Ricoh R3111x Series - Manual (Page 12)

R3111x
12
OPERATION
•
Operation of R3111xxxxA
Vref
Ra
Rb
Rc
V
DD
OUT
GND
Tr.1
Nch
Comparator
OUT pin should be pulled-up to
V
DD
or an external voltage level.
Block Diagram (R3111xxxxA)
1 3 5
A
B
t
PLH
2 4
GND
GND
V
DDL
-V
DET
+V
DET
Detector Threshold
Released Voltage
Minimum Operating Voltage
Pull-up Voltage
Detector Threshold
Hysteresis
Supply Voltage
(V
DD
)
Output Voltage
(V
OUT
)
Step 1 2 3 4 5
Comparator ( + )
Pin Input Voltage
I II II II I
Comparator Output H L Indefinite L H
Tr.1 OFF ON Indefinite ON OFF
Output Tr. Nch OFF ON Indefinite ON OFF
I ×V
DD
Rb +Rc
Ra +Rb+Rc
II ×V
DD
Rb
Ra +Rb
Operation Diagram
•
Explanation of operation
Step 1. The output voltage is equal to the pull-up voltage.
Step 2. At Point “A”, Vref
>
= V
DD
×(Rb+Rc)/(Ra+Rb+Rc) is true, as a result, the output of comparator is reversed
from "H" to "L", therefore the output voltage becomes the GND level. The voltage level of Point A means
a detector threshold voltage (
−V
DET
).
Step 3. When the supply voltage is lower than the minimum operating voltage, the operation of the output
transistor becomes indefinite. The output voltage is equal to the pull-up voltage.
Step 4. The output Voltage is equal to the GND level.
Step 5. At Point “B”, Vref
<
=
V
DD
×Rb/(Ra+Rb) is true, as a result, the output of comparator is reversed from "L" to
"H", then the output voltage is equal to the pull-up voltage. The voltage level of Point B means a released
voltage (
+V
DET
).
∗) The difference between a released voltage and a detector threshold voltage is a detector threshold hysteresis.
Output
Delay Time