Datasheet L5971D, L5971 Datasheet (SGS Thomson Microelectronics)



1.5A STEP DOWN SWITCHING REGULATOR

UP TO 1.5A STEPDOWN CONVERTER
OPERATING INPUT VOLTAGE FROM 6.5V

TO 28V
PRECISE 1.26V (±1%) INTERNAL REFER-

ENCE VOLTAGE
OUTPUT VOLTAGE ADJUSTABLE FROM

1.26VTO 20V
SWITCHINGFREQUENCY ADJUSTABLE UP

TO 500KHz
VOLTAGEFEEDFORWARD
ZEROLOAD CURRENTOPERATION
INTERNAL CURRENT LIMITING (PULSE-BY-

PULSEAND HICCUPMODE)
INHIBIT FOR ZERO CURRENT CONSUMP-

TION
PROTECTION AGAINST FEEDBACK DIS-

CONNECTION
THERMAL SHUTDOWN
SOFTSTART FUNCTION

DESCRIPTION

The L5971 is a step down monolithic power
switching regulator delivering 1.5A at a voltage
between 1.26V and 20V (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 0.25Ω)toob­tainvery high efficency and high switchingspeed.

TYPICAL APPLICATIONCIRCUIT

L5971

Minidip

ORDERING NUMBERS: L5971 (Minidip)

A switching frequency up to 500KHz is achiev­able (the maximum power dissipation of the pack­ages must be observed).
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 SO16 for
SMD assembly.

Typical Applications:

- High efficiencystep-downconverter

- Portable computers

- Batterycharger

- Distributedpower

- PDAsand MobileComminicators

SO16W

L5971D (SO16)

Vi=6V to 28V

May 2000

C1

47µF

30V

R1

22K

C2

1.2nF
C5

47nF

5(11)

3(4)

2(3)

7(13)

L5971

1(2)

R2

9.1K
C4

22nF

4(5,6)

6(12)

100nF

8(14)

C6

D98IN832C

D1

STPS

3L40U

L1

30µH

C

8

330µF

VO=2.5V/1.5A

R

3

R

4

1/11

L5971

BLOCKDIAGRAM

COMP

FB

2

7

8

1.26V

SS_INH

THERMAL

SHUTDOWN

INHIBIT SOFTSTART

E/A

OSCILLATOR

VOLTAGES

MONITOR

PWM

1.26V

INTERNAL

REFERENCE

R

Q

S

INTERNAL

SUPPLY

5.1V

DRIVE

VCC

5

CBOOT

CHARGE

CBOOT

CHARGE

AT LIGHT

LOADS

6

BOOT

3

OSC GND OUT

1

4

D98IN833

PIN CONNECTIONS

16
15
14
13
12
11
10

N.C.1
N.C.
FB
COMP
BOOT
VCC
N.C.

9

GND

SS_INH

OSC
OUT

1
2
3
4 VCC

D97IN595

FB8
COMP

7

BOOT

6
5

Minidip

N.C.

GND

SS_INH

OSC
OUT
OUT

N.C.
N.C. N.C.

2
3
4
5
6
7
8

D97IN596

SO16W

PIN FUNCTIONS

DIP SO (*) Name Function

1 2 GND Ground
2 3 SS_INH A logic signal (active low) disables the device (sleep mode operation).

3 4 OSC An external resistor connected between the unregulated input voltage and this pin and

4 5, 6 OUT Stepdown regulator output
511 V

CC

6 12 BOOT A capacitor connected between this pin and OUT allows to drive the internal VDMOS
7 13 COMP E/A output to be used for frequency compensation
8 14 FB Stepdown feedback input. Connecting directly this pin to the output 1.26V is obtained; a

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

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).

a capacitor connected from this pin to ground fix the switching frequency. (Line feed
forward is automatically obtained)

Not regulated DC input voltage

voltage divider is requested for higher output voltages

2/11

THERMALDATA

Symbol Parameter Minidip SO16 Unit

R

th(j-amb)

(*) Package mounted on board.

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

ABSOLUTE MAXIMUM RATINGS

L5971

Symbol

Minidip S016

V

V

V

5,V3

V

4

I

4

6-V5

V

6

7,V2

V

8

V11,V4Input voltage 30 V

V5,V

I5,I

V12-V

V

12

V13,V

V

14

P

tot

Output DC voltage

6

Output peak voltage at t = 0.1µs f=200KHz
Maximum output current int. limit.

6

11

Bootstrap voltage 45 V
Analogs input voltage (VCC= 12V) 10 V

3

(VCC= 20V) 6

Power dissipation a T

Parameter Value Unit

-1

-5

V
V

14 V

V

-0.3

≤ 60°C Minidip 1W

amb

V

SO16 0.8 W

T

j,Tstg

Junction and storage temperature -40 to 150 °C

ELECTRICAL CHARACTERISTICS (Tj = 25°C, Cosc = 2.7nF, Rosc = 20kΩ,VCC = 12V, unless other-
wisespecified.) * SpecificationReferedto Tj from 0 to 125°C

Symbol Parameter Test Condition Min. Typ. Max. Unit

DYNAMICCHARACTERISTIC

V

I

V

o

V

d Dropout voltage Vcc = 10V; Io = 1.5A 0.44 0.55 V

I

l Maximum limiting current Vcc = 6.5 to 25V * 2 2.5 3 A

f

s Switching frequency * 90 100 110 KHz

SVRR Supply voltage ripple rejection V

Operating input voltage range * 6.5 28 V
Output voltage Io= 0.5A 1.247 1.26 1.273 V

I

= 0.2 to 1.5A 1.235 1.26 1.285 V

o

V

= 6.5to 25V * 1.21 1.26 1.31 V

cc

* 0.88 V

Efficiency V

Voltage stability of switching

o = 3.3V; Io = 1.5A 85 %

i =Vcc+2VRMS;Vo =Vref;

I

= 1.5A; f

o

ripple

= 100Hz

60 dB

Vcc = 6.5 to 25V 3 6 %

frequency
Temp. stability of switching

j = 0 to 125°C4%

T

frequency

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
I

sLL Isource Low level * 5 15 µA

3/11

L5971

ELECTRICAL CHARACTERISTICS (continued)

Symbol Parameter Test Condition Min. Typ. Max. Unit

DC Characteristics

Iqop Total operating quiescent

current

I

q Quiescent current Duty Cycle = 0; V

I

qst-by

Total stand-by quiescent
current

Error Amplifier

V

FB

R

L Line regulation Vcc = 6.5 to 25V 5 10 mV

V

oH High level output voltage V

V

oL Low level output voltage V

I

o source Source output current V

I

o sink Sink output current V

I

b Source bias current 2 3 µA

SVRR E/A Supply voltage ripple rejection V

gm Transconductance I

Voltage Feedback Input 1.247 1.26 1.273 V

Ref. voltage stability vs
temperature

DC open loop gain R

OscillatorSection

Ramp Valley 0.74 0.81 0.88 V
Ramp peak Vcc= 6.5V 1.80 1.87 1.94 V

Maximum duty cycle 95 97 %
Maximum Frequency Duty Cycle = 0%

Pin 5 (Pin 11) 3 4.5 mA

= 1.7V 2.8 3.5 mA

FB

V

<0.9V 100 200 µA

inh

Vcc = 25V; V

<0.9V 150 300 µA

inh

* 0.4 mV/°C

= 0.8V 8.7 V

FB

= 1.7V 0.65 V

FB

= 3V; VFB= 0.8V 180 250 µA

comp

= 3V; VFB= 1.7V 200 300 µA

comp

comp=Vfb
L

comp

V

comp

; Vcc = 6.5 to 25V 60 80 dB

= ∞ 50 57 dB

= -0.1 to 0.1mA

4.3 mS

=6V

Vcc = 25V 4.72 4.79 4.86 V

500 kHz

R

= 13kΩ,C

osc

= 820pF

osc

4/11

Figure1. Testand valutation board circuit.

L5971

Vi=6V to 28V

C1

47µ

30V

R

1

22K

C

F

1.2nF

2

5(11)

7(13)

L5971

R

2

9.1K
C

22nF

3(4)

2(3)

C

5

47nF

8(14)

4(5,6)

6(12)

1(2)

C

6

STPS

3L40U

D98IN832C

D1

100nF

4

Figure2. PCBand componentlayout of the figure 1.

L1

30µH

C

330µF

VO(V) R3 (KΩ)R4(KΩ)

V

=2.5V/1.5A

O

1.8 1 2

1.5 0.5 2

R

3

8

R

4

2.5 2 2

3.3 8.2 4.7

5.1 12 3.6
12 27 3
15 23 2

SOLDER SIDE

COMPONENT SIDE

5/11

L5971

Figure3. Quiescentdraincurrent vs. input

voltage.

Iq

(mA)

5

200KHz
R1=22K
C2=1.2nF

4

3

100KHz;
R1=20K
C2=2.7nF

0Hz

2

1

0 5 10 15 20 25

D98IN942

Tamb=25°
0% DC

C

Vcc(V)

Figure5. Stand-bydrain currentvs. input

voltage

Ibias

(µA)

150

Vss=GND

140
130
120
110

Tj=25°C

100

90
80
70
60

0 5 10 15 20 25 VCC(V)

D98IN944

Tj=125°C

Figure7. Switchingfrquency vs. R1 and C2

fsw

(KHz)

500

D97IN784

Tamb=25°C

Figure 4. Quiescent current vs. junction

temperature

V

CC

0% DC

=2.7nF

2

D98IN943

=20V

Iq

(mA)

5

4

3

200KHz; R

100KHz;

R

=20K;

1

=22K; C2=1.2nF

1

C

0Hz

2

1

-50 -30 -10 10 30 50 70 90 110 Tj(°C)

Figure 6. LineRegulation

VO
(V)

3.377

3.376

3.375

Tj=125°C

3.374

3.373

3.372

3.371

3.370
0 5 10 15 20 25 VCC(V)

D98IN945

Tj=25°C

Figure 8. Switching Frequency vs. input

voltage.

fsw

(KHz)

107.5

D98IN947

6/11

200

0.82nF

1.2nF

100

50

20

2.2nF

3.3nF

4.7nF

5.6nF

10

5

0 20 40 60 80 R1(KΩ)

105.0

102.5

Tj=25°C

100.0

97.5

95.0

92.5

90.0
0 5 10 15 20 25 VCC(V)

L5971

Figure9. Switchingfrequency vs. junction

temperature.

fsw

(KHz)

105

100

95

90

-50 0 50 100 Tj(°C)

D97IN785

Figure11. Efficiency vs output voltage.

(%)

96
94
92
90
88
86
84

η

100KHz

200KHz

V
I

O

CC

=1.5A

D98IN948

=20V

Figure 10. Dropout voltage between pin 5

and 4.

∆V

(V)

0.5

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 IO(A)

D97IN736

Tj=125°C

Tj=25°C

Tj=-25°C

Figure 12. Efficiency vs. output current.

η

(%)

90

85

80

=12V

V

CC

V

=18V

CC

fsw=200KHz
VO=5.1V

D98IN949

VCC=8V

82

0 5 10 15 20 25 VO(V)

Figure13. Efficiency vs output current.

η

(%)

90

85

V

CC

=12V

V

CC

VCC=8V

=18V

80

75

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

D98IN950

fsw=200KHz
VO=3.36V

75

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

Figure 14. Efficiency vs. output current.

η

(%)

90

85

80

75

Vcc=8V

Vcc=12V

Vcc=18V

70

65

60

0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 Io(A)

D98IN941

Fsw=200KHz
Vo=2.5V

7/11

L5971

Figure 15. Load transient.

Figure17. Soft start capacitorselectionvs. In-

ductor and V

L

(µH)

150

ccmax

D98IN953

fsw=200KHz

Figure 16. Soft start capacitorselection vs. In-

ductorand V

L

(µH)

160

120

80

40

0

fsw=100KHz

20 22 24 26 28

ccmax

680nF

D98IN952

470nF

330nF

220nF

100nF

V

CCmax

(V)

Figure 18. Open loop frequencyand phase of

erroramplifier.

GAIN

(dB)

50

0

GAIN

D97IN787

Phase

0

100

50

0

20 22 24 26 28 V

56nF

47nF

33nF

22nF

CCmax

(V)

-50

-100

-150

-200
10 10

45

90

Phase

135

3

2

10

5

4

10

10

7

6

10

10

8

f(Hz)10

8/11

L5971

DIM.

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

mm inch

OUTLINE AND

MECHANICAL DATA

Minidip

9/11

L5971

DIM.

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

A 2.35 2.65 0.093 0.104

A1 0.1 0.3 0.004 0.012

B 0.33 0.51 0.013 0.020

C 0.23 0.32 0.009

D 10.1 10.5 0.398 0.413

E 7.4 7.6 0.291 0.299

e 1.27 0.050

H 10 10.65 0.394 0.419

h 0.25 0.75 0.010 0.030

L 0.4 1.27 0.016 0.050

K0°(min.)8° (max.)

mm inch

0.013

OUTLINE AND

MECHANICAL DATA

SO16 Wide

L

hx

45

A

B

e

K

A1

C

H

D

16

9

E

1

8

10/11

L5971

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