ADCMP392 datasheet(15/17 Pages) AD

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Data Sheet

ADCMP391/ADCMP392/ADCMP393

Rev. D | Page 15 of 17

Resistor values from the calculation are nonindustry standard,

using industry standard resistor values resulted in a new RDIV

value of 99.8 kΩ. Due to the discrepancy of the calculated resistor

value to the industry standard value, the threshold of each

comparator also changed. Calculate the new threshold values

by using a simple voltage divider formula:

V1 = VREFR1/RDIV

(37)

where V1 =





kΩ

99.8

kΩ

26.7

= 267.54 mV.

Therefore, V2 = 463.93 mV, V3 = 607.21 mV, and V4 = 712.42 mV.

Because the threshold of each comparator has changed, the time

when each comparator changes its output has also changed.

Calculate the new delay values for each comparator by using the

following equation:























REF

MIRROR

PULLUP

(38)

where t1 = −1 μF(10 kΩ + 150 kΩ)ln











 

267

= 49.81 ms.

Therefore, t2 = 99.78 ms, t3 = 149.52 ms, and t4 = 199.4 ms.

To calculate t5 through t8, use Equation 32 to Equation 35:

















REF

MIRROR

where t5 = −150 kΩ × 1 μF × ln













712.42

= 50.86 ms.

Therefore, t6 = 74.83 ms, t7 = 115.2 ms, and t8 = 197.78 ms.

THRESHOLD AND TIMEOUT PROGRAMMABLE

VOLTAGE SUPERVISOR

Figure 36 shows a circuit configuration for a programmable

threshold and timeout circuit. The timeout, tRESET, defines the

duration that the input voltage (VIN) must be kept above the

threshold voltage to toggle the RESET signal, preventing the

device from operating when VIN is not stable. If VIN falls below

the threshold voltage, the RESET signal toggles quickly.

RESET

OUTB

OUTA

RPULLUP

VCC

VIN

VREF

Figure 36. Programmable Threshold and Timeout Circuit

RESET

VTH

VIN

tRESET

Figure 37. Threshold and Timeout Programmable Voltage Supervisor

Timing Diagram

During startup, the ADCMP391/ADCMP392/ADCMP393

guarantee a low output state when VCC is still below the UVLO

threshold, preventing the voltage supervisor from toggling.

When VIN reaches the threshold set by the resistor divider (R1

and R2) and VREF, OUT1 changes from low to high and starts to

charge the timeout capacitor (CT). If VIN is kept above the threshold

voltage and the voltage in CT reaches VREF, OUT2 toggles. If VIN

falls below the threshold voltage while CT is charging, the timeout

capacitor quickly discharges, preventing OUT2 from toggling

while VIN is not stable.

In the condition that VIN is tied to VCC, the circuit operates

when VCC is more than the minimum operating voltage.

The threshold voltage (VTH) is configured by changing the

resistor divider or VREF. Calculate the threshold voltage by











 



REF

(39)

Timeout is adjusted by changing the values of the pull-up

resistor or the timeout capacitor. To set the timeout value,

determine the allowable current flowing through RPULLUP, IPULLUP.

When IPULLUP is known, calculate RPULLUP and CT by the following

formulas:

RPULLUP = VCC/IPULLUP

(40)

















REF

PULLUP

RESET

(41)

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