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PDF L4975 Data sheet ( Hoja de datos )

Número de pieza L4975
Descripción 5A SWITCHING REGULATOR
Fabricantes STMicroelectronics 
Logotipo STMicroelectronics Logotipo



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® L4975A
5A SWITCHING REGULATOR
5A OUTPUT CURRENT
5.1V TO 40V OUTPUT VOLTAGE RANGE
0 TO 90% DUTY CYCLE RANGE
INTERNAL FEED-FORWARD LINE REGULA-
TION
INTERNAL CURRENT LIMITING
PRECISE 5.1V ± 2% ON CHIP REFERENCE
RESET AND POWER FAIL FUNCTIONS
SOFT START
INPUT/OUTPUT SYNC PIN
UNDER VOLTAGE LOCK OUT WITH HYS-
TERETIC TURN-ON
PWM LATCH FOR SINGLE PULSE PER PE-
RIOD
VERY HIGH EFFICIENCY
SWITCHING FREQUENCY UP TO 500KHz
THERMAL SHUTDOWN
CONTINUOUS MODE OPERATION
DESCRIPTION
The L4975A is a stepdown monolithic power
switching regulator delivering 5A at a voltage vari-
able from 5.1 to 40V.
BLOCK DIAGRAM
MULTIPOWER BCD TECHNOLOGY
Multiwatt15V
ORDERING NUMBER: L4975A
Realized with BCD mixed technology, the device
uses a DMOS output transistor to obtain very high
efficiency and very fast switching times. Features
of the L4975A include reset and power fail for mi-
croprocessors, feed forward line regulation, soft
start, limiting current and thermal protection. The
device is mounted in a 15-lead multiwatt plastic
power package and requires few external compo-
nents. Efficient operation at switching frequencies
up to 500KHz allows reduction in the size and
cost of external filter components.
June 2000
1/21
This is advanced information on a new product now in development or undergoing evaluation. Details are subject to change without notice.

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L4975 pdf
stability of the loop can be adjusted by an exter-
nal RC network connected to the output of the er-
ror amplifier. A voltage feedforward control has
been added to the oscillator, this maintains supe-
rior line regulation over a wide input voltage
range. Closing the loop directly gives an output
voltage of 5.1V, higher voltages are obtained by
inserting a voltage divider.
At turn on output overcurrents are prevented by
the soft start function (fig. 2). The error amplifier is
initially clamped by an external capacitor Css and
allowed to rise linearly under the charge of an in-
ternal constant current source.
Output overload protection is provided by a cur-
rent limit circuit (fig. 3). The load current is sensed
by an internal metal resistor connected to a com-
parator. When the load current exceeds a preset
threshold the output of the comparator sets a flip
flop which turns off the power DMOS. The next
clock pulse, from an internal 40kHz oscillator will
reset the flip flop and the power DMOS will again
conduct. This current protection method, ensures
Figure 4: Reset and Power Fail Functions.
L4975A
a constant current output when the system is
overloaded or short circuited and limits the
switching frequency, in this condition, to 40kHz.
The Reset and Power fail circuitry (fig 4) gener-
ates an output signal when the supply voltage ex-
ceeds a threshold programmed by an external
voltage divider. The reset signal, is generated
with a delay time programmed by an external ca-
pacitor on the delay pin. When the supply voltage
falls below the threshold or the output voltage
goes below 5V the reset output goes low immedi-
ately. The reset output is an open collector-drain.
Fig 4A shows the case when the supply voltage is
higher than the threshold, but the output voltage
is not yet 5V.
Fig 4B shows the case when the output is 5.1V
but the supply voltage is not yet higher than the
fixed threshold.
The thermal protection disables circuit operation
when the junction temperature reaches about
150°C and has an hysterysis to prevent unstable
conditions.
A
B
5/21

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L4975 arduino
Figure 7A
Figure 7B
L4975A
11/21

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