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 VCC 1 8 RST(*RST) VBAT 2 7 NMI NC 3 6 IN VOUT 4 5 GND 8-Pin DIP (300mil) VCC 1 8 RST(*RST) VBAT 2 7 NMI NC 3 6 IN VOUT 4 5 GND 8-Pin SO (150mil) DS1836A/C (*DS1836B/D) PIN DESCRIPTION VCC VBAT NC VOUT GND IN NMI RST (*RST) - Power Supply Input - Battery Supply Input - No Connect - Power Supply Output - Ground - Sense Input - Non-maskable Interrupt - 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 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. 1 of 9 020702 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 2 of 9 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 10kW resistor would be a typical value for the pull-up resistor. TYPICAL APPLICATION Figure 2 3 of 9 DS1836A/B/C/D NON-MASKABLE INTERRUPT CIRCUIT EXAMPLE Figure 3 VSENSE = R1 + R2 x 1.25 R2 Example: VSENSE = 4.50V at the trip point 100kW = R2 Therefore: 4.5 = R1 + 100k x 1.25 100k R1 = 260kW TIMING DIAGRAM: NON-MASKABLE INTERRUPT Figure 4 4 of 9 DS1836A/B/C/D OUTPUT VALID CONDITIONS The DS1836 can maintain valid outputs as long as one input remains above 1.2V. However, the RST outputs on the DS1836A (or C) use a push-pull output structure which can maintain a valid output below 1.2V on an input. To sink current below 1.2V a resistor can be connected from RST to GND (see Figure 5). This arrangement will maintain a valid value on the RST outputs even if all supply inputs are at 0V. During conditions when the RST is in the inactive or high state this arrangement will draw current through the pull down resistor. A value of about 100 kW should be adequate to maintain a valid condition. The DS1836 NMI output requires a pull-up resistor on the output to maintain a valid output. The value of the resistor is not critical in most cases but must be set low enough to pull the output to a high state. A common value used is 10kWs (see Figure 3). APPLICATION DIAGRAM: RST VALID TO 0V VCC ON THE DS1836A OR DS1836C Figure 5 TIMING DIAGRAM: POWER-UP Figure 6 5 of 9 DS1836A/B/C/D TIMING DIAGRAM: POWER-DOWN Figure 7 TIMING DIAGRAM: POWER SWITCH Figure 8 6 of 9 DS1836A/B/C/D ABSOLUTE MAXIMUM RATINGS* Voltage on VCC or VBAT Pin Relative to Ground Voltage on any I/O Pin Relative to Ground** Operating Temperature Range Storage Temperature Range Soldering Temperature -0.5V to +7.0V -0.5V to VOUT + 0.5V -40°C to +85°C -55°C to +125°C 260°C for 10 seconds * This is a stress rating only and functional operation of the device at these or any other conditions above those indicated in the operation sections of this specification is not implied. Exposure to absolute maximum rating conditions for extended periods of time may affect reliability. **The voltage input on IN can exceed VCC/VBAT if the input current is less than 10mA. RECOMMENDED DC OPERATING CONDITIONS PARAMETER SYMBOL MIN Supply Voltage VCC Secondary Supply Voltage VBAT 7 of 9 (-40°C to +85°C) TYP MAX UNITS NOTES 1.2 5.5 V 1 1.2 5.5 V 1 DS1836A/B/C/D DC ELECTRICAL CHARACTERISTICS PARAMETER (-40°C to +85°C; VCC = 1.2V to 5.5V) SYMBOL VOH MIN VCC -0.5 Input Leakage IIL -1.0 Output Current @ 2.4V IOH Output Current @ 0.4V IOL Operating Current @ * 5.5VIN ICC 35 Operating Current @ * 3.6VIN ICC 25 Output Voltage @ -500mA TYP MAX UNITS NOTES V 1 mA 2 mA 3 mA 3 55 mA 4 40 mA 5 VCC -0.1 +1.0 350 +10 Supply Output Current ICC01 100 mA 6 Supply Output Current ICC02 100 mA 7 Supply Output Voltage (VCC) VOUT VCC -0.5 VCC -0.3 V 1, 8 Supply Output Voltage (VBAT) VOUT VBAT -0.5 VBAT -0.3 V 1, 9 RST VCC Trip Point DS1836A(or B)-05 VCCTP 4.50 4.63 4.75 V 1 RST VCC Trip Point DS1836A(or B)-10 VCCTP 4.25 4.37 4.50 V 1 RST VCC Trip Point DS1836C(or D)-10 VCCTP 2.80 2.88 2.97 V 1 RST VCC Trip Point DS1836C(or D)-20 VCCTP 2.67 2.72 2.80 V 1 Power Supply Trip Points (VCC to VBAT) DS1836 C or D VCCFTP 2.60 2.65 2.70 V 1, 10 Power Supply Trip Points (VBAT to VCC) DS1836 C or D VCCRTP 2.70 2.75 2.80 V 1, 10 0.10 mA 11 VBAT Leakage Current ICC03 Power Supply Trip Points (VCC to VBAT) DS1836 A or B VCCFTP 3.80 3.85 3.9 V 1, 10 Power Supply Trip Points (VBAT to VCC) DS1836 A or B VCCRTP 3.90 3.95 4.0 V 1, 10 IN Input Trip Point VTP 1.15 1.25 1.35 V 1 Output Capacitance COUT 10 pF 8 of 9 DS1836A/B/C/D AC ELECTRICAL CHARACTERISTICS PARAMETER SYMBOL tIPD VTP to NMI Delay Reset Active Time VCC Slew Rate (VINTP(MIN) to VINTP(MAX)) VCC Detect to RST VCC Slew Rate (VINTP(MAX) to VINTP(MIN)) (-40°C to +85°C; VCC = 1.2V to 5.5V) MIN tRST 200 tR 0 tRPU 200 tF 300 TYP 350 MAX 1 UNITS 500 ms ms ns 350 500 ms ms VCC Detect to RST tRPD 2 VCC to VBAT (VCC falling through 2.6V) tFSW 1 ms VBAT to VCC (VCC rising through 2.8V) tRSW 1 ms 10 ms NOTES: 1) All voltages are referenced to ground. 2) Measured with outputs open and inputs at VCC or GND. 3) Measured with outputs open and VCC or VBAT < 2.7V. 4) Measured with outputs open and both VCC and VBAT < 5.5V. 5) Measured with outputs open and both VCC and VBAT < 3.6V. 6) VOUT = VCC - 0.3V. 7) VOUT = VBAT - 0.3V. 8) VCC < 2.7V. 9) VBAT < 2.0V and VCC < 1.9V. 10) VCCFTP is offset by approximately 0.1V from VCCRTP. 11) VBAT in the off state and VBAT < VCC (VBAT > VCC and VBAT in the off state 1mA maximum). 12) tR = 5ms with one supply < 2.5V. 9 of 9 NOTES 12