Up to 1A step down switching regulator
Features
■ Up to 1A output current
■ Operating input voltage from 4.4V to 36V
■ 3.3V / (±2%) reference voltage
■ Output voltage adjustable from 1.2V to 35V
■ Low dropout operation: 100% duty cycle
■ 250KHz 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
L5970D
SO8
Description
The L5970D is a step down monolithic power
switching regulator capable to deliver up to 1A at
output voltages from 1.2V to 35V.
The device uses an internal P-Channel D-MOS
transistor (with a typical Rdson of 250mΩ) as
switching element to minimize the size of the
external components.
An internal oscillator fixes the switching frequency
at 250KHz.
Having a minimum input voltage of 4.4V only, it is
particularly suitable for 5V 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.
Figure 1. Test application circuit
VIN = 4.4V to 35V
C1
10µF
35V
CERAMIC
3.3V
C4
22nF
C3
220pF
VREF
VCC
SYNC.
COMP
4.7K
R3
6
8
2
4
INH.
L5970D
3
7
1
5
GND
D98IN954C
OUT
FB
L1 33µH
D1
STPS2L40U
R1
5.6K
R2
3.3K
VOUT=3.3V
C2
100µF
10V
October 2007 Rev 16 1/16
www.st.com
16
Contents L5970D
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 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
8 Order code . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
9 Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
2/16
L5970D 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
6VREF
7 GND Ground.
8 VCC Unregulated DC input voltage.
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 1.23V. An external resistive divider is required for higher
output voltages.
3.3V V
. No cap is requested for stability.
REF
8
7
6
5
VCC
GND
VREF
FB
3/16
Electrical data L5970D
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 = 0.1µs
-1 to 40
-5 to 40
Maximum output current int. limit.
Analog pins 4 V
5
INH -0.3V to V
SYNC -0.3 to 4 V
Power dissipation at TA ≤ 60°C 0.75 W
Operating junction temperature range -40 to 150 °C
Storage temperature range -55 to 150 °C
V
V
CC
2.2 Thermal data
Table 3. Thermal data
Symbol Parameter SO8 Unit
R
thJA
1. Package mounted on board
Maximum thermal resistance junction-ambient
120
(1)
°C/W
4/16
L5970D Electrical characteristics
3 Electrical characteristics
Table 4. Electrical characteristics
( TJ = 25°C, VCC = 12V, unless otherwise specified)
Symbol Parameter Test condition Min Typ Max Unit
V
CC
Operating input
voltage range
Vo = 1.235V; Io = 2A
(1)
4.4 36 V
R
DS(on)
I
l
f
s
Mosfet on
Resistance
Maximum limiting
current
Switching frequency
VCC = 4.4V to 36V
Duty cycle 0 100 %
Dynamic characteristics (see test circuit ).
V
5
Voltage feedback
h Efficiency
4.4V < V
20mA < I
VO = 5V, VCC = 12V
DC characteristics
I
qop
I
I
qst-by
q
Total operating
quiescent current
Quiescent current
Total stand-by
quiescent current
Duty cycle = 0;
VFB = 1.5V
V
inh
VCC = 36V;
V
inh
CC
> 2.2V
> 2.2V
< 36V,
< 2A
O
(1)
0.250 0.5 Ω
1.5 1.87 2.25 A
(1)
212 250 280 KHz
225 250 275 KHz
1.220 1.235 1.25 V
(1)
1.198 1.235 1.272 V
90 %
(1)
(1)
(1)
35mA
50 100 µA
80 150 µA
2.5 mA
Inhibit
Error amplfier
V
OH
V
OL
I
o source
INH threshold
voltage
High level output
voltage
Low level output
voltage
Source output
current
Device ON 0.8 V
Device OFF 2.2 V
V
= 1V
FB
VFB = 1.5V
V
= 1.9V;
COMP
= 1V
V
FB
3.5 V
0.4 V
200 300 µA
5/16
Electrical characteristics L5970D
Table 4. Electrical characteristics
(continued)
( TJ = 25°C, VCC = 12V, unless otherwise specified)
Symbol Parameter Test condition Min Typ Max Unit
= 1.9V;
V
I
o sink
I
b
Sink output current
Source bias current 2.5 4 µA
DC open loop gain
gm Transconductance
Sync function
High input voltage
Low input voltage
Slave sink current
Master output
amplitude
Output pulse width
COMP
V
FB
= 1.5V
11.5 mA
RL = ∞ 50 65 dB
I
= -0.1mA to
comp
0.1mA
= 1.9V
V
COMP
= 4.4V to 36V 2.5 V
V
CC
= 4.4V to 36V 0.74 V
V
CC
V
= 0.74V
sync
V
= 2.33V
sync
= 3mA
I
source
no load,
V
= 1.65V
sync
(2)
0.11
0.21
2.75 3 V
0.20 0.35 µs
2.3 mS
REF
0.25
0.45mAmA
V
Reference section
Reference voltage 3.234 3.3 3.366 V
(1)
3.2 3.3 3.399 V
510mV
Line regulation
Load regulation
I
= 0 to 5mA
REF
= 4.4V to 36V
V
CC
I
= 0mA
REF
= 4.4V to 36V
V
CC
I
= 0 to 5mA 8 15 mV
REF
Short circuit current 10 18 30 mA
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.
6/16
L5970D Typical characteristics
0
4 Typical characteristics
Figure 3. Junction temperature vs
Tj(°C)
130
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
output current
Vcc=5V
Tamb=25°C
Io(A)
Vo=3.3V
Vo=2.5V
Vo=1.8V
Figure 4. Load regulator
Vo (V)
3.312
3.308
3.304
3.296
3.292
3.288
3.284
3.28
3.276
Vcc = 12V
Vo = 3.3V
3.3
Tj = 25°C
Tj = 125°C
00.511.5
Io (A)
Figure 5. Junction temperature vs
Tj(°C)
130
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
output current
Vcc=12V
Tam b =2 5 °C
Io(A)
Vo=5V
Vo=3.3V
Vo=2.5V
Figure 7. Junction temperature vs
Tj(°C)
140
120
100
80
60
40
20
0
0.2 0.4 0.6 0.8 1 1.2 1.4
output current
Vcc=24V
Tamb=25°C
Vo=18V
Io(A)
Vo=12V
Vo=5V
Figure 6. Line regulator
Vo (V)
3.312
Vcc = 12V
3.308
3.304
Vo = 3. 3V
Tj = 25°C
3.3
3.296
3.292
3.288
Tj = 125°C
3.284
3.28
3.276
01020304
Vcc (V)
Figure 8. Output voltage vs junction
temperature
Vo (V)
1.25
1.24
1.23
1.22
Vcc = 12V
1.21
1.2
-50 0 50 100 150
Tj (°C)
Vcc=12V
7/16
Typical characteristics L5970D
Figure 9. Quiescent current vs
Iq (mA)
2
junction temperature
Figure 10. Switching frequency vs
junction temperature
Fsw (KHz)
260
1.8
1.6
Vcc = 12V
1.4
DC = 0%
1.2
-50
050
100 150
Tj (°C)
Figure 11. Shutdown current vs junction
Ishd (µA)
70
60
50
40
30
-50
temperature
Vcc = 12V
0
50 100 150
Tj (°C)
250
240
230
220
-50 0 50 100 150
Vcc = 12V
Vo = 3.3V
Tj (C)
Figure 12. Efficiency vs output current
94
92
90
88
86
84
82
80
Efficiency (%)
78
76
74
72
70
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
Vo=3.3V
Vo=2.5V
Vo=1.8V
Vcc=5V
Io (A)
Figure 13. Efficiency vs output current
92
90
Vo=5V
88
86
Vo=3.3V
84
82
80
78
Efficiency (%)
Vo=2.5V
76
74
Vcc=12V
72
70
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
Io (A)
8/16
L5970D Application circuit
5 Application circuit
Figure 14. Demo board application circuit
VIN = 4.4V to 25V
C1
10µF
25V
CERAMIC
3.3V
C4
22nF
C3
220pF
VREF
VCC
SYNC.
COMP
4.7K
R3
6
8
2
4
INH.
L5970D
3
7
1
5
GND
D03IN1437
OUT
FB
L1 33µH
D1
STPS2L25U
R1
5.6K
R2
3.3K
Table 5. Component list
Reference Part number Description Manufacturer
C1 GRM32DR61E106KA12L 10µF, 25V MURATA
C2 POSCAP 10TPB100M 100µF, 10V 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
VOUT=3.3V
C2
100µF
10V
D1 STPS2L25U 2A, 25V STMicroelectronics
L1 DO3316P-333 33µH, 2A COILCRAFT
9/16
Application circuit L5970D
Figure 15. PCB layout (component side)
Figure 16. PCB layout (bottom side)
Figure 17. PCB layout (front side)
10/16
L5970D Application ideas
6 Application ideas
Figure 18. Dual output voltage with auxiliary winding
N1/N2=2
VIN=12V
C1
10uF
25V
Ceramic
C2
220pF
C3
22nF
R3
4.7k
VCC
COMP
SYNC VREF
8
U1
L5970D
4
2
6
GND
3.3V
OUT
1
FB
5
3
7
INH
D1
STPS25L25U
Figure 19. Buck-boost regulator
VIN=12V
C1
10uF
25V
Ceramic
C2
10uF
35V
Cerami c
C3
220pF
C4
22nF
R3
4.7k
VCC
COMP
SYNC
8
U1
L5970
4
6
2
VREF
GND
3.3V
OUT
1
FB
5
3
7
INH
24k
2.7k
D2
1N4148
Lp=22uH
L1
33uH
D1
STPS2L25U
C5
100uF
16V
C4
100uF
10V
VOUT=-12V/0.3A
VOUT1=5V
30mA
VOUT=3.3V
0.5A
C5
47uF
10V
Vin=12V Vout=-12V Iout=0.5A Efficiency=81%
Figure 20. Positive Buck-Boost regulator
VIN=5V
C1
10uF
C2
25V
220pF
Cer amic
Vin=5V Vout=12V Iout=0.3 A Effici ency=76%
C3
22nF
R3
4.7k
VCC
COMP
SYNC VREF
8
L5970
4
6
2
3.3 V
U1
GND
OUT
1
FB
5
3
7
INH
Figure 21. Synchronization example
VIN
VCC
8
COMP
SYNC VREF
L5970D
4
6
2
7
GND
D1
STPS2L25U
OUT
1
FB
5
3
INH
VCC
COMP
L1
33uH
M1
STN4NE03L
8
4
2
SYNC VREF
D2
STPS2L25U
L5970D
6
GND
VOUT=12V/0.3A
24k
C4
100uF
16V
2.7k
OUT
1
FB
5
3
7
INH
11/16
Package mechanical data L5970D
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
12/16
L5970D Package mechanical data
Table 6. SO-8 mechanical data
Dim.
Min Typ Max Min Typ Max
A 1.35 1.75 0.053 0.069
A1 0.10 0.25 0.004 0.010
A2 1.10 1.65 0.043 0.065
B 0.33 0.51 0.013 0.020
C 0.19 0.25 0.007 0.010
(1)
D
4.80 5.00 0.189 0.197
E 3.80 4.00 0.15 0.157
e 1.27 0.050
H 5.80 6.20 0.228 0.244
h 0.25 0.50 0.010 0.020
L 0.40 1.27 0.016 0.050
k 0° (min.), 8° (max.)
ddd 0.10 0.004
1. Dimensions D does not include mold flash, protru-sions or gate burrs. Mold flash, potrusions or gate burrs
shall not exceed 0.15mm (.006inch) in total (both side).
mm. inch
Figure 22. Package dimensions
13/16
Order codes L5970D
8 Order codes
Table 7. Order codes
Part number Package Packaging
L5970D SO8 Tube
L5970D013TR SO8 Tape and reel
14/16
L5970D Revision history
9 Revision history
Table 8. Revision history
Date Revision Changes
26-Jan-2007 14 Updated Table 5 on page 9
16-Mar-2007 15 Mechanical data typo
16-Oct-2007 16 Updated Section 5: Application circuit on page 9
15/16
L5970D
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