L5973AD
2 A switch step down switching regulator
Features
■
■
■
■
■
■
■
■
■
■
■
■
■
2 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
500 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
HSOP8 exposed pad
Description
The L5973AD is a step down monolithic power
switching regulator with a switch current limit of
2 A so it is able to deliver more than 1.5 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 R
thJA
down to
approximately 40 °C/W.
The device uses an internal P-Channel D-MOS
transistor (with a typical of 200 mΩ) as switching
element to avoid the use of bootstrap capacitor
and guarantee high efficiency.
An internal oscillator fixes the switching frequency
at 500 kHz to minimize the size of external
components.
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.
Applications
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■
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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: chargers, car battery, DC-DC
converters
Figure 1.
Test application circuit
3.3V
VIN = 4V to 35V
VREF
VCC
SYNC.
C1
10μF
35V
CERAMIC
COMP
C4
22nF
C3
220pF
R3
4.7K
6
8
2
4
INH
1
OUT
L1 15μH
D1
STPS340U
5
FB
GND
R2
3.3K
VOUT=3.3V
L5973AD
3
7
R1
5.6K
C2
330μF
10V
D03IN1453
November 2009
Doc ID 9552 Rev 9
1/22
www.st.com
22
Contents
L5973AD
Contents
1
Pin settings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1
1.2
Pin connection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
Pin description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
2
Electrical data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
2.1
2.2
Maximum ratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
Thermal data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
3
4
Electrical characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Functional description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
4.1
4.2
4.3
4.4
4.5
4.6
4.7
4.8
Power supply and voltage reference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Voltages monitor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Oscillator and synchronization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Current protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Error amplifier . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
PWM comparator and power stage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Inhibit function . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
Thermal shutdown . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
5
Additional features and protections . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
5.1
5.2
5.3
5.4
Feedback disconnection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Output overvoltage protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Zero load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Application circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
6
7
8
9
Application ideas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
Package mechanical data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
Order code . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
2/22
Doc ID 9552 Rev 9
L5973AD
Pin settings
1
1.1
Pin settings
Pin connection
Figure 2.
Pin connection (top view)
OUT
SYNC
INH
COMP
1
2
3
4
D98IN955
8
7
6
5
VCC
GND
VREF
FB
1.2
Pin description
Table 1.
N°
1
Pin description
Type
OUT
Regulator output.
Master/slave synchronization. When it is open, a signal synchronous with the
turn-off of the internal power is present at the pin. When connected to an
external signal at a frequency higher than the internal one, then the device is
synchronized by the external signal.
Connecting together the SYNC pin of two devices, the one with the higher
frequency works as master and the other one, works as slave.
A logical signal (active high) disables the device. With IHN higher than 2.2 V
the device is OFF and with INH lower than 0.8V, the device is ON.
If INH is not used the pin must be grounded. When it is open, an internal pull-
up disables the device.
E/A output to be used for frequency compensation.
Stepdown feedback input. Connecting the output voltage directly to this pin
results in an output voltage of 1.235 V. An external resistor divider is required
for higher output voltages (the typical value for the resistor connected
between this pin and ground is 4.7 K).
Reference voltage of 3.3 V. No filter capacitor is needed to stability.
Ground.
Unregulated DC input voltage.
Description
2
SYNC
3
INH
4
COMP
5
FB
6
7
8
VREF
GND
VCC
Doc ID 9552 Rev 9
3/22
Electrical data
L5973AD
2
2.1
Electrical data
Maximum ratings
Table 2.
Symbol
V
8
V
1
I
1
V
4
, V
5
V
3
V
2
P
TOT
T
J
T
STG
Input voltage
Output DC voltage
Output peak voltage at t = 0.1
μs
Maximum output current
Analog pins
INH
SYNC
Power dissipation at T
A
≤
60 °C
Operating junction temperature range
Storage temperature range
Absolute maximum ratings
Parameter
Value
40
-1 to 40
-5 to 40
int. limit.
4
-0.3V to V
CC
-0.3 to 4
2.25
-40 to 150
-55 to 150
V
W
°C
°C
V
Unit
V
V
V
2.2
Thermal data
Table 3.
Symbol
R
thJA
Thermal data
Parameter
Maximum thermal resistance junction-ambient
HSOP8
Exposed pad
40
(1)
Unit
°C/W
1. Package mounted on board
4/22
Doc ID 9552 Rev 9
L5973AD
Electrical characteristics
3
Electrical characteristics
T
J
= 25 °C, V
CC
= 12 V, unless otherwise specified
Table 4.
Symbol
V
CC
R
DS(on)
I
l
f
s
Electrical characteristics
Parameter
Test condition
Min
4
0.250
V
CC
= 4.4 V to 36 V
2
2.3
500
0
100
Typ
Max
36
0.5
3.5
Unit
V
Ω
A
kHz
%
Operating input voltage
V
o
= 1.235 V; I
o
= 2 A
range
MOSFET on
resistance
Maximum limiting
current
Switching frequency
Duty cycle
Dynamic characteristics
(see test circuit).
V
5
Voltage feedback
Efficiency
4.4 V < V
CC
< 36 V,
20 mA < I
O
< 2 A
V
O
= 5 V, V
CC
= 12 V
1.220
1.235
90
1.25
V
%
η
DC characteristics
I
qop
I
q
I
qst-by
Inhibit
Device ON
INH threshold voltage
Device OFF
Error amplifier
V
OH
V
OL
I
o source
I
o sink
I
b
High level output
voltage
Low level output
voltage
Source output current
VFB = 1 V
VFB = 1.5 V
V
COMP
= 1.9 V;
V
FB
= 1 V
V
COMP
= 1.9 V;
V
FB
= 1.5 V
200
300
3.5
0.4
V
V
μA
2.2
V
0.8
V
Total operating
quiescent current
Quiescent current
Total stand-by
quiescent current
Duty cycle = 0;
V
FB
= 1.5 V
V
inh
> 2.2 V
50
5
7
2.7
100
mA
mA
μA
Sink output current
Source bias current
DC open loop gain
1
1.5
2.5
4
mA
μA
dB
R
L
=
∞
50
57
Doc ID 9552 Rev 9
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Power technology
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