ADCMP391 datasheet(12/17 Pages) AD

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ADCMP391/ADCMP392/ADCMP393

Data Sheet

Rev. D | Page 12 of 17

WINDOW COMPARATOR FOR NEGATIVE VOLTAGE

MONITORING

Figure 30 shows the circuit configuration for negative supply

voltage monitoring. To monitor a negative voltage, a reference

voltage is required to connect to the end node of the voltage

divider circuit, in this case, VREF.

OUTA

INA+

VREF

INA–

OUTB

INB+

INB–

VNL

VNH

VREF

Figure 30. Negative Undervoltage/Overvoltage Monitoring Configuration

Equation 7, Equation 9, and Equation 10 need some minor

modifications for use with negative voltage monitoring. The

reference voltage, VREF, is added to the overall voltage drop;

therefore, it must be subtracted from VM, VUV, and VOV before

using each of them in Equation 7, Equation 9, and Equation 10.

To monitor a negative voltage level, the resistor divider circuit

divides the voltage differential level between VREF and the

negative supply voltage into the high-side voltage, VNH, and the

low-side voltage, VNL. The high-side voltage, VNH, is connected

to INC+, and the low-side voltage, VNL, is connected to IND−.

To trigger an overvoltage condition, the monitored voltage must

exceed the nominal voltage in terms of magnitude, and the

high-side voltage (in this case, VNH) on the INC+ pin must be

more negative than ground. Calculate the high-side voltage,

VNH, by the following:

(

)

REF

GND

























−

(11)

In addition,

(

)

REF

−

(12)

Therefore, RZ, which sets the desired trip point for the

overvoltage monitor, is calculated by

(

)

(

)

REF

−

(13)

To trigger an undervoltage condition, the monitored voltage

must be less than the nominal voltage in terms of magnitude,

and the low-side voltage (in this case, VNL) on the IND− pin

must be more positive than ground. Calculate the low-side

voltage, VNL, by the following:

(

)

REF

GND

























−

(14)

Because RZ is already known, RY can be expressed as follows:

(

)

(

)

REF

−

(15)

When RY and RZ are known, RX is then calculated by

(

)

REF

−

(16)

PROGRAMMABLE SEQUENCING CONTROL CIRCUIT

The circuit shown in Figure 31 is used to control the power

supply sequencing. The delay is set by the combination of the

pull-up resistor (RPULLUP), the load capacitor (CL), and the

resistor divider network.

OUTA

INA+

INB+

INC+

IND+

INA–

INB–

INC–

IND–

OUTB

OUTC

OUTD

RPULLUP

VREF/VCC

SEQ

Figure 31. Programmable Sequencing Control Circuit

Figure 32 shows a simplified block diagram for the

programmable sequencing control circuit. The application

delays the enable signal, EN, of the external regulators (LDO x)

in a linear order when the open-drain signal (SEQ) changes

from low to high impedance.

The ADCMP391/ADCMP392/ADCMP393 have a defined

output state during startup, which prevents any regulator from

turning on if VCC is still below the UVLO threshold.

OUT

GND

LDO 1

3.0V

3.3V

OUT

GND

LDO 2

1.8V

OUT

GND

LDO 3

2.5V

OUT

GND

LDO 4

1.2V

GND

VREF/VCC

SEQ

Figure 32. Simplified Block Diagram of a Programmable

Sequencing Control Circuit

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