ST L5973D User Manual

2.5 A switch step down switching regulator

Features

■ 2.5 A internal switch

■ Operating input voltage from 4 V to 36 V

■ 3.3 V / (±2%) reference voltage

■ Output voltage adjustable from 1.235 V to 35 V

■ Low dropout operation: 100 % duty cycle

■ 250 kHz internally fixed frequency

■ Voltage feedforward

■ Zero load current operation

■ Internal current limiting

■ Inhibit for zero current consumption

■ Synchronization

■ Protection against feedback disconnection

■ Thermal shutdown

Applications

■ Consumer: STB, DVD, TV, VCR, car radio,

LCD monitors

■ Networking: XDSL, modems, DC-DC modules

■ Computer: printers, audio/graphic cards,

optical storage, hard disk drive

■ Industrial: changers, car battery, DC-DC

converters

Figure 1. Test application circuit

VREF

VIN = 4.4V to 35V

C1

10µF

35V

CERAMIC

3.3V

SYNC.

COMP

C4

22nF

C3

220pF

VCC

R3

4.7K

6

8

2

4

L5973D

3

L5973D

HSOP8 exposed pad

Description

The L5973D is a step down monolithic power
switching regulator with a minimum switch current
limit of 2.5 A so it is able to deliver more than 2 A
DC current to the load depending on the
application conditions.
The output voltage can be set from 1.235 V to
35 V. The high current level is also achieved
thanks to an SO8 package with exposed frame,
that allows to reduce the Rth(j-amb) down to
approximately 40 °C/W.
The device uses an internal P-channel D-MOS
transistor (with a typical Rdson of 250 mΩ) as
switching element to minimize the size of the
external components.
An internal oscillator fixes the switching frequency
at 250 kHz.
Having a minimum input voltage of 4 V only, it is
particularly suitable for 5 V bus, available in all
computer related applications.
Pulse by pulse current limit with the internal
frequency modulation offers an effective constant
current short circuit protection.

OUT

1

5

7

GNDINH

FB

L1 15µH

D1

STPS340U

R1

5.6K

R2

3.3K

VOUT=3.3V

C2

330µF

10V

D03IN1439

January 2008 Rev 16 1/17

www.st.com

17

Contents L5973D

Contents

1 Pin settings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

1.1 Pin connection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

1.2 Pin description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

2 Electrical data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

2.1 Maximum ratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

2.2 Thermal data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

3 Electrical characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

4 Typical characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

5 Application circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

6 Application ideas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

7 Package mechanical data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

8 Order code . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

9 Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

2/17

L5973D Pin settings

1 Pin settings

1.1 Pin connection

Figure 2. Pin connection (top view)

COMP

1.2 Pin description

Table 1. Pin description

N° Type Description

1 OUT Regulator output.

2 SYNC Master/slave synchronization.

3INH

4 COMP E/A output for frequency compensation.

5FB

OUT

SYNC

INH

1

2

3

4

D98IN955

A logical signal (active high) disables the device. If INH not used the pin
must be grounded. When it is open an internal pull-up disable the
device.

Feedback input. Connecting directly to this pin results in an output
voltage of 1.23 V. An external resistive divider is required for higher
output voltages.

8

7

6

5

VCC

GND

VREF

FB

6 VREF 3.3 V V

7 GND Ground.

8 VCC Unregulated DC input voltage.

. No cap is requested for stability.

REF

3/17

Electrical data L5973D

2 Electrical data

2.1 Maximum ratings

Table 2. Absolute maximum ratings

Symbol Parameter Value Unit

V

8

V

1

I

1

V

, V

4

V

3

V

2

P

TOT

T

J

T

STG

Input voltage 40 V

Output DC voltage
Output peak voltage at t = 0.1 µs

Maximum output current int. limit.

Analog pins 4 V

5

INH -0.3 V to V

SYNC -0.3 to 4 V

Power dissipation at TA ≤ 60 °C 2.25 W

Operating junction temperature range -40 to 150 °C

Storage temperature range -55 to 150 °C

2.2 Thermal data

Table 3. Thermal data

Symbol Parameter

R

thJA

1. Package mounted on board

Maximum thermal resistance junction-ambient 40

-1 to 40

-5 to 40

CC

HSOP8

Exposed Pad

(1)

V
V

Unit

°C/W

4/17

L5973D Electrical characteristics

3 Electrical characteristics

Table 4. Electrical characteristics

( TJ = 25 °C, VCC = 12 V, unless otherwise specified)

Symbol Parameter Test condition Min Typ Max Unit

V

R

DS(on)

f

CC

I

s

l

Operating input
voltage range

Mosfet on
Resistance

Maximum limiting
current

Switching frequency

= 1.235 V; Io = 2 A

V

o

V

CC

Duty cycle 0 100 %

Dynamic characteristics (see test circuit ).

V

5

Voltage feedback

h Efficiency V

4.4 V < V
20 mA < I

= 5 V, VCC = 12 V 90 %

O

DC characteristics

I

qop

I

I

qst-by

q

Total operating
quiescent current

Quiescent current

Total stand-by
quiescent current

Duty Cycle = 0;
V

FB

V

inh

V

CC

V

inh

Inhibit

(1)

(1)

436V

0.250 0.5 Ω

= 4.4 V to 36 V 2.5 3 3.5 A

(1)

212 250 280 kHz

225 250 275 kHz

CC

O

= 1.5 V

> 2.2 V

= 36 V;

> 2.2 V

< 36 V,

< 2 A

1.220 1.235 1.25 V

(1)

1.198 1.235 1.272 V

(1)

(1)

(1)

35mA

50 100 µA

80 150 µA

2.5 mA

Error amplfier

V

OH

V

OL

I

o source

I

o sink

INH threshold
voltage

High level output
voltage

Low level output
voltage

Source output
current

Sink output current

Device ON 0.8 V

Device OFF 2.2 V

VFB = 1 V 3.5 V

VFB = 1.5 V 0.4 V

V

= 1.9 V;

COMP

= 1 V

V

FB

= 1.9 V;

V

COMP

VFB = 1.5 V

200 300 µA

11.5 mA

5/17

Electrical characteristics L5973D

Table 4. Electrical characteristics (continued)

( TJ = 25 °C, VCC = 12 V, unless otherwise specified)

Symbol Parameter Test condition Min Typ Max Unit

I

b

Source bias current 2.5 4 µA

DC open loop gain R

gm Transconductance

Sync function

High input voltage V

Low input voltage V

Slave sink current

Master output
amplitude

Output pulse width

Reference section

Reference voltage 3.234 3.3 3.366 V

Line regulation

Load regulation I

Short circuit current 10 18 30 mA

= ∞ 50 57 dB

L

= -0.1 mA to

I

comp

0.1 mA
= 1.9 V

V

COMP

= 4.4 V to 36 V 2.5 V

CC

= 4.4 V to 36 V 0.74 V

CC

= 0.74 V

V

sync

V

= 2.33 V

sync

= 3 mA 2.75 3 V

I

source

(2)

no load,
V

= 1.65 V

sync

I

= 0 to 5 mA

REF

= 4.4 V to 36 V

V

CC

I

= 0 mA

REF

= 4.4 V to 36 V

V

CC

= 0 to 5 mA 8 15 mV

REF

0.11

0.21

0.20 0.35 µs

(1)

3.2 3.3 3.399 V

2.3 mS

REF

0.25

0.45mAmA

510mV

V

1. Specification Referred to TJ from -40 to 125 °C. Specification over the -40 to +125 TJ Temperature range
are assured by design, characterization and statistical correlation.

2. Guaranteed by design.

6/17

L5973D Typical characteristics

4 Typical characteristics

Figure 3. Line regulation Figure 4. Shutdown current vs junction

Vo (V)

3.312
Vcc = 12V

3.308
Vo = 3.3V

3.304

3.3

3.296

3.292

3.288

3.284

3.28

3.276

010203040

Tj = 25°C

Tj = 125°C

Vcc (V)

Ishd (µA)

70

60

50

40

30

-50

temperature

Vcc = 12V

0

50 100 150

Tj (°C)

Figure 5. Output voltage vs junction

Vo (V)

1.25

1.24

1.23

1.22

1.21

1.2

-50 0 50 100 150

temperature

Vcc = 12V

Vcc=12V

Tj (°C)

Figure 7. Quiescent current vs junction

Iq (mA)

2

1.8

temperature

Figure 6. Switching frequency vs

junction temperature

Fsw (KHz)

260

250

240

230

220

-50 0 50 100 150

Vcc = 12V
Vo = 3.3V

Tj (°C)

1.6

1.4

1.2

-50

Vcc = 12V
DC = 0%

050

Tj (°C)

100 150

7/17

Typical characteristics L5973D

Figure 8. Junction temperature vs

Tj(°C)

120
110
100

90
80
70
60
50
40
30
20

0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 2.2 2.4 2.6

Figure 10. Efficiency vs output current Figure 11. Efficiency vs output current

output current

Vin=5V
Tamb=25°C

Io(A)

Vo=3.3V

Vo=2.5V

Vo=1.8V

Figure 9. Junction temperature vs

output current

Tj (°C)

120

110

Vin=12V

100

Tamb=25°C

90

80

70

60

50

40

30

20

0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 2.2 2.4 2.6

Io (A)

Vo=5V

Vo=2.5V

Vo=3.3V

95
93
91
89
87
85
83
81
79
77

Efficiency (%)

75
73
71
69
67

0.1 0.3 0.5 0.7 0.9 1.1 1.3 1.5 1.7 1.9 2.1 2.3

Vo=2.5V

Vo=1.8V

Vin=5V

Vo=3.3V

Io (A)

91
89
87
85
83
81
79
77
75

Efficiency (%)

73
71

Vin=12V

69
67
65

0.1 0.3 0.5 0.7 0.9 1.1 1.3 1.5 1.7 1.9 2.1 2.3

Vo=5V

Vo=3.3V

Vo=2.5V

Io (A)

8/17

L5973D Application circuit

5 Application circuit

In figure 6 is shown the demonstration board application circuit, where the input supply
voltage, V
the output voltage is adjustable from 1.235 V to V

Figure 12. Demonstration board application circuit

, can range from 4 V to 25 V due to the rated voltage of the input capacitor and

CC

CC

.

VIN = 4.4V to 25V

C1

10µF

25V

CERAMIC

3.3V

C4

22nF

C3

220pF

VREF

VCC

SYNC.

COMP

R3

4.7K

6

8

2

4

L5973D

3

7

GNDINH

D03IN1440

OUT

1

5

FB

L1 15µH

D1

STPS2L25U

R1

5.6K

R2

3.3K

Table 5. Component list

Reference Part number Description Manufacturer

C1 GRM32DR61E106KA12L 10 µF, 25 V Murata

C2 POSCAP 6TPB330M 330 µF, 6.3 V Sanyo

C3 C1206C221J5GAC 220 pF, 5%, 50 V KEMET

C4 C1206C223K5RAC 22 nF, 10%, 50 V KEMET

R1 5.6 K, 1%, 0.1 W 0603 Neohm

VOUT=3.3V

C2

330µF

6.3V

R2 3.3 K, 1%, 0.1 W 0603 Neohm

R3 4.7 K, 1%, 0.1 W 0603 Neohm

D1 STPS2L25U 2 A, 25 V ST

L1 DO3316P-153 15 µH, 3 A COILCRAFT

9/17

Application circuit L5973D

Figure 13. PCB layout (component side)

Figure 14. PCB layout (bottom side)

Figure 15. PCB layout (front side)

Below some graphs show the T

versus output current in different conditions of the input and

J

output voltage and some efficiency measurements.

10/17

L5973D Application ideas

6 Application ideas

Figure 16. Positive buck-boost regulator

Figure 17. Buck-boost regulator

Figure 18. Dual output voltage with auxiliary winding

11/17

Application ideas L5973D

When an output voltage below the internal reference (1.235 V) is required, the circuit
reported in the figure 18 can been used. In this case the minimum voltage reachable is 0.6 V
and can be easily calculated with the following formula:

V

= V

OUT

FB

- [(V

If the load is not present, a resistor connected between V
to avoid that the voltage across C

- VFB)x(R2 / R1)]

REF

increases.

OUT

and GND is required in order

OUT

The value of this resistor has to be calculated taking into account that the current flowing
through this resistance has to be higher than the current flowing through R

.

2

Figure 19. Output voltage below the 1.235 V internal voltage reference

12/17

L5973D Package mechanical data

7 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

13/17

Package mechanical data L5973D

Table 6. HSOP8 mechanical data

mm inch

Dim

Min Typ Max Min Typ Max

A 1.70 0.0669

A1 0.00 0.10 0.00 0.0039

A2 1.25 0.0492

b 0.31 0.51 0.0122 0.0201

c 0.17 0.25 0.0067 0.0098

D 4.80 4.90 5.00 0.1890 0.1929 0.1969

D1 3 3.1 3.2 0.118 0.122 0.126

E 5.80 6.00 6.20 0.2283 0.2441

E1 3.80 3.90 4.00 0.1496 0.1575

E2 2.31 2.41 2.51 0.091 0.095 0.099

e1.27

h 0.25 0.50 0.0098 0.0197

L 0.40 1.27 0.0157 0.0500

k0° (min), 8° (max)

ccc 0.10 0.0039

Figure 20. Package dimensions

14/17

L5973D Order code

8 Order code

Table 7. Order code

Part number Package Packaging

L5973D HSOP8 (Exposed pad) Tube

L5973D013TR HSOP8 (Exposed pad) Tape and reel

15/17

Revision history L5973D

9 Revision history

pp

Table 8. Revision history

Date Revision Changes

01-Nov-2005 10 Updated package information

22-May-2006 11

13-Nov-2006 12 Typo in order codes

26-Jan-2007 13 Updated Table 4 on page 5

17-Oct-2007 14 Updated Section 5: Application circuit on page 9

24-Oct-2007 15 Updated Table 6 on page 14

07-Jan-2008 16 Updated Table 6 on page 14

Electrical characteristic Tab l e 4 updated, new application idea

Figure 19 added, new template

16/17

L5973D

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