MAX3318CAP+ Maxim Integrated, MAX3318CAP+ Datasheet - Page 12

• Manufacturer Part Number: MAX3318CAP+
• Description: RS-232 Interface IC
• Manufacturer: Maxim Integrated
• Series: MAX3316, MAX3317, MAX3318, MAX3319r

Specifications of MAX3318CAP+

• Data Rate: 460 Kbps
• Operating Supply Voltage: 2.5 V
• Supply Current: 1 mA
• Operating Temperature Range: 0 C to + 70 C
• Function: Transceiver
• Number Of Drivers: 2
• Number Of I/os: 8
• Number Of Receivers: 2
• Propagation Delay Time Ns: 0.175 us
• Shutdown: Yes

Low-Power Dual-/Triple-Voltage SC70 µP
Supervisory Circuits
Figure 4. Using Power-Fail Input to Monitor an Additional
Power Supply
The power-fail comparator has a typical input hystere-
sis of 2.5mV. This is sufficient for most applications in
which a power-supply line is being monitored through
an external voltage-divider. If additional noise margin is
desired, connect a resistor between PFO and PFI, as
Figure 5. Interfacing to µPs with Bidirectional Reset I/O
12
V
V
B) V
A) V
EXT_TH
EXT_TH
V
CC
V
IN
IN
CC
1 V
IS NEGATIVE
IS POSITIVE
______________________________________________________________________________________
CC
2
R1
R2
R1
R2
V
V
CC
CC
2
1
MAX6737
MAX6739
MAX6743
MAX6744
MAX6745
PFI
PFI
GND
MAX6742
MAX6745
MAX6742
MAX6745
GND
GND
RESET
Adding Hysteresis to the
PFO
PFO
Power-Fail Comparator
RESET TO OTHER SYSTEM COMPONENTS
V
V
EXT_TH
EXT_TH
4.7kΩ
V
= V
= R
PFI
TH-PFI
2
= 488mV
(
RESET
(V
(
TH-PFI
R1 + R2
R2
)
)
GND
(
µP
)
R
1
1
+
R
1
2
)
-
V
R
CC
1
shown in Figure 6. Select the values of R1, R2, and R3
such that PFI sees V
its power-fail trip point (V
its power-good trip point (V
dow extends between the specified V
thresholds. R3 adds the additional hysteresis by sink-
ing current from the R1/R2 divider network when the
PFO output is logic low and sourcing current into the
network when PFO is logic high. R3 is typically an order
of magnitude greater than R1 or R2.
The current through R2 should be at least 1µA to ensure
that the 10nA (max) PFI input current does not significant-
ly shift the trip points. Therefore, for most applications:
PFO is an open-drain output requiring an external
pullup resistor, R4. Select R4 to be less than 1% of R3.
V
V
V
R2 = 488kΩ (FOR >1µA R2 CURRENT)
R3 = (R1 x V
R4 ≤ 0.01 x R3
Many dual-voltage processors/ASICs require specific
power-up/power-down sequences for the I/O and core
supplies.
Figure 6. Adding Hysteresis to Power Fail for Push-Pull PFO
R
GOOD
FAIL
PU
V
1
EXT
=
R1
R2
= V
R2 < V
= DESIRED V
R
2
= DESIRED V
PULLUP
PFI
(
V
GOOD
MAX6742
MAX6745
TH-PFI
PU
GND
R3
Power Sequencing Applications
) / (V
(FOR OPEN-DRAIN PFO)
-
PFO
V
/ 1mA < 0.488V / 1mA < 488kΩ
EXT
TH PFI
GOOD
EXT
TH-PFI
V
V
V
R2 = 200kΩ (FOR > 2.5µA R2 CURRENT)
R1 = R2 ((V
R3 = (R1 x V
GOOD
FAIL
OH
−
V
PULLUP
= V
FAIL VOLTAGE THRESHOLD
= DESIRED V
= DESIRED V
GOOD VOLTAGE THRESHOLD
CC
R4
FAIL
1 (FOR PUSH-PULL PFO)
)
- V
GOOD
OH
V
(488mV) when V
GOOD
−
) / (V
TH PFI
PFO
FAIL
V
- V
) and when V
IN
EXT
(
GOOD
EXT
TH-PFI
V
-
FAIL VOLTAGE THRESHOLD
TH PFI GOOD
GOOD VOLTAGE THRESHOLD
)
- V
) - (V
). The hysteresis win-
-
FAIL
TH-PFI
)
(
FAIL
)(V
V
V
GOOD
PU
- V
and V
EXT
FAIL
EXT
V
V
GOOD
FAIL
) / V
-
V
rises to
PU
FAIL
falls to
) / V
GOOD
TH-PFI
)