MC78T00 Datasheet, PDF (6/12 Pages) Motorola, Inc – THREE-AMPERE POSITIVE FIXED VOLTAGE REGULATORS

MC78T00 Series
VOLTAGE REGULATOR PERFORMANCE
The performance of a voltage regulator is specified by its
immunity to changes in load, input voltage, power dissipation,
and temperature. Line and load regulation are tested with a
pulse of short duration (< 100µs) and are strictly a function of
electrical gain. However, pulse widths of longer duration (>
1.0 ms) are sufficient to affect temperature gradients across
the die. These temperature gradients can cause a change in
the output voltage, in addition to changes caused by line and
load regulation. Longer pulse widths and thermal gradients
make it desirable to specify thermal regulation.
Thermal regulation is defined as the change in output
voltage caused by a change in dissipated power for a
specified time, and is expressed as a percentage output
voltage change per watt. The change in dissipated power
can be caused by a change in either the input voltage or the
load current. Thermal regulation is a function of IC layout and
die attach techniques, and usually occurs within 10 ms of a
change in power dissipation. After 10 ms, additional changes
in the output voltage are due to the temperature coefficient of
the device.
Figure 1 shows the line and thermal regulation response of
a typical MC78T05AC to a 20 W input pulse. The variation of
the output voltage due to line regulation is labeled Πand the
thermal regulation component is labeled . Figure 2 shows
the load and thermal regulation response of a typical
MC78T05AC to a 20 W load pulse. The output voltage
variation due to load regulation is labeled Πand the thermal
regulation component is labeled .
Figure 1. MC78T05AC Line and Thermal Regulation
2
Figure 2. MC78T05AC Load and Thermal Regulation
2
2
1
18
8.0
t, TIME (2.0 ms/DIV)
Vout = 5.0 V
Vin = 8.0 V → 18 V → 8.0 V
Iout = 2.0 A
1 = Regline = 2.4 mV
2 _{= Regtherm = 0.0015%VO/W}
1
2
2.0
0
t, TIME (2.0 ms/DIV)
Vout = 5.0 V
Vin = 15
Iout = 0 A → 2.0 A → 0 A
1 = Regline = 4.4 mV
2 _{= Regtherm = 0.0015%VO/W}
Representative Schematic Diagram
1.0k
1.0k
Q1
Q2
Q4
Q5
Q9
300
Q8
Q3 3.6k
6.4k
Q10
Q20
Q22
1.0k
3.0k
Q19
5.6k
Q16
10pF
Q23
Input
210 ^Q21
6.7V
16k
Q24 ¹⁰⁰
Q25
200
Q26
Q27
300
13 0.12
520
50
Q12
Q6
Q7
2.0k
2.6k 8.0–15 VO
5.0 VO
3.9k
6.0k
Q17
40
pF
Q18
Q11 Q13
Q15
6.0k _Q14
2.8k
200
Output
Gnd
6
MOTOROLA ANALOG IC DEVICE DATA