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R5973AD Schematic ( PDF Datasheet ) - STMicroelectronics

Teilenummer R5973AD
Beschreibung Up to 1.5A step-down switching regulator
Hersteller STMicroelectronics
Logo STMicroelectronics Logo 




Gesamt 30 Seiten
R5973AD Datasheet, Funktion
R5973AD
Up to 1.5 A step-down switching regulator for aerospace
applications
Datasheet - preliminary data
– Designed and manufactured to meet sub-
ppm quality goals
– Advanced mold and frame designs for
superior resilience in harsh environments
(acceleration, EMI, thermal, humidity)
– Extended screening capability on request
HSOP8 - exposed pad
Features
General features
– 1.5 A DC output current
– Operating input voltage from 4 V to 36 V
– 3.3 V / (± 2%) reference voltage
– Large ambient temperature range:
-40 °C to 125 °C
– Output voltage adjustable from 1.235 V to
VIN
– Low dropout operation: 100% duty cycle
– 500 kHz internally fixed frequency
– Voltage feed-forward
– Zero load current operation
– Internal current limiting
– Inhibit for zero current consumption
– Synchronization
– Protection against feedback disconnection
– Thermal shutdown
Aerospace and defense features
– Suitable for use in aerospace and defense
applications
– Dedicated traceability and part marking
– Production parts approval documents
available
– Adapted extended life time and
obsolescence management
– Extended product change notification
process
Applications
Dedicated to aerospace applications
Description
The R5973AD is a step-down monolithic power
switching regulator with a minimum switch current
limit of 1.8 A, so it is able to deliver up to 1.5 A DC
current to the load depending on the application
conditions. The output voltage can be set from
1.235 V to VIN. The high current level is also
achieved thanks to an HSOP8 package with an
exposed frame, that allows to reduce the Rth(JA)
down to approximately 40 °C/W. The device uses
an internal P-channel DMOS transistor (with
a typical RDS(on) of 250 m) as a switching
element to minimize the size of the external
components. An internal oscillator fixes the
switching frequency at 500 kHz. The large
ambient temperature range makes it ideal for
aerospace and defense applications. A pulse-by-
pulse current limit with the internal frequency
modulation offers an effective constant current
short-circuit protection.
October 2014
DocID027027 Rev 1
This is preliminary information on a new product now in development or undergoing evaluation. Details are subject to
change without notice.
1/38
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R5973AD Datasheet, Funktion
Electrical characteristics
3 Electrical characteristics
R5973AD
TJ = -40 °C to 125 °C, VCC = 12 V, unless otherwise specified.
Symbol
Table 4. Electrical characteristics
Parameter
Test condition
Min. Typ. Max.
VCC
RDS(on)
Operating input voltage range
MOSFET on resistance
IL Maximum limiting current(1)
fSW Switching frequency
Duty cycle
Dynamic characteristics
V5 Voltage feedback
h Efficiency
DC characteristics
VCC = 5 V
VCC = 5 V, TJ = 25 °C
4.4 V < VCC < 36 V
V0 = 5 V, VCC = 12 V
4 36
0.250 0.5
1.8 2.3
2 2.3
425 500 575
0 100
1.198 1.235 1.272
90
Iqop
Iq
Iqst-by
Inhibit
Total operating quiescent
current
Quiescent current
Duty cycle = 0; VFB = 1.5 V
Total standby quiescent current Vinh > 2.2 V
57
2.7
50 100
INH threshold voltage
Device ON
Device OFF
0.8
2.2
Error amplifier
VOH
VOL
Io source
Io sink
Ib
High level output voltage
Low level output voltage
Source output current
Sink output current
Source bias current
DC open loop gain
gm Transconductance
Synch function
VFB = 1 V
VFB = 1.5 V
VCOMP = 1.9 V; VFB = 1 V
VCOMP = 1.9 V; VFB = 1.5 V
RL =
ICOMP = -0.1 mA to 0.1 mA;
VCOMP = 1.9 V
3.5
0.4
190 300
1 1.5
2.5 4
50 57
2.3
High input voltage
Low input voltage
Slave synch current(2)
VCC = 4.4 to 36 V
VCC = 4.4 to 36 V
Vsynch = 0.74 V, Vsynch = 2.33 V
2.5
0.11
0.21
VREF
0.74
0.25
0.45
Unit
V
A
kHz
%
V
%
mA
mA
A
V
V
V
V
A
mA
A
dB
mS
V
V
mA
6/38 DocID027027 Rev 1

6 Page









R5973AD pdf, datenblatt
Functional description
R5973AD
strong overcurrent or short-circuit conditions could be not properly limited. For this reason
the switching frequency is also reduced, thus keeping the inductor current under its
maximum threshold. The frequency shifter (Figure 4) functions based on the feedback
voltage. As the feedback voltage decreases (due to the reduced duty cycle), the switching
frequency decreases also.
Figure 6. Current limitation circuitry
5.5
5.6
12/38
Error amplifier
The voltage error amplifier is the core of the loop regulation. It is a transconductance
operational amplifier whose non inverting input is connected to the internal voltage
reference (1.235 V), while the inverting input (FB) is connected to the external divider or
directly to the output voltage. The output (COMP) is connected to the external
compensation network. The uncompensated error amplifier has the following
characteristics:
Table 5. Uncompensated error amplifier characteristics
Description
Values
Transconductance
Low frequency gain
Minimum sink/source voltage
Output voltage swing
Input bias current
2300 µS
65 dB
1500 µA/300 µA
0.4 V/3.65 V
2.5 µA
The error amplifier output is compared to the oscillator sawtooth to perform PWM control.
PWM comparator and power stage
This block compares the oscillator sawtooth and the error amplifier output signals to
generate the PWM signal for the driving stage.
The power stage is a highly critical block, as it functions to guarantee a correct turn ON and
turn OFF of the PDMOS. The turn ON of the power element, or more accurately, the rise
DocID027027 Rev 1

12 Page





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