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ADM1087 Voltage Sequencer with Active Low, Open-Drain Enable Output

The ADM1085-ADM1088 are Simple Sequencing™ circuits which provide a time delay between the enabling of voltage regulators at power-up in multiple supply systems. When the output voltage of the first regulator reaches a preset threshold, a time delay is initiated before an enable signal allows subsequent regulators to power-up. Any number of these devices can be cascaded with regulators to allow sequencing of multiple power supplies.

Threshold levels can be set with a pair of external resistors in a voltage divider configuration. By choosing appropriate resistor values, the threshold can be adjusted to monitor voltages as low as 0.6V.

The ADM1086 and ADM1088 have push-pull output stages, with active-high (ENOUT) and active-low (ENOUT) logic outputs, respectively. Similarly, the ADM1085 has an active-high (ENOUT) logic output and the ADM1087 has an active-low (ENOUT) output. Both the ADM1085 and ADM1087 have open-drain output stages which can be pulled up to voltage levels as high as 22V through an external resistor. This level shifting property of the ADM0185 and ADM1087 ensures compatibility with enable input logic levels of different regulators and converters.

All four models have a dedicated enable input pin which allows the output signal to the regulator to be controlled externally. This is an active-high input (ENIN) for the ADM1085 and ADM1086, and an active-low input (ENIN) for the ADM1087 and ADM1088.

The Simple Sequencers™ are specified over the extended –40°C to +125°C temperature range, and with low current consumption of 15µA (typ) and 6-lead SC70 packaging, they are suitable for low power portable applications.

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Reference Materials

• Product Selection Guide：Supervisory Devices Complementary Parts Guide for Altera FPGAs
• Product Selection Guide：Supervisory Devices Complementary Parts Guide for Xilinx FPGAs
• Solutions Bulletins & Brochures：Power Supply Sequencing Bulletin (2007)