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Step - Down
1A step down switching regulator
Datasheet
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(254 kb)
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(15 kb)
Last Updated: 03/04/2007
Pages: 17
Untitled Document
Generic Part Number
Orderable Part Number
Status
L4976
L4976
Active
L4976D013TR
Active
L4976D
Active
Related Application Notes
APPLICATION IDEAS: DRIVING LEDs USING L497x, L597x, L692x DC-DC CONVERTERS FAMILIES
Related Information
DC-DC Conversion Product Page
Related User Manuals
Low voltage motor control demo kit
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L4976
1A step down switching regulator
Features
Up to 1A step down converter Operating input voltage from 8v to 55v Precise 5.1V reference voltage Output voltage adjustable from 0.5V to 50V Switching frequency adjustable up to 300kHz Voltage feedforward Zero load current operation Internal current limiting (pulse-bypulse and hiccup mode) Protection against feedback disconnection Thermal shutdown
DIP8 SO16W
Description
The L4976 is a step down monolithic power switching regulator delivering 1A at a voltage between 3.3V and 50V (selected by a simple external divider). Realized in BCD mixed technology, the device uses an internal power DMOS transistor (with a typical Rds(ON) of 0.25) to obtain very high efficency and high switching speed. A switching frequency up to 300KHz is achievable (the maximum power dissipation of the packages must be observed). A wide input voltage range between 8V to 55V and output voltages regulated from 3.3V to 40V cover the majority of today's applications. Features of this new generations of DC-DC converter include pulse-by-pulse current limit, hiccup mode for short circuit protection, voltage feedforward regulation, protection against feedback loop disconnection and thermal shutdown. The device is available in plastic dual in line, MINIDIP 8 for standard assembly, and SO16W for SMD assembly.
Figure 1.
Typical application circuit
5 R1 20K 3 C1 220F 63V C7 220nF C2 2.7nF 2 7
Vi=8V to 55V 8
L4976
4 1 6 L1 260H (77120) D1 GI SB360 C8 330F VO=3.3V/1A
R2 9.1K C4 22nF
C6 100nF
April 2007
Rev 7
1/17
www.st.com 17
Contents
L4976
Contents
1 2 Block diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 Pin settings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
2.1 2.2 Pin connection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 Pin description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
3
Electrical data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
3.1 3.2 3.3 Maximum ratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 Thermal data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 Operating temperature rating . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
4 5 6 7 8
Electrical characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 Typical charcteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 Package mechanical data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 Order code . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
2/17
L4976
Block diagram
1
Block diagram
Figure 2. Block diagram
VCC 5 THERMAL SHUTDOWN VOLTAGES MONITOR CBOOT CHARGE V REF 2 VR E F 5.1V COMP FB 7 8 E/A 3.3V PWM R S Q DRIVE OSCILLATOR 1 GND CBOOT CHARGE AT LIGHT LOADS INTERNAL REFERENCE 6
BOOT
3.3V
3 OSC
4 OUT
3/17
Pin settings
L4976
2
2.1
Pin settings
Pin connection
Figure 3. Pin connection (top view)
N.C. 1 2 3 4 5 6 7 8 16 15 14 13 12 11 10 9 N.C. N.C. FB COMP BOOT VCC N.C. N.C.
GND VREF OSC OUT
1 2 3 4
8 7 6 5
FB COMP BOOT VCC
GND VREF OSC OUT OUT N.C. N.C.
DIP8
SO16
2.2
Pin description
Table 1. Pin description
N Pin DIP8 1 2 SO16W (1) 2 3 Name GND VREF Ground 5.1V Reference voltage with 20mA current capability. An external resistor connected between the unregulated input voltage and this pin and a capacitor connected from this pin to ground fix the switching frequency. (Line feed forward is automatically obtained) Stepdown regulator output. Unregulated DC input voltage. A capacitor connected between this pin and OUT allows to drive the internal VDMOS. E/A output to be used for frequency compensation. Stepdown feedback input. Connecting directly to this pin results in an output voltage of 3.3V. An external resistive divider is required for higher output voltages. Description
3
4
OSC
4 5 6 7 8
5, 6 11 12 13 14
OUT VCC BOOT COMP FB
1. Pins 1, 7, 8, 9, 10, 15 and 16 are not internally, electrically connected to the die.
4/17
L4976
Electrical data
3
3.1
Electrical data
Maximum ratings
Table 2. Absolute maximum ratings
Symbol Parameter DIP8 V5 V4 I4 V6-V5 V6 V7 V8 S016W V11 V5, V6 Output peak voltage at t = 0.1s, f = 200kHz I5, I6 V12-V11 V12 V13 V14 Bootstrap voltage Analogs input voltage (VCC = 24V) (VCC = 20V) Power dissipation a TA 60C Junction and storage temperature DIP8 SO16 Maximum output current -5 internal limit 14 70 12 6 -0.3 1 0.8 -40 to 150 V V V V V W W C V Input voltage Output DC voltage 58 -1 V V Value Unit
PTOT TJ,TSTG
3.2
Thermal data
Table 3. Thermal data
Symbol RthJA Parameter Maximum thermal resistance junction-ambient DIP8 90 (1) S016W 110 (1) Unit C/W
1. Package mounted on board
3.3
Operating temperature rating
Table 4. Operating temperature rating
Symbol TJ Parameter Junction temperature range Value -40 to 150 Unit C
5/17
Electrical characteristics
L4976
4
Electrical characteristics
Table 5. Electrical characteristics (TJ = 25C, COSC = 2.7nF, ROSC = 20k, VCC = 24V, unless otherwise specified.)
Symbol Dynamic characteristic VI Operating input voltage range VO = 3.3 to 50V; IO = 1A (1) IO = 0.5A VO Output voltage IO = 0.2 to 1A VCC = 8 to 55V (1) Vd
Il
Parameter
Test condition
Min
Typ
Ma x
Unit
8 3.33 3.292 3.22 3.36 3.36 3.36 0.29
55 3.39 3.427 3.5 0.367 0.587
V V V V V V A %
Dropout voltage Maximum limiting current Efficiency
VCC = 10V; IO = 1A
(1)
VCC = 8 to 55V (1) VO = 3.3V; IO = 1A
(1)
1.5
2 85
2.5
fs
Switching frequency Supply voltage ripple rejection Voltage stability of switching frequency Temp. stability of switching frequency
90 60
100
110
KHz dB
SVRR
VI = VCC + 2VRMS; VO = Vref; IO = 1.A; fripple = 100Hz VCC = 8 to 55V TJ = 0 to 125C
3 4
6
% %
Reference section Reference voltage Iref = 0 to 10mA; (1) VCC = 8 to 55V Line regulation Iref = 0mA; VCC = 8 to 55V Load regulation Shor t circuit current Vref = 0 to 5mA; VCC = 0 to 20mA 30 2 6 65 10 25 100 mV mV mA 5 10 mV 5.0 4.950 5.1 5.1 5.2 5.250 V V
6/17
L4976
Electrical characteristics
Table 5. Electrical characteristics (continued) (TJ = 25C, COSC = 2.7nF, ROSC = 20k, VCC = 24V, unless otherwise specified.)
Symbol DC Characteristics
Iqop Iq
Parameter
Test condition
Min
Typ
Ma x
Unit
Total operating quiescent current Quiescent current Duty Cycle = 0; VFB = 3.8V
4 2.5
6 3.5
mA mA
Error Amplifier VFB RL Voltage feedback input Line regulation Ref. voltage stability vs temperature VoH VoL IO source IO sink
Ib
3.33 VCC = 8 to 55V
(1)
3.36 5 0.4
3.39 10
V mV mV/ C V
High level output voltage Low level output voltage Source output current Sink output current Source bias current Supply voltage ripple rejection DC open loop gain
VFB = 2.5V VFB = 3.8V Vcomp = 6V; VFB = 2.5V Vcomp = 6V; VFB = 3.8V
10.3 0.65 180 200 220 300 2 3
V A A A dB dB ms
SVRR E/A
Vcomp = Vfb; VCC = 8 to 55V RL = Icomp = -0.1 to 0.1mA Vcomp = 6V
60 50
80 57 2.5
gm
Transconductance
Oscillator section Ramp valley Ramp peak Maximum duty cycle Maximum frequency
1. Specification refered to Tj from 0 to 125C
0.78 VCC = 8V VCC = 55V 2 9 95 Duty cycle = 0% Rosc = 13kW, Cosc = 820pF
0.85 2.15 9.6 97
0.92 2.3 10.2
V V V %
300
kHz
7/17
Typical charcteristics
L4976
5
Typical charcteristics
Figure 4.
Iq (mA)
200KHz R1=22K C2=1.2nF 100KHz R1=20K C2=2.7nF
Quiescent drain current vs. input voltage
D97IN724
Figure 5.
VO (V) 3.378 3.376 3.374
Line regulation
D97IN734
VCC=35V
5
Tj=25C
4
3.372 3.370
Tj=125C
3
0Hz
3.368 3.366
2
Tamb=25C 0% DC
3.364 3.362 3.360
0 5 10 15 20 25 30 35 40 45 50 Vcc(V)
1
0
0.2 0.4 0.6 0.8 1.0 1.2 1.4 IO(A)
Figure 6.
Quiescent current vs. junction Figure 7. temperature
D97IN731
Switching frquency vs. R1 and C2
D97IN784
Iq (mA) 5
fsw (KHz) 500
0.8
200KHz R1=22K C2=1.2nF 100KHz R1=20K C2=2.7nF 0Hz
Tamb=25C
200 100 50 20
2nF 1.2 nF
2.2 nF
4
3
VCC=35V 0% DC
3.3n
F 4.7n F
2
5.6n
F
10
1 -50 -30 -10 10 30 50 70 90 110 Tj(C)
5
0
20
40
60
80
R1(K)
8/17
L4976 Figure 8.
VO (V) 3.377
Tj=125C
Typical charcteristics Load regulation
D97IN733
Figure 9.
fsw (KHz) 107.5 105.0 102.5
Tj=25C
Switching frequency vs. input voltage
D97IN735
3.376 3.375 3.374 3.373 3.372 3.371 3.370 0 5 10 15 20 25 30 35 40 45 50 VCC(V)
Tj=25C
100.0 97.5 95.0 92.5 90.0 0 5 10 15 20 25 30 35 40 45 50 VCC(V)
Figure 10. Switching frequency vs. junction temperature
fsw (KHz)
D97IN785
Figure 11. Efficiency vs. output current
V (V) 0.5
Tj=125C
D97IN736
105
0.4
Tj =2 5 C
100
0.3 0.2
Tj=-25C
95
0.1 0.0
90 -50 0 50 100 Tj(C)
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 IO(A)
Figure 12. Dropout voltage between pin 5 Figure 13. Efficiency vs. output current and 4
V (V) 0.5 0.4
Tj =2
Tj=125C
D97IN736
(%) 90 85
VCC=12V VCC=24V VCC=8V
D97IN739
C 5
80 75
VCC=48V
0.3 0.2 0.1 0.0 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 IO(A)
Tj=-25C
70 65 60
fsw=100KHz VO=3.36V
0
0.2 0.4 0.6 0.8 1.0 1.2 1.4 IO(A)
9/17
Typical charcteristics Figure 14. Efficiency vs output voltage
(%) 96 94 92
100KHz 200KHz
D97IN737
L4976 Figure 15. Efficiency vs. output current
(%) 90 85 80
VCC=12V VCC=24V
D97IN740
VCC=8V
90 88 86 84 82 0 5 10 15 20 25 VO(V)
VCC=35V IO=1.5A
VCC=48V
75 70 65 60
fsw=200KHz VO=5.1V
0
0.2 0.4 0.6 0.8 1.0 1.2 1.4 IO(A)
Figure 16. Efficiency vs. output current
(
D97IN741
Figure 17. Efficiency vs. Vo
Pdiss (mW)
VCC=35V fsw=100KHz
D97IN744
%)
VCC=8V
90 85 80 75 70 65 60
800
VCC=12V VCC=24V
IO=1.5A
600
IO=1A
400
VCC=48V fsw=200KHz VO=3.36V
IO=0.5A
200
55 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 IO(A)
0
0
5
10
15
20
25
30 V0(V)
Figure 18. Efficiency vs. VCC
Figure 19. Pulse by pulse limiting current vs. junction temperature.
D97IN742
(%)
V0 =5 .1V-f
SW =1
Ilim (A) 2.9 2.8
fsw=100KHz VCC=35V
D97IN747
00KH
z
85
V0
=5
.1V
-fS
W=
20
0K
V0 =
Hz
100
2.7
KHz
80
3.36
V
V-f
0 =3
SW =
.36
2.6 2.5
V-
fS
W=
75
20
0K
IO=1.5A
Hz
2.4
70
2.3
0
10
20
30
40
50 VCC(V)
-50 -25
0
25
50
75 100 125 Tj(C)
10/17
L4976 Figure 20. Power dissipation vs. VCC
Pdiss (mW)
VO=5.1V fsw=100KHz
D97IN743
Typical charcteristics Figure 21. Load transient
800
600
IO=1.5A IO=1A
400
IO=0.5A
200
0
0
10
20
30
40
50 VCC(V)
Figure 22. Line transient
VCC (V) 30
D97IN786
Figure 23. Open loop frequency and phase of error amplifier
GAIN (dB) 50
D97IN787
Phase
20
0
GAIN
0 45 90
Phase
10 1
IO = 1A fsw = 100KHz
VO (mV) 100 0
-50 -100 -150
2
135
-100
1ms/DIV
-200 10 102 103 104 105 106 107 108 f(Hz)
11/17
Package mechanical data
L4976
6
Package mechanical data
In order to meet environmental requirements, ST offers these devices in ECOPACK packages. These packages have a Lead-free second level interconnect . The category of second level interconnect is marked on the package and on the inner box label, in compliance with JEDEC Standard JESD97. The maximum ratings related to soldering conditions are also marked on the inner box label. ECOPACK is an ST trademark. ECOPACK specifications are available at: www.st.com
12/17
L4976 Figure 24. DIP8 mechanical data & package dimensions
mm D IM . MIN. A a1 B b b1 D E e e3 e4 F I L Z 3.18 7.95 2.54 7.62 7.62 6.6 5.08 3.81 1.52 0.125 0.51 1.15 0.356 0.204 1.65 0.55 0.304 10.92 9.75 0.313 0.100 0.300 0.300 0.260 0.200 0.150 0.060 TYP. 3.32 0.020 0.045 0.014 0.008 0.065 0.022 0.012 0.430 0.384 M AX . MIN. TYP. 0.131 MAX. inch
Package mechanical data
OUTLINE AND MECHANICAL DATA
DIP-8
13/17
Package mechanical data Figure 25. SO16Wide mechanical data & package dimensions
mm DIM. MIN. A A1 B C D (1) E e H h L k ddd 10.0 0.25 0.40 2.35 0.10 0.33 0.23 10.10 7.40 1.27 10.65 0.75 1.27 0.394 0.010 0.016 TYP. MAX. 2.65 0.30 0.51 0.32 10.50 7.60 MIN. 0.093 0.004 0.013 0.009 0.398 0.291 0.050 0.419 0.030 0.050 TYP. MAX. 0.104 0.012 0.200 0.013 0.413 0.299 inch
L4976
OUTLINE AND MECHANICAL DATA
0 (min.), 8 (max.) 0.10 0.004
(1) "D" dimension does not include mold flash, protusions or gate burrs. Mold flash, protusions or gate burrs shall not exceed 0.15mm per side.
SO16 (Wide)
0016021 C
14/17
L4976
Order code
7
Order code
Table 6. Order code
Part number L4976 L4976D L4976D013TR Package DIP8 SO16W SO16W Packaging Tube Tube Tape and reel
15/17
Revision history
L4976
8
Revision history
Table 7. Revision history
Date 5-Aug-2001 3-Apr-2007 Revision 6 7 First Issue Document reformatted, updated dropout voltage values in Table 5 on page 6 Changes
16/17
L4976
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