Low Power-Loss Voltage Regulators
PQ30RV1/PQ30RV11/PQ30RV2/PQ30RV21
■ ON/OFF Operation
D2
D1
V
ADJ
R
2
V
O
VIN
1●
2●
4●
R
2
D2
R1
+
3●
R
L
RD
R
3
CO
CIN
R
1
RL
V
ADJ
VO’
High : Output OFF
Low : Output ON
VC
Equivalent Circuit
in OFF-state
¡ON/OFF operation is available by mounting externally D2 and R3.
¡When VADJ is forcibly raised above Vref (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, VADJ must be higher then Vref MAX., and at the same time must be lower than
maximum rating 7V.
In OFF-state, the load current flows to RL from VADJ through R2. Therefore the value of R2 must be as high as possible.
¡VO'=VADJ X RL/(RL+R2)
occurs at the load. OFF-state equivalent circuit R1 up to 10Ω is allowed. Select as high value of RL and R2 as possible in this range.
In some case, as output voltage is getting lower (VO<1V) , impedance of load resistance rises. In such condition, it is sometime
impossible to obtain the minimum value of VO'. So add the dummy resistance indicated by RD in the figure to the circuit parallel to
the load.
■ An Example of ON/OFF Circuit Using the 1-chip Microcomputer Output Port (PQ30RV1)
<Specification>
Output port of microcomputer
VOH (max) =0.5 V
VOH (min) =2.4 V (IOH=0.2mA)
MAX. rating of IOH=0.5mA
Output should be set as follows.
15.6V RL=52Ω (IO=0.3A)
From VO=1.25V (1+R2/R1) we get VO=15.6V.
R2/R1=11.48
Assuming that VF(max)=0.8V for D2 in case of VOH(min)=2.4V, we get VADJ=VOH(min)-VF(max)=2.4V-0.8V=1.6V. From
Vref(max)=1.3V we get R3=0 Ω
If R1=10kΩ, we get R2=11.48 X R1=114.8kΩ and IOH as follows, ingnoring RL (52 Ω) :
IOH=1.6V X (R1+R2) /R1 X R2
=1.6V X (10kΩ+114.8k Ω) /10k Ω X 114.8k Ω=0.17mA
Hence, IOH<0.2mA. Therefore VOH(min)is ensured.
Next, assuming that VF(min) =0.5V for D2 in case of VOH(max), we get:
IOH=(5V-0.5V) (R1+R2) /R1 X R2=0.49mA which is less than the rating.
Figure 1 shows the VO-VC characteristics when R1=10kΩ, R2=115kΩ, R3=0 Ω, VIN=17V, RL=52Ω, and D1=1S2076A (Hitachi).
SHARP [ SHARP ELECTRIONIC COMPONENTS ]
