LTC2960
APPLICATIONS INFORMATION
The closest 1% resistor value is 34k. R3 is easily obtained
from:
to a user defined voltage up to 36V with a resistor. The
open-drainpull-upvoltagemaybegreaterthanV .Select
CC
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.
R3 = R
– R1 – R2 = 8M – 499k – 34k
SUM
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:
7.5
+
6
+
V
= 6.4V, V
= 6.028V
IN
RST
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
4.5
3
desired falling threshold (V ) using:
FT
1.5
0
RnB
RnA VTH
V
V
FT
0.4V
FT
=
– 1=
– 1
0
1.5
3
4.5
(V)
6
7.5
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
plushysteresis, RSTisallowedtopullhigh. Ifindependent
operation of the status outputs is desired, simply omit the
OUT and MR connection.
V
CC
2960 F03
Figure 3. OUT vs VCC (LTC2960-1) Externally Configured for 6V
Threshold with RST Tied to VCC Through Pull-up Resistor
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 pin to either a supply
or GND. Using the active pull-up configuration, DV tied
V1
V2
CC
LTC2960-1/
R2B R1B
LTC2960-3
CC
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
ADJ
RST
+
IN
OUT
MR
DV toa1.6Vto5.5Vsupply.InFigure4(b),theLTC2960-3
CC
2960 F02
R2A R1A
hasopen-drainoutputsconfiguredbytyingtheDV pinto
CC
ground. When DV is connected to ground both outputs
CC
are open-drain and pull-up resistors are required.
Figure 2. Dual Voltage Monitoring
Some applications require RST and/or OUT outputs to
be valid with V down to ground when DV is tied to
CC
CC
V . Active pull-up satisfies this requirement with the ad-
CC
SELECTING OUTPUT LOGIC STYLE
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
logicinputs). Theresistorvalueshouldbesmallenoughto
The LTC2960 status outputs are available in two options:
open-drain (LTC2960-1/LTC2960-2) or active pull-up with
theDV pinreplacingtheRTpin(LTC2960-3/LTC2960-4).
CC
The open-drain option allows the outputs to be pulled up
2960f
9
Linear Systems [ Linear Systems ]
