Datasheet

LTC2909
14
2909fb
APPLICATIO S I FOR ATIO
WUU
U
This imposes a practical limit of 1F (9 second timeout) if
the length of timeout during power-up needs to be longer
than 200ms. If the power-up timeout is not important,
larger capacitors may be used, subject to the limitation
that the capacitor leakage current must not exceed 500nA,
or the function of the timer will be impaired.
⎯
R
⎯
S
⎯
T Output Characteristics
The DC characteristics of the
⎯
R
⎯
S
⎯
T pull-down strength
are shown in the Typical Performance Characteristics
section.
⎯
R
⎯
S
⎯
T is an open-drain pin and thus requires an
external pull-up resistor to the logic supply.
⎯
R
⎯
S
⎯
T may be
pulled above V
CC
, providing the voltage limits of the pin
are observed.
The open-drain nature of the
⎯
R
⎯
S
⎯
T pin allows for wired-OR
connection of several LTC2909s to monitor more than two
supplies (see Typical Applications). Other logic with open-
drain outputs may also connect to the
⎯
R
⎯
S
⎯
T line, allowing
other logic-determined conditions to issue a reset.
As noted in the discussion of power up and power down,
the circuits that drive
⎯
R
⎯
S
⎯
T are powered by V
CC
. During a
fault condition, V
CC
of at least 0.5V guarantees a V
OL
of
0.15V at
⎯
R
⎯
S
⎯
T .
V
CC
ADJ1
LTC2909-2.5
REF
ADJ2
RST
SEL
R
PU
10k
R
N2A
1.37M
15V
5V
–5V
–15V
3.3V
2.5V
R
N1A
133k
R
N2B
3.09M
R
N1B
107k
R
P2A
1.15M
R
P1A
137k
R
P2B
3.09M
R
P1B
115k
C
TMR1
2.2nF
C
TMR2
2.2nF
C
BYP1
100nF
C
BYP2
100nF
TMR
GND
V
CC
ADJ1
LTC2909-3.3
REF
ADJ2
2909 TA02
RST
SEL
TMR
GND
SYSTEM
Six Supply Undervoltage Monitor with 2.5V Reset Output and 20ms Timeout
TYPICAL APPLICATIO S
U
±12V UV Monitor Powered from
12V, 20ms Timeout (1.8V Logic Out)
V
CC
ADJ1
LTC2909-2.5
REF
R
P1B2
681k
ADJ2
RST
SEL
TMR
M1
GND
R
P1B
13.7k
R
P1A
18.7k
R
P2A2
169k
V
UV(RISING)
: 43.3V
V
UV(FALLING)
: 38.7V
V
OV(RISING)
: 71.6V
V
OV(FALLING)
: 70.2V
R
P2A
1.43M
V
IN
36V TO 72V
R
P2B
1.91M
R
CC
27k
0.25W
C
BYP
100nF
5V
R
PU
10k
2909 TA03
M1, M2: FDG6301N OR SIMILAR
IF LOADING OF RST WILL EXCEED 1nF,
A 1nF BYPASS CAPACITOR ON M1’s
DRAIN IS RECOMMENDED
M2
SYSTEM
V
CC
ADJ1
LTC2909-2.5
1.8V
REF
ADJ2
RST
SEL
R
N1
107k
R
PU
10k
FAULT
OUTPUT
C
TMR
2.2nF
2909 TA01b
R
P2
1.07M
12V
–12V
R
P1
49.9k
*OPTIONAL FOR ESD
MANUAL
RESET
PUSHBUTTON
C
BYP
100nF
R
N2
2.49M
10k*
R
CC
10k
TMR
GND
48V Telecom UV/OV Monitor with Hysteresis