LTC2960
APPLICATIONS INFORMATION
The closest 1% resistor value is 34k. R3 is easily obtained
from:
R3 = R
SUM
– R1 – R2 = 8M – 499k – 34k
R3 = 7.467MΩ
The closest 1% resistor value is 7.5MΩ. Plugging the
standard values back into the equations yields the design
values for the falling reset and IN
+
voltages:
V
IN+
= 6.4V, V
RST
= 6.028V
Figure 2 demonstrates how the inputs can be biased
to monitor two voltages (V1, V2). In this example, four
resistors are required. Calculate each divider ratio for the
desired falling threshold (V
FT
) using:
V
RnB V
FT
=
– 1=
FT
– 1
0.4V
RnA V
TH
In Figure 2, OUT is tied back to the
MR
input, making the
state of the
RST
output dependent upon both V1 and V2. If
V1 and V2 are both above the configured falling threshold
plus hysteresis,
RST
is allowed to pull high. If independent
operation of the status outputs is desired, simply omit the
OUT and
MR
connection.
V1
V2
R2B
R1B
LTC2960-1/
LTC2960-3
ADJ
RST
OUT (V)
to a user defined voltage up to 36V with a resistor. The
open-drain pull-up voltage may be greater than V
CC
. Select
a resistor compatible with desired output rise time and
load current specifications. Figure 3 demonstrates typical
LTC2960-1 OUT output behavior. When the status outputs
are low, power is dissipated in the pull-up resistors.
7.5
6
4.5
3
1.5
0
0
1.5
3
4.5
V
CC
(V)
6
7.5
2960 F03
Figure 3. OUT vs V
CC
(LTC2960-1) Externally Configured for 6V
Threshold with
RST
Tied to V
CC
Through Pull-up Resistor
IN
+
R2A
R1A
MR
OUT
2960 F02
The outputs of both the LTC2960-3 and LTC2960-4 can be
configured as either low voltage active pull-up or open-
drain. This is done by tying the DV
CC
pin to either a supply
or GND. Using the active pull-up configuration, DV
CC
tied
to a supply, lowers power dissipation by eliminating the
static current drawn by pull-up resistors when the outputs
are low and improves output rise time. In Figure 4(a), an
LTC2960-3 has active pull-up outputs configured by tying
DV
CC
to a 1.6V to 5.5V supply. In Figure 4(b), the LTC2960-3
has open-drain outputs configured by tying the DV
CC
pin to
ground. When DV
CC
is connected to ground both outputs
are open-drain and pull-up resistors are required.
Some applications require
RST
and/or OUT outputs to
be valid with V
CC
down to ground when DV
CC
is tied to
V
CC
. Active pull-up satisfies this requirement with the ad-
dition of an optional external resistor from the output to
ground. The resistor provides a path for leakage currents,
preventing the output from floating to undetermined volt-
ages when connected to high impedance (such as CMOS
logic inputs). The resistor value should be small enough to
2960f
Figure 2. Dual Voltage Monitoring
SELECTING OUTPUT LOGIC STYLE
The LTC2960 status outputs are available in two options:
open-drain (LTC2960-1/LTC2960-2) or active pull-up with
the DV
CC
pin replacing the RT pin (LTC2960-3/LTC2960-4).
The open-drain option allows the outputs to be pulled up
9
LINEAR [ LINEAR INTEGRATED SYSTEMS ]
