LTC2901 Linear Technology, LTC2901 Datasheet - Page 11

• Manufacturer Part Number: LTC2901
• Description: Programmable Quad Supply Monitor with Adjustable Reset and Watchdog Timers
• Manufacturer: Linear Technology

APPLICATIO S I FOR ATIO
In a negative adjustable application, the minimum value
for R4 is limited by the sourcing capability of V
With no other load on V
Tables 2 and 3 offer suggested 1% resistor values for
various adjustable applications.
Although all four supply monitor comparators have built-
in glitch immunity, bypass capacitors on V1 and V2 are
recommended because the greater of V1 or V2 is also the
V
are allowed.
Power-Down
On power-down, once any of the V
their threshold, RST and COMPX are held at a logic low.
A logic low of 0.4V is guaranteed until both V1 and V2
drop below 1V. If the bandgap reference becomes invalid
(V
above 2.4V max.
CC
CC
1.21V 1mA = 1.21k .
for the chip. Filter capacitors on the V3 and V4 inputs
< 2V typ), the part will reprogram once V
Figure 6. Setting the Negative Adjustable Trip Point
Figure 5. Setting the Positive Adjustable Trip Point
V3 OR V4
V
TRIP
V
R4
1%
R3
1%
TRIP
R3
1%
R4
1%
12
13
U
V
V4
REF
REF
U
+
–
, R4 (minimum) is:
0.5V
–
+
LTC2901
+
–
LTC2901
W
X
inputs drop below
2901 F06
2901 F05
REF
U
( 1mA).
CC
rises
Table 2. Suggested 1% Resistor Values for the ADJ Inputs
Table 3. Suggested 1% Resistor Values for the –ADJ Input
Monitor Output Rise and Fall Time Estimation
All of the outputs (RST, COMPX, WDO) have strong pull-
down capability. If the external load capacitance (C
for a particular output is known, output fall time (10% to
90%) is estimated using:
where R
transistor. The typical performance curve (V
demonstrates that the pull-down current is somewhat
linear versus output voltage. Using the 25 C curve, R
estimated to be approximately 40 . Assuming a 150pF
load capacitance, the fall time is about 13.2ns.
Although the outputs are considered to be “open-drain,”
they do have a weak pull-up capability (see COMPX or RST
V
V
t
FALL
SUPPLY
SUPPLY
–5.2
–10
–12
7.5
3.3
2.5
1.8
1.5
1.2
0.9
–2
–5
12
10
8
6
5
3
1
PD
(V)
(V)
2.2 • R
is the on-resistance of the internal pull-down
PD
V
V
–11.30
TRIP
TRIP
11.25
4.725
3.055
2.325
1.685
1.410
1.120
0.933
0.840
–1.87
–4.64
–4.87
–9.31
2.82
9.4
7.5
5.6
• C
7
(V)
(V)
LOAD
R3 (k )
R3 (k )
2150
1780
1400
1300
1020
1130
86.6
68.1
845
511
464
365
237
182
124
187
464
487
931
LTC2901
OL
R4 (k )
R4 (k )
2901is sn2901
100
100
100
100
100
100
100
100
100
100
100
100
100
100
121
121
121
121
121
vs I
11
LOAD
SINK
PD
is
)
)