Philips Semiconductors

Product data

NE56632-XX

Active-LOW system reset with adjustable delay time

2002 Mar 25

9

TECHNICAL DISCUSSION

The NE56632-XX is a bipolar IC designed to provide power source

monitoring and a system reset function in the event the power sags

below an acceptable level for the system to operate reliably. The

reset threshold incorporates a typical hysteresis of 50 mV to prevent

erratic reasserts from being generated. An internal delay time circuit

provides a adjustable power-on reset delay of typically 200

µs to

200 ms using an external capacitor.

The output of the NE56632-XX utilizes an open collector topology,

be regarded as a disadvantage, it is advantageous in many

sensitive applications. Because the open collector output cannot

source reset current when both are operated from a common supply,

the NE56632-XX offers a safe interconnect to a wide variety of

microprocessors.

The NE56632-XX operates at low supply currents, typically 3

µA,

while offering precision threshold detection (

±1.5%).

Figure 22 is a functional block diagram of the NE56632-XX. The

temperature range. The reference voltage is connected to the

non-inverting inputs of the threshold Comparator 1 and

Comparator 2, while the inverting input of Comparator 1 monitors

the supply voltage through a voltage divider (R1 and R2). The output

of the comparator drives the series base resistor, R3 of a common

emitter amplifier, Q1. The collector of Q1 is connected to the

inverting terminal of Comparator 2. The output of Comparator 2 is

connected to the series base resistor, R4 of the output common

emitter transistor, Q2. The open collector output of Q2 provides the

reset output.

The Delay Time Control is outputted at the junction of the collector

of Q1 and the inverting input of Comparator 2. The reset release

When the supply voltage sags to the threshold detection voltage, the

resistor divider network supplies a voltage to the inverting terminal of

of the comparator to go to a HIGH state. This causes the common

emitter amplifier, Q1 to turn ON pulling down the non-inverting

terminal of Comparator 2 which causes its output to go to a HIGH

state. This HIGH output level turns on the output common emitter

transistor, Q2. The collector output of Q2 is pulled LOW through the

external pull-up resistor, thereby asserting the Active-LOW reset.

Threshold hysteresis is established by turning on the bipolar common

emitter transistor, Q1 when the input threshold Comparator 1 goes

threshold level. With the output of Q1 connected to the non-inverting

terminal of Comparator 2, the non-inverting terminal has a level near

ground at about 0.4 V when the reset is asserted (Active-LOW). For

the Comparator 2 to reverse its output, the Comparator 1 output and

Q1 must overcome the additional pull-down voltage present on the

inverting input of Comparator 2. The differential voltage required to

do this establishes the hysteresis voltage of the sensed threshold

voltage. Typically, it is 50 mV.

device will assert a Reset LOW output at or near ground potential.

Hysteresis voltage = Release voltage – Detection Threshold voltage

where:

0.65 V, the output is undefined and the output reset low assertion is

zero.

3

4

R3

Q1

Q2

R4

2

GND

SUB

COMP2

COMP1

(SUBSTRATE)

R2

R1

1

TC

5

SL01607

Figure 22. Functional diagram.