MC34160_06 Datasheet, PDF (6/10 Pages) ON Semiconductor – 100 mA, 5.0 V Voltage Regulator and Supervisory Circuit for Microprocessors

MC34160, MC33160
Comparators
Three separate comparators are incorporated for voltage
monitoring. Their outputs can provide diagnostic information
to the microprocessor, preventing system malfunctions.
The Reset Comparator Inverting Input is internally
connected to the 2.6 V reference while the Noninverting
Input monitors V_O. The Reset Output is active low when
V_O falls approximately 180 mV below its regulated
voltage. To prevent erratic operation when crossing the
comparator threshold, 70 mV of hysteresis is provided.
The Power Warning Comparator is typically used to
detect an impending loss of system power. The Inverting
Input is internally connected to the reference, fixing the
threshold at 2.6 V. The input power source V_in is monitored
by the Noninverting Input through the R₁/R₂ divider
(Figure 11). This input features an adjustable 10 mA to 50
mA current sink I_H that is programmed by the value selected
for resistor R_H. A default current of 6.5 mA is provided if
R_H is omitted. When the comparator input falls below 2.6
V, the current sink is activated. This produces hysteresis if
V_in is monitored through a series resistor (R₁). The
comparator thresholds are defined as follows:
V_th(lower) = V_ref
V_th(upper) = V_ref
R1
1 + _R2
R1
1 + _R2
− I_IB R₁
+ I_H R₁
The nominal hysteresis current I_H equals 1.2 V/R_H
(Figure 5).
The Uncommitted Comparator can be used to
synchronize the microprocessor with the ac line signal for
timing functions, or for synchronous load switching. It can
also be connected as a line loss detector as shown in
Figure 12. The comparator contains 200 mV of hysteresis
preventing erratic output behavior when crossing the input
threshold.
The Power Warning and Uncommitted Comparators
each have a transistor base−emitter connected across their
inputs. The base input normally connects to a voltage
reference while the emitter input connects to the voltage to
be monitored. The transistor limits the negative excursion
on the emitter input to − 0.7 V below the base input by
supply current from V_CC. This clamp current will prevent
forward biasing the IC substrate. Zener diodes are
connected to the comparator inputs to enhance the ICs
electrostatic discharge capability. Resistors R₁ and R_in
must limit the input current to a maximum of ±2.0 mA.
Each comparator output consists of an open collector
NPN transistor capable of sinking 2.0 mA with a saturation
voltage less than 0.4 V, and standing off 40 V with minimal
leakage. Internal bias for the Reset and Power Warning
Comparators is derived from either V_CC or the regulator
output to ensure functionality when either is below
nominal.
Heat Tab Package
The MC34160 is contained in a 16 lead plastic
dual−in−line package in which the die is mounted on a
special Heat Tab copper alloy lead frame. This tab consists
of the four center ground pins that are specifically designed
to improve thermal conduction from the die to the
surrounding air. The pictorial in Figure 9 shows a simple
but effective method of utilizing the printed circuit board
medium as a heat dissipator by soldering these tabs to an
adequate area of copper foil. This permits the use of
standard board layout and mounting practices while having
the ability to more than halve the junction to air thermal
resistance. The example and graph are for a symmetrical
layout on a single sided board with one ounce per square
foot copper.
V_CC
V_in
C_in
14
R₁
Chip
Disable
15
R₂
2.6 V
AC
Line
9
R_H ¹⁰
2
R_in
1
+
2.6 V
Reference
Thermal
Shutdown
−
+
+
0.913 R
11
+
.01 R −
7
Reset
R
Power
16
− ^Warning
+
8
I_H
I_H On/Off
+
Uncommitted
Comparator
+
−
6
4, 5, 12, 13
V_O
C_O
MPU Reset
V_ref
Power Warning
Line Sync.
+
−
=
Sink Only
Positive True Logic
Figure 11. Typical Microprocessor Application
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