NCV8502 Series
APPLICATION NOTES
V
IN
NCV8502
V
IN
V
ADJ
V
BAT
C2
0.1
mF
R1
294 k
R2
100 k
V
OUT
MJD31C
>1 Amp
5.0 V
C
IN
*
0.1
mF
V
OUT
NCV8502
RESET
R
RST
C
OUT
**
10
mF
C1
47
mF
*C
IN
required if regulator is located far from the power supply filter
**C
OUT
required for stability. Capacitor must operate at minimum
temperature expected
Figure 18. Test and Application Circuit Showing
Output Compensation
Figure 16. Additional Output Current
Adding Capability
Figure 16 shows how the adjustable version of parts can
be used with an external pass transistor for additional current
capability. The setup as shown will provide greater than 1
Amp of output current.
FLAG MONITOR
Figure 17 shows the FLAG Monitor waveforms as a result
of the circuit depicted in Figure 14. As the output voltage
falls (V
OUT
), the Monitor threshold is crossed. This causes
the voltage on the FLAG output to go low sending a warning
signal to the microprocessor that a RESET signal may occur
in a short period of time. T
WARNING
is the time the
microprocessor has to complete the function it is currently
working on and get ready for the RESET shutdown signal.
V
OUT
SETTING THE DELAY TIME
The delay time is controlled by the Reset Delay Low
Voltage, Delay Switching Threshold, and the Delay Charge
Current. The delay follows the equation:
tDELAY
+
[CDELAY(Vdt
*
Reset Delay Low Voltage)]
Delay Charge Current
Example:
Using C
DELAY
= 33 nF.
Assume reset Delay Low Voltage = 0.
Use the typical value for V
dt
= 1.8 V.
Use the typical value for Delay Charge Current = 2.5
mA.
tDELAY
+
[33 nF(1.8
*
0)]
+
23.8 ms
2.5
mA
MON
FLAG Monitor
Ref. Voltage
RESET
FLAG
STABILITY CONSIDERATIONS
The output or compensation capacitor helps determine
three main characteristics of a linear regulator: start−up
delay, load transient response and loop stability.
The capacitor value and type should be based on cost,
availability, size and temperature constraints. A tantalum or
aluminum electrolytic capacitor is best, since a film or
ceramic capacitor with almost zero ESR can cause
instability. The aluminum electrolytic capacitor is the least
expensive solution, but, if the circuit operates at low
temperatures (−25°C to −40°C), both the value and ESR of
the capacitor will vary considerably. The capacitor
manufacturers data sheet usually provides this information.
The value for the output capacitor C
OUT
shown in Figure 18
should work for most applications, however it is not
necessarily the optimized solution.
T
WARNING
Figure 17. FLAG Monitor Circuit Waveform
http://onsemi.com
10
ONSEMI [ ON SEMICONDUCTOR ]
