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(R)
L4978
2A STEP DOWN SWITCHING REGULATOR
UP TO 2A STEP DOWN CONVERTER OPERATING INPUT VOLTAGE FROM 8V TO 55V PRECISE 3.3V (1%) INTERNAL REFERENCE VOLTAGE OUTPUT VOLTAGE ADJUSTABLE FROM 3.3V TO 50V SWITCHING FREQUENCY ADJUSTABLE UP TO 500KHz VOLTAGE FEEDFORWARD ZERO LOAD CURRENT OPERATION INTERNAL CURRENT LIMITING (PULSE-BYPULSE AND HICCUP MODE) INHIBIT FOR ZERO CURRENT CONSUMPTION PROTECTION AGAINST FEEDBACK DISCONNECTION THERMAL SHUTDOWN SOFT START FUNCTION DESCRIPTION The L4978 is a step down monolithic power switching regulator delivering 2A 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 D-MOS transistor (with a typical Rdson of 0.25) to obtain very high efficency and high switching speed. TYPICAL APPLICATION CIRCUIT
Vi=8V to 55V 5 R1 20K 3 C1 220F 63V C7 220nF C2 2.7nF 2 7
Minidip
SO16W
ORDERING NUMBERS: L4978 (Minidip) L4978D (SO16)
A switching frequency up to 500KHz 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 50V 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, soft-start, protection against feedback loop disconnection, inhibit for zero current consumption and thermal shutdown. The device is available in plastic dual in line, MINIDIP 8 for standard assembly, and SO16W for SMD assembly.
8
L4978
4 1 6 L1 126H (77120) D1 GI SB560 C8 330F VO=3.3V/2A
C5 100nF
R2 9.1K C4 22nF
C6 100nF
D98IN837A
May 2000
1/12
L4978
BLOCK DIAGRAM
VCC 5 THERMAL SHUTDOWN VOLTAGES MONITOR CBOOT CHARGE SS_INH 2 INHIBIT SOFTSTART 3.3V COMP FB 7 8 E/A INTERNAL REFERENCE INTERNAL SUPPLY 5.1V 6 PWM
BOOT
R S
3.3V
Q DRIVE
OSCILLATOR 1 GND
CBOOT CHARGE AT LIGHT LOADS
3 OSC
4 OUT
D97IN594
PIN CONNECTIONS
N.C. GND
1 2 3 4 5 6 7 8
D97IN596
16 15 14 13 12 11 10 9
N.C. N.C. FB COMP BOOT VCC N.C. N.C.
GND SS_INH OSC OUT
1 2 3 4
D97IN595
8 7 6 5
FB COMP BOOT VCC
SS_INH OSC OUT OUT N.C. N.C.
Minidip
SO16W
PIN FUNCTIONS
DIP 1 2 SO (*) 2 3 Name GND SS_INH Function Ground A logic signal (active low) disables the device (sleep mode operation). A capacitor connected between this pin and ground determines the soft start time. When this pin is grounded disables the device (driven by open collector/drain). 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 DMOS Transistors 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.
3
4
OSC
4 5 6 7 8
5, 6 11 12 13 14
OUT VCC BOOT COMP FB
(*) Pins 1, 7, 8, 9, 10, 15 and 16 are not internally, electrically connected to the die.
2/12
L4978
THERMAL DATA
Symbol R th(j-amb) Parameter Thermal Resistance Junction to ambient Max. Minidip 90 (*) SO16 110 (*) Unit C/W
(*) Package mounted on board.
ABSOLUTE MAXIMUM RATINGS
Symbol Minidip V5 V4 I4 V6-V5 V6 V7 V2 V8 Ptot Tj,Tstg S016 V11 V5,V6 I5,I6 V12-V11 V12 V13 V3 V14 Bootstrap voltage Analogs input voltage (VCC = 24V) Analogs input voltage (VCC = 24V) (VCC = 20V) Power dissipation a Tamb 60C Junction and storage temperature Minidip SO16 Input voltage Output DC voltage Output peak voltage at t = 0.1s f=200KHz Maximum output current Parameter Value 58 -1 -5 int. limit. 14 70 12 13 6 -0.3 1 0.8 -40 to 150 V V V V V V W W C Unit V V V
ELECTRICAL CHARACTERISTICS (Tj = 25C, Cosc = 2.7nF, Rosc = 20k, VCC = 24V, unless otherwise specified.) * Specification Refered to T j from 0 to 125C
Symbol Parameter Test Condition Min. Typ. Max. Unit
Dynamic Characteristic
VI Vo Operating input voltage range Output voltage Vo = 3.3 to 50V; Io = 2A Io = 0.5A Io = 0.2 to 2A Vcc = 8 to 55V Vcc = 10V; Io = 2A Vcc = 8 to 55V Vo = 3.3V; Io = 2A Vi = Vcc+2VRMS; Vo = Vref; Io = 2.5A; f ripple = 100Hz Vcc = 8 to 55V Tj = 0 to 125C
* * * * *
8 3.33 3.292 3.22
Vd Il fs SVRR
Dropout voltage Maximum limiting current Efficiency Switching frequency Supply voltage ripple rejection Voltage stability of switching frequency Temp. stability of switching frequency
3.36 3.36 3.36 0.58 3 87 100
2.5 90 60
55 3.39 3.427 3.5 0.733 1.173 3.5 110
V V V V V V A % KHz dB % %
3 4
6
Soft Start
Soft start charge current Soft start discharge current 30 6 40 10 50 14 A A V A 3/12
Inhibit
VLL IsLL Low level voltage Isource Low level
* *
5
0.9 15
L4978
ELECTRICAL CHARACTERISTICS (continued)
Symbol Parameter Total operating quiescent current Quiescent current Total stand-by quiescent current Test Condition Min. Typ. 4 Duty Cycle = 0; VFB = 3.8V Vinh <0.9V Vcc = 55V; Vinh <0.9V 3.33 Vcc = 8 to 55V 2.5 100 150 Max. 6 3.5 200 300 Unit mA mA A A V mV mV/C V V A A A dB dB mS
DC Characteristics
Iqop Iq Iqst-by
Error Amplifier
VFB RL Voltage Feedback Input Line regulation Ref. voltage stability vs temperature 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 Transconductance
*
10.3
3.36 5 0.4
3.35 10
VoH VoL Io source Io sink Ib SVRR E/A gm
VFB = 2.5V VFB = 3.8V Vcomp = 6V; V FB = 2.5V Vcomp = 6V; V FB = 3.8V Vcomp = Vfb; Vcc = 8 to 55V RL = Icomp = -0.1 to 0.1mA Vcomp = 6V
0.65 180 200 60 50 220 300 2 80 57 2.5
3
Oscillator Section
Ramp Valley Ramp peak Maximum duty cycle Maximum Frequency Vcc = 8V Vcc = 55V Duty Cycle = 0% Rosc = 13k, Cosc = 820pF 0.78 2 9 95 0.85 2.15 9.6 97 0.92 2.3 10.2 500 V V V % kHz
4/12
L4978
Figure 1. Test and evaluation board circuit.
Vi=8V to 55V 5 R1 20K 3 C1 220F 63V C7 220nF C2 2.7nF 2 7 8
L4978
4 1 6 L1 126H (77120) D1 GI SB560 C8 330F
VO=3.3V/2A
R3
C5 100nF
R2 9.1K C4 22nF
C6 100nF
R4
D98IN834A
C1=220F/63V EKE C2=2.7nF C5=100nF C6=100nF C7=220nF/63V C8=330F/35V CG Sanyo L1=126H KoolMu 77120 - 55 Turns - 0.5mm R1=20K R2=9.1K D1=GI SB560
L4978
VO (V) 3.3 5.1 12 15 18 24 R3(K) 0 2.7 12 16 20 30 4.7 4.7 4.7 4.7 4.7 R4(K)
Figure 2. PCB and component layout of the figure 1.
5/12
L4978
Figure 3. Quiescent drain current vs. input voltage.
Iq (mA)
200KHz R 1=22K C 2=1.2nF 100KHz R 1=20K C 2=2.7nF
D97IN724
Figure 4. Quiescent current vs. junction temperature
Iq (mA) 5
D97IN731
5
200KHz R1=22K C2=1.2nF 100KHz R1 =20K C2 =2.7nF 0Hz
4
4
3
0Hz
3
VCC=35V 0% DC
2
Tamb=25C 0% DC
2
1 0 5 10 15 20 25 30 35 40 45 50 Vcc(V)
1 -50 -30 -10 10 30 50 70 90 110 Tj(C)
Figure 5. Stand by drain current vs. input voltage
Ibias (A) 150 140 130 120 110 100 90 80 70 60
Tj=125C Vss=GND Tj=25C
D97IN732
Figure 6. Line Regulation
VO (V) 3.377
Tj=125C
D97IN733
3.376 3.375
Tj=25C
3.374 3.373 3.372 3.371 3.370 0 5 10 15 20 25 30 35 40 45 50 VCC(V) 0 5 10 15 20 25 30 35 40 45 50 VCC(V)
Figure 7. Load regulation
VO (V) 3.378 3.376
D98IN835
Figure 8. Switching frquency vs. R1 and C2
fsw (KHz) 500
0.8
D97IN784
V CC=35V
Tamb=25C
3.374 3.372 3.370 3.368 3.366 3.364 3.362 3.360 0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 IO(A)
Tj=125C Tj=25C
200 100 50 20
2nF 1.2 nF
2.2
nF
F 4.7n 5.6n F F
3.3n
10 5 0 20 40 60 80 R1(K)
6/12
L4978
Figure 9. Switching Frequency vs. input voltage.
fsw (KHz) 107.5 105.0 102.5 100.0 97.5 95.0 92.5 90.0 0 5 10 15 20 25 30 35 40 45 50 VCC(V)
Tj=25C
D97IN735
Figure 10. Switching frequency vs. junction temperature.
fsw (KHz)
D97IN785
105
100
95
90 -50 0 50 100 Tj(C)
Figure 11. Dropout voltage between pin 5 and 4.
V (V) 0.7 0.6
D98IN836
Figure 12. Efficiency vs output voltage.
[%] 98 96
fsw=100kHz
Tj=125C
94 92
fsw=200kHz
0.5
Tj
=2
C 5
90 88
0.4 0.3 0.2 0.1 0.0 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 IO(A)
Tj=-25C
86 84 82 80
Vcc=35V Io=2A
0
5
10
15 Vo [V]
20
25
30
Figure 13. Efficiencyvs. output current.
[%] 95
Vcc=8V Vcc=12V
Figure 14. Efficiencyvs. output current.
[%] 95 90 85
Vcc=8V
90
85
Vcc=24V
Vcc=12V
80
80 75 70
fsw=100kHz Vo=5.1V Vcc=24V
75
Vcc=48V
70
65
65 60
Vcc=48V
Vo=3.36V fsw=100kHz
60
0
0.2 0.4 0.6 0.8
1 1.2 1.4 1.6 1.8 Io [A]
2
2.2
0
0.2 0.4 0.6 0.8
1 1.2 1.4 1.6 1.8 Io [A]
2
2.2
7/12
L4978
Figure 15. Efficiencyvs. output current.
(%) 90 85 80
VCC=48V VCC=12V VCC=24V
D97IN740
Figure 16. Efficiencyvs. output current.
(%) 90 85 80 75 70
VCC=48V VCC=8V VCC=12V VCC=24V
D97IN741
V CC=8V
75 70 65 60
fsw=200KHz VO=5.1V
65 60
fsw=200KHz VO=3.36V
0
0.2 0.4 0.6 0.8 1.0 1.2 1.4 IO(A)
55 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 IO(A)
Figure 17. Efficiencyvs. Vcc.
n [%] 90
Vo=5.1V fsw=100kHz
Figure 18. Power dissipation vs. Vcc.
Pdiss [mW] 1000
Vo=5.1V fsw=100kHz
800 85
Vo=5.1V fsw=200kHz Vo=3.36 fsw=100kHz V Io=2A
600
Io=1A Io=1.5A
80
Vo=3.36V fsw=200kHz
400
75
Io=2A
Io=0.5A
200
70 0 10 20 30 Vcc [V] 40 50 60
0 0 10 20 30 Vcc [V] 40 50 60
Figure 19. DevicePower dissipation vs.Vo
Pdiss [mW] 1400
Vcc=35V fsw=100kHz Io=2A
Figure 20. Pulse by pulse limiting current vs. junction temperature.
Ilim (A) 2.9 2.8
fsw=100KHz VCC=35V
D97IN747
1200
1000
Io=1.5A
800
2.7
600
Io=1A
2.6 2.5 2.4
400
Io=0.5A
200
0 0 10 20 Vo [V] 30
2.3 -50 -25 0 25 50 75 100 125 Tj(C)
8/12
L4978
Figure 22. Line transient.
VCC (V) 30 20 10 1
IO = 1A fsw = 100KHz
Figure 21. Load transient.
D97IN786
VO (mV) 100 0 -100
1ms/DIV
2
Figure 23. Soft start capacitor selection Vs inductor and Vccmax.
L (H)
fsw=100KHz
D97IN745
Figure 24. Soft start capacitor selection vs. Inductor and Vccmax.
L (H)
D97IN746
680nF 470nF
fsw=200KHz
56nF
400
330nF
300
47nF
300
200
200
220nF
33nF
22nF
100
100
100nF
0 15 20 25 30 35 40 45 50 VCCmax(V)
0 15 20 25 30 35 40 45 50 VCCmax(V)
Figure 25. Open loop frequency and phase of error amplifier
GAIN (dB) 50
GAIN
D97IN787
Phase
0 -50 -100
Phase
0 45 90 135
-150 -200 10
10 2 103 104 105 106 10 7 108 f(Hz)
9/12
L4978
DIM. MIN. A a1 B b b1 D E e e3 e4 F I L Z 3.18 7.95 0.51 1.15 0.356 0.204
mm TYP. 3.32 0.020 1.65 0.55 0.304 10.92 9.75 2.54 7.62 7.62 6.6 5.08 3.81 1.52 0.125 0.313 0.045 0.014 0.008 MAX. MIN.
inch TYP. 0.131 MAX.
OUTLINE AND MECHANICAL DATA
0.065 0.022 0.012 0.430 0.384 0.100 0.300 0.300 0.260 0.200 0.150 0.060
Minidip
10/12
L4978
DIM. MIN. A A1 B C D E e H h L K 10 0.25 0.4 2.35 0.1 0.33 0.23 10.1 7.4
mm TYP. MAX. 2.65 0.3 0.51 0.32 10.5 7.6 1.27 10.65 0.75 1.27 0.394 0.010 0.016 MIN. 0.093 0.004 0.013 0.009 0.398 0.291
inch TYP. MAX. 0.104 0.012 0.020 0.013 0.413 0.299 0.050 0.419 0.030 0.050
OUTLINE AND MECHANICAL DATA
0 (min.)8 (max.)
SO16 Wide
L
h x 45
A B e K H D A1 C
16
9
E 1 8
11/12
L4978
Information furnished is believed to be accurate and reliable. However, STMicroelectroni cs assumes no responsibility for the consequences of use of such information nor for any infringement of patents or other rights of third parties which may result from its use. No license is granted by implication or otherwise under any patent or patent rights of STMicroelectronics. Specification mentioned in this publication are subject to change without notice. This publication supersedes and replaces all information previously supplied. STMicroelectronics products are not authorized for use as critical components in life support devices or systems without express written approval of STMicroelectronics. The ST logo is a registered trademark of STMicroelectronics (c) 2000 STMicroelectronics - Printed in Italy - All Rights Reserved STMicroelectronics GROUP OF COMPANIES Australia - Brazil - China - Finland - France - Germany - Hong Kong - India - Italy - Japan - Malaysia - Malta - Morocco Singapore - Spain - Sweden - Switzerland - United Kingdom - U.S.A. http://www.st.com
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