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LTC2900-1CMS Datasheet Download

Part No.:
LTC2900-1CMS
Download:
Download Datasheet
Description:
[Programmable Quad Supply Monitor with Adjustable Reset Timer]
File Size:
200 K
Page:
16 Pages
Logo:
Manufacturer:
LINER [ LINEAR TECHNOLOGY ]
PCB Prototype
 LTC2900-1CMS Datasheet Page:5LTC2900-1CMS Datasheet Page:6LTC2900-1CMS Datasheet Page:7LTC2900-1CMS Datasheet Page:8LTC2900-1CMS Datasheet Page:10LTC2900-1CMS Datasheet Page:11LTC2900-1CMS Datasheet Page:12LTC2900-1CMS Datasheet Page:13 
LTC2900
APPLICATIO S I FOR ATIO
Power-Up
The greater of V1, V2 is the internal supply voltage (V
CC
).
On power-up, V
CC
will power the drive circuits for the RST
pin. This ensures that the RST output will be low as soon
as V1 or V2 reaches 1V. The RST output will remain low until
the part is programmed. After programming, if any one of
the V
X
inputs is below its programmed threshold, RST will
be a logic low. Once all the V
X
inputs rise above their thresh-
olds, an internal timer is started and RST is released after
the programmed delay time. If V
CC
< (V3 – 1) and V
CC
< 2.4V,
the V3 input impedance will be low (1kΩ typ).
Monitor Programming
The LTC2900 input voltage combination is selected by
placing the recommended resistive divider from V
REF
to
GND and connecting the tap point to V
PG
, as shown in
Figure 4. Table 1 offers recommended 1% resistor values
LTC2900
8
V
REF
7
V
PG
6
GND
R1
1%
R2
1%
2900 F04
Figure 4. Monitor Programming
for the various modes. The last column in Table 1 specifies
optimum V
PG
/V
REF
ratios (±0.01) to be used when pro-
gramming with a ratiometric DAC.
During power-up, once V1 or V2 reaches 2.4V max, the
monitor enters a programming period of approximately
150µs during which the voltage on the V
PG
pin is sampled
and the monitor is configured to the desired input combi-
nation. Do not add capacitance to the V
PG
pin. Immediately
after programming, the comparators are enabled and
supply monitoring will begin.
U
Table 1. Voltage Threshold Programming
MODE
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
V1 (V) V2 (V) V3 (V) V4 (V) R1 (kΩ) R2 (kΩ)
5.0
5.0
3.3
3.3
3.3
5.0
5.0
5.0
5.0
5.0
3.3
3.3
3.3
5.0
5.0
5.0
3.3
3.3
2.5
2.5
2.5
3.3
3.3
3.3
3.0
3.0
2.5
2.5
2.5
3.3
3.3
3.0
ADJ
ADJ
ADJ
ADJ
1.5
2.5
2.5
2.5
2.5
ADJ
1.8
1.8
1.8
1.8
1.8
1.8
ADJ
–ADJ
ADJ
–ADJ
ADJ
ADJ
1.8
1.5
ADJ
ADJ
1.5
ADJ
–ADJ
–ADJ
ADJ
ADJ
Open
93.1
86.6
78.7
71.5
66.5
59.0
53.6
47.5
40.2
34.8
28.0
22.1
16.2
9.53
Short
Short
9.53
16.2
22.1
28.0
34.8
40.2
47.5
53.6
59.0
66.5
71.5
78.7
86.6
93.1
Open
V
PG
V
REF
0.000
0.094
0.156
0.219
0.281
0.344
0.406
0.469
0.531
0.594
0.656
0.719
0.781
0.844
0.906
1.000
W
U U
Supply Monitoring
The LTC2900 is a low power, high accuracy program-
mable quad supply monitoring circuit with a common
reset output and a manual reset input. Reset timing is
adjustable using an external capacitor. Single pin pro-
gramming selects 1 of 16 input voltage monitor combina-
tions. All four voltage inputs must be above predetermined
thresholds for the reset not to be invoked. The LTC2900
will assert the reset output during power-up, power-down
and brownout conditions on any one of the voltage inputs.
The inverting inputs on the V3 and/or V4 comparators are
set to 0.5V when the positive adjustable modes are se-
lected (Figure 5). The tap point on an external resistive
divider, connected between the positive voltage being
2900f
9