February 2009 Rev 18 1/28
28
L4973
3.5 A step down switching regulator
Features
■Up to 3.5 A step down converter
■Operating input voltage from 8 V to 55 V
■3.3 V and 5.1 V (±1%) fixed output, and
adjustable outputs from:
– 0.5 V to 50 V (3.3 type)
– 5.1 V to 50 V (5.1 type)
■Frequency adjustable up to 300 kHz
■Voltage feed forward
■Zero load current operation (min. 1 mA)
■Internal current limiting (pulse by pulse and
HICCUP mode)
■Precise 5.1 V (1.5%) reference voltage
externally available
■Input/output synchronization function
■Inhibit for zero current consumption (100 mA
typ. at VCC = 24 V)
■Protection against feedback disconnection
■Thermal shutdown
■Output over voltage protection
■Soft-start function
Description
The L4973 is a step down monolithic power
switching regulator delivering 3.5 A at fixed
voltages of 3.3 V or 5.1 V and using a simple
external divider output adjustable voltage up to
50V. Realized in BCD mixed technology, the
device uses an internal power D-MOS transistor
(with a typical RDS(on) of 0.15 Ω) to obtain very
high efficiency and very fast switching times.
Switching frequency up to 300 kHz are achievable
(the maximum power dissipation of the packages
must be observed).
A wide input voltage range between 8 V to 55 V
and output voltages regulated from 3.3 V to 40 V
cover the majority of the today applications.
Features of this new generation of DC-DC
converter includes pulse by pulse current limit,
hiccup mode for output short circuit protection,
voltage feed forward regulation, soft-start,
input/output synchronization, protection against
feedback loop disconnection, inhibit for zero
current consumption and thermal shutdown.
Packages available are in plastic dual in line, DIP-
18 (12+3+3) for standard assembly, and SO20
(12+4+4) for SMD assembly.
DIP-18 (12+3+3) SO-20 (12+4+4)
www.st.com
Figure 1. Internal schematic diagram
L4973
VCC (8V to 55V)
CIN C2
ROSC
COSC D1
L1
COUT
VO(3.3V or 5.1V)
CBOOT
4,5,6,10
13,14,15
7
9
8
1
11
3
D97IN554A
17
RCOMP
CCOMP
CSS
2
16
12
Contents L4973
2/28
Contents
1 Block diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
2 Pin settings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
2.1 Pin connection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
2.2 Pin description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
3 Electrical data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
3.1 Maximum ratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
3.2 Thermal data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
4 Electrical characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
5 Evaluation board . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
6 Application circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
7 Typical characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
8 Application ideas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
9 Package mechanical data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
10 Order code . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
11 Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
L4973 Block diagram
3/28
1 Block diagram
Figure 2. Block diagram
2 Pin settings
2.1 Pin connection
Figure 3. Pin connection (top view)
VREF
GOOD 5.1V
COMP
VFB
SYNC
BOOT
DRIVER
HICCUP CURRENT
LIMITING
INTERNAL
REFERENCE
SS
INH
ZERO CURRENT
INHIBIT
D94IN161B
+
-
3.3V
V5.1
E/A
SOFT
START
5.1V
3.3V
THERMAL
SHUTDOWN
INTERNAL
SUPPLY 5.1V
-
+
PWM
CURRENT
LIMITING
R
S
Q
Q
CBOOT
CHARGE
OSCILLATOR
OUTOUTGNDOSC
V
CC
V
CC
17(19)
11(12)
12(13)
18(20)
1(1) 2(2) 3(3)
9(10)
8(9)7(8)16(18)10(11)
4,5,6,13,14,15
(4,5,6,7,14,15,16,17)
Pin x = Powerdip
Pin
(
x
)
= S020
OSC
OUT
OUT
GND
GND
VCC
GND
VCC
BOOT
1
3
2
4
5
6
7
8
9 INH
VFB
COMP
GND
GND
GND
V5.1
SS
SYNC18
17
16
15
14
12
13
11
10
D94IN162A
OSC
OUT
OUT
GND
GND
GND
GND
VCC
VCC
VFB
COMP
GND
GND
GND
GND
V5.1
SS
SYNC1
3
2
4
5
6
7
8
9
18
17
16
15
14
12
13
11
19
10
20
BOOT INH
D94IN163A
DIP -18 (12+3+3) SO20 (12+4+4)
Pin settings L4973
4/28
2.2 Pin description
Note: 1 The maximum power dissipation of the package must be observed.
Table 1. Pin description
N° Pin
Name Description
DIP-18 SO-20
11 12 COMP E/A output to be used for frequency compensation
10 11 INH
A logic signal (active high) disables the device (sleep
mode operation). If not used it must be connected to
GND; if floating the device is disabled.
9 10 BOOT
A capacitor connected between this pin and the output
allows to drive the internal D-MOS.
18 20 SYNC Input/Output synchronization.
7,8 8,9 VCC Unregulated DC input voltage
2,3 2,3 OUT Stepdown regulator output.
12 13 VFB
Stepdown feedback input. Connecting the output
directly to this pin results in an output voltage of 3.3 V
for the L4973V3.3 and 5.1 V for L4973V5.1. An external
resistive divider is required for higher output voltages.
For output voltage resistive divider is required for higher
output voltages. For output voltage less than 3.3 V, see
Note: 1 and Figure 33.
16 18 V5.1 Reference voltage externally available.
4,5,6
13,14,15
4,5,6,7
14,15,16,17 GND Signal ground
1 1 OSC
An external resistor connected between the unregulated
input voltage and Pin 1 and a capacitor connected from
Pin 1 to ground fixes the switching frequency. (Line feed
forward is automatically obtained)
L4973 Electrical data
5/28
3 Electrical data
3.1 Maximum ratings
3.2 Thermal data
Table 2. Absolute maximum ratings
Symbol
Parameter Value Unit
DIP-18 S0-20
V
7
,V
8
V
9
,V
8
Input voltage 58 V
V
2
,V
3
V
2
,V
3
Output DC voltage
Output peak voltage at t = 0.1 μs f = 200 kHz
-1
- 5
V
V
I
2
,I
3
I
2
,I
3
Maximum output current int. limit.
V
9
-V
8
V
10
-V
8
14 V
V
9
V
10
Bootstrap voltage 70 V
V
11
V
12
Analogs input voltage (V
CC
= 24 V)12 V
V
17
V
19
Analogs input voltage (V
CC
= 24 V) 13 V
V
12
V
13
(V
CC
= 20 V) 6
-0.3
V
V
V
18
V
20
(V
CC
= 20 V) 5.5
0.3
V
V
V
10
V
11
Inhibit V
CC
-0.3
V
V
P
tot
DIP 12+3+3
Power dissipation a Tpins ≤ 90 °C
(T
A
= 70 °C no copper area)
(T
A
= 70 °C 4 cm copper area on PCB)
5
1.3
2
W
W
W
SO-20
Power dissipation a T
pins
= 90 °C 4W
T
J
,T
STG
Junction and storage temperature -40 to 150 °C
Table 3. Thermal data
Symbol Parameter DIP-18 SO-20 Unit
RthJP Maximum thermal resistance junction-pin 12 15 °C/W
RthJA Maximum thermal resistance junction-ambient 60 (1)
1. Package mounted on board
80 (1) °C/W
Electrical characteristics L4973
6/28
4 Electrical characteristics
Table 4. Electrical characteristics
(Refer to the test circuit,V
CC
= 24 V; T
J
= 25 °C, C
OSC
= 2.7 nF;
R
OSC
= 20 kΩ; unless otherwise specified)
Symbol Parameter Test condition Min Typ Max Unit
Dynamic characteristics
Input voltage range (1) V
O
= V
REF
to 40 V; I
O
= 3.5A (2) 855V
Output voltage
L4973V5.1
I
O
= 1 A 5.05 5.1 5.15 V
I
O
= 0.5 A to 3.5 A V
CC
= 8 V
to 55 V
5.00 5.1 5.20 V
(2) 4.95 5.1 5.25 V
Output voltage
L4973V3.3
I
O
= 1 A 3.326 3.36 3.393 V
I
O
= 0.5 A to 3.5 A V
CC
= 8 V
to 40 V
3.292 3.36 3.427 V
(2) 3.26 3.36 3.46 V
R
DS(on
) V
CC
= 10.5 V I
O
= 3.5 A 0.15 0.22 Ω
(2) 0.35 Ω
Maximum limiting
current V
CC
= 8 V to 55 V
(2) 3.8 4.5 5.5 A
4 4.5 5.5 A
ηEfficiency V
O
= 5.1 V; I
O
= 3.5 A 90 %
V
O
= 3.3 V; I
O
= 3.5 A 85 %
Switching frequency (2) 90 100 110 kHz
Supply voltage ripple
rejection
V
i
= V
CC
+2 V
RMS
V
O
= V
ref
;
I
O
= 1 A; f
ripple
= 100 Hz 60 dB
Δfs
w
Switching frequency
stability vs., supply
voltage
V
CC
= 8 V to 55 V 2 5 %
Reference section
Reference voltage I
ref
= 0 to 20 mA;
V
CC
= 8 to 55 V
5.025 5.1 5.175 V
(2) 4.950 5.1 5.250 V
Line regulation I
ref
= 0 mA;
V
CC
= 8 to 55 V 5 10 mV
Load regulation V
ref
= 0 to 5 mA;
V
CC
= 0 to 20 mA
2
6
10
25
mV
mV
Short circuit current 30 65 100 mA
L4973 Electrical characteristics
7/28
Soft-start
Soft-start charge current 30 45 60 μA
Soft-start discharge
current 15 22 30 μA
Inhibit
High level voltage (2) 3.0 V
Low level voltage (2) 0.8 V
I
source
high level V
INH
= 3 V (2) 10 16 50 μA
I
source
low level V
INH
= 0.8 V (2) 10 15 50 μA
DC characteristics
Total operating
quiescent current Duty cycle = 50 % 4 6 mA
Quiescent current Duty cycle = 0 2.7 4 mA
Total stand-by quiescent
current
V
CC
= 24 V; V
INH
= 5 V 100 200 μA
V
CC
= 55 V; V
INH
= 5 V 150 300 μA
Error amplifier
High level output voltage 11.0 V
Low level output voltage 0.65 V
Source bias current 1 2 3 μA
Source output current 200 300 600 μA
Sink output current 200 300 μA
Supply voltage ripple
rejection
V
COMP
= VFB
C
REF
= 4.7 μF 1-5 mA load
current
60 80 dB
DC open loop gain R
L
= ∞ 50 60 dB
Transconductance I
comp
= -0.1 to 0.1 mA;
V
comp
= 6 V 2.5 mS
Oscillator section
Ramp valley 0.78 0.85 0.92 V
Ramp peak V
CC
= 8 V
V
CC
= 55 V
1.9
9
2.1
9.6
2.3
10.2
V
V
Maximum duty cycle 95 97 %
Table 4. Electrical characteristics (continued)
(Refer to the test circuit,V
CC
= 24 V; T
J
= 25 °C, C
OSC
= 2.7 nF;
R
OSC
= 20 kΩ; unless otherwise specified)
Symbol Parameter Test condition Min Typ Max Unit
Electrical characteristics L4973
8/28
Maximum frequency Duty cycle = 0%;
R
OSC
=13 kΩ; C
OSC
= 820 pF; 300 kHz
Sync function
High input voltage V
CC
= 8 V to 55 V 3.5 V
Low input voltage V
CC
= 8 V to 55 V 0.9 V
Slave sink current 0.15 0.25 0.45 mA
Master output amplitude I
source
= 3 mA 4 4.5 V
Output pulse width No load, V
sync
= 4.5 V 0.20 0.35 μs
1. Pulse testing with a low duty cycle
2. Specifications referred to TJ from -40 °C to 125 °C.
Table 4. Electrical characteristics (continued)
(Refer to the test circuit,V
CC
= 24 V; T
J
= 25 °C, C
OSC
= 2.7 nF;
R
OSC
= 20 kΩ; unless otherwise specified)
Symbol Parameter Test condition Min Typ Max Unit
L4973 Evaluation board
9/28
5 Evaluation board
Figure 4. Evaluation board circuit
Table 5. Component list (fsw = 150 kHz, VOUT = 5 V)
Reference Description Part number Manufacturer
R1 Resistor 15 kΩ 1%
R2 Resistor 15 kΩ 1%
R3 Resistor 2.7 kΩ 1%
R4 Resistor 4.99 kΩ 1%
R5 Not mounted
R6 Not mounted
R7 Not mounted
C1 Capacitor 2.7 nF 5%
C2 Capacitor 470 nF 5%
C3 Capacitor 1 μF 5%
C4 Capacitor 22 nF 5%
C5 Capacitor 150 pF 5%
C6 Not mounted
C7 Not mounted
C8 Capacitor 220 nF 5%
C9 Capacitor 220 nF 5%
C10 Capacitor 470 μF 63V EKY-630ELL471ML20S Nippon Chemi-con
signal GND
GND plane
signal GND
C4
22n
C4
22n
C3A
1u
C3A
1u
C13
NM
C13
NM
R7
NM
R7
NM
R2
15k
R2
15k
C11
150u 50v
C11
150u 50v
1
2
3
JP1JP1
R5
NM
R5
NM
C5
150p
C5
150p
C3
NM
C3
NM
GNDGND
C7
NM
C7
NM
R6 NMR6 NM
GNDGND
OSC
1
OUT 2
OUT 3
GND 4
GND 5
GND 6
VCC 7
VCC 8
BOOT 9
INH 10
COMP
11
VFB
12
GND 13
GND 14
GND 15
V5.1
16
SS
17
SYNC 18
U1
L4973 DIP 18
U1
L4973 DIP 18
L1 68uHL1 68uH
C9
220n
C9
220n
R3
2.7k
R3
2.7k
C2
470n
C2
470n
C12
150u 50v
C12
150u 50v
C1
2.7n
C1
2.7n
C6
NM
C6
NM
Q2
NM
Q2
NM
R1
15k
R1
15k
R4
4.99k
R4
4.99k
1 2
D1
STPS5L60
D1
STPS5L60
VoutVout
VinVin
C10
470u 63v
C10
470u 63v
C8 220nC8 220n
C14
NM
C14
NM
SYNCHSYNCH
Evaluation board L4973
10/28
Reference Description Part number Manufacturer
C11 Capacitor 150 μF 35 V EKY-350ELL151MHB5D Nippon Chemi-con
C11 Capacitor 150 μF 35 V EKY-350ELL151MHB5D Nippon Chemi-con
C13 Capacitor 100 nF 5 %
C14 Not mounted
L1 68 μH IRMS = 3.4 A ISAT = 6.7 A DO5040H-683MLD Coilcraft
U1 L4973V3.3 STMicroelectronics
Table 6. Resistor divider for VOUT = 12 V
Reference Description Part number Manufacturer
R3 Resistor 2.7 kΩ 1%
R4 Resistor 1 kΩ 1%
Table 7. Resistor divider for VOUT = 3.3 V
Reference Description Part number Manufacturer
R3 Resistor 2.7 kΩ 1%
R4 Not mounted
Table 5. Component list (fsw = 150 kHz, VOUT = 5 V) (continued)
L4973 Evaluation board
11/28
Figure 5. Evaluation board (components side)
Figure 6. Evaluation board (solder side)
Application circuit L4973
12/28
6 Application circuit
Figure 7. Application circuit (see Figure 4 part list)
Figure 8. Application circuit (see Figure 4 part list)
L4973V5.1
VCC
C1 C2
R2
C7
C3 C4 C5
C6
R1 D1
L1
3 x
C0 C12
Vo
C8
4,5,6
13,14,15
7,8 10 18 9
1
17
16
INH SYNC
11 2,3
12
D97IN665A
L4973V3.3
VCC
C1 C2
R2
C7
C3 C4 C5
C6
R1 D1
L1
3 x
C0 C12
Vo
C8
4,5,6
13,14,15
7,8 10 18 9
1
17
16
INH SYNC
11 2,3
12
D97IN664A
L4973 Typical characteristics
13/28
7 Typical characteristics
Figure 9. Quiescent drain current vs.
input voltage (0% duty cycle)
Figure 10. Quiescent drain current vs.
junction temperature
Figure 11. Stand by drain current vs.
input voltage
Figure 12. Reference voltage vs.
junction temperature (pin 16)
0 1020304050V
CC(V)
2.0
2.5
3.0
3.5
4.0
4.5
5.0
Ibias
(mA)
Tamb=25˚C
0% DC
D97IN633A
100KHz-R2=20K
C7=2.7nF
200KHz-R2=22K
C7=1.2nF
0Hz
-50 0 50 100 T
j(
˚C
)
2.5
3.0
3.5
4.0
Ibias
(mA)
D97IN634
100KHz-R2=20K
C7=2.7nF
200KHz-R2=22K
C7=1.2nF
0Hz
0% DC
VCC = 35V
0 1020304050V
CC(V)
50
100
150
Ibias
(μA)
D97IN635A
25˚C
125˚C
Vinh = 5V
-40 0 40 80 T
j(
˚C
)
-20 20 60 100
5.0
5.05
5.1
5.15
VREF
(V)
D97IN637
Vcc=35V
Pin 16
Typical characteristics L4973
14/28
Figure 13. Reference voltage vs.
input voltage (pin 16)
Figure 14. Reference voltage vs.
reference input current
Figure 15. Inhibit current vs. inhibit
voltage (pin 10)
Figure 16. Line regulation (see Figure 7)
0 1020304050V
CC(V)
5.0
5.05
5.1
5.15
VREF
(V)
D97IN636A
Tj=25˚C
Pin 16
0 1020304050I
REF(mA)
4.9
5.0
5.1
5.2
VREF
(V)
D97IN638
Tj=25˚C
Vcc=10V
Vcc=40V
0 15 Vinh
(
V
)
105
-50
0
50
100
Iinh
(μA)
D97IN651
Tj=0˚C
Tj=25˚C
Tj=125˚C
Vcc=35V
Pin 10
0 1020304050V
CC(V)
5.06
5.08
5.1
5.12
VO
(V)
D97IN639A
Tj=25˚C
Tj=125˚C
IO = 1A
L4973 Typical characteristics
15/28
Figure 17. Load regulation (see
Figure 7)
Figure 18. Line regulation (see Figure 8)
Figure 19. Load regulation (see
Figure 4)
Figure 20. Switching frequency vs.
R2 and C7 (Figure 4)
0123I
O(A)
5.0
5.05
5.1
5.15
VO
(V)
D97IN640
Tj=25˚C
Tj=125˚C
VCC = 35V
0 1020304050V
CC(V)
3.3
3.31
3.32
3.34
VO
(V)
3.33
3.35
D97IN660A
Tj=25˚C
Tj=125˚C
IO = 1A
0123I
O(A)
3.3
3.31
3.33
3.35
VO
(V)
3.32
3.34
D97IN661
Tj=25˚C
Tj=125˚C
VCC = 35V
0 20 40 60 80 R2(K
Ω
)
5
10
20
50
100
200
500
fsw
(KHz)
D97IN630
0.82nF
1.2nF
2.2nF
3.3nF
4.7nF
5.6nF
Tamb=25˚C
Typical characteristics L4973
16/28
Figure 21. Switching frequency vs.
input voltage
Figure 22. Switching frequency vs.
junction temperature
(see Figure 4)
Figure 23. Dropout voltage between pin
7,8 and 2,3
Figure 24. Efficiency vs. output voltage
(see Figure 6)
0 1020304050V
CC(V)
90
95
100
105
fsw
(KHz)
D97IN631
Tamb=25˚C
-50 0 50 100 T
j(
˚C
)
90
95
100
105
fsw
(KHz)
D97IN632
0123I
O(A)
0
0.2
0.4
0.6
ΔV
(V)
D97IN643
Tj=0˚C
Tj=125˚C
Tj=25˚C
0102030 V
O(V)40
86
88
90
92
η
(%)
94
96
98
D97IN641
200KHz
100KHz
IO = 3A
VCC = 50V
L4973 Typical characteristics
17/28
Figure 25. Dropout voltage between pin
7,8 and 2,3
Figure 26. Efficiency vs. output voltage
(see Figure 4)
Figure 27. Efficiency vs. output voltage
(Diode STPS745D)
Figure 28. Efficiency vs. output current
(see Figure 7)
0123I
O(A)
0
0.2
0.4
0.6
ΔV
(V)
D97IN643
Tj=0˚C
Tj=125˚C
Tj=25˚C
0102030 V
O(V)40
86
88
90
92
η
(%)
94
96
98
D97IN641
200KHz
100KHz
IO = 3A
VCC = 50V
0101520 V
O(V)30525
86
88
90
92
η
(%)
94
96
98
D97IN642
200KHz
100KHz
IO = 3A
VCC = 35V
0123I
O(A)
80
85
90
95
η
(%)
D97IN645
Vcc=12V
Vcc=24V
Vcc=48V
VO = 5.1V
fsw = 100KHz
Typical characteristics L4973
18/28
Figure 29. Efficiency vs. output current
(see Figure 7)
Figure 30. Efficiency vs. output current
(see Figure 8)
Figure 31. Efficiency vs. output current
(see Figure 8)
Figure 32. Power dissipation vs. input
voltage (device only)
(see Figure 7)
0123I
O(A)
75
80
85
90
η
(%)
D97IN646
Vcc=12V
Vcc=24V
Vcc=48V
VO = 5.1V
fsw = 200KHz
0123I
O(A)
75
80
85
90
η
(%)
D97IN644
Vcc=12V
Vcc=24V
Vcc=48V
VO = 3.3V
fsw = 100KHz
0123I
O(A)0.5 1.5 2.5 3.5
70
75
85
η
(%)
80
90
D97IN662
Vcc=48V
Vcc=12V
Vcc=24V
VO = 3.3V
fsw = 200KHz
0 10 30 40 Vcc
(
V
)
20 50
0
0.5
1.0
1.5
Pdiss
(W)
D97IN647A
IO=3.5A
IO=3A
IO=2A
IO=2.5A
VO = 5.1V
fsw = 100KHz
L4973 Typical characteristics
19/28
Figure 33. Power dissipation vs. output
voltage (device only)
Figure 34. Pulse by pulse limiting
current vs.
junction temperature
Figure 35. Load transient Figure 36. Line transient
0 5 15 20 VO(V)10 25 30
0
0.5
1.0
1.5
Pdiss
(W)
2.0
2.5
3.0
D97IN648
IO=3.5A
IO=3A
IO=1A
IO=2A
IO=2.5A
VCC = 35V
fsw = 100KHz
-40 -20 60 80 T
j(
˚C
)
0 12020 40 100
4.2
4.4
4.6
4.8
Ilim
(A)
5
5.2
D97IN652
Vcc=35
1
2
IO
(A)
3
2
1
VO
(mV)
100
0
-100
D97IN649
T
T
200μs/DIV
VCC = 35V
fsw = 100KHz
2
1
D97IN650
VCC
(V)
30
20
10
VO
(mV)
100
0
-100
1ms/DIV
IO = 1A
fsw = 100KHz
Typical characteristics L4973
20/28
Figure 37. Source current rise and fall
time, pin 2, 3 (see Figure 4)
Figure 38. Soft-start capacitor selection
vs. inductor and V
CC
max (ref.
AN938)
Figure 39. Soft-start capacitor selection
vs. inductor and V
CC
max (ref.
AN938)
Figure 40. Open loop frequency and
phase of error amplifier
25 30 35 40 Vi
(
V
)
5045
0
50
100
150
Lomax
(μH)
200
250
300
D97IN653
Css=100nF
Css=220nF
Css=470nF
Css=680nF
Css=820nF
Css=1μF
fsw = 100KHz
15 20 25 30 Vi
(
V
)
4035 45 50
0
50
100
150
Lomax
(μH)
D97IN654
Css=22nF
Css=33nF
Css=47nF
Css=56nF
Css=68nF
fsw = 200KHz
10 103105107f
(
Hz
)
102104106108
-200
-150
-100
-50
GAIN
(dB)
0
50
Phase
0
45
90
135
D97IN663
GAIN
Phase
L4973 Application ideas
21/28
8 Application ideas
Figure 41. 3.5 A at VO < 3.3 V (see part list Figure 4)
Figure 42. 12 V to 3.3 V high performance buck converter (fsw = 200 kHz)
L4973V3.3
VCC
C1 C2
R2
C7
C3 C4
C5
C6
R1 D1
L1
3 x
C0
Vo
C8
4,5,6
13,14,15
7,8 10 18 9
1
17
INH SYNC
11
2,3
12
16
R3
D97IN666A
R5
VPR5R3
1 3.6K 4.7K
1.5 2K 2K
2 4.7K 3.6K
2.5 7.5K 3.6K
3 5.1K 1K
VO=3.36-1.74• R3
R5
L1 KoolMm 77120- 24 Turns- 0.9mm
D1 STPS1025
L4973V3.3
VCC
12V±5%
C1
560uF-25V
HFQ
Panasonic
C2
220nF
R2
22k
C7
1.2nF
C3
33nF
C4
1uF
C5
220pF
C6
22nF
R1
9k1
D1
L1
C9
470uF-25V
HFQ
Panasonic
Vo=3.33V
Io=3.5A
C8
220nF
4,5,6
13,14,15
7,8 10 18 9
1
17
16
INH SYNC
11
2,3
12
0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 Io(A)
80
82
84
86
88
90
92
η
(%)
D97IN668A
Application ideas L4973
22/28
Figure 43. Synchronization example
Figure 44. Multi output not isolated (pin out referred to DIP12+3+3)
L4973 L4973
18 18
VCC2
D97IN669
1
7,8
VCC1
1
7,8
4,5,6
13,14,15
4,5,6
13,14,15
L4973 L4973
18 18
VCC
1
7,8
1
7,8
4,5,6
13,14,15
4,5,6
13,14,15
L4973
VCC
C1 C2
R2
C7
C3 C4 C5
C6
R1 D1
L1
C9 C10
Vo1
C8
4,5,6
13,14,15
7,8 10 18 9
1
17
16
INH SYNC
11 2,3
12
C11
Vo2
n1
n2
D2
D97IN667A
VO2 = VO1
n1 + n2
n1
PO2 < 20% PO1
L4973 Package mechanical data
23/28
9 Package mechanical data
In order to meet environmental requirements, ST offers these devices in different grades of
ECOPACK® packages, depending on their level of environmental compliance. ECOPACK®
specifications, grade definitions and product status are available at: www.st.com. ECOPACK
is an ST trademark.
Package mechanical data L4973
24/28
Table 8. DIP-18 mechanical data
Dim.
mm. inch
Min Typ Max Min Typ Max
a1 0.51 0.020
B 0.85 1.40 0.033 0.055
b 0.50 0.020
b1 0.38 0.50 0.015 0.020
D 24.80 0.976
E 8.80 0.346
e 2.54 0.100
e3 20.32 0.800
F 7.10 0.280
I 5.10 0.201
L 3.30 0.130
Z 2.54 0.100
Figure 45. Package dimensions
L4973 Package mechanical data
25/28
Table 9. SO-20 mechanical 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) 12.60 13.00 0.496 0.512
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
Figure 46. Package dimensions
Order code L4973
26/28
10 Order code
Table 10. Order code
Part number Package Packaging
L4973D3.3, E-L4973D3.3 SO-20 Tube
L4973D3.3-013TR, E-L4973D3.3-TR SO-20 Tape and reel
L4973D5.1 SO-20 Tube
L4973D5.1-013TR SO-20 Tape and reel
L4973V3.3, E-L4973V3.3 DIP-18 Tube
L4973V5.1, E-L4973V5.1 DIP-18 Tube
L4973 Revision history
27/28
11 Revision history
Table 11. Document revision history
Date Revision Changes
12-Sep-2001 13 First Issue
07-May-2005 14 Updated the Layout look & feel.
Changed name of the D1 on the fig. 5.
14-Dec-2005 15 Added the ECOPACK part numbers in the Table 1. Order Codes.
06-Dec-2006 16 The document has been reformatted, and order codes updated
07-May-2007 17 New data on Ta b l e 4
26-Feb-2009 18 Updated Section 5: Evaluation board on page 9
L4973
28/28
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