Low Power-Loss Voltage Regulators
s
ON/OFF Operation
D
1
PQ30RV1/PQ30RV11/PQ30RV2/PQ30RV21
V
ADJ
D
2
V
IN
1
q
2
q
R
2
4
q
3
q
D
2
+
V
O
R
1
R
L
R
2
C
IN
V
ADJ
R
1
R
3
C
O
R
L
V
O
’
R
D
V
C
High : Output OFF
Low : Output ON
Equivalent Circuit
in OFF-state
¡ON/OFF
operation is available by mounting externally D
2
and R
3
.
¡When
V
ADJ
is forcibly raised above V
ref
(1.25V TYP) by applying the external signal, the output is turned off (pass transistor of
regulator is turned off). When the output is OFF, V
ADJ
must be higher then V
ref
MAX., and at the same time must be lower than
maximum rating 7V.
In OFF-state, the load current flows to R
L
from V
ADJ
through R
2
. Therefore the value of R
2
must be as high as possible.
¡V
O
'=V
ADJ
X
R
L
/(R
L
+R
2
)
occurs at the load. OFF-state equivalent circuit R
1
up to 10Ω is allowed. Select as high value of R
L
and R
2
as possible in this range.
In some case, as output voltage is getting lower (V
O
<1V) , impedance of load resistance rises. In such condition, it is sometime
impossible to obtain the minimum value of V
O
'. So add the dummy resistance indicated by R
D
in the figure to the circuit parallel to
the load.
s
An Example of ON/OFF Circuit Using the 1-chip Microcomputer Output Port (PQ30RV1)
<Specification>
Output port of microcomputer
V
OH
(max)
=0.5
V
V
OH
(min)
=2.4
V (I
OH
=0.2mA)
MAX. rating of I
OH
=0.5mA
Output should be set as follows.
15.6V R
L
=52Ω
(I
O
=0.3A)
From V
O
=1.25V
(1+R
2
/R
1
) we get V
O
=15.6V.
R
2
/R
1
=11.48
Assuming that V
F
(max)=0.8V for D
2
in case of V
OH
(min)=2.4V, we get V
ADJ
=V
OH
(min)-V
F
(max)=2.4V-0.8V=1.6V. From
V
ref
(max)=1.3V we get R
3
=0
Ω
If R
1
=10k
Ω,
we get R
2
=11.48 X
R
1
=114.8k
Ω
and I
OH
as follows, ingnoring R
L
(52
Ω)
:
I
OH
=1.6V X
(R
1
+R
2
) /R
1
X
R
2
=1.6V X
(10k
Ω+114.8k Ω)
/10k
Ω
X
114.8k
Ω=0.17mA
Hence, I
OH
<0.2mA. Therefore V
OH
(min)is ensured.
Next, assuming that V
F
(min)
=0.5V
for D
2
in case of V
OH
(max), we get:
I
OH
=(5V-0.5V)
(R
1
+R
2
) /R
1
X
R
2
=0.49mA
which is less than the rating.
Figure 1 shows the V
O
-V
C
characteristics when R
1
=10k
Ω,
R
2
=115k
Ω,
R
3
=0
Ω,
V
IN
=17V,
R
L
=52
Ω,
and D
1
=1S2076A
(Hitachi).
SHARP [ SHARP ELECTRIONIC COMPONENTS ]
