L4973
3.5 A step down switching regulator
Features
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■
■
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 V
CC
= 24 V)
Protection against feedback disconnection
Thermal shutdown
Output over voltage protection
Soft-start function
DIP-18 (12+3+3)
SO-20 (12+4+4)
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 R
DS(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.
8
12
9
1
4,5,6,10
13,14,15
C
BOOT
V
O
(3.3V or 5.1V)
L1
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Figure 1.
Internal schematic diagram
V
CC
(8V to 55V)
R
OSC
7
L4973
16
17
11
C
IN
C2
3
2
R
COMP
C
OSC
C
SS
C
COMP
D1
C
OUT
D97IN554A
February 2009
Rev 18
1/28
www.st.com
28
Contents
L4973
Contents
1
2
Block diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
Pin settings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
2.1
2.2
Pin connection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
Pin description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
3
Electrical data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
3.1
3.2
Maximum ratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Thermal data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
4
5
6
7
8
9
10
11
Electrical characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Evaluation board . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Application circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
Typical characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Application ideas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
Package mechanical data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
Order code . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
2/28
L4973
Block diagram
1
Block diagram
Figure 2.
Block diagram
INH
10(11)
V5.1
16(18)
7(8)
V
CC
8(9)
CBOOT
CHARGE
ZERO CURRENT
INHIBIT
VREF
GOOD
INTERNAL
REFERENCE
INTERNAL
SUPPLY
5.1V
V
CC
5.1V
3.3V
SS
17(19)
SOFT
START
HICCUP CURRENT
LIMITING
COMP
11(12)
THERMAL
SHUTDOWN
5.1V
3.3V
+
E/A
-
CURRENT
LIMITING
R
S
Q
Q
9(10)
BOOT
VFB
-
+
PWM
12(13)
SYNC
18(20)
OSCILLATOR
DRIVER
1(1)
OSC
4,5,6,13,14,15
(4,5,6,7,14,15,16,17)
GND
2(2)
OUT
3(3)
OUT
D94IN161B
Pin x = Powerdip
Pin (x) = S020
2
2.1
Pin settings
Pin connection
Figure 3.
Pin connection (top view)
OSC
OUT
OUT
GND
GND
GND
GND
V
CC
V
CC
BOOT
D94IN162A
D94IN163A
OSC
OUT
OUT
GND
GND
GND
V
CC
V
CC
BOOT
1
2
3
4
5
6
7
8
9
18
17
16
15
14
13
12
11
10
SYNC
SS
V5.1
GND
GND
GND
VFB
COMP
INH
1
2
3
4
5
6
7
8
9
10
20
19
18
17
16
15
14
13
12
11
SYNC
SS
V5.1
GND
GND
GND
GND
VFB
COMP
INH
DIP -18 (12+3+3)
SO20 (12+4+4)
3/28
Pin settings
L4973
2.2
Pin description
Table 1.
Pin description
N° Pin
Name
DIP-18
11
10
SO-20
12
11
COMP
INH
E/A output to be used for frequency compensation
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.
A capacitor connected between this pin and the output
allows to drive the internal D-MOS.
Input/Output synchronization.
Unregulated DC input voltage
Stepdown regulator output.
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.
Reference voltage externally available.
Signal ground
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)
Description
9
18
7,8
2,3
10
20
8,9
2,3
BOOT
SYNC
V
CC
OUT
12
13
VFB
16
4,5,6
13,14,15
18
4,5,6,7
14,15,16,17
V5.1
GND
1
1
OSC
Note:
1
The maximum power dissipation of the package must be observed.
4/28
L4973
Electrical data
3
3.1
Electrical data
Maximum ratings
Table 2.
Symbol
Parameter
DIP-18
V
7
,V
8
V
2
,V
3
I
2
,I
3
V
9
-V
8
V
9
V
11
V
17
V
12
V
18
V
10
S0-20
V
9
,V
8
V
2
,V
3
I
2
,I
3
V
10
-V
8
V
10
V
12
V
19
V
13
V
20
V
11
Bootstrap voltage
Analogs input voltage (
V
CC
= 24 V
)
Absolute maximum ratings
Value
58
-1
-5
int. limit.
14
70
12
13
6
-0.3
5.5
0.3
V
CC
-0.3
5
1.3
2
4
-40 to 150
V
V
V
V
V
V
V
V
V
V
W
W
W
W
°C
Unit
V
V
V
Input voltage
Output DC voltage
Output peak voltage at t = 0.1
μs
f = 200 kHz
Maximum output current
Analogs input voltage (V
CC
= 24 V)
(V
CC
= 20 V)
(V
CC
= 20 V)
Inhibit
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)
SO-20
Power dissipation a T
pins
= 90 °C
P
tot
T
J
,T
STG
Junction and storage temperature
3.2
Thermal data
Table 3.
Symbol
R
thJP
R
thJA
Thermal data
Parameter
Maximum thermal resistance junction-pin
Maximum thermal resistance junction-ambient
DIP-18
12
60
(1)
SO-20
15
80
(1)
Unit
°C/W
°C/W
1. Package mounted on board
5/28
