ADM8611/ADM8612/ADM8613/ADM8614/ADM8615

Data Sheet

Rev. G | Page 14 of 17

LOW POWER DESIGN TECHINQUES

With their ultralow power consumption level, the ADM8611/

ADM8612/ADM8613/ADM8614/ADM8615 are ideal for battery-

powered, low power applications where every bit of power matters.

In addition to using low power ICs, good circuit design practices

can help the user further reduce the overall system power loss.

Digital Inputs

The digital inputs of the ADM8611/ADM8612/ADM8613/

ADM8614/ADM8615 voltage supervisors are designed with

CMOS technology to minimize power consumption. The nature of

the voltage level on the input approaches its undefined logic range,

as shown in Figure 11. To minimize this effect, follow these

recommendations:



If the digital input does not need to be toggled in a particular

design, tie it directly to the VCC or GND pin of the device.



ADM8611/ADM8612/ADM8613/ADM8614/ADM8615 are

the ideal choice for driving the digital signal line.



Using push-pull outputs with a logic high level near the

minimum logic high specification of the digital input is

usually not recommended. One exception is if the input is

required to be driven high only infrequently for a relatively

short period.



Open-drain outputs with a pull-up resistor to VCC can be

used to drive digital signal lines. Open-drain outputs are

best suited for driving lines that are required to be driven

low only infrequently for a relatively short period.



The leakage current on both the digital input and the open-

drain output determines the size of the pull-up resistor

needed and, in turn, decides the power loss through the

resistor while driving the input low.



The MR pin on the ADM8611, ADM8612, ADM8613, and

ADM8615 features an internal pull-up resistor. The infrequent

usage of this pin makes its power loss while driven to logic

low negligible.

WDI Input

When the watchdog input (WDI) is driven by a push-pull

ADM8613/ADM8614/ADM8615, neither a high nor a low input

logic causes the system to consume additional current. To reduce

the total current consumption, increase the speed of the input

transition to the number of transitions. One high to low or low

to high transition within the watchdog timeout period is sufficient

to prevent the watchdog timer from generating a reset output.

If the watchdog input is driven by a push-pull output with a logic

high level near the minimum logic high specification of the digital

input, then a logic high input may cause CMOS shoot through

ADM8615. To minimize the power loss in this setup, use short

positive pulses to drive the WDI pin. The ideal pulse width is as

small as possible but greater than the required minimum pulse

width of the WDI input. One pulse within the watchdog timeout

period is sufficient to prevent the watchdog timer from generating

a reset output.

Figure 34. Using a Push-Pull Output with a Lower Logic High Level to VCC,

Similarly, if an open-drain input/output with a pull-up resistor

to VCC is used to drive WDI, a logic low input causes additional

current flowing through the pull-up resistor. A short negative

pulse technique can minimize the long-term current consumption.

Figure 35. Short Negative Pulse on the WDI Pin to Reduce Leakage Current

Through the Pull-Up Resistor

WD_DIS Input

For the ADM8613 and ADM8614, the watchdog disable input

(WD_DIS) disables the watchdog function during system

prototyping or during power-up to allow extra time for

processor initialization.

To disable the watchdog timer function during power-up after a

reset deassertion, the processor configures its input/output and

drives WD_DIS high within the watchdog timeout period. If

there is not enough time to configure the input/output or if an

open-drain input/output is used to drive WD_DIS, an external

pull-up resistor is required to keep the watchdog function disabled

during power-up. Extra current is consumed through the pull-up

resistor to enable the watchdog function. The leakage current

on both WD_DIS and the input/output that drives it determines

the size of the pull-up resistor needed and, in turn, determines

the power loss through the resistor while driving the input low.

ADM8614

MICROPROCESSOR

VCC

WDI

WATCHDOG

OUTPUT

2.5V

1.5V

HIGH

LOW

PUSH-PULL

OUTPUT

ADM8614

MICROPROCESSOR

VCC

WDI

2.5V

HIGH

LOW

OPEN-DRAIN

OUTPUT

WATCHDOG

OUTPUT