isl21440 Intersil Corporation, isl21440 Datasheet - Page 11

• Manufacturer Part Number: isl21440
• Description: Micropower Voltage Reference With Comparator
• Manufacturer: Intersil Corporation

Typical Performance Curves
Functional Description
Device Power
The ISL21440 device has a single positive supply pin, V+,
and two other supply pins, V- and GND. Normally for
single supply applications the V- pin is tied to system
ground as well as the GND pin. The separate ground pin
allows the comparator to be powered by split supplies
from ±1.0V to ±5.5V. Note that the minimum supply
voltage will be 0.8V above the comparator maximum
input level for accurate operation.
Comparator Section
The comparator inputs can swing from the negative
supply (GND pin) to within 0.8V of the positive supply
(V+). Alternatively, with the comparator input set at
the 1.182V reference level, the minimum input voltage
for accurate operation is 2.0V. If the inputs are
expected to see voltage levels above V+ or below
ground, they should be clamped with low leakage
Schottky diodes.
The CMOS output swings essentially from the GND
potential to V+ potential, depending on load current. If
loads in excess of 1mA are expected, then a 0.1µF
decoupling capacitor at the V+ pin should be added.
Voltage Reference Section
The voltage reference is a micropower FGA reference
and is set to 1.182V ±0.5% at the factory. The
reference output can source up to 2mA but the sink
capability is very limited at only 10µA, maximum.
Small value capacitors, up to 10nF, can be used on the
reference output to lower noise if desired.
Applications Information
Handling and Board Mounting
FGA references provide excellent initial accuracy and
low temperature drift at the expense of very little
FIGURE 23. POWER-UP/DOWN OUTPUT RESPONSE (V+ = 3V, IN+ = V+, IN- = V
11
-0.5
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0
0
0.2
0.4
0.6
ISL21440
(Continued)
0.8
TIME (ms)
1.0 1.2
power drain. There are some precautions to take to
insure this accuracy is not compromised. Excessive
heat during solder reflow can cause excessive initial
accuracy drift, so the recommended +260°C max
temperature profile should not be exceeded. Expect up
to 1mV drift from the solder reflow process.
FGA references are susceptible to excessive
X-radiation like that used in PC board manufacturing.
Initial accuracy can change 10mV or more under
extreme radiation. If an assembled board needs to be
X-rayed, care should be taken to shield the FGA
reference device.
Hysteresis
The Hysteresis function allows for changing the value of
the reference switchover point depending on the
previouse state of the comparator. This works to remove
the effects of noise or glitches in the voltage detection
input and provide more reliable output transitions.
Hysteresis is added to the ISL21440 by connecting one
resistor between the REF and HYST pins (R
another resistor(R
ground. The hysteresis voltage (V
twice the voltage difference between the HYST pin and
REF pin (V
voltage is 1.182V (V
two resistors are shown as follows:
I
the reference, usually 5µA is a safe value but for
lowest power, 0.1µA can be used.
If the hysteresis is not used, the HYST pin should be
tied to the REF pin.
R
R
REF
REF
HYST
is chosen to be less than the maximum output of
=
OUT
=
V
1.4
(
H
1.182 V
H
⁄
(
2 ∗ I
= 2 * (V
1.6
REF
–
V+
H
1.8
)
HYST
2 ⁄
=
) I
REF
REF
(
⁄
V
2.0
REF
) between the HYST pin and
REF
), Equations 1 and 2 for these
- V
=
–
HYST
V
V
HYST
HYST
)). Since the reference
H
) I
⁄
) is designed to be
⁄
I
REF
REF
REF
)
December 7, 2009
REF
), and
(EQ. 1)
(EQ. 2)
FN6532.0