MAXIM DS1836, DS1836A, DS1836B, DS1836C, DS1836D User Manual
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DS1836/A/B/C/D
3.3V/5V MicroManage
FEATURES
5V or 3.3V power-on reset
True 3V operation power switch
Switches to battery at 3.8V (2.6V for 3.3V
versions)
Excellent for systems designed to operate
with dual power supplies
Asserts resets during power transients
Maintains reset for 350ms after VCC returns to
an in-tolerance condition
Reduces need for discrete components
Precision temperature-compensated voltage
reference and voltage sensor
8-pin DIP or space saving 8-pin SO surface
mount available
CMOS reset output for low current operation
Operating temperature of -40°C to +85°C
Perfect for PIC microprocessor applications
PIN ASSIGNMENT
V
V
V
V
V
V
1
CC
2
BAT
3
NC
4
OUT
8-Pin DIP (300mil)
CC
BAT
NC
OUT
1
2
3
4
8-Pin SO (150mil)
8
7
6
5
8
7
6
5
DS1836A/C (*DS1836B/D)
PIN DESCRIPTION
RST(*RST)
NMI
IN
GND
RST(*RST)
NMI
IN
GND
VCC - Power Supply Input
V
- Battery Supply Input
BAT
NC - No Connect
V
- Power Supply Output
OUT
GND - Ground
IN - Sense Input
NMI - Non-maskable Interrupt
RST (*RST) - Reset Output
DESCRIPTION
The DS1836 MicroManager performs three vital system functions. First, a precision temperaturecompensated reference and comparator circuit monitor the status of the voltage on VCC and when an outof-tolerance condition is detected, an internal power-fail signal is generated that forces the reset active. If
V
continues to degrade, it switches to the battery supply when VCC drops below 3.8V (2.6V for 3.3V
CC
versions). When VCC exceeds 3.9V (2.8V for 3.3V versions); V
Reset will remain active for 350 ms after V
returns to an in-tolerance condition.
CC
Lastly, the DS1836 supports a sense input that sends a non-maskable interrupt whenever the sense input
drops below 1.25V.
will again be supplied from VCC.
OUT
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DS1836A/B/C/D
OPERATION
Power Monitor
The DS1836 provides the functions of detecting out-of-tolerance conditions on a 3.3V or 5V power
supply and warning a processor-based system of impending power failure. When VCC is detected as out of
tolerance the RST will be forced active. When VCC returns to a valid state the RST will remain active for
about 350ms and then return to an inactive state until the next V
out-of-tolerance condition.
CC
On power-up reset is kept active for approximately 350ms after the power supply input has reached the
selected tolerance. This allows the power supply and system power to stabilize before RST is released.
Power Switch (DS1836A & B)
The DS1836 switches the V
current from the V
input until VCC exceeds 3.9V. When VCC exceeds 3.9V V
BAT
to VCC and will not switch back to V
will be drawn from the supply with the highest voltage: either VCC or V
output between VCC and V
OUT
until VCC drops below 3.8V. When VCC is below 3.8V, power
BAT
. On the initial power-up, V
BAT
switches from V
OUT
.
BAT
OUT
draws
BAT
Power Switch (DS1836C & D)
The DS1836 switches the V
current from the V
input until VCC exceeds 2.8V. When VCC exceeds 2.8V V
BAT
to VCC and will not switch back to V
will be drawn from the supply with the highest voltage either VCC or V
output between VCC and V
OUT
until VCC drops below 2.6V. When VCC is below 2.6V, power
BAT
. On the initial power up, V
BAT
switches from V
OUT
.
BAT
OUT
draws
BAT
BLOCK DIAGRAM Figure 1
* DS1836B and DS1836D
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DS1836A/B/C/D
Non-Maskable Interrupt
The DS1836 generates a non-maskable interrupt (NMI ) for early warning of a power failure. A precision
comparator monitors the voltage level at the IN pin relative to an on-chip reference generated by an
internal band gap. The IN pin is a high impedance input allowing for a user-defined sense point. An
external resistor voltage divider network (Figure 3) is used to interface with high voltage signals. This
sense point may be derived from a regulated supply or from a higher DC voltage level closer to the main
system power input. Since the IN trip point V
is 1.25V, the proper values for R1 and R2 can be
TP
determined by the equation as shown in Figure 3. Proper operation of the DS1836 requires that the
maximum voltage at the IN pin be limited to the active supply (V
allowable voltage at the supply being monitored (V
) can also be derived as shown in Figure 3. A
MAX
CC
or V
). Therefore, the maximum
BAT
simple approach to solving the equation is to select a value for R2 high enough to keep power
consumption low and solve for R1. The flexibility of the IN input pin allows for detection of power loss
at the earliest point in a power supply system, maximizing the amount of time for system shutdown
between NMI and RST (or RST ).
A pull-up resistor is required for proper operation of the NMI open-drain output. A 10kΩ resistor would
be a typical value for the pull-up resistor.
TYPICAL APPLICATION Figure 2
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