LTC2909CTS85#PBF Linear Technology, LTC2909CTS85#PBF Datasheet - Page 12

• Manufacturer Part Number: LTC2909CTS85#PBF
• Manufacturer: Linear Technology

Specifications of LTC2909CTS85#PBF

• Voltage Supervisor Type: Voltage Monitor
• Number Of Voltage Supervisors: 3
• Monitored Supervisor Voltage: 3.3
• Operating Supply Voltage (min): 0.5V
• Operating Supply Voltage (max): 6V
• Package Type: TSOT-23
• Operating Temperature Classification: Commercial
• Operating Temp Range: 0C to 70C
• Pin Count: 8
• Mounting: Surface Mount
• Lead Free Status / RoHS Status: Compliant

APPLICATIO S I FOR ATIO
LTC2909
For a positive-monitoring application, R
by:
For a negative-monitoring application:
Note that the value V
tive application.
The LTC2909 can also be used to monitor a single supply
for both UV and OV. This may be accomplished with three
resistors, instead of the four required for two independent
supplies. Confi gurations are shown in Figures 3 and 4.
R
For a given R
For monitoring a negative supply with a given R
For example, consider monitoring a –5V supply at ±10%. For
this supply application: V
12
P4
Figure 3. Setting UV and OV Trip Point for a Positive Supply
R
R
R
R
R
R
P2
N2
or R
P
P
N
N
5
6
5
6
= R
= R
=
=
=
=
N4
R
R
R
R
P1
N1
P
P
N
N
may be chosen as is R
V
4
4
4
4
(2V
MON
(1 – 2V
P4
(
(
V
V
2
1 2
R
R
R
OV
UV
, monitoring a positive supply:
1
P6
P5
P4
TRIP
V
–
–
V
UV
–
UV
–
V
U
V
UV
TRIP
V
–
V
UV
– 1)
TRIP
UV
OV
ADJ1
ADJ2
1
0.5V
)
)
)
OV
1
1
V
V
U
should be negative for a nega-
OV
UV
–
–
+
–
= –5.575V and V
V
V
OV
U
V V
+
–
+
–
P1
W
above.
P2
2909 F03
is then chosen
UV
= –4.425V.
U
N4
:
Suppose we wish to consume about 5μA in the divider, so
R
1% standard values have been chosen). Suggested values
of resistors for 5% monitoring are shown in Table 3.
V
The LTC2909 contains an accurate third 10% undervoltage
monitor on the V
11.5% below the V
standard part (LTC2909-2.5) is confi gured to monitor a
2.5V supply (UVLO threshold of 2.213V), but versions
to monitor 3.3V and 5.0V (UVLO of 2.921V and 4.425V,
respectively) are available.
For applications that do not need V
2.5V version should be used, and the UVLO will simply
guarantee that the V
proper threshold and timer accuracy before the timeout
begins.
Setting the Reset Timeout
The reset timeout of the LTC2909 may be confi gured
in one of three ways: internal 200ms, programmed by
external capacitor and no timeout (comparator mode).
The mode of the timer is determined by the connection
of the TMR pin.
In externally-controlled mode, the TMR pin is connected
by a capacitor to ground. The value of that capacitor allows
for selection of a timeout ranging from about 400μs to 10
seconds. See the following section for details.
N4
CC
Figure 4. Setting UV and OV Trip Point for a Negative Supply
= 100k. We then fi nd R
Monitoring/UVLO
V
MON
R
R
R
N4
N5
N6
CC
pin. This monitor is fi xed at a nominal
CC
CC
REF
ADJ1
ADJ2
is above the minimum required for
specifi ed in the part number. The
0.5V
N5
+
–
= 21.0k, R
+
–
+
–
CC
N6
= 1.18M (nearest
monitoring, the
2909 F04
2909fb