Rainbow Electronics MAX6338 - Manual (Page 4)

_______________Detailed Description
The MAX6338 is a low-power (25µA), quad voltage
monitor designed for multivoltage systems. Preset volt-
age options for +5.0V, +3.3V, +3.0V, +2.5V, +1.8V, and
-5.0V make these quad monitors ideal for applications
such as telecommunications, desktop and notebook
computers, high-end printers, data storage equipment,
and networking equipment.
The MAX6338 has an internally trimmed threshold that
minimizes or eliminates the need for external compo-
nents. The four open-drain outputs have weak (10µA)
internal pullups to V
CC , allowing them to interface easily
with other logic devices. The MAX6338 can monitor
power supplies with either 5% or 10% tolerance specifi-
cations, depending on the selected version. An addi-
tional high-input-impedance comparator option can be
used as an adjustable voltage monitor, general-pur-
pose comparator, or digital level translator.
The weak internal pullups can be overdriven by external
pullups to any voltage from 0 to +5.5V. Internal circuitry
prevents current flow from the external pullup voltage to
V
CC . The outputs can be wire-ORed for a single “power
good” signal.
The MAX6338 has either one or two auxiliary inputs and
two or three factory-programmed threshold voltages, or
four fixed voltages. The inverting input of all compara-
tors is connected to a 1.23V bandgap reference for all
positive voltages. The noninverting terminals are acces-
sible through internal resistive voltage-dividers with
preset factory threshold voltages. In the case of auxil-
iary (AUX) input, the positive terminal of the comparator
is accessible directly for setting the threshold for the
monitored voltage.
When any of the inputs (IN1–IN4) are higher than the
threshold level, the output is high. The output goes low
as the input drops below the threshold voltage monitor.
The undervoltage lockout circuitry remains active and
the outputs remain low with V
CC down to 1V (Figure 1).
Applications Information
Hysteresis
When the voltage on one comparator input is at or near
the voltage on the other input, ambient noise generally
causes the comparator output to oscillate. The most
common way to eliminate this problem is through hys-
teresis. When the two comparator input voltages are
equal, hysteresis causes one comparator input voltage
to move quickly past the other, thus taking the input out
of the region where oscillation occurs. Standard com-
parators require hysteresis to be added through the
use of external resistors. The external resistive network
usually provides a positive feedback to the input in
order to cause a jump in the threshold voltage when
MAX6338
Quad Voltage Monitor in µMAX Package
4 _______________________________________________________________________________________
Pin Description
PIN NAME FUNCTION
1 IN1 Input Voltage 1. See Selector Guide for monitored voltages.
2 IN2 Input Voltage 2. See Selector Guide for monitored voltages.
3 IN3 Input Voltage 3. See Selector Guide for monitored voltages.
4 IN4 Input Voltage 4. See Selector Guide for monitored voltages.
5 GND Ground
6 OUT4
Output 4. OUT4 goes low when V IN4 falls below its absolute threshold. OUT4 is open drain with a 10µA
internal pullup to V CC .
7 OUT3
Output 3. OUT3 goes low when V IN3 falls below its absolute threshold. OUT3 is open drain with a 10µA
internal pullup to V CC .
8 OUT2
Output 2. OUT2 goes low when V IN2 falls below its absolute threshold. OUT2 is open drain with a 10 µA
internal pullup to V CC .
9 OUT1
Output 1. OUT1 goes low when V IN1 falls below its absolute threshold. OUT1 is open drain with a 10 µA
internal pullup to V CC .
10 V CC
Power Supply. Connect V CC to a +2.5V to +5.5V supply. An undervoltage lockout circuit forces all OUT_
pins low when V CC drops below 2.5V.