adm6339farjz-rl7 Analog Devices, Inc., adm6339farjz-rl7 Datasheet - Page 8

• Manufacturer Part Number: adm6339farjz-rl7
• Description: Quad Voltage Microprocessor Supervisory Circuit
• Manufacturer: Analog Devices, Inc.

ADM6339
THEORY OF OPERATION
The ADM6339 is a compact, low power supervisory circuit that
is capable of monitoring up to four voltages in a multisupply
application.
The device includes several factory-set voltage threshold options
for monitoring −5.0 V, 1.8 V, 2.5 V, 3.0 V, 3.3 V, and 5.0 V
supplies. The ADM6339 is available with one to three adjustable
threshold options. The adjustable voltage threshold options
available are 1.23 V, 0.62 V, and −0.5 V. See the Ordering Guide
section for a list and description of all available options.
INPUT CONFIGURATION
Built-in hysteresis improves the ADM6339’s immunity to short
input transients, without noticeably reducing the threshold
accuracy. The internal comparators each have a hysteresis of
0.3% with respect to the reset threshold voltage. (The IN
of the ADM6339Q model has a hysteresis of 0.47% with respect
to its reset threshold voltage of −0.487 V.)
Monitored inputs are resistant to short power supply glitches.
Figure 6 depicts the ADM6339 glitch immunity data. To
increase noise immunity in noisy applications, place a 0.1 μF
capacitor between the IN
to IN
IN
device’s power supply input. Do not allow unused monitor
inputs to float or to be grounded. Unused IN
positive thresholds can be connected directly to the IN
Unused IN
more negative supply.
MONITORING NEGATIVE VOLTAGES < −5.0 V
A number of ADM6339 models include a pretrimmed threshold
option to monitor −5.0 V voltage levels. Use a low impedance
resistor divider network similar to that shown in Figure 14 to
monitor supplies more negative than −5.0 V .
The current through the external resistor divider should be
greater than the input current for the −5.0 V monitor options.
2
must always be used for normal operation because it is the
1
, IN
MONITORED
3
SUPPLIES
, and IN
4
options with negative thresholds must be tied to a
Figure 13. Typical Applications Circuit
4
also improves noise immunity.
2
input and ground. Adding capacitance
ADM6339
IN
IN
IN
IN
1
2
3
4
GND
RESET
MICROPROCESSOR
3
or IN
4
inputs with
2
input.
4
input
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For an input monitor current error of <1%, the resistor network
current should be greater than or equal to 2 mA (for I
maximum). Set R
V
where:
R
V
V
For example, when monitoring a nominal voltage of −12 V,
V
using the previous equation, R
USER ADJUSTABLE THRESHOLD OPTIONS
The ADM6339 offers the choice of three adjustable IN
threshold voltages: 1.23 V, 0.62 V, or −0.5 V.
When using an adjustable threshold of 1.23 V (typical), to
monitor a voltage greater than 1.23 V, connect a resistor divider
network to the device as shown in Figure 15. V
threshold voltage, can be expressed as
The ADM6339 has a guaranteed input current of ±0.1 µA on its
1.23 V adjustable input. Resistor values up to 100 kΩ can be
used for R
The same approach is taken when using the 0.62 V (typical)
adjustable threshold input. Use the following equation to solve
for the values of R
The 0.62 V (typical) adjustable threshold input offers high
threshold accuracy of ±0.8%.
2
INTH
INTH
TH
INTH
≤ 2.49 kΩ.
is the internal threshold voltage.
R
V
V
reset threshold voltage, using the following equation:
is the desired threshold voltage.
= −11.1 V, V
1
INTH
INTH
= R
2
= 1.23 V((R
= 0.62 V((R
2
with <1% error.
((V
Figure 15. Setting the 1.23 V Adjustable Monitor
INTH
Figure 14. Negative Voltage Monitoring
2
1
TH
/V
= 2.5 kΩ. Calculate R
V
and R
INTH
V
= −4.63 V, and R
TH
INTH
R
R
1
1
2
1
R
R
) − 1)
+ R
+ R
1
2
2
:
2
2
)/(R
)/(R
1
V
ADM6339
= 3.48 kΩ.
REF
2
2
))
))
ADM6339
= 1.23V
2
= 2.49 kΩ. Therefore,
1
based on the desired
INTH
, the desired
IN4
= 20 µA
x
input