MAX968EUA-T Maxim Integrated Products, MAX968EUA-T Datasheet - Page 10

• Manufacturer Part Number: MAX968EUA-T
• Description: Comparator ICs Quad, Micropower, Ul tra-Low-Voltage, Rai
• Manufacturer: Maxim Integrated Products

Single/Dual/Quad, Micropower,
Ultra-Low-Voltage, Rail-to-Rail I/O Comparators
Figure 2 illustrates the case in which IN- has a fixed
voltage applied, and IN+ is varied. If the inputs were
reversed, the figure would be the same, except with an
inverted output.
To add hysteresis to the MAX965/MAX967/MAX968/
MAX969, connect resistor R1 between REF and HYST,
and connect resistor R2 between HYST and GND
(Figure 3). If additional hysteresis is not required,
connect HYST to REF. When hysteresis is added, the
upper and lower trip points change by the same
amount in opposite directions. The hysteresis band (the
difference between the upper and lower trip points,
V
and REF. The HYST input voltage range is from REF
down to (REF - 50mV). This yields a hysteresis band
from ±1mV to a maximum of ±50mV. Calculate the val-
ues of R1 and R2 for the desired hysteresis band with
the following formulas:
where I
not exceed the REF source capability (12µA typical),
and is significantly larger than the HYST leakage cur-
rent (5nA typical). I
are good choices. If 2.4MΩ is chosen for R2 (I
0.5µA), the equation for R1 and V
mated as:
In the MAX967/MAX968/MAX969, the HYST pin pro-
grams the same hysteresis for all comparators in the
package.
10
Figure 3. Programming the HYST Pin
HB
) is approximately twice the voltage between HYST
______________________________________________________________________________________
REF
R1 = V
R2 = (V
R1(kΩ) = 2 x V
(the current sourced by the reference) does
R2
R1
I
REF
HB
REF
MAX965/MAX967/MAX968/MAX969
REF
/ I
- V
REF
values between 0.1µA and 4µA
REF
HYST
HB
HB
GND
+1.6V TO +5.5V
) / I
MAX965
MAX967
MAX968
MAX969
(mV)
V
Adding Hysteresis to the
CC
REF
HB
can be approxi-
REF
=
Due to the internal structure of the input developed for
ultra-low-voltage operation, the hysteresis band varies
with common-mode voltage. The graph Programmed
Hysteresis vs. Common-Mode Voltage in the Typical
Operating Characteristics shows this variation. Notice
that the hysteresis band increases to almost twice the
calculated value toward the ends of the common-mode
range. This is apparent only when programming addi-
tional hysteresis using the HYST pin. The hysteresis
band is constant when HYST is connected to REF.
The MAX966/MAX970 do not have a HYST pin for pro-
gramming hysteresis. Hysteresis can be generated with
three resistors using positive feedback (Figure 4). This
method generally draws more current than the method
using the HYST pin on the MAX965/MAX967/MAX968/
MAX969. Also, the positive feedback method slows
hysteresis response time. Use the following procedure
to calculate the resistor values:
1) Select R3. The leakage current of IN+ is under 5nA,
2) Choose the hysteresis band required (V
Figure 4. External Hysteresis
so the current through R3 should be at least 500nA
to minimize errors caused by leakage current. The
current through R3 at the trip point is (V
R3. Taking into consideration the two possible out-
put states and solving for R3 yields two formulas:
and
Use the smaller of the two resulting resistor values.
For example, if V
the two resistor values are 2.4MΩ and 7.6mΩ. For
R3, choose the 2.2MΩ standard value.
example, choose 50mV.
V
IN
R3 = V
R3 = (V
Adding Hysteresis to the MAX966/MAX970
R1
R2
REF
REF
REF
/ 500nA
V
- V
REF
CC
= 1.2V and V
R3
) / 500nA
GND
V
V
CC
CC
MAX966
MAX970
OUT
CC
REF
= 5.0V, then
HB
R4
). For this
- V
OUT
) /