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MAX805_ESA Datasheet(PDF) 6 Page - Maxim Integrated Products |
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MAX805_ESA Datasheet(HTML) 6 Page - Maxim Integrated Products |
6 / 12 page _______________Detailed Description Reset Output A microprocessor’s (µP’s) reset input starts the µP in a known state. These µP supervisory circuits assert reset to prevent code execution errors during power-up, power- down, brownout conditions, or a watchdog timeout. – R — E — S — E — T – is guaranteed to be a logic low for 0V < VCC < VRST, provided that VBATT is greater than 1V. Without a backup battery, – R — E — S — E — T – is guaranteed valid for VCC > 1V. Once VCC exceeds the reset threshold, an internal timer keeps – R — E — S — E — T – low for the reset timeout period; after this interval, – R — E — S — E — T – goes high (Figure 2). If a brownout condition occurs (VCC dips below the reset threshold), – R — E — S — E — T – goes low. Each time – R — E — S — E — T – is asserted, it stays low for the reset timeout period. Any time VCC goes below the reset threshold, the internal timer restarts. The watchdog timer can also initiate a reset. See the Watchdog Input section. The MAX804_/MAX805_ active-high RESET output is open drain, and the inverse of the MAX690_/MAX704_/ MAX802_/MAX806_ – R — E — S — E — T – output. Reset Threshold The MAX690T/MAX704T/MAX805T are intended for 3.3V systems with a ±5% power-supply tolerance and a 10% system tolerance. Except for watchdog faults, reset will not assert as long as the power supply remains above 3.15V (3.3V - 5%). Reset is guaranteed to assert before the power supply falls below 3.0V. The MAX690S/MAX704S/MAX805S are designed for 3.3V ±10% power supplies. Except for watchdog faults, they are guaranteed not to assert reset as long as the supply remains above 3.0V (3.3V - 10%). Reset is guaranteed to assert before the power supply falls below 2.85V (VCC - 14%). The MAX690R/MAX704R/MAX805R are optimized for monitoring 3.0V ±10% power supplies. Reset will not occur until VCC falls below 2.7V (3.0V - 10%), but is guaranteed to occur before the supply falls below 2.59V (3.0V - 14%). The MAX802R/S/T, MAX804R/S/T, and MAX806R/S/T are respectively similar to the MAX690R/S/T, MAX805R/S/T, and MAX704R/S/T, but with tightened reset and power-fail threshold tolerances. 3.0V/3.3V Microprocessor Supervisory Circuits 6 _______________________________________________________________________________________ ______________________________________________________________Pin Description 1 VOUT Supply Output for CMOS RAM. When VCC is above the reset threshold, VOUT is connected to VCC through a p-channel MOSFET switch. When VCC falls below VSW and VBATT, VBATT connects to VOUT. Connect to VCC if no battery is used. 2 VCC Main Supply Input 3 GND Ground 4 PFI Power-Fail Input. When PFI is less than VPFT or when VCC falls below VSW, – P — F — O – goes low; otherwise, – P — F — O – remains high. Connect to ground if unused. 7 – R — E — S — E — T – Active-Low Reset Output. Pulses low for 200ms when triggered, and stays low whenever VCC is below the reset threshold or when – M — R – is a logic low. It remains low for 200ms after either VCC rises above the reset threshold, the watchdog triggers a reset, or – M — R – goes from low to high. — – M — R – Manual Reset Input. A logic low on – M — R – asserts reset. Reset remains asserted as long as – M — R – is low and for 200ms after – M — R – returns high. This active-low input has an internal 70µA pullup current. It can be driven from a TTL or CMOS logic line, or shorted to ground with a switch. Leave open if unused. 6 WDI Watchdog Input. If WDI remains high or low for 1.6s, the internal watchdog timer runs out and reset is triggered. The internal watchdog timer clears while reset is asserted or when WDI sees a rising or falling edge. The watchdog function cannot be disabled. 5 – P — F — O – Power-Fail Output. When PFI is less than VPFT, or VCC falls below VSW, – P — F — O – goes low; otherwise, – P — F — O – remains high. Leave open if unused. 8 VBATT Backup-Battery Input. When VCC falls below VSW and VBATT, VOUT switches from VCC to VBATT. When VCC rises above the reset threshold, VOUT reconnects to VCC. VBATT may exceed VCC. Connect to VCC if no battery is used. — RESET Active-High, Open-Drain Reset Output is the inverse of – R — E — S — E — T – . NAME FUNCTION MAX690 MAX802 1 2 PIN 3 4 — — 6 5 8 7 MAX804 MAX805 1 2 3 4 7 6 — 5 8 — MAX704 MAX806 |
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