DS1836/A/B/C/D
3.3V/5V MicroManager
www.maxim-ic.com
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
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RST(*RST) |
VCC |
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8 |
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7 |
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VBAT |
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NMI |
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3 |
6 |
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IN |
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NC |
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4 |
5 |
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GND |
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VOUT |
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8-Pin DIP (300mil) |
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VCC |
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8 |
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RST(*RST) |
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VBAT |
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7 |
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NMI |
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NC |
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6 |
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IN |
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VOUT |
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GND |
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8-Pin SO (150mil)
DS1836A/C (*DS1836B/D)
PIN DESCRIPTION
VCC |
- Power Supply Input |
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VBAT |
- Battery Supply Input |
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NC |
- No Connect |
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VOUT |
- Power Supply Output |
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GND |
- Ground |
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IN |
- Sense Input |
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- Non-maskable Interrupt |
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NMI |
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(*RST) |
- Reset Output |
RST |
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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 out- of-tolerance condition is detected, an internal power-fail signal is generated that forces the reset active. If VCC continues to degrade, it switches to the battery supply when VCC drops below 3.8V (2.6V for 3.3V versions). When VCC exceeds 3.9V (2.8V for 3.3V versions); VOUT will again be supplied from VCC. Reset will remain active for 350 ms after VCC returns to an in-tolerance condition.
Lastly, the DS1836 supports a sense input that sends a non-maskable interrupt whenever the sense input drops below 1.25V.
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121906 |
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 VCC out-of-tolerance condition.
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 VOUT output between VCC and VBAT. On the initial power-up, VOUT draws current from the VBAT input until VCC exceeds 3.9V. When VCC exceeds 3.9V VOUT switches from VBAT
to VCC and will not switch back to VBAT until VCC drops below 3.8V. When VCC is below 3.8V, power will be drawn from the supply with the highest voltage: either VCC or VBAT.
Power Switch (DS1836C & D)
The DS1836 switches the VOUT output between VCC and VBAT. On the initial power up, VOUT draws current from the VBAT input until VCC exceeds 2.8V. When VCC exceeds 2.8V VOUT switches from VBAT
to VCC and will not switch back to VBAT until VCC drops below 2.6V. When VCC is below 2.6V, power will be drawn from the supply with the highest voltage either VCC or VBAT.
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 VTP is 1.25V, the proper values for R1 and R2 can be 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 (VCC or VBAT). Therefore, the maximum allowable voltage at the supply being monitored (VMAX) can also be derived as shown in Figure 3. A
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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