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ADM1065ASUZ Datasheet(PDF) 14 Page - Analog Devices |
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ADM1065ASUZ Datasheet(HTML) 14 Page - Analog Devices |
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14 / 28 page 
ADM1065 Rev. D | Page 14 of 28 OUTPUTS SUPPLY SEQUENCING THROUGH CONFIGURABLE OUTPUT DRIVERS The data driving each of the PDOs can come from one of three sources. The source can be enabled in the PDOxCFG configu- ration register (see the AN-698 Application Note for details). Supply sequencing is achieved with the ADM1065 using the programmable driver outputs (PDOs) on the device as control signals for supplies. The output drivers can be used as logic enables or as FET drivers. The data sources are as follows: • Output from the SE. • Directly from the SMBus. A PDO can be configured so that the SMBus has direct control over it. This enables software control of the PDOs. Therefore, a microcontroller can be used to initiate a software power-up/power-down sequence. The sequence in which the PDOs are asserted (and, therefore, the supplies are turned on) is controlled by the sequencing engine (SE). The SE determines what action is taken with the PDOs, based on the condition of the ADM1065 inputs. Therefore, the PDOs can be set up to assert when the SFDs are in tolerance, the correct input signals are received on the VXx digital pins, no warnings are received from any of the inputs of the device, and at other times. The PDOs can be used for a variety of functions. The primary function is to provide enable signals for LDOs or dc-to-dc converters that generate supplies locally on a board. The PDOs can also be used to provide a PWRGD signal when all the SFDs are in tolerance or a RESET output if one of the SFDs goes out of specification (this can be used as a status signal for a DSP, FPGA, or other microcontroller). • On-chip clock. A 100 kHz clock is generated on the device. This clock can be made available on any of the PDOs. It can be used, for example, to clock an external device such as an LED. DEFAULT OUTPUT CONFIGURATION All of the internal registers in an unprogrammed ADM1065 device from the factory are set to 0. Because of this, the PDOx pins are pulled to GND by a weak (20 kΩ) on-chip pull-down resistor. As the input supply to the ADM1065 ramps up on VPx or VH, all PDOx pins behave as follows: • Input supply = 0 V to 1.2 V. The PDOs are high impedance. The PDOs can be programmed to pull up to a number of different options. The outputs can be programmed as follows: • Input supply = 1.2 V to 2.7 V. The PDOs are pulled to GND by a weak (20 kΩ) on-chip pull-down resistor. • Supply > 2.7 V. Factory programmed devices continue to pull all PDOs to GND by a weak (20 kΩ) on-chip pull-down resistor. Programmed devices download current EEPROM configuration data, and the programmed setup is latched. The PDO then goes to the state demanded by the configuration. This provides a known condition for the PDOs during power-up. • Open drain (allowing the user to connect an external pull- up resistor). • Open drain with weak pull-up to VDD. • Open drain with strong pull-up to VDD. • Open drain with weak pull-up to VPx. • Open drain with strong pull-up to VPx. • Strong pull-down to GND. The internal pull-down can be overdriven with an external pull- up of suitable value tied from the PDOx pin to the required pull-up voltage. The 20 kΩ resistor must be accounted for in calculating a suitable value. For example, if PDOx must be pulled up to 3.3 V, and 5 V is available as an external supply, the pull-up resistor value is given by • Internally charge-pumped high drive (12 V, PDO1 to PDO6 only). The last option (available only on PDO1 to PDO6) allows the user to directly drive a voltage high enough to fully enhance an external N-FET, which is used to isolate, for example, a card- side voltage from a backplane supply (a PDO can sustain greater than 10.5 V into a 1 μA load). The pull-down switches can also be used to drive status LEDs directly. 3.3 V = 5 V × 20 kΩ/(RUP + 20 kΩ) Therefore, RUP = (100 kΩ − 66 kΩ)/3.3 V = 10 kΩ PDO SE DATA CFG4 CFG5 CFG6 SMBus DATA CLK DATA VP1 SEL VP4 VDD VFET (PDO1 TO PDO6 ONLY) Figure 19. Programmable Driver Output |
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