ON MC3425 Power supply supervisory/ over and undervoltage protection circuit Datasheet

Order this document by MC3425/D
The MC3425 is a power supply supervisory circuit containing all the
necessary functions required to monitor over and undervoltage fault
conditions. These integrated circuits contain dedicated over and
undervoltage sensing channels with independently programmable time
delays. The overvoltage channel has a high current Drive Output for use in
conjunction with an external SCR Crowbar for shutdown. The undervoltage
channel input comparator has hysteresis which is externally programmable,
and an open–collector output for fault indication.
• Dedicated Over and Undervoltage Sensing
•
•
•
•
•
•
POWER SUPPLY SUPERVISORY/
OVER AND UNDERVOLTAGE
PROTECTION CIRCUIT
SEMICONDUCTOR
TECHNICAL DATA
Programmable Hysteresis of Undervoltage Comparator
Internal 2.5 V Reference
300 mA Overvoltage Drive Output
8
30 mA Undervoltage Indicator Output
1
Programmable Time Delays
P1 SUFFIX
PLASTIC PACKAGE
CASE 626
4.5 V to 40 V Operation
MAXIMUM RATINGS
Symbol
Value
Unit
Power Supply Voltage
Rating
VCC
40
Vdc
Comparator Input Voltage Range (Note 1)
VIR
–0.3 to +40
Vdc
IOS(DRV)
Internally
Limited
mA
Indicator Output Voltage
VIND
0 to 40
Vdc
Indicator Output Sink Current
IIND
30
mA
Power Dissipation and Thermal Characteristics
Maximum Power Dissipation @ TA = 70°C
Thermal Resistance, Junction–to–Air
PD
RθJA
1000
80
mW
°C/W
Drive Output Short Circuit Current
Operating Junction Temperature
TJ
+150
°C
Operating Ambient Temperature Range
TA
0 to +70
°C
Tstg
–55 to +150
°C
Storage Temperature Range
NOTE: 1. The input signal voltage should not be allowed to go negative by more than 300 mV
NOTE: 1. or positive by more than 40 V, independent of VCC, without device destruction.
PIN CONNECTIONS
O.V. DRV
Output
1
8
VCC
O.V. DLY
2
7
Gnd
O.V. Sense
3
6
U.V. IND
Output
U.V. Sense
4
5
U.V. DLY
Simplified Application
(Top View)
Overvoltage Crowbar Protection, Undervoltage Indication
Vin
Vout
DC
Power
Supply
+
Cout
MC3425
Undervoltage
Indication
ORDERING INFORMATION
Device
Operating
Temperature Range
Package
MC3425P1
TA = 0° to +70°C
Plastic DIP
 Motorola, Inc. 1996
MOTOROLA ANALOG IC DEVICE DATA
Rev 2
1
MC3425
ELECTRICAL CHARACTERISTICS (4.5 V ≤ VCC ≤ 40 V; TA = Tlow to Thigh [Note 2], unless otherwise noted.)
Characteristics
Symbol
Min
Typ
Max
Unit
REFERENCE SECTION
Sense Trip Voltage (Referenced Voltage)
VCC = 15 V
TA= 25°C
Tlow to Thigh (Note 2)
VSense
Line Regulation of VSense
4.5 V ≤ VCC ≤ 40 V; TJ = 25°C
Power Supply Voltage Operating Range
Power Supply Current
VCC = 40 V; TA = 25°C; No Output Loads
O.V. Sense (Pin 3) = 0 V;
U.V. Sense (Pin 4) = VCC
O.V. Sense (Pin 3) = VCC;
U.V. Sense (Pin 4) = 0 V
Vdc
2.4
2.33
2.5
2.5
2.6
2.63
Regline
–
7.0
15
mV
VCC
4.5
–
40
Vdc
ICC(off)
–
8.5
10
mA
ICC(on)
–
16.5
19
mA
IIB
–
1.0
2.0
µA
INPUT SECTION
Input Bias Current, O.V. and U.V. Sense
Hysteresis Activation Voltage, U.V. Sense
VCC = 15 V; TA = 25°C;
IH = 10%
IH = 90%
VH(act)
V
–
–
0.6
0.8
–
–
IH
9.0
12.5
16
VOL(DLY)
VOH(DLY)
–
VCC–0.5
0.2
VCC–0.15
0.5
–
Delay Pin Source Current
VCC = 15 V; VDLY = 0 V
IDLY(source)
140
200
260
µA
Delay Pin Sink Current
VCC = 15 V; VDLY = 2.5V
IDLY(sink)
1.8
3.0
–
mA
Drive Output Peak Current (TA = 25°C)
IDRV(peak)
200
300
–
mA
Drive Output Voltage
IDRV = 100 mA; TA = 25° C
VOH(DRV)
VCC–2.5
VCC–2.0
–
V
Drive Output Leakage Current
VDRV = 0 V
IDRV(leak)
–
15
200
nA
Hysteresis Current, U.V. Sense
VCC = 15 V; TA = 25°C; U.V. Sense (Pin 4) = 2.5 V
Delay Pin Voltage (IDLY = 0 mA)
Low State
High State
µA
V
OUTPUT SECTION
Drive Output Current Slew Rate (TA = 25°C)
di/dt
–
2.0
–
A/µs
IDRV(trans)
–
1.0
–
mA
(Peak)
Indicator Output Saturation Voltage
IIND = 30 mA; TA = 25°C
VIND(sat)
–
560
800
mV
Indicator Output Leakage Current
VOH(IND) = 40 V
IIND(leak)
–
25
200
nA
Vth(OC)
2.33
2.5
2.63
V
tPLH(IN/OUT)
–
1.7
–
µs
tPLH(IN//DLY)
–
700
–
ns
Drive Output VCC Transient Rejection
VCC = 0 V to 15 V at dV/dt = 200 V µs;
O.V. Sense (Pin 3) = 0 V; TA = 25°C
Output Comparator Threshold Voltage (Note 3)
Propagation Delay Time
(VCC = 15 V; TA = 25°C)
Input to Drive Output or Indicator Output
100 mV Overdrive, CDLY = 0 µF
Input to Delay
2.5 V Overdrive (0 V to 5.0 V Step)
NOTES: 2. Tlow to Thigh = 0° to +70°C
3. The Vth(OC) limits are approximately the VSense limits over the applicable temperature range.
2
MOTOROLA ANALOG IC DEVICE DATA
12
TA = 25°C
10
8.0
VCC = 40 V
6.0
VCC
= 15 V
4.0
VCC = 5.0 V
2.0
0
0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
VH(act), HYSTERESIS ACTIVATION VOLTAGE (V)
1.6
Figure 3. Hysteresis Current
versus Temperature
IH, HYSTERESIS CURRENT (µA)
15.0
U.V. Sense = 2.5 V
14.0
13.0
12.0
11.0
10.0
–55
–25
0
25
50
75
TA, AMBIENT TEMPERATURE (°C)
100
125
Figure 5. Output Delay Time versus
Delay Capacitance
t DLY , OUTPUT DELAY TIME (mS)
100
10
VCC = 15 V
TA = 25°C
1.0
0.1
2.5 CDLY
200 µA
tDLY =
0.01
0.001
0.0001
0.001
0.01
0.1
1.0
CDLY, DELAY PIN CAPACITANCE (µF)
MOTOROLA ANALOG IC DEVICE DATA
Figure 2. Hysteresis Activation Voltage
versus Temperature
1.2
VH(act) = Voltage Level at
which Hysteresis Current
(IH) is 90% of full value.
VCC = 5.0 V
1.0
0.8
VCC = 15 V
VCC = 40 V
0.6
0.4
0.2
0
–55
–25
0
25
50
75
TA, AMBIENT TEMPERATURE (°C)
100
125
Figure 4. Sense Trip Voltage Change
versus Temperature
0
VSense* = 2.400 V
* = 2.500 V
* = 2.600 V
–10
–20
VCC = 15 V
*VSense at TA = 25°C
–30
–40
–50
–55
–25
0
25
50
75
100
125
TA, AMBIENT TEMPERATURE (°C)
10
IDLY(source), DELAY PIN SOURCE CURRENT ( µ A)
IH, HYSTERESIS CURRENT (µA)
14
∆ V Sense , SENSE TRIP VOLTAGE CHANGE (mW)
Figure 1. Hysteresis Current versus
Hysteresis Activation Voltage
V H(act) , HYSTERESIS ACTIVATION VOLTAGE (V)
MC3425
Figure 6. Delay Pin Source Current
versus Temperature
260
240
VCC = 40 V
220
VCC = 15 V
200
VCC = 5.0 V
180
160
–55
–25
0
25
50
75
TA, AMBIENT TEMPERATURE (°C)
100
125
3
5.0
VCC = 15 V
1.0% Duty Cycle @ 300 Hz
TA = 25°C
4.0
3.0
2.0
1.0
0
0
100
200
300
400
IDRV(peak), DRIVE OUTPUT PEAK CURRENT (mA)
Figure 8. Indicator Output Saturation Voltage
versus Output Sink Current
0.4
0.3
0.2
VCC = 15 V
TA = 25°C
0.1
0
0
10
28
VCC = 15 V
IDRV(peak) = 200 mA
1.0% Duty Cycle @ 300 Hz
2.420
2.380
2.340
2.300
–55
4
30
40
Figure 10. Power Supply Current
versus Voltage
2.500
2.460
20
IIND, INDICATOR OUTPUT SINK CURRENT (mA)
Figure 9. Drive Output Saturation Voltage
versus Temperature
I CC, POWER SUPPLY CURRENT (mA)
V OH(DRV), DRIVE OUTPUT SATURATION VOTLAGE (V)
V OH(DRV), DRIVE OUTPUT SATURATION VOLTAGE (V)
Figure 7. Drive Output Saturation Voltage
versus Output Peak Current
V IND(sat) , INDICATOR OUTPUT SATURATION VOLTAGE (V)
MC3425
Curve O.V. Sense U.V. Sense
A
VCC
Gnd
B
Gnd
VCC
24
20
A
16
12
B
8.0
4.0
TA = 25°C
0
–25
0
25
50
75
TA, AMBIENT TEMPERATURE (°C)
100
125
0
5.0
10
15
20
25
30
35
40
VCC, POWER SUPPLY VOLTAGE (V)
MOTOROLA ANALOG IC DEVICE DATA
MC3425
APPLICATIONS INFORMATION
Figure 11. Overvoltage Protection and
Undervoltage Fault Indication with
Programmable Delay
Figure 12. Overvoltage Protection of 5.0 V
Supply with Line Loss Detector
+VO
R1A
Vin
VO = 5.0 V
VO(trip) = 6.25 V
+5.0V
Power
Supply
8
VCC
15k
R1B
4
8
VCC
+
Power
Supply
4.5V to 40V
–
4
IH
R2B
CDLY
CDLY
U.V. Sense
Pin 4
Gnd
1+
Figure 13. Overvoltage Audio Alarm Circuit
+VO
2.5V
OFF
ON
Figure 14. Programmable Frequency Switch
Input Signal
12V
8
VCC
5.0µF
8
VCC
3
+
12V
Power
Supply
Alarm On when:
VO = 13.6 V
O.V.
Sense
O.V.
DRV
I.V. p–p
Output Pulse when:
1
f(input) <
25000 CDLY
10k
3
1
O.V. 1
DRV
O.V.
Sense
10k
2.7k
2.5V
U.V. DLY
Pin 5
U.V. IND
Pin 6
R1A
R2A
tDLY = 12500 CDLY
12k
0.33µF
0.01µF
R1B R2B
, VO(trip) – 2.5 V
R1B + R2B
U.V. Hysteresis = IH
U.V.
O.V.
DLY Gnd DLY
2
7
5
100
U.V.
O.V.
DLY Gnd DLY
2
7
5
O.V. 1
DRV
O.V.
Sense
10k
O.V. 1
DRV
O.V.
Sense
Line Loss
Output
MC3425
3
MC3425
3
R2A
U.V. 6
IND
U.V.
Sense
U.V. 6
IND
U.V.
Sense
AC Line
U.V. Fault
Indicator
1.0k
1.0k
MC3425
MC3425
4
82k
6.8k
U.V.
Sense
4
100Ω
U.V. O.V.
DLY DLY Gnd
5
2
7
U.V.
Sense
O.V.
U.V.
DLY Gnd DLY
5
7
2
0.1µF
CDLY
0.1µF
Gnd
O.V. Sense
Pin 3
2.5V
O.V. DLY
Pin 2
2.5V
ON
O.V. DRV
Pin 1
MOTOROLA ANALOG IC DEVICE DATA
OFF
5
MC3425
CIRCUIT DESCRIPTION
source, IDLY(source), charging the external delay capacitor
(CDLY) to 2.5 V.
The MC3425 is a power supply supervisory circuit
containing all the necessary functions required to monitor
over and undervoltage fault conditions. The block diagram
is shown below in Figure 15. The Overvoltage (O.V.) and
Undervoltage (U.V.) Input Comparators are both
referenced to an internal 2.5 V regulator. The U.V. Input
Comparator has a feedback activated 12.5 µA current sink
(IH) which is used for programming the input hysteresis
voltage (VH). The source resistance feeding this input (RH)
determines the amount of hysteresis voltage by VH = IHRH
= 12.5 × 10–6 RH.
Separate Delay pins (O.V. DLY, U.V. DLY.) are provided for
each channel to independently delay the Drive and Indicator
outputs, thus providing greater input noise immunity. The two
Delay pins are essentially the outputs of the respective input
comparators, and provide a constant current source,
IDLY(source), of typically 200 µA when the noninverting input
voltage is greater than the inverting input level. A capacitor
connected from these Delay pins to ground, will establish a
predictable delay time (tDLY) for the Drive and Indicator
outputs. The Delay pins are internally connected to the
noninverting inputs of the O.V. and U.V. Output Comparators,
which are referenced to the internal 2.5 V regulator.
Therefore, delay time (tDLY) is based on the constant current
Vref CDLY
2.5 CDLY
= 12500 CDLY
tDLY =
=
IDLY(source) 200 µA
Figure 5 provides CDLY values for a wide range of time
delays. The Delay pins are pulled low when the respective
input comparator’s noninverting input is less than the
inverting input. The sink current, IDLY(sink), capability of the
Delay pins is ≥ 1.8 mA and is much greater than the typical
200 µA source current, thus enabling a relatively fast delay
capacitor discharge time.
The Overvoltage Drive Output is a current–limited
emitter–follower capable of sourcing 300 mA at a turn–on
slew rate at 2.0 A/µs, ideal for driving “Crowbar” SCR’s. The
Undervoltage Indicator Output is an open–collector, NPN
transistor, capable of sinking 30 mA to provide sufficient drive
for LED’s, small relays or shut–down circuitry. These current
capabilities apply to both channels operating simultaneously,
providing device power dissipation limits are not exceeded.
The MC3425 has an internal 2.5 V bandgap reference
regulator with an accuracy of ± 4.0% for the basic device.
Figure 15. Representative Block Diagram
VCC
8
+
+
O.V.
Sense
200µA
+ Input
Comparator
– O.V.
3
+
200µA
+ Input
Comparator
– U.V.
U.V.
Sense
+
+Output
Comparator
– O.V.
4
–
Output
Comparator
+ U.V.
+
1
O.V.
DRV
6
U.V.
IND
2.5V
Reference
Regulator
IH
12.5µA
Input Section
5
2
U.V. O.V.
DLY DLY
7
Gnd
Output Section
Note: All voltages and currents are nominal.
6
MOTOROLA ANALOG IC DEVICE DATA
MC3425
CROWBAR SCR CONSIDERATIONS
Referring to Figure 16, it can be seen that the crowbar
SCR, when activated, is subject to a large current surge from
the output capacitance, Cout. This capacitance consists of
the power supply output capacitors, the load’s decoupling
capacitors, and in the case of Figure 16A, the supply’s input
filter capacitors. This surge current is illustrated in Figure 17,
and can cause SCR failure or degradation by any one of
three mechanisms: di/dt, absolute peak surge, or I2t. The
interrelationship of these failure methods and the breadth of
the applications make specification of the SCR by the
semiconductor manufacturer difficult and expensive.
Therefore, the designer must empirically determine the SCR
and circuit elements which result in reliable and effective OVP
operation. However, an understanding of the factors which
influence the SCR’s di/dt and surge capabilities simplifies
this task.
1. di/dt
As the gate region of the SCR is driven on, its area of
conduction takes a finite amount of time to grow, starting as a
very small region and gradually spreading. Since the anode
current flows through this turned–on gate region, very high
current densities can occur in the gate region if high anode
currents appear quickly (di/dt). This can result in immediate
destruction of the SCR or gradual degradation of its forward
blocking voltage capabilities – depending on the severity of
the occasion.
The value of di/dt that an SCR can safely handle is
influenced by its construction and the characteristics of the
gate drive signal. A center–gate–fire SCR has more di/dt
capability than a corner–gate–fire type, and heavily
overdriving ( 3 to 5 times IGT) the SCR gate with a fast < 1.0
µs rise time signal will maximize its di/dt capability. A typical
maximum number in phase control SCRs of less than 50
A(RMS) rating might be 200 A/µs, assuming a gate current of
five times IGT and < 1.0 µs rise time. If having done this, a di/dt
problem is seen to still exist, the designer can also decrease
the di/dt of the current waveform by adding inductance in
series with the SCR, as shown in Figure 18. Of course, this
reduces the circuit’s ability to rapidly reduce the dc bus
voltage and a tradeoff must be made between speedy
voltage reduction and di/dt.
Figure 16. Typical Crowbar Circuit Configurations
(A) SCR Across Input of Regulator
Series
Regulator
Vin
Vout
MC3425
+
+
Cin
Cout
(B) SCR Across Output of Regulator
*
Series
Regulator
Vin
+
Cin
Vout
Cout
+
MC3425
*Needed if supply is not current limited.
MOTOROLA ANALOG IC DEVICE DATA
7
MC3425
Figure 17. Crowbar SCR Surge Current Waveform
l
lpk
di
dt
Surge Due to
Output Capacitor
Current Limited
Supply Output
t
2. Surge Current
If the peak current and/or the duration of the surge is
excessive, immediate destruction due to device overheating
will result. The surge capability of the SCR is directly
proportional to its die area. If the surge current cannot be
reduced (by adding series resistance – see Figure 18) to a
safe level which is consistent with the system’s requirements
for speedy bus voltage reduction, the designer must use a
higher current SCR. This may result in the average current
capability of the SCR exceeding the steady state current
requirements imposed by the DC power supply.
Figure 18. Circuit Elements Affecting
SCR Surge & di/dt
RLead
LLead
ESR
ESL
Output
Cap
R
L
A WORD ABOUT FUSING
Before leaving the subject of the crowbar SCR, a few
words about fuse protection are in order. Referring back to
Figure 16A, it will be seen that a fuse is necessary if the
power supply to be protected is not output current limited.
This fuse is not meant to prevent SCR failure but rather to
prevent a fire!
In order to protect the SCR, the fuse would have to
possess an I2t rating less than that of the SCR and yet have
a high enough continuous current rating to survive normal
supply output currents. In addition, it must be capable of
successfully clearing the high short circuit currents from the
supply. Such a fuse as this is quite expensive, and may not
even be available.
The usual design compromise then is to use a garden
variety fuse (3AG or 3AB style) which cannot be relied on to
blow before the thyristor does, and trust that if the SCR does
fail, it will fail short circuit. In the majority of the designs, this
will be the case, though this is difficult to guarantee. Of
course, a sufficiently high surge will cause an open. These
comments also apply to the fuse in Figure 16B.
CROWBAR SCR SELECTION GUIDE
As an aid in selecting an SCR for crowbar use, the
following selection guide is presented.
Device
IRMS
ITSM
MCR310 Series
MCR16 Series
MCR25 Series
2N6501 Series
MCR69 Series
MCR264 Series
MCR265 Series
10 A
16 A
25 A
25 A
25 A
40 A
55 A
100 A
150 A
300 A
300 A
750 A
400 A
550 A
To
MC3423
R & L EMPIRICALLY DETERMINED!
UNDERVOLTAGE SENSING
An undervoltage sense circuit
designed, as shown in Figure
equations:
V
CCU
R1
12.5
with hysteresis may be
11, using the following
* VCC1
+
mA
2.5
R1
R2 +
V CC1 * 2.5
where: VCCU is the designed upper trip point
(output indicator goes off)
VCC1 is the lower trip point
(output indicator goes on)
8
MOTOROLA ANALOG IC DEVICE DATA
MC3425
OUTLINE DIMENSIONS
P1 SUFFIX
PLASTIC PACKAGE
CASE 626–05
ISSUE K
8
5
NOTES:
1. DIMENSION L TO CENTER OF LEAD WHEN
FORMED PARALLEL.
2. PACKAGE CONTOUR OPTIONAL (ROUND OR
SQUARE CORNERS).
3. DIMENSIONING AND TOLERANCING PER ANSI
Y14.5M, 1982.
–B–
1
4
F
–A–
NOTE 2
L
C
J
–T–
N
SEATING
PLANE
D
H
M
K
DIM
A
B
C
D
F
G
H
J
K
L
M
N
MILLIMETERS
MIN
MAX
9.40
10.16
6.10
6.60
3.94
4.45
0.38
0.51
1.02
1.78
2.54 BSC
0.76
1.27
0.20
0.30
2.92
3.43
7.62 BSC
–––
10_
0.76
1.01
INCHES
MIN
MAX
0.370
0.400
0.240
0.260
0.155
0.175
0.015
0.020
0.040
0.070
0.100 BSC
0.030
0.050
0.008
0.012
0.115
0.135
0.300 BSC
–––
10_
0.030
0.040
G
0.13 (0.005)
M
MOTOROLA ANALOG IC DEVICE DATA
T A
M
B
M
9
MC3425
NOTES
10
MOTOROLA ANALOG IC DEVICE DATA
MC3425
NOTES
MOTOROLA ANALOG IC DEVICE DATA
11
MC3425
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12
◊
*MC3425/D*
MOTOROLA ANALOG IC DEVICE
DATA
M3425/D
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