LTC1921IMS8 Linear Technology, LTC1921IMS8 Datasheet - Page 8

• Manufacturer Part Number: LTC1921IMS8
• Description: IC DUAL PWR SUPPLY MONITOR 8MSOP
• Manufacturer: Linear Technology

Specifications of LTC1921IMS8

• Applications: Dual Power Supply Monitor
• Voltage - Supply: 10 V ~ 80 V
• Current - Supply: 160µA
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 8-MSOP, Micro8™, 8-uMAX, 8-uSOP,
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Voltage - Input: -

LTC1921
APPLICATIO S I FOR ATIO
internal impedance to the return (RTN) pin. The applica-
tion must be designed so that an open fuse condition will
force the fuse input (FUSE A or FUSE B) to be outside the
specified window around the supply pins, such as with a
weak pull-up resistor to RTN, so that the LTC1921 can
properly indicate a fault at OUT F. If supply diodes that
exhibit high reverse leakage, such as Schottky diodes, are
used, then the values of the pull-up resistors must be
reduced accordingly.
The FUSE A and FUSE B pins may also be used in
conjunction with V
son, provided that one of the circuit nodes to be compared
can provide the small amount of supply current required
to bias the IC. The LTC1921 is ideally suited for compari-
son functions in a circuit where only high supply voltages
are available.
Output Pins
The output pins in the LTC1921 are designed to shunt
external optoisolator diodes or LEDs during a supply or
fuse fault condition. Up to three diodes may be used in
8
SUPPLY A
SUPPLY B
–48V
–48V
RETURN
A
U
–48V
and V
F1
F2
U
B
for simple window compari-
R1
100k
R2
100k
1
8
2
7
W
V
V
FUSE A
FUSE B
A
B
LTC1921
RTN
D2
D1
3
OUT A
OUT B
OUT F
U
1921 F02
4
5
6
MOC207
MOC207
MOC207
R3
47k
1/4W
Figure 2.
series, one for each output. In this configuration
(Figure 2), a diode connected between OUT F and RTN will
indicate the condition of both fuses. A diode connected
between OUT A and OUT F will indicate the condition of
supply A (V
OUT A will indicate the condition of supply B (V
resistor connected from OUT B to the negative supply is
required to bias the diodes. The LTC1921 is designed to
allow the current from this resistor to flow through the
diodes during normal supply conditions and intact fuses,
and will shunt this current away from the proper diodes
during a fault condition. These diodes will further clamp
the output pin potentials to RTN in order to keep the
outputs within rated voltages. If LEDs are used instead of
optoisolators, they should be green since they will be lit
when the supplies are within the proper voltage range.
The LTC1921 may be connected in such a way as to OR
various outputs to allow the use of fewer optocouplers or
LEDs (Figures 3a and 3b). One and two diode circuits are
shown.
47k
47k
47k
= LOGIC COMMON
–48V OUT
5V
FUSE
STATUS
5V
SUPPLY A
STATUS
5V
SUPPLY B
STATUS
A
) and a diode connected between OUT B and
0: LED/PHOTODIODE ON
1: LED/PHOTODIODE OFF
*IF BOTH FUSES (F1 AND F2) ARE OPEN,
OK: WITHIN SPECIFICATION
OV: OVERVOLTAGE
UV: UNDERVOLTAGE
UV OR OV
UV OR OV
ALL STATUS OUTPUTS WILL BE HIGH
SINCE R3 WILL NOT BE POWERED
V
FUSE A
= V
= V
V
OK
OK
V
V
A
A
A
A
A
UV OR OV
UV OR OV
V
FUSE B
= V
= V
OK
OK
V
V
V
B
B
B
B
B
SUPPLY A
FUSE STATUS
STATUS
0
0
1
1
0
1
1
1*
SUPPLY B
STATUS
0
1
0
1
B
). A
1921f