L5973D

2.5A SWITCH STEP DOWN SWITCHING REGULATOR

■ 2.5A INTERNAL SWITCH

■ OPERATING INPUT VOLTAGE FROM 4.4V TO 36V
■ 3.3V / (±2%) REFERENCE VOLTAGE
■ OUTPUT VOLTAGE ADJUSTABLE FROM
1.235V TO 35V
■ LOW DROPOUT OPERATION: 100% DUTY HSOP8 - EXPOSED PAD
CYCLE ORDERING NUMBER: L5973D
■ 250KHz INTERNALLY FIXED FREQUENCY
■ VOLTAGE FEEDFORWARD
■ ZERO LOAD CURRENT OPERATION DESCRIPTION
■ INTERNAL CURRENT LIMITING The L5973D is a step down monolithic power switch-
■ INHIBIT FOR ZERO CURRENT ing regulator with a minimum switch current limit of
CONSUMPTION 2.5A so it is able to deliver more than 2A DC current
■ SYNCHRONIZATION to the load depending on the application conditions.
■ PROTECTION AGAINST FEEDBACK The output voltage can be set from 1.235V to 35V.
DISCONNECTION The high current level is also achieved thanks to an
■ THERMAL SHUTDOWN SO8 package with exposed frame, that allows to re-
duce the Rth(j-amb) down to approximately 40°C/W
The device uses an internal P-Channel D-MOS tran-
sistor (with a typical Rdson of 250mΩ) as switching
APPLICATIONS: element to minimize the size of the external compo-
■ CONSUMER: STB, DVD, TV, VCR,CAR nents.
RADIO, LCD MONITORS An internal oscillator fixes the switching frequency at
■ NETWORKING: XDSL, MODEMS,DC-DC 250KHz.
MODULES Having a minimum input voltage of 4.4V only, it is
■ COMPUTER: PRINTERS, AUDIO/GRAPHIC particularly suitable for 5V bus, available in all com-
CARDS, OPTICAL STORAGE, HARD DISK puter related applications.
DRIVE Pulse by pulse current limit with the internal frequen-
■ INDUSTRIAL: CHARGERS, CAR BATTERY cy modulation offers an effective constant current
DC-DC CONVERTERS short circuit protection.

TEST APPLICATION CIRCUIT

VREF
3.3V 6 OUT L1 15µH VOUT=3.3V
1
VIN = 4.4V to 35V VCC
8 D1
L5973D STPS340U R1
SYNC. 2 5.6K C2
COMP 5 330µF
C1 4 3 7 FB 10V
10µF C4
22nF INH GND
35V R2
CERAMIC 3.3K
C3 R3
220pF 4.7K

D03IN1439

May 2003 1/10

L5973D

PIN CONNECTION

OUT 1 8 VCC
SYNC 2 7 GND
INH 3 6 VREF
COMP 4 5 FB
D98IN955

PIN DESCRIPTION
N° Pin Function
1 OUT Regulator Output.
2 SYNC Master/slave synchronization.
3 INH 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.
4 COMP E/A output for frequency compensation.
5 FB Feedback input. Connecting directly to this pin results in an output voltage of 1.23V. An external
resistive divider is required for higher output voltages.
6 VREF 3.3V VREF. No cap is requested for stability.
7 GND Ground.
8 VCC Unregulated DC input voltage.

THERMAL DATA
Symbol Parameter Value Unit

Rth (j-amb) Thermal Resistance Junction to ambient Max. 40 (*) °C/W

(*) Package mounted on board

ABSOLUTE MAXIMUM RATINGS

Symbol Parameter Value Unit
V8 Input Voltage 40 V

V1 Output DC voltage -1 to 40 V
Output peak voltage at t = 0.1µs -5 to 40 V
I1 Maximum output current int. limit.

V4, V5 Analog pins 4 V

V3 INH -0.3V to VCC

V2 SYNC -0.3 to 4 V

Ptot Power dissipation at Tamb ≤ 60°C 2.25 W

Tj Operating junction temperature range -40 to 150 °C

Tstg Storage temperature range -55 to 150 °C

2/10
 L5973D

ELECTRICAL CHARACTERISTICS (Tj = 25°C, VCC = 12V, unless otherwise specified.)

(*) Specification Referred to Tj from -40 to 125°C (1).
Symbol Parameter Test Condition Min. Typ. Max. Unit
VCC Operating input voltage range Vo = 1.235V; Io = 2A * 4.4 36 V
RDSON Mosfet on Resistance * 0.150 0.5 Ω
Il Maximum limiting current VCC = 4.4V to 36V 2.5 3 3.5 A
fs Switching frequency * 212 250 280 KHz
225 250 275 KHz
Duty cycle 0 100 %
DYNAMIC CHARACTERISTICS (see test circuit ).
V5 Voltage feedback 4.4V < VCC < 36V, 1.220 1.235 1.25 V
20mA < IO < 2A * 1.198 1.235 1.272 V
η Efficiency VO = 5V, VCC = 12V 90 %
DC CHARACTERISTICS
Iqop Total Operating Quiescent * 3 5 mA
Current
Iq Quiescent current Duty Cycle = 0; VFB = 1.5V 2.5 mA
Iqst-by Total stand-by quiescent current Vinh > 2.2V * 50 100 µA
VCC = 36V; Vinh > 2.2V * 80 150 µA
INHIBIT
INH Threshold Voltage Device ON 0.8 V
Device OFF 2.2 V
ERROR AMPLIFIER
VOH High level output voltage VFB = 1V 3.5 V
VOL Low level output voltage VFB = 1.5V 0.4 V
Io source Source output current VCOMP = 1.9V; VFB = 1V 200 300 µA
Io sink Sink output current VCOMP = 1.9V; VFB = 1.5V 1 1.5 mA
Ib Source bias current 2.5 4 µA
DC open loop gain RL = ∞ 50 57 dB
gm Transconductance Icomp = -0.1mA to 0.1mA 2.3 mS
VCOMP = 1.9V
SYNC FUNCTION
High Input Voltage VCC = 4.4V to 36V 2.5 VREF V
Low Input Voltage VCC = 4.4V to 36V 0.74 V
Slave Sink Current Vsync = 0.74V 0.11 0.25 mA
Vsync = 2.33V 0.21 0.45 mA
Master Output Amplitude Isource = 3mA 2.75 3 V
Output Pulse Width no load, Vsync = 1.65V 0.20 0.35 µs
REFERENCE SECTION
Reference Voltage 3.234 3.3 3.366 V
IREF = 0 to 5mA * 3.2 3.3 3.399 V
VCC = 4.4V to 36V
Line Regulation IREF = 0mA 5 10 mV
VCC = 4.4V to 36V
Load Regulation IREF = 0 to 5mA 8 15 mV
Short Circuit Current 10 8 30 mA
Notes: 1. Specification over the -40 to +125 Tj Temperature range are assured by design, characterization and statistical correlation.
2. Guaranteed by design.

3/10
L5973D

Figure 1. Line Regulation Figure 4. Shutdown Current vs.Junction

Vo (V)
Temperature
3.312 Ishd (µA)
3.308 Vcc = 12V 70
Vo = 3.3V Tj = 25°C
3.304
3.3 60
Vcc = 12V
3.296
3.292
Tj = 125°C 50
3.288
3.284
40
3.28
3.276
0 10 20 30 40 30
Vcc (V)
-50 0 50 100 150
Tj (°C)
Figure 2. Output Voltage vs. Junction
Temperature Figure 5. Switching Frequency vs.Junction
Vo (V) Temperature
1.25
Fsw (KHz)
260
1.24

250
1.23

1.22 240
Vcc = 12V
1.21 230 Vcc = 12V
Vcc=12V Vo = 3.3V

1.2 220
-50 0 50 100 150 -50 0 50 100 150
Tj (°C) Tj (°C)

Figure 3. Quiescent Current vs. Junction

Temperature
Iq (mA)
2

1.8

1.6
Vcc = 12V
DC = 0%
1.4

1.2

-50 0 50 100 150

Tj (°C)

4/10
 L5973D

APPLICATION CIRCUIT
In figure 6 is shown the demo board application circuit, where the input supply voltage, Vcc, can range from 4.4V
to 25V due to the rated voltage of the input capacitor and the output voltage is adjustable from 1.235V to Vcc.

Figure 6. Demo board Application Circuit

VREF
3.3V 6 OUT L1 15µH VOUT=3.3V
1
VIN = 4.4V to 25V VCC
8 D1
L5973D STPS2L25U R1
SYNC. 2 5.6K C2
COMP 5 330µF
C1 4 3 7 FB 6.3V
10µF C4
22nF INH GND
25V R2
CERAMIC 3.3K
C3 R3
220pF 4.7K

D03IN1440

Table 1. Component List

Reference Part Number Description Manufacturer

C1 10µF, 25V TOKIN

C2 POSCAP 6TPB330M 330µF, 6.3V Sanyo

C3 C1206C221J5GAC 220pF, 5%, 50V KEMET

C4 C1206C223K5RAC 22nF, 10%, 50V KEMET

R1 5.6K, 1%, 0.1W 0603 Neohm

R2 3.3K, 1%, 0.1W 0603 Neohm

R3 4.7K, 1%, 0.1W 0603 Neohm

D1 STPS2L25U 2A, 25V ST

L1 DO3316P-153 15µH, 3A COILCRAFT

5/10
L5973D

Figure 7. PCB layout (component side)

42mm

34mm

Figure 8. PCB layout (bottom side)

Figure 9. PCB layout (front side)

Below some graphs show the Tj versus output current in different conditions of the input and output voltage and
some efficiency measurements.

6/10
 L5973D

Figure 10. Junction Temperature vs. Output Figure 12. Efficiency vs. Output Current
Current (VCC = 5V) (VCC = 5V)
Tj(°C)
120 95
110 Vo=3.3V 93
Vin=5V Vo=2.5V
Vo=3.3V
100 Tamb=25°C 91
89
90 87

Efficiency (%)
80 85
Vo=1.8V Vo=2.5V
70 83
81
60
79 Vo=1.8V
50 77
40 75
73
30 Vcc=5V
71
20 69
0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 2.2 2.4 2.6 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
Io(A) Io (A)

Figure 11. Junction Temperature vs. Output Figure 13. Efficiency vs. Output Current
Current (VCC = 12V) (VCC = 12V)
Tj (°C)
120
91
110 Vo=5V 89
Vin=12V Vo=3.3V
100 Tamb=25°C 87 Vo=5V
90 85
Efficiency (%)

83
80 Vo=2.5V Vo=3.3V
81
70 79
77 Vo=2.5V
60
75
50 73
40 71 Vcc=12V
30 69
67
20
65
0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 2.2 2.4 2.6 0.1 0.3 0.5 0.7 0.9 1.1 1.3 1.5 1.7 1.9 2.1 2.3
Io (A)
Io (A)

7/10
L5973D

APPLICATION IDEAS

Figure 14. Positive Buck-Boost regulator

L1 D2
15uH STPS2L25U VOUT=12V/0.6A
VIN=5V Vcc OUT
8 1
D1
L5973D STPS2L25U 24k
COMP FB
4 5 C4
C1
2 6 7 3 M1 100uF
10uF
C2 C3 STN4NE03L 16V
10V
220pF 22nF SYNC VREF GND INH 2.7k
Ceramic
R3
4.7k 3.3V

Figure 15. Buck-Boost regulator

L1
OUT 15uH
VIN=5V Vcc
8 1
D1
L5973D STPS2L25U
COMP FB 2.7k VOUT=-12V/0.6A
4 5
C1 C2
10uF 10uF 2 6 7 3
10V 25V C3 C4 C5
22nF SYNC VREF GND INH 100uF
Ceramic Ceramic 220pF 24k
R3 16V
4.7k 3.3V

Figure 16. Dual output voltage with auxiliary winding

D2 VOUT1=5V
N1/N2=2 1N4148 50mA

VIN=12V VCC Lp=22uH

OUT
8 1
VOUT=3.3V
D1
0.5A
STPS25L25U
COMP L5973D FB
4 5 C4 C5
C1
2 6 7 3 100uF 47uF
10uF
C3 10V 10V
25V C2
22nF SYNC VREF GND INH
Ceramic 220pF
R3
4.7k 3.3V

8/10
 L5973D

mm inch
DIM. OUTLINE AND
MIN. TYP. MAX. MIN. TYP. MAX.
MECHANICAL DATA
A 1.350 1.750 0.531 0.069

A1 0.100 0.250 0.004 0.010

A2 1.100 1.650 0.043 0.065

B 0.330 0.510 0.013 0.020

C 0.190 0.250 0.07 0.010

D 4.800 5.000 0.189 0.197

E 3.800 4.000 0.150 0.157

e 1.270 0.05

H 5.800 6.200 0.228 0.244

h 0.250 0.500 0.010 0.020

L 0.400 1.270 0.016 0.05

k 0˚ (min), 8˚ (max)

ddd 0.100 0.010

HSOP8
(1) Dimension D does not include mold flash, protusions (Exposed Pad)
or gate burrs shall not exeed 0.15mm (both side).

Exposed Pad:
D1 = 3.1mm
E1 = 2.41mm

7195016

9/10
L5973D

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. 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

 2003 STMicroelectronics - All Rights Reserved
STMicroelectronics GROUP OF COMPANIES
Australia - Brazil - Canada - China - Finland - France - Germany - Hong Kong - India - Israel - Italy - Japan -Malaysia - Malta - Morocco -
Singapore - Spain - Sweden - Switzerland - United Kingdom - United States.
http://www.st.com

10/10