-up switc hing regulator
utilizing the UC2577. The regulator produces an output
voltage highe r than th e inpu t volta ge. The UC 2577 turns
its switc h on and off at a fixed f requency of 52kHz, thus
storing en ergy in the in ductor ( L). When the NPN switch
is on, the inductor c urrent is charged at a rat e 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 (C
OUT
) at a rate of (V
OUT
- VIN)/L. The energy stored in the inductor is thus transferred to the
output.
The output volt age is controlled by the amount of energy
transferred, which is controlled by modulating the peak
inductor current. This modulation is accomplished by
feeding a po rtion of the out put voltage to an error amplifier which am plifies th e difference between the feedback
voltage and an internal 1.23V precision reference voltage. The output of the error amplifier is then compared to
a voltage 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 c ontrols the peak switch current to maintain a constant output voltage. Figure 2 shows voltage
and current waveforms for the circuit. Formulas for calculation are shown in Figure 3.
STEP-UP REGULATOR DESIGN PROCEDURE
Refer to the Block Diagram
Given:
V
INmin
= Minimum input supply voltage
V
OUT
= Regulated output voltage
UC2577-ADJ
Step-up (Boost) Regulator
Duty Cycle D
V
OUT
+ VF − V
IN
V
OUT
+ V
F
− V
SAT
≈
V
OUT
− V
IN
V
OUT
Avg. Inductor
Current
I
IND(AVG)
I
LOAD
1 −
D
Inductor
Current Ripple
∆I
IND
VIN − V
SAT
L
•
D
52,000
Peak Inductor
Current
I
IND(PK)
I
LOAD
1−D
+
∆
I
IND
2
Peak Switch
Current
I
SW(PK)
I
LOAD
1−D
+
∆I
IND
2
Switch Voltage
when Off
V
SW(OFF)
V
OUT
+ V
F
Diode Reverse
Voltage
V
R
V
OUT
- V
SAT
Avg. Diode
Current
I
D(AVG)
I
LOAD
Peak Diode
Current
I
D(PK)
I
LOAD
1−D
+
∆I
IND
2
.
Power
Dissipation
P
D
0.25Ω
I
LOAD
1−D
2
D +
I
LOAD
• D • V
IN
50
(1−D)
VF = Forward Biased Diode Voltage, I
LOAD
= Output Load
Figure 2. Step-up Regulator Waveforms
First, determi ne if the UC2577 can provide these values
of V
OUT
and I
LOADmax
when operatin g with the mi nimum
value of V
IN
. The upper l imit s for V
OUT
and I
LOADmax
are
given by the following equations.
V
OUT
≤ 60V and
V
OUT
≤ 10 • V
INmin
I
LOADmax
≤
2.1A • V
INmin
V
OUT
These limits m ust be gr eater t han or equa l to the values
specified in this application.
1. Output Voltage Section
Resistors R1 and R2 are u sed 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 compar es it to an internal 1.23V reference. Select R1 and R2 such that:
R1
R2
=
V
OUT
1.23V
− 1
Figure 3. Step-up Regulator Formulas
APPLICATIONS INFORMATION
4
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):
D
max
=
V
OUT
+ VF − V
INmin
V
OUT
+ VF − 0.6V
where typicall y VF = 0.5V for Schottky diodes and VF =
0.8V for fast recovery diodes.
E • T, the product of volts • time that charges the inductor:
E • T =
D
max
• (V
INmin
− 0.6V)10
6
52,000Hz
(V• µs
)
I
IND, DC
, the average inductor current under full load:
I
IND, DC
=
1.05 • I
LOADmax
1 − D
max
B. Identify Inductor Value:
1. From Figure 4, identify the inductor code for the region
indicated b y the intersection of E • T and I
IND, DC
. This
code gives the inductor value in microhenries. The L or H
prefix sig nifies whethe r the inductor i s rated for a maximum E • T of 90Vµs (L) or 250Vµs (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:
0.3 0.4
0.45
0.35
0.5
0.6
0.7 0.8 0.9 1.0 1.5 2.0 2.5 3.0
20
30
35
25
40
45
50
60
70
80
90
100
200
150
L47
L68
L100L150L220L330
H2200
L680
H1500
H1000 H680 H470 H330 H220
H150
L470
E·T (V·µs)
I
IND, DC
(A)
Figure 4. Inductor Selection Graph
If L
min
is smaller than the inductor values found in step
B1, go on to step C. Otherwise, the inductor value found
in step B1 is too low; an appropriate inductor code
should be obtained from the graph as follows:
1. Find the lowest value inductor that is greater than
L
min
.
2. 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 ind uctor fr om the table of Figure 5 which cross
references the in duc tor code s t o th e par t numbers of the
three differe nt m anuf act ure rs. The i ndu ctors l isted in thi s
table have the following characteristics:
AIE
(ferrite, po t-core inductors): Benefits of this type
are low etectromagnetic interference (EMI), small
physical size, and very low power dissipation (core
loss).
Pulse
(powdered iro n, 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.
UC2577-ADJ
Note: 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.
APPLICATIONS INFORMATION (cont.)
5
UC2577-ADJ
3. Compensation Network (RC, CC) and Output
Capacitor (C
OUT
) Selection
The compensation network consists of resistor R
C
and
capacitor C
C
which for m a simple pole-zero network and
stabilize the regulator. The values of R
C
and CC depend
upon the volt age gain of the regulator, I
LOADmax
, the in-
ductor L, and output capacitance C
OUT
. A procedure to
calculate and select the values for R
C
, CC, and C
OUT
which 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 i s recommended,
such as measur ing V
OUT
transient responses to pulsing
I
LOAD
.
A. Calculate the maximum value for RC.
RC ≤
750 • I
LOADmax
• V
OUT
2
V
INmin
2
Select a r esistor less than or equal to this value, not to
exceed 3kΩ.
B. Calculate the minimum value for C
OUT
using the fol-
lowing two equations.
C
OUT
≥
0.19
•
L • R
C
•
I
LOADmax
V
INmin
• V
OUT
and
C
OUT
≥
V
INmin
• RC
•
(
V
INmin
+
(3.74
• 105 • L
))
487,800 • V
OUT
3
The larger of these two values is the minimum value that
ensures stability.
C. Calculate the minimum value of CC.
CC ≥
58.5
• V
OUT
2
• C
OUT
R
C
2
• V
INmin
The compensation capacitor is also used in the soft start
function of the regulator. When the input voltage is applied to the pa rt, the switch duty cy cle is increased slowl y
at a rate def ined 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 a bout 90% and draw large currents from
the input supply. For proper soft starting, the value for C
C
should be equal or greater than 0.22µF.
Figure 6 lists several types of alumi num electrolytic ca-
pacitors which 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 char ges t he ca paci tor during each switchi ng cycle. For step-up and flyback regulators, the formula for
ripple current is:
I
RIPPLErms
=
I
LOADmax
•
D
max
1
−
D
max
Choose a capac itor that is rated at l east 50% higher than
this value at 52kHz.
Equivalent S eries Resistance (ESR):
This is the primary
cause of ou tput r ipple vol tage, and it also affects the val ues of R
C
and CC needed to stabilize the regulator. As a
result, th e preceding calculations for C
C
and RC are only
valid if the ESR does not exceed the maximum value
specified by the following equations.
ESR ≤
0.01 • 15V
I
RIPPLE
(
P−P
)
and ≤
8.7 • 10
−
3
• V
IN
I
LOADmax
where
I
RIPPLE(P−P
)
=
1.15 • I
LOADmax
1
−
D
max
Select a capacitor with an ESR, at 52kHz, that is less
than or equa l to th e lower value cal culated. Most electrolytic capacitors specify ESR at 120kHz which is 15% to
30% higher than at 52kHz. 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 ≥ 470µF), and capacitors with
high WVDC, or by paralleling smaller value capacitors.
Inductor
Code
Manufacturer’s Part Number
AIE Pulse Renco
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. Pet ersbu rg, 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
Figure 5. Table of Stan dardized Inducto rs an d
Manufacturer’s Part Numbers
APPLICATIONS INFORMATION (cont.)
6
UNITRODE CORPORATI ON
7 CONTINENTAL BLVD. • MERRIMACK, NH 03054
TEL. (603) 424- 24 10 • FAX (603) 424-3460
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), V IN sh ould be bypa ssed to gr ound. A good quality 0.1µF capacitor with low ESR should provide sufficient decoupling. If the U C2577 is located far from the
supply source filter capacitors, an additional electrolytic
(47µF, for example) is required.
Nichicon -
Types PF, PX, or PZ
927 East StateParkway, Schaumburg, IL 60173
(708)843-7500
United Chemi-CON -
Types LX, SXF, or SXJ
9801 West Higgens, Rosemont, IL 60018
(708)696-2000
Figure 6. Aluminum Electrolytic Capacitors Recommended
for Switching Regulators
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 curre nt of th e UC 25 77. Therefore a sui ta bl e 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
I
LOADmax
and I
Dpk
. Because of their low forward voltage
drop (and thus higher regulator efficiencies), Schottky
barrier dio de s are of ten used in switching regulators. Refer to Figure 7 for recommended part numbers and voltage ratings of 1A and 3A diodes.
V
OUTmax
Schottky Fast Recovery
1A 3A 1A 3A
20V
1N5817 1N5820
MBR120P MBR320P
30V
1N5818 1N5821
MBR130P MBR330P
11DQ03 31DQ03
40V
1N5819 1N5822
MBR140P MBR340P
11DQ04 31DQ04
50V
MBR150 MBR350 1N4933
11DQ05 31DQ05 MUR105
100V
1N4934 MR851
MUR110 30DL1
10DL1 MR831
MBRxxx and MURxxx are manufactured by Mot oro la .
1DDxxx, 11Cxx and 31Dxx are manufactured by
International Rectifier
Figure 7. Diode Selection Chart
UC2577-ADJ
ORDERING INFORMATION
Unitrode Type Number
UC2577T-ADJ 5 Pin TO-220 Plastic Package
UC2577TD-ADJ 5 Pin TO-263 Plastic Package
APPLICATIONS INFORMATION (cont.)
7
IMPORTANT NOTICE
T exas Instruments and its subsidiaries (TI) reserve the right to make changes to their products or to discontinue
any product or service without notice, and advise customers to obtain the latest version of relevant information
to verify, before placing orders, that information being relied on is current and complete. All products are sold
subject to the terms and conditions of sale supplied at the time of order acknowledgement, including those
pertaining to warranty, patent infringement, and limitation of liability.
TI warrants performance of its semiconductor products to the specifications applicable at the time of sale in
accordance with TI’s standard warranty. Testing and other quality control techniques are utilized to the extent
TI deems necessary to support this warranty. Specific testing of all parameters of each device is not necessarily
performed, except those mandated by government requirements.
CERT AIN APPLICATIONS USING SEMICONDUCTOR PRODUCTS MAY INVOLVE POTENTIAL RISKS OF
DEATH, PERSONAL INJURY, OR SEVERE PROPERTY OR ENVIRONMENTAL DAMAGE (“CRITICAL
APPLICATIONS”). TI SEMICONDUCTOR PRODUCTS ARE NOT DESIGNED, AUTHORIZED, OR
WARRANTED TO BE SUITABLE FOR USE IN LIFE-SUPPORT DEVICES OR SYSTEMS OR OTHER
CRITICAL APPLICATIONS. INCLUSION OF TI PRODUCTS IN SUCH APPLICA TIONS IS UNDERSTOOD T O
BE FULLY AT THE CUSTOMER’S RISK.
In order to minimize risks associated with the customer’s applications, adequate design and operating
safeguards must be provided by the customer to minimize inherent or procedural hazards.
TI assumes no liability for applications assistance or customer product design. TI does not warrant or represent
that any license, either express or implied, is granted under any patent right, copyright, mask work right, or other
intellectual property right of TI covering or relating to any combination, machine, or process in which such
semiconductor products or services might be or are used. TI’s publication of information regarding any third
party’s products or services does not constitute TI’s approval, warranty or endorsement thereof.
Copyright 1999, Texas Instruments Incorporated
Loading...