Datasheet

ManualsBrandsSTMICROELECTRONICS ManualsVoltage Regulators7A. pow switch re L4977A [STM]

1/13

L4978

May 2005

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 DESCRIPTION

The L4978 is a step down monolithic power

switching regulator delivering 2A at a voltage be-

tween 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 R

dson

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 packages

must be observed). A wide input voltage range be-

tween 8V to 55V and output voltages regulated

from 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, 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, DIP-

8 for standard assembly, and SO16W for SMD as-

sembly.

2A STEP DOWN SWITCHING REGULATOR

Figure 2. Typical Application Circuit

D98IN837A

L4978

220µF

63V

330µF

=3.3V/2A

Vi=8V to 55V

20K

2.7nF

9.1K

22nF

126µH

(77120)

PS3L60U

100nF

220nF

100nF

Rev. 9

gure 1.

ages

Table 1. Order Codes

Part Number Package

L4978 DIP-8

L4978D SO16

L4978D013TR SO16 in Tape & Reel

DIP-8 SO16W

Summary of content (13 pages)

PAGE 1
L4978 2A STEP DOWN SWITCHING REGULATOR 1 ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ 2 Features Figure 1. Packages 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.
PAGE 2
L4978 Table 2. Block Diagram VCC 5 THERMAL SHUTDOWN VOLTAGES MONITOR CBOOT CHARGE 2 SS_INH INHIBIT SOFTSTART 3.3V INTERNAL REFERENCE INTERNAL SUPPLY 5.1V 7 COMP 6 E/A 8 FB PWM R 3.3V Q S CBOOT CHARGE AT LIGHT LOADS DRIVE OSCILLATOR 1 3 OSC BOOT 4 GND D97IN594 OUT Figure 3. Pins Connection (Top view) N.C. 1 16 N.C. GND 2 15 N.C. SS_INH 3 14 FB GND 1 8 FB SS_INH 2 7 COMP OSC 4 13 COMP OSC 3 6 BOOT OUT 5 12 BOOT OUT 4 5 VCC OUT 6 11 VCC N.C.
PAGE 3
L4978 Table 3. Pin Description (continued) N° Pin Name Function 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.
PAGE 4
L4978 Table 6. Electrical Characteristcs (Tj = 25°C, Cosc = 2.7nF, Rosc = 20kΩ, VCC = 24V, unless otherwise specified). “● " Specification Referred to Tj from 0 to 125°C Symbol Parameter Test Condition Min. Typ. Max. Unit 55 V DYNAMIC CHARACTERISTIC VI Operating input voltage range Vo = 3.3 to 50V; Io = 2A Vo Output voltage Io = 0.5A ● Io = 0.2 to 2A Vcc = 8 to 55V Vd Dropout voltage Vcc = 10V; Io = 2A Maximum limiting current Vcc = 8 to 55V Efficiency Vo = 3.3V; Io= 2A ● 8 3.33 3.
PAGE 5
L4978 Table 6. Electrical Characteristcs (Tj = 25°C, Cosc = 2.7nF, Rosc = 20kΩ, VCC = 24V, unless otherwise specified). “● " Specification Referred to Tj from 0 to 125°C Symbol Parameter Test Condition Min. Typ. Max. Unit 0.78 0.85 0.92 V Vcc = 8V 2 2.15 2.3 V Vcc = 55V 9 9.6 10.2 V 95 97 300 kHz OSCILLATOR SECTION Ramp Valley Ramp peak Maximum duty cycle Maximum Frequency Duty Cycle = 0% Rosc = 13kΩ, Cosc = 820pF % Figure 4. Test and evaluation board circuit.
PAGE 6
L4978 Figure 6. Quiescent drain current vs. input voltage. Iq (mA) D97IN724 200KHz R1=22K C2=1.2nF 5 Figure 9. Line Regulation . VO (V) D97IN733 3.377 Tj=125˚C 3.376 100KHz R1=20K C2=2.7nF 4 3.375 Tj=25˚C 3.374 3 0Hz 3.373 3.372 2 3.371 Tamb=25˚C 0% DC 3.370 1 0 5 10 15 20 25 30 35 40 45 50 Figure 7. Quiescent current vs. junction temperature D97IN731 Iq (mA) 200KHz R1=22K C2=1.2nF 5 4 0 Vcc(V) 5 10 15 20 25 30 35 40 45 50 VCC(V) Figure 10. Load regulation . VO (V) 3.
PAGE 7
L4978 Figure 12. Switching Frequency vs. input voltage.. fsw (KHz) D97IN735 Figure 15. Efficiency vs output voltage. . [%] 98 fsw=100kHz 96 107.5 94 105.0 fsw=200kHz 92 102.5 Tj=25˚C 90 100.0 88 97.5 86 95.0 84 92.5 82 80 90.0 0 5 10 15 20 25 30 35 40 45 50 VCC(V) Figure 13. Switching frequency vs. junction temperature. fsw (KHz) D97IN785 Vcc=35V Io=2A 0 5 10 15 Vo [V] 20 25 30 Figure 16. Efficiency vs. output current. .
PAGE 8
L4978 Figure 18. Efficiency vs. output current. . Figure 21. Power dissipation vs. Vcc. . Pdiss [mW] D97IN740 η (%) 1000 VCC=8V 90 Vo=5.1V fsw=100kHz VCC=12V 800 Io=2A VCC=24V 85 600 80 Io=1A VCC=48V Io=1.5A 75 400 70 fsw=200KHz VO=5.1V Io=0.5A 200 65 0 60 0 0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 IO(A) Figure 19. Efficiency vs. output current. . η (%) 40 50 60 Pdiss [mW] Vcc=35V fsw=100kHz 1200 VCC=12V 80 30 Vcc [V] 1400 VCC=8V 85 20 Figure 22. Device Power dissipation vs.
PAGE 9
L4978 Figure 27. Soft start capacitor selection Vs inductor and Vccmax. Figure 24. Load transient. . L (µH) D97IN746 56nF fsw=200KHz 300 47nF 200 33nF 22nF 100 0 15 20 25 30 35 40 45 50 VCCmax(V) Figure 25. Line transient. . Figure 28. Open loop frequency and phase of error amplifier .
PAGE 10
L4978 3 Package Informations Figure 29. DIP-8 Mechanical Data & Package Dimensions mm inch DIM. MIN. A TYP. MIN. 3.32 TYP. MAX. 0.51 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 E 0.020 10.92 7.95 9.75 0.430 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 Z 3.18 OUTLINE AND MECHANICAL DATA 0.131 a1 D 10/13 MAX. 3.81 1.52 0.125 0.150 0.
PAGE 11
L4978 Figure 30. SO16 Wide Mechanical Data & Package Dimensions mm inch DIM. 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 ddd OUTLINE AND MECHANICAL DATA 0˚ (min.), 8˚ (max.) 0.10 0.
PAGE 12
L4978 Table 7. Revision History Date Revision October 2001 8 First Issue May 2005 9 Modified D1 on the Fig. 4.
PAGE 13
L4978 Information furnished is believed to be accurate and reliable. However, STMicroelectronics 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. Specifications mentioned in this publication are subject to change without notice.