ASM1832

February 2005 rev 1.5 ASM1832 3.3V µP Power Supply Monitor and Reset Circuit Devices are available in 8-pin PDIP, 8-pin SO and compact 8pin MicroSO packages. General Description The ASM1832 is a fully integrated microprocessor supervisor. It can halt and restart a “hung-up” microprocessor, restart a microprocessor after a power failure. It has a watchdog timer and external reset override. RESET and RESET outputs are push-pull. A precision temperature-compensated reference and Key Features • • • • • • • • • • • 3.3V supply monitor Push-pull output Selectable watchdog period Debounce manual push-button reset input Precision temperature-compensated voltage reference and comparator. Power-up, power-down and brown out detection 250ms minimum reset time Active LOW and HIGH reset signal Selectable trip point tolerance: 10% or 20% Low-cost 8-pin DIP/SO and 8-pin Micro SO packages Wide operating temperature -40°C to +85°C comparator circuits monitor the 3.3V, VCC input voltage status. During power-up or when the VCC power supply falls outside selectable tolerance limits, both RESET and RESET become active. When VCC rises above the threshold voltage, the reset signals remain active for an additional 250ms minimum, allowing the power supply and system microprocessor to stabilize. The trip point tolerance signal, TOL, selects the trip level tolerance to be either 10% or 20%. A debounced manual reset input, PBRST, activates the reset outputs for a minimum period of 250ms. There is a watchdog timer to stop and restart a microprocessor that is “hung-up”. The watchdog timeouts periods are selectable: 150ms, 610ms, and 1200ms. If the ST input is not strobed LOW before the time-out period expires, a reset is generated. Applications • • • • • Microprocessor systems Computers Controllers Portable instruments Automotive systems Typical Operating Circuit 3.3V Block Diagram ASM1832 Tolerance Selection + VCC 40KΩ PBRST Push Button Debounce Voltage Sense Comparator Watchdog Transition Detector Reset & Watchdog Timer RESET Reference VCC VCC VCC ASM1832 ST I/O µP TOL RESET - RESET GND TD TOL RESET TD ST GND Alliance Semiconductor 2575 Augustine Drive . Santa Clara, CA 95054 . Tel: 408.855.4900 . Fax: 408.855.4999 . www.alsc.com Notice: The information in this document is subject to change without notice February 2005 rev 1.5 ASM1832 Pin Configuration PBRST TD TOL GND 1 2 3 4 8 VCC ST RESET RESET ASM1832 7 6 5 Pin Description Pin # 8-Pin Package 1 2 Pin Name PBRST TD Function Debounced manual pushbutton reset input. Watchdog time delay selection. (tTD = 150ms for TD = GND, tTD = 610ms for TD=Open, and tTD = 1200ms for TD = VCC). Selects 10% (TOL connected to GND) or 20% (TOL connected to VCC) trip point tolerance. Ground. Active HIGH reset output. RESET is active: 1. If VCC falls below the reset voltage trip point. 3 4 TOL GND 5 RESET 2. If PBRST is LOW. 3. If ST is not strobed LOW before the timeout period set by TD expires. 4. During power-up. Active LOW reset output. (See RESET). Strobe input. 3.3V power. 6 7 8 RESET ST VCC 3.3V µP Power Supply Monitor and Reset Circuit Notice: The information in this document is subject to change without notice 2 of 9 February 2005 rev 1.5 ASM1832 . the microprocessor or Tolerance Select TOL = VCC TOL = GND Tolerance TRIP Point Voltage (V) Min 20% 10% 2.47 2.80 Nom 2.55 2.88 Max 2.64 2.97 Detailed Description The ASM1832 monitors microcontroller power supply and issues reset signals, both active HIGH and active LOW, that halt processor operation whenever the power supply voltage levels are outside a predetermined tolerance. RESET and RESET outputs RESET and RESET signals are active for a minimum of 250ms after the supply has returned to in-tolerance level. This allows the power supply and monitored processor to stabilize before instruction execution is allowed to begin. Trip Point Tolerance Selection The TOL input is used to determine the level VCC can vary below 3.3V without asserting a reset. With TOL conected to VCC, RESET and RESET become active whenever VCC falls below 2.64V. RESET and RESET become active when the VCC falls below 2.98V if TOL is connected to ground. After VCC has risen above the trip point set by TOL, RESET and RESET remain active for a minimum time period of 250ms. On power-down, once VCC falls below the reset threshold RESET stays LOW and is guaranteed to be 0.4V or less until VCC drops below 1.2V. The reset output on the ASM1832 uses a push-pull drive stage that can maintain a valid output below 1.2V. To sink current with VCC below 1.2V, a resistor can be connected from the reset pin (RESET) to Ground. This configuration will give a valid value on the reset output with VCC approaching 0V. During both power up and down, the configuration will draw current when the RESET is in the high state. The value of 100KΩ should be adequate to maintain a valid condition. The active HIGH reset signal is valid down to a VCC level of 1.2V also. tR VCCTP(MAX) VCCTP tRPU VCC VOH RESET VCCTP(MIN) ~ ~ ~ ~ Figure 1: Timing Diagram : Power Up VOL RESET ~ ~ VCC VCCTP (MAX) VCCTP VCCTP (MIN) tF RESET tRPD VOH VOL ~~ ~~ RESET Figure 2: Timing Diagram : Power Down ASM1832 RESET 100kΩ Microprocessor RESET Application Information Manual Reset Operation Push-button switch input, PBRST, allows the user to override the internal trip point detection circuits and issue reset ~ 3.3V µP Power Supply Monitor and Reset Circuit Notice: The information in this document is subject to change without notice 3 of 9 February 2005 rev 1.5 signals. The pushbutton input is debounced and is pulled HIGH through an internal 40kΩ resistor. When PBRST is held LOW for the minimum time tPB, both resets become active and remain active for a minimum time period of 250ms after PBRST returns HIGH. ASM1832 minimum timeout period, reset signals become active. On power-up after the supply voltage returns to an in-tolerance condition, the reset signal remains active for 250ms minimum, allowing the power supply and system microprocessor to stabilize. ST Pulses as short as 20ns can be detected. The debounced input is guaranteed to recognize pulses greater than 20ms. No external pull-up resistor is required, since PBRST is pulled HIGH by an internal 40kΩ resistor. The PBRST can be driven from a TTL or CMOS logic line or shorted to ground with a mechanical switch. RESET ST Valid Strobe Valid Strobe Invalid Strobe tST tRST tTD (min) tTD (max) ~ ~ PBRST tPDLY VIL tPB VIH Note: ST is ignored whenever a reset is active Figure 5: Timing Diagram: Strobe Input Timeouts periods of approximately 150ms, 610ms or 1,200ms are selected through the TD pin. ~ ~ tRST RESET RESET TD Voltage level VOH VOL Watchdog Time-out Period (ms) Min Nom 150 610 1200 Max 250 1000 2000 Figure 3: Timing Diagram: Pushbutton Reset ~~ ~~ Supply Voltage ASM1832 1 2 3 4 PBRST TD TOL GND VCC 8 ST RESET RESET GND Floating VCC 62.5 250 500 The watchdog timer can not be disabled. It must be strobed with a high-to-low transition to avoid watchdog timeout and I/O 7 6 5 reset. µP Supply Voltage ASM1832 1 2 3 4 PBRST TD TOL GND VCC 8 ST RESET RESET MREQ RESET Figure 4: Application Circuit: Pushbutton Reset 7 6 5 µP RESET Address Bus Watchdog Timer and ST Input A watchdog timer stops and restarts a microprocessor that is “hung-up”. The µP must toggle the ST input within a set period (as selectable through TD input) to verify proper software execution. If the ST is not toggled low within the Decoder Figure 6: Application Circuit: Watchdog Timer 3.3V µP Power Supply Monitor and Reset Circuit Notice: The information in this document is subject to change without notice 4 of 9 February 2005 rev 1.5 ASM1832 Absolute Maximum Ratings Parameter Voltage on VCC Voltage on ST, TD Voltage on PBRST, RESET, RESET Operating Temperature Range Soldering Temperature (for 10 sec) Storage Temperature ESD rating HBM MM Min -0.5 -0.5 -0.5 -40 Max 7 VCC + 0.5 VCC + 0.5 +85 +260 Unit V V V °C °C °C KV V -55 +125 2 200 Note: 1. Voltages are measured with respect to ground 2. These are stress ratings only and functional implication is not implied. Exposure to absolute maximum ratings for extended periods may affect device reliability. DC Electrical Characteristics Unless otherwise stated, 1.2 =2.7V Min 500 250 VCC - 0.3V Typ 1200 610 VCC - 0.1V 350 Max 2000 1000 Unit ms ms V µA mA 10 -1.0 1.0 0.4 40 20 5 7 µA V kΩ µA pF pF ms PBRST pin Outputs open, VCC