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PDF LM2984CT Data sheet ( Hoja de datos )
| Número de pieza | LM2984CT | |
| Descripción | LM2984C Microprocessor Power Supply System | |
| Fabricantes | National Semiconductor | |
| Logotipo |  |
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May 1989
LM2984C Microprocessor Power Supply System
General Description
The LM2984C positive voltage regulator features three in-
dependent and tracking outputs capable of delivering the
power for logic circuits peripheral sensors and standby
memory in a typical microprocessor system The LM2984C
includes circuitry which monitors both its own high-current
output and also an external mP If any error conditions are
sensed in either a reset error flag is set and maintained until
the malfunction terminates Since these functions are in-
cluded in the same package with the three regulators a
great saving in board space can be realized in the typical
microprocessor system The LM2984C also features very
low dropout voltages on each of its three regulator outputs
(0 6V at the rated output current) Furthermore the quies-
cent current can be reduced to 1 mA in the standby mode
Designed also for vehicular applications the LM2984C and
all regulated circuitry are protected from reverse battery in-
stallations or 2-battery jumps Familiar regulator features
such as short circuit and thermal overload protection are
also provided Fixed outputs of 5V are available in the plas-
tic TO-220 power package
Features
Y Three low dropout tracking regulators
Y Output current in excess of 500 mA
Y Low quiescent current standby regulator
Y Microprocessor malfunction RESET flag
Y Delayed RESET on power-up
Y Accurate pretrimmed 5V outputs
Y Reverse battery protection
Y Overvoltage protection
Y Reverse transient protection
Y Short circuit protection
Y Internal thermal overload protection
Y ON OFF switch for high current outputs
Y 100% electrical burn-in in thermal limit
Typical Application Circuit
LM2984C
Order Number LM2984CT
See NS Package Number TA11B
COUT must be at least 10 mF to
maintain stability May be increased
without bound to maintain regulation
during transients Locate as close as
possible to the regulator This capac- TL H 8821–1
itor must be rated over the same op-
erating temperature range as the
regulator The equivalent series re-
sistance (ESR) of this capacitor is
critical see curve
C1995 National Semiconductor Corporation TL H 8821
RRD-B30M115 Printed in U S A
1 page  
Electrical Characteristics (Continued)
VIN e 14V IOUT e 5 mA Ibuf e 5 mA Istby e 5 mA Rt e 130k Ct e 0 33 mF Cmon e 0 47 mF Tj e 25 C (Note 6) unless
otherwise specified
Parameter
Conditions
Typical
Tested
Limit
(Note 2)
Design
Limit
(Note 3)
Units
Computer Monitor Reset Functions
Ireset Low
Vreset Low
Rt voltage
Power On Reset
Delay
VOUT Low
Reset Threshold
VOUT High
Reset Threshold
Reset Output
Leakage
VIN e 4V Vrst e 0 4V
VIN e 4V Irst e 1 mA
(Pin 2)
VmPmon e 5V
(Tdly e 1 2 Rt Ct)
(Note 4)
(Note 4)
VmPmon e 5V Vrst e 12V
5
0 10
1 22
1 22
50
50
4 00
4 00
5 50
5 50
0 01
2
0 40
1 15
1 30
45
55
3 60
4 40
5 25
6 00
1
1 mAmin
Vmax
Vmin
Vmax
msmin
msmax
Vmin
Vmax
Vmin
Vmax
mAmax
mPmon Input
Current (Pin 4)
mPmon Input
Threshold Voltage
mP Monitor Reset
Oscillator Period
mP Monitor Reset
Oscillator Pulse Width
Minimum mP Monitor
Input Pulse Width
VmPmon e 2 4V
VmPmon e 0 4V
VmPmon e 0V
(Twindow e 0 82 RtCmon)
VmPmon e 0V
(RESETpw e 2000 Cmon)
(Note 5)
75
0 01
1 22
1 22
50
50
10
10
2
25
10
0 80
2 00
45
55
07
13
0 80
2 00
05
20
mAmax
mAmax
Vmin
Vmax
msmin
msmax
msmin
msmax
msmax
Reset Fall Time
Rrst e 10k Vrst e 5V Crst s 10 pF
0 20
1 00
msmax
Reset Rise Time
Rrst e 10k Vrst e 5V Crst s 10 pF
0 60
1 00
msmax
On Off Switch Input
Current (Pin 8)
VON e 2 4V
VON e 0 4V
7 5 25
0 01 10
mAmax
mAmax
On Off Switch Input
Threshold Voltage
1 22
1 22
0 80
2 00
0 80
2 00
Vmin
Vmax
Note 1 Thermal resistance without a heatsink for junction-to-case temperature is 3 C W Thermal resistance case-to-ambient is 40 C W
Note 2 Tested Limits are guaranteed and 100% production tested
Note 3 Design Limits are guaranteed (but not 100% production tested) over the indicated temperature and supply voltage range These limits are not used to
calculate outgoing quality levels
Note 4 An internal comparator detects when the main regulator output (VOUT) drops below 4 0V or rises above 5 5V If either condition exists at the output the
Reset Error Flag is held low until the error condition has terminated The Reset Error Flag is then allowed to go high again after a delay set by Rt and Ct (See
Applications Section )
Note 5 This parameter is a measure of how short a pulse can be detected at the mP Monitor Input This parameter is primarily influenced by the value of Cmon
(See Typical Performance Characteristics and Applications Section )
Note 6 To ensure constant junction temperature low duty cycle pulse testing is used
5
5 Page 
Typical Performance Characteristics (Continued)
Output Voltage
Device Dissipation vs
Ambient Temperature
Output Capacitor ESR
(Standby Output Pin 9)
TL H 8821 – 8
Output Capacitor ESR
(Buffer Output Pin 10)
TL H 8821 – 9
Output Capacitor ESR
(Main Output Pin 11)
TL H 8821–13
Application Hints
OUTPUT CAPACITORS
The LM2984C output capacitors are required for stability
Without them the regulator outputs will oscillate sometimes
by many volts Though the 10 mF shown are the minimum
recommended values actual size and type may vary de-
pending upon the application load and temperature range
Capacitor effective series resistance (ESR) also affects the
IC stability Since ESR varies from one brand to the next
some bench work may be required to determine the mini-
mum capacitor value to use in production Worst case is
usually determined at the minimum ambient temperature
and the maximum load expected
Output capacitors can be increased in size to any desired
value above the minimum One possible purpose of this
would be to maintain the output voltages during brief condi-
tions of negative input transients that might be characteris-
tic of a particular system
Capacitors must also be rated at all ambient temperatures
expected in the system Many aluminum type electrolytics
will freeze at temperatures less than b30 C reducing their
effective capacitance to zero To maintain regulator stability
down to b40 C capacitors rated at that temperature (such
as tantalums) must be used
Each output must be terminated by a capacitor even if it is
not used
STANDBY OUTPUT
The standby output is intended for use in systems requiring
standby memory circuits While the high current regulator
TL H 8821 – 14
TL H 8821 – 15
outputs are controlled with the ON OFF pin described later
the standby output remains on under all conditions as long
as sufficient input voltage is supplied to the IC Thus memo-
ry and other circuits powered by this output remain unaffect-
ed by positive line transients thermal shutdown etc
The standby regulator circuit is designed so that the quies-
cent current to the IC is very low (k1 5 mA) when the other
regulator outputs are off
The capacitor on the output of this regulator can be in-
creased without bound This will help maintain the output
voltage during negative input transients and will also help to
reduce the noise on all three outputs Because the other
two track the standby output therefore any noise reduction
here will also reduce the other two noise voltages
BUFFER OUTPUT
The buffer output is designed to drive peripheral sensor cir-
cuitry in a mP system It will track the standby and main
regulator within a few millivolts in normal operation There-
fore a peripheral sensor can be powered off this supply and
have the same operating voltage as the mP system This is
important if a ratiometric sensor system is being used
The buffer output can be short circuited while the other two
outputs are in normal operation This protects the mP sys-
tem from disruption of power when a sensor wire etc is
temporarily shorted to ground i e only the sensor signal
would be interrupted while the mP and memory circuits
would remain operational
The buffer output is similar to the main output in that it is
controlled by the ON OFF switch in order to save power in
11
11 Page | ||
| Páginas | Total 14 Páginas | |
| PDF Descargar | [ Datasheet LM2984CT.PDF ] | |
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