LINEAR TECHNOLOGY LTC1921, LTC1921i Technical data

Final Electrical Specifications

查询LTC1921CMS8供应商

LTC1921

Dual –48V Supply

and Fuse Monitor

FEATURES

■

Independently Monitors Two –48V Supplies for
– Undervoltage Faults: –38.5V ±1V
– Overvoltage Faults: –70V ±1.5V

■

Accurately Detects Undervoltage Fault Recovery:
–43V ±0.5V

■

Monitors Two External Fuses

■

Operates from –10V to –80V

■

Tolerates DC Faults to –100V

■

Tolerates Accidental Supply Reversal to 100V

■

Withstands Transient Voltages Up to 200V/–200V

■

Small Footprint: 8-Lead MSOP Package

■

Requires No Precision External Components

■

Specified from –40°C to 85°C

MAX

MAX

MAX

U

APPLICATIO S

■

Telecom Backplanes or Switch Cards

■

Networking Backplanes or Switch Cards

■

High Voltage Fuse Monitoring

U

May 2002

DESCRIPTIO

The LTC®1921 monitors two independent –48V supplies,
including their fuses, and drives up to three optoisolators
to indicate status, in accordance with standard backplane
specifications. Requiring only three noncritical resistors
and optoisolators, the LTC1921 replaces multiple voltage
comparators, a voltage reference and several precision
resistors.

The monitor features dual supply overvoltage and under­voltage detection circuits. The preset trip thresholds in­clude overvoltage, undervoltage and undervoltage recovery
that are guaranteed over temperature and meet or exceed
common backplane specifications. Additional built-in cir­cuitry detects the condition of supply fuses. Overvoltage
and undervoltage detectors ignore fast supply transients,
eliminating false detection. The LTC1921 operates from
–10V to –80V with a typical power dissipation of less than
10mW.

The LTC1921 is available in an 8-pin MSOP package.

, LTC and LT are registered trademarks of Linear Technology Corporation.

TYPICAL APPLICATIO

–48V

RETURN

R1

100k

SUPPLY A

–48V

SUPPLY B

–48V

F1

F2

U

R2
100k

1

8

2

RTN

A

V

B

LTC1921
FUSE A
FUSE B

D1 MURS320

D2 MURS320

3

OUT FV

OUT A

OUT B

47k 47k

47k

MOC207

4

MOC207

57

MOC207

6

R3
47k
1/4W

FUSE GOOD

SUPPLY A GOOD

SUPPLY B GOOD

LOGIC

SUPPLY

SUPERVISOR

µP

LOGIC

COMMON

–48V LOAD

1921 TA01

1921i

Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However, no responsibility is assumed for its use. Linear Technology Corporation makes no represen­tation that the interconnection of its circuits as described herein will not infringe on existing patent rights.

1

LTC1921

1
2
3
4

V

A

FUSE A

RTN

OUT F

8
7
6
5

V

B

FUSE B
OUT B
OUT A

TOP VIEW

MS8 PACKAGE

8-LEAD PLASTIC MSOP

WWWU

ABSOLUTE AXI U RATI GS

PACKAGE/ORDER I FOR ATIO

UU

W

(Note 1) All voltages referred to RTN

Supply Voltage

(VA, VB, FUSE A, FUSE B) ....................... 100V to –100V

ORDER PART

NUMBER

Transient Voltage (VA, VB, FUSE A, FUSE B)

(Note 2) ........................................................ 0V to 200V

Transient Voltage (VA, VB, FUSE A, FUSE B)

(Note 2) ......................................................0V to –200V

OUT A, OUT B, OUT F Pins ......................... 0.3V to – 8V

Maximum Junction Temperature ......................... 150°C

Operating Temperature Range

LTC1921CMS8 ........................................ 0°C to 70°C

T

= 150°C, θJA = 250°C/W

JMAX

Consult LTC Marketing for parts specified with wider operating temperature ranges.

LTC1921CMS8
LTC1921IMS8

MS8 PART MARKING

LTZV
LTZU

LTC1921IMS8 .................................... –40°C to 85°C

Storage Temperature Range ................. –65°C to 150°C

Lead Temperature (Soldering, 10 sec)..................300°C

ELECTRICAL CHARACTERISTICS

temperature range, otherwise specifications are at TA = 25°C. (Note 3) RTN = 0V, VA = –48V, VB = –48V, FUSE A = –48V,
FUSE B = –48V, unless otherwise noted.

PARAMETER CONDITIONS MIN TYP MAX UNITS
Power Supply

Supply Voltage Range (RTN – VA, RTN –␣ VB) ● 10 80 V
Supply Current (IA + IB) –160 –250 µA

Supply Monitor

Undervoltage Threshold ● –39.5 –37.5 V
Undervoltage Recovery Threshold ● –43.5 –42.5 V
Overvoltage Threshold ● –71.5 –68.5 V
Overvoltage Threshold Hysteresis ● 1 1.6 V

Fuse Monitor

Input Resistance, FUSE A, FUSE B 11 MΩ
Fuse Comparison Threshold |V

Output

Propagation Delay C
Output Switch Resistance, OUT F, OUT A, OUT B VA = VB = –35V, V

Output Switch Off Leakage 500 pA
Output Switch Resistance in Undervoltage Lockout, VA = VB = –10V, I

OUT F, OUT A, OUT B V

FUSEA

– VA|, |V

– VB| 2.5 V

FUSEB

The ● denotes specifications which apply over the full operating

● –300 µA

LTC1921C ● 0.9 4.5 V
LTC1921I

= 100pF, Overdrive = 1V 220 µs

OUT

= V

I

= 10mA ● 50 Ω

OUT

= –10V, VB = 0V, I

A

VA = 0V, VB = –10V, I

FUSEA

= 10mA ● 60 Ω

OUT

OUT
OUT

= 0V 25 Ω

FUSEB

= 10mA ● 80 Ω
= 10mA ● 80 Ω

● 0.5 4.5 V

Note 1: Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.

Note 2: Transient voltage for less than 10µs. This parameter is not 100%
tested. Voltage should not exceed 200V between any two pins.

2

Note 3: All currents into device pins are positive; all currents out of device
pins are negative. All voltages are referenced to RTN unless otherwise
specified.

1921i

UW

TEMPERATURE (°C)

–50

OUTPUT R

DS(ON)

(Ω)

20

25

30

10 50

1921 G03

15

10

–30 –10

30 70 90

5

0

OUT A (OUT F = 0V)

OUT F, OUT B (OUT A = 0V)

VA = –35V
V

B

= –35V

I = –10mA

TYPICAL PERFOR A CE CHARACTERISTICS

Supply Current vs Supply Voltage

SUPPLY CURRENT (µA)

400

350

300

250

200

150

100

50

VA = VB = V

0

0

= V

FUSEA

FUSEB

20 40 60 1007010 30 50 90

SUPPLY VOLTAGE (V)

80

1921 G01

180

160

140

120

100

80

60

SUPPLY CURRENT (µA)

VA = –48V

40

= –48V

V

B

= –48V

V

20

FUSEA

= –48V

V

FUSEB

0

–30 –10 10 30 50 70

–50

+ I

I

A

B

IA, I

B

TEMPERATURE (°C)

1921 G02

Undervoltage Threshold
vs TemperatureSupply Current vs Temperature

–37.5
–37.7
–37.9
–38.1
–38.3
–38.5
–38.7
–38.9
–39.1

UNDERVOLTAGE THRESHOLD (V)

–39.3
–39.5

90

–50 –30 –10 10

LTC1921

30 50 70

TEMPERATURE (°C)

90

1921 G04

Undervoltage Recovery Threshold
vs Temperature

–42.5
–42.6
–42.7
–42.8
–42.9
–43.0
–43.1
–43.2
–43.3
–43.4

UNDERVOLTAGE RECOVERY THRESHOLD (V)

–43.5

–50 –30 –10 10

TEMPERATURE (°C)

30 50 70

Fuse Window Positive Threshold
vs Temperature

2.7

2.5

2.3

1921 G05

Overvoltage Threshold
vs Temperature

–68.0

–68.5

–69.0

–69.5

–70.0

–70.5

–71.0

OVERVOLTAGE THRESHOLD (V)

–71.5

–72.0

90

–50 –30 –10 10

Fuse Window Negative Threshold
vs Temperature

–2.0

–2.2

–2.4

TEMPERATURE (°C)

30 50 70

1921 G06

Overvoltage Hysteresis
vs Temperature

1.50

1.45

1.40

1.35

1.30

1.25

1.20

1.15

1.10

OVERVOLTAGE HYSTERESIS (V)

1.05

90

1.00
–50 –30 –10 10

Output R

TEMPERATURE (°C)

DS(ON)

30 50 70

vs Temperature

90

1921 G07

2.1

1.9

FUSE POSITIVE THRESHOLD (V)

1.7

1.5
–50 –30 –10 10

TEMPERATURE (°C)

30 50 70

1921 G08

–2.6

–2.8

–3.0

FUSE NEGATIVE THRESHOLD (V)

90

–3.2

–50 –30 –10 10

TEMPERATURE (°C)

30 50 70

90

1921 G09

1921i

3

LTC1921

UW

TYPICAL PERFOR A CE CHARACTERISTICS

Undervoltage Response Time

10000

TA = 25°C

1000

RESPONSE TIME (µs)

100

U

4.5

4.6

SUPPLY STEP FROM UNDERVOLTAGE

RECOVERY THRESHOLD (V)

4.8

4.9 5.0 5.1

UU

5.24.7

1921 G10

PI FU CTIO S

VA (Pin 1):
is compared to the valid supply voltage window and the
result is output at OUT A (Pin 5). Supply current is drawn
from this pin as well as from VB (Pin 8).

FUSE A (Pin 2): This pin monitors the state of a fuse by
comparing the voltage at this pin to the voltage at V
(Pin␣ 1). The result is output at OUT F (Pin 4).

RTN (Pin 3): Supply Return Reference. This pin must be
at an equal or higher potential than the other pins and
should be wired to the –48V return.

OUT F (Pin 4): This pin indicates the state of the external
fuses by ORing the comparisons made to the FUSE A and
FUSE B pins. If V
window around VA) and V
exhibit a high internal impedance to the RTN pin. If
V

FUSEA

internally to the RTN pin and can shunt enough current to
turn off an optocoupler or LED wired between these pins.
OUT F should be clamped externally so that it cannot be
driven more than 8V below RTN. This is done automati­cally by the optocoupler or LED diodes shown in the
application circuits.

OUT A (Pin 5): Indicates the State of VA. If VA is within the
specified voltage window (neither undervoltage nor over­voltage), OUT A will exhibit a high internal impedance to the

Supply to be Monitored. The voltage at this pin

FUSEA

≠ VA or V

≅ VA (V

FUSEB

≠ VB, then OUT F is shorted

FUSEB

is within the specified

FUSEA

≅ VB, then OUT F will

A

Overvoltage Response Time

10000

TA = 25°C

1000

RESPONSE TIME (µs)

100

1.3

1.5

SUPPLY STEP FROM OVERVOLTAGE

RECOVERY THRESHOLD (V)

1.9

2.1 2.3

2.51.7

1921 G11

OUT F pin. If VA is outside the specified overvoltage or
undervoltage limits, then OUT A is shorted internally to the
OUT F pin and can shunt enough current to turn off an
optocoupler or LED wired between these pins. OUT A should
be clamped externally so that it cannot be driven more than
8V below RTN. This is done automatically by the
optocoupler or LED diodes shown in the application circuits.

OUT B (Pin 6): Indicates the State of VB. If VB is within the
specified voltage window (neither undervoltage nor over­voltage), OUT B will exhibit a high internal impedance to the
OUT A pin. If VB is outside the specified overvoltage or
undervoltage limits, then OUT B is shorted internally to the
OUT A pin and can shunt enough current to turn off an
optocoupler or LED wired between these pins. OUT B should
be clamped externally so that it cannot be driven more than
8V below RTN. This is done automatically by the
optocoupler or LED diodes shown in the application circuits.

FUSE B (Pin 7): This pin monitors the state of a fuse by
comparing the voltage at this pin to the voltage at V

B

(Pin␣ 8). The result is output at OUT F (Pin 4).
VB (Pin 8):

Supply to be Monitored. The voltage at this pin
is compared to the valid supply voltage window and the
result is output at OUT B (Pin 6). Supply current is drawn
from this pin as well as from VA (Pin 1).

1921i

4