L4978

May 2005

2A STEP DOWN SWITCHING REGULATOR

Figure 1. Packages

Table 1. Order Codes

Part Number Package

L4978 DIP-8

L4978D SO16

L4978D013TR SO16 in Tape & Reel

DIP-8 SO16W

1 Features 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 300KHz 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

2 DESCRIPTIONThe L4978 is a step down monolithic powerswitching regulator delivering 2A at a voltage be-tween 3.3V and 50V (selected by a simple externaldivider). Realized in BCD mixed technology, thedevice uses an internal power D-MOS transistor(with a typical Rdson of 0.25Ω) to obtain very high

efficency and high switching speed.

A switching frequency up to 300KHz is achievable(the maximum power dissipation of the packagesmust be observed). A wide input voltage range be-tween 8V to 55V and output voltages regulatedfrom 3.3V to 50V cover the majority of today’s ap-plications. Features of this new generations of DC-DC converter include pulse-by-pulse current limit,hiccup mode for short circuit protection, voltagefeedforward regulation, soft-start, protectionagainst feedback loop disconnection, inhibit forzero current consumption and thermal shutdown.

The device is available in plastic dual in line, DIP-8 for standard assembly, and SO16W for SMD as-sembly.

Figure 2. Typical Application Circuit

D98IN837A

5

2

8

4

1

L4978

C1220µF63V

C8330µF

VO=3.3V/2A

Vi=8V to 55V

R120K

C22.7nF

R29.1K

C422nF

3

7 L1 126µH(77120)

6

D1ST

PS3L60UC5

100nF

C7220nF

C6100nF

1/13Rev. 9

L4978

Table 2. Block Diagram

Figure 3. Pins Connection (Top view)

Table 3. Pin Description

N° Pin Name Function

1 2 GND Ground

2 3 SS_INH 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).

3 4 OSC 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)

INHIBIT SOFTSTART

VOLTAGESMONITOR

THERMALSHUTDOWN

E/APWM

3.3V

OSCILLATOR

R

SQ

INTERNALREFERENCE

INTERNALSUPPLY

3.3V 5.1V

DRIVE

CBOOTCHARGE

CBOOTCHARGEAT LIGHTLOADS

2

7

8FB

COMP

SS_INH

3 1 4

6

5

BOOT

OSC GND OUT

VCC

D97IN594

GND

SS_INH

OSC

OUT

1

3

2

4 VCC

BOOT

COMP

FB8

7

6

5

D97IN595

N.C.

GND

SS_INH

OSC

OUT

N.C.

OUT

N.C. N.C.

N.C.

BOOT

VCC

COMP

FB

N.C.

N.C.1

3

2

4

5

6

7

8

14

13

12

11

10

9

15

16

D97IN596

DIP-8 SO16W

2/13

L4978

(*) Pins 1, 7, 8, 9, 10, 15 and 16 are not internally, electrically connected to the die.

Table 4. Thermal Data

(*) Package mounted on board.

Table 5. Absolute Maximum Ratings

4 5, 6 OUT Stepdown regulator output

5 11 VCC Unregulated DC input voltage

6 12 BOOT A capacitor connected between this pin and OUT allows to drive the internal DMOS Transistors

7 13 COMP E/A output to be used for frequency compensation

8 14 FB 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.

Symbol Parameter Minidip SO16 Unit

Rth(j-amb) Thermal Resistance Junction to ambient Max. 90 (*) 110 (*) °C/W

Symbol Parameter Value Unit

Minidip S016

V5 V11 Input voltage 58 V

V4 V5,V6 Output DC voltageOutput peak voltage at t = 0.1ms f=200KHz

-1-5

VV

I4 I5,I6 Maximum output current int. limit.

V6-V5 V12-V11 14 V

V6 V12 Bootstrap voltage 70 V

V7 V13 Analogs input voltage (VCC= 24V) 12 V

V2 V3 Analogs input voltage (VCC= 24V) 13 V V8 V14 (VCC= 20V) 6

-0.3

VV

Ptot Power dissipation a Tamb ≤ 60°CDIP-8SO16

10.8

WW

Tj,Tstg Junction and storage temperature -40 to 150 °C

Table 3. Pin Description (continued)

N° Pin Name Function

3/13

L4978

Table 6. Electrical Characteristcs(Tj = 25°C, Cosc = 2.7nF, Rosc = 20kΩ, VCC = 24V, unless otherwise specified). “" Specification Referredto Tj from 0 to 125°C

Symbol Parameter Test Condition Min. Typ. Max. Unit

DYNAMIC CHARACTERISTIC

VI Operating input voltage range Vo = 3.3 to 50V; Io = 2A 8 55 V

Vo Output voltage Io = 0.5A 3.33 3.36 3.39 V

Io = 0.2 to 2A Vcc = 8 to 55V

3.292 3.36 3.427 V 3.22 3.36 3.5 V

Vd Dropout voltage Vcc = 10V; Io = 2A 0.58 0.733 V 1.173 V

Il Maximum limiting current Vcc = 8 to 55V 2.5 3 3.5 A

Efficiency Vo = 3.3V; Io= 2A 87 %

fs Switching frequency 90 100 110 KHz

SVRR Supply voltage ripple rejection Vi = Vcc+2VRMS; Vo= Vref; Io = 2.5A; f ripple= 100Hz

60 dB

Switching Frequency Stability vs. Vcc

Vcc = 8 to 55V 3 6 %

Temp. stability of switching frequency

Tj = 0 to 125°C 4 %

SOFT START

Soft start charge current 30 40 50 µA

Soft start discharge current 6 10 14 µA

INHIBIT

VLL Low level voltage 0.9 V

IsLL Isource Low level 5 15 µA

DC CHARACTERISTICS

Iqop Total operating quiescent current

4 6 mA

Iq Quiescent current Duty Cycle = 0; VFB= 3.8V 2.5 3.5 mA

Iqst-by Total stand-by quiescent current

Vinh < 0.9V 100 200 µA

Vcc = 55V; Vinh<0.9V 150 300 µA

ERROR AMPLIFIER

VFB Voltage Feedback Input 3.33 3.36 3.39 V

RL Line regulation Vcc = 8 to 55V 5 10 mV

Ref. voltage stability vs temperature

0.4 mV/°C

VoH High level output voltage VFB = 2.5V 10.3 V

VoL Low level output voltage VFB = 3.8V 0.65 V

Io source Source output current Vcomp= 6V; VFB= 2.5V 180 220 µA

Io sink Sink output current Vcomp = 6V; VFB= 3.8V 200 300 µA

Ib Source bias current 2 3 µA

SVRR E/A Supply voltage ripple rejection Vcomp = VFB; Vcc = 8 to 55V 60 80 dB

DC open loop gain RL= ∞ 50 57 dB

gm Transconductance Icomp = -0.1 to 0.1mA Vcomp = 6V

2.5 mS

4/13

L4978

Figure 4. Test and evaluation board circuit.

Figure 5. PCB and component layout of the figure 4.

OSCILLATOR SECTION

Ramp Valley 0.78 0.85 0.92 V

Ramp peak Vcc = 8V 2 2.15 2.3 V

Vcc = 55V 9 9.6 10.2 V

Maximum duty cycle 95 97 %

Maximum Frequency Duty Cycle = 0% Rosc = 13kΩ, Cosc = 820pF

300 kHz

Table 6. Electrical Characteristcs(Tj = 25°C, Cosc = 2.7nF, Rosc = 20kΩ, VCC = 24V, unless otherwise specified). “" Specification Referredto Tj from 0 to 125°C

Symbol Parameter Test Condition Min. Typ. Max. Unit

D98IN834B

5

2

8

4

1

L4978

C1220µF63V

C8330µF

VO=3.3V/2A

Vi=8V to 55V

R120K

C22.7nF

R29.1K

C422nF

3

7 L1 126µH(77120)

6

D1STPS3L60U

C5100nF

C7220nF

C6100nF

R3

R4

C1=220µF/63V EKE C2=2.7nFC5=100nFC6=100nFC7=220nF/63VC8=330µF/35V CG SanyoL1=126µH KoolMu 77120 - 55 Turns - 0.5mmR1=20KR2=9.1KD1=STPS3L60U

VO(V) R3(KΩ) R4(KΩ)

3.3

5.1

12

15

18

24

0

2.7

12

16

20

30

4.7

4.7

4.7

4.7

4.7

L4978

5/13

L4978

Figure 6. Quiescent drain current vs. input voltage.

Figure 7. Quiescent current vs. junction temperature

Figure 8. Stand by drain current vs. input voltage.

Figure 9. Line Regulation.

Figure 10. Load regulation.

Figure 11. Switching frquency vs. R1 and C2.

0 5 10 15 20 25 30 35 40 45 50 Vcc(V)1

2

3

4

5

Iq(mA)

200KHzR1=22KC2=1.2nF

0Hz

D97IN724

Tamb=25˚C0% DC

100KHzR1=20KC2=2.7nF

-50 -30 -10 10 30 50 70 90 110 Tj(˚C)1

2

3

4

5

Iq(mA)

D97IN731

0Hz

200KHzR1=22KC2=1.2nF

VCC=35V0% DC

100KHzR1=20KC2=2.7nF

0 5 10 15 20 25 30 35 40 45 50 VCC(V)60

70

80

90

100

110

120

130

140

150

Ibias(µA)

D97IN732

Tj=25˚C

Tj=125˚C

Vss=GND

0 5 10 15 20 25 30 35 40 45 50 VCC(V)3.370

3.371

3.372

3.373

3.374

3.375

3.376

3.377

VO(V)

D97IN733

Tj=25˚C

Tj=125˚C

0 0.2 0.4 0.6 1.0 1.2 1.4 1.6 IO(A)0.8 1.83.360

3.362

3.364

3.366

3.368

3.370

3.372

3.374

3.376

3.378

VO(V)

Tj=25˚C

Tj=125˚C

VCC=35V

D98IN835

0 20 40 60 80 R1(KΩ)5

10

20

50

100

200

500

fsw(KHz)

D97IN784

0.82nF

1.2nF

2.2nF

3.3nF

4.7nF

5.6nF

Tamb=25˚C

6/13

L4978

Figure 12. Switching Frequency vs. input voltage..

Figure 13. Switching frequency vs. junction temperature.

Figure 14. Dropout voltage between pin 5 and 4.

Figure 15. Efficiency vs output voltage..

Figure 16. Efficiency vs. output current..

Figure 17. Efficiency vs. output current..

0 5 10 15 20 25 30 35 40 45 50 VCC(V)90.0

92.5

95.0

97.5

100.0

102.5

105.0

107.5

fsw(KHz)

D97IN735

Tj=25˚C

-50 0 50 100 Tj(˚C)90

95

100

105

fsw(KHz)

D97IN785

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 IO(A)1.6 1.80.0

0.1

0.2

0.3

0.4

0.5

∆V(V)

0.6

0.7

Tj=25˚C

Tj=125˚C

D98IN836

Tj=-25˚C

0 5 10 15 20 25 3080

82

84

86

88

90

92

94

96

98

Vo [V]

[%]

fsw=100kHz

fsw=200kHz

Vcc=35VIo=2A

Vcc=12V

Vcc=8V

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 2.260

65

70

75

80

85

90

95

Io [A]

[%]

Vcc=8V

Vcc=12V

Vcc=24V

Vcc=48V

fsw=100kHzVo=5.1V

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 2.260

65

70

75

80

85

90

95

Io [A]

[%]

Vcc=8V

Vcc=12V

Vcc=24V

Vcc=48V

Vo=3.36V fsw=100kHz

7/13

L4978

Figure 18. Efficiency vs. output current. .

Figure 19. Efficiency vs. output current. .

Figure 20. Efficiency vs. Vcc..

Figure 21. Power dissipation vs. Vcc..

Figure 22. Device Power dissipation vs. Vo.

Figure 23. Pulse by pulse limiting current vs. junction temperature..

0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 IO(A)60

65

70

75

80

85

90

η(%)

D97IN740

VCC=8V

fsw=200KHzVO=5.1V

VCC=12V

VCC=24V

VCC=48V

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 IO(A)55

60

65

70

75

80

85

90

η(%)

D97IN741

VCC=8V

fsw=200KHzVO=3.36V

VCC=12V

VCC=24V

VCC=48V

Io=2A

0 10 20 30 40 50 6070

75

80

85

90

Vcc [V]

n [%]

Vo=5.1V fsw=100kHz

Vo=5.1V fsw=200kHz

Vo=3.36V fsw=100kHz

Vo=3.36V fsw=200kHz

Io=0.5A

Io=2A

Io=1A

0 10 20 30 40 50 600

200

400

600

800

1000

Vcc [V]

Pdiss [mW]

Io=1.5A

Vo=5.1V fsw=100kHz

Io=2A

Io=1A

0 10 20 300

200

400

600

800

1000

1200

1400

Vo [V]

Pdiss [mW]

Io=0.5A

Io=1.5A

Vcc=35V fsw=100kHz

-50 -25 0 25 50 75 100 125 Tj(˚C)2.3

2.4

2.5

2.6

2.7

2.8

2.9

Ilim(A)

D97IN747

fsw=100KHzVCC=35V

8/13

L4978

Figure 24. Load transient. .

Figure 25. Line transient. .

Figure 26. Soft start capacitor selection Vs inductor and Vccmax.

Figure 27. Soft start capacitor selection Vs inductor and Vccmax.

Figure 28. Open loop frequency and phase of error amplifier .

2

1

D97IN786VCC(V)

30

20

10

VO(mV)

100

0

-1001ms/DIV

IO = 1Afsw = 100KHz

15 20 25 30 35 40 45 50 VCCmax(V)0

100

200

300

400

L(µH)

D97IN745

680nF

fsw=100KHz470nF

330nF

220nF

100nF

15 20 25 30 35 40 45 50 VCCmax(V)

0

100

200

300

L(µH)

56nFfsw=200KHz

D97IN746

47nF

33nF

22nF

10 103 105 107 f(Hz)102 104 106 108-200

-150

-100

-50

GAIN(dB)

0

50

Phase

0

45

90

135

D97IN787

GAIN

Phase

9/13

L4978

3 Package Informations

Figure 29. DIP-8 Mechanical Data & Package Dimensions

OUTLINE ANDMECHANICAL DATA

DIM.mm inch

MIN. TYP. MAX. MIN. TYP. MAX.

A 3.32 0.131

a1 0.51 0.020

B 1.15 1.65 0.045 0.065

b 0.356 0.55 0.014 0.022

b1 0.204 0.304 0.008 0.012

D 10.92 0.430

E 7.95 9.75 0.313 0.384

e 2.54 0.100

e3 7.62 0.300

e4 7.62 0.300

F 6.6 0.260

I 5.08 0.200

L 3.18 3.81 0.125 0.150

Z 1.52 0.060

DIP-8

10/13

L4978

Figure 30. SO16 Wide Mechanical Data & Package Dimensions

OUTLINE ANDMECHANICAL DATA

DIM.mm inch

MIN. TYP. MAX. MIN. TYP. MAX.

A 2.35 2.65 0.093 0.104

A1 0.10 0.30 0.004 0.012

B 0.33 0.51 0.013 0.200

C 0.23 0.32 0.009 0.013

D (1) 10.10 10.50 0.398 0.413

E 7.40 7.60 0.291 0.299

e 1.27 0.050

H 10.0 10.65 0.394 0.419

h 0.25 0.75 0.010 0.030

L 0.40 1.27 0.016 0.050

k 0˚ (min.), 8˚ (max.)

ddd 0.10 0.004

(1) “D” dimension does not include mold flash, protusions or gateburrs. Mold flash, protusions or gate burrs shall not exceed0.15mm per side.

SO16 (Wide)

0016021 C

11/13

L4978

Table 7. Revision History

Date Revision Description of Changes

October 2001 8 First Issue

May 2005 9 Modified D1 on the Fig. 4.

12/13

Information furnished is believed to be accurate and reliable. However, STMicroelectronics assumes no responsibility for the consequencesof 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 grantedby implication or otherwise under any patent or patent rights of STMicroelectronics. Specifications mentioned in this publication are subjectto change without notice. This publication supersedes and replaces all information previously supplied. STMicroelectronics products are notauthorized 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.All other names are the property of their respective owners

© 2005 STMicroelectronics - All rights reserved

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L4978