R3111x
OPERATION
• Operation of R3111xxxxA
VDD
Comparator
Ra
OUT pin should be pulled-up to
DD or an external voltage level.
OUT
V
Rb
Rc
Vref
Nch
Tr.1
GND
Block Diagram (R3111xxxxA)
1
2
3
4
5
Step
Comparator (
1
I
2
II
L
3
II
4
II
L
5
I
Released Voltage +VDET
Detector Threshold
Hysteresis
B
A
+)
Detector Threshold
Supply Voltage
(VDD
-
V
DET
Pin Input Voltage
)
Comparator Output
Tr.1
H
Indefinite
H
Minimum Operating Voltage VDDL
GND
OFF ON Indefinite ON OFF
Output Tr.
Nch OFF ON Indefinite ON OFF
Rb+Rc
×VDD
Pull-up Voltage
I
Ra+Rb+Rc
Output
Delay Time
Output Voltage
(VOUT
)
Rb
II
×VDD
t
PLH
Ra+Rb
GND
Operation Diagram
• Explanation of operation
Step 1. The output voltage is equal to the pull-up voltage.
>
Step 2. At Point “A”, Vref VDD×(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 (−VDET).
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 VDD×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 (+VDET).
∗) The difference between a released voltage and a detector threshold voltage is a detector threshold hysteresis.
12
RICOH [ RICOH ELECTRONICS DEVICES DIVISION ]
