Ricoh R3111x Series - Manual (Page 13)

R3111x
13
•
Operation of R3111xxxxB
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 (R3111xxxxB)
t
PLH
GND
GND
V
DDL
-V
DET
+V
DET
Detector Threshold
Released Voltage
Minimum Operating Voltage
Pull-up Voltage
1 2 3
A
B Detector Threshold
Hysteresis
Supply Voltage
(V
DD
)
Output Voltage
(V
OUT
)
Step 1 2 3
Comparator ( −)
Pin Input Voltage
I II I
Comparator Output L H L
Tr.1 OFF ON OFF
Output Tr. Nch ON OFF ON
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 GND level.
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 "L" to "H", therefore the output voltage becomes the pull-up voltage. The voltage level of Point A
means a detector threshold voltage (
−V
DET
).
Step 3. At Point “B”, Vref <
= V
DD
×Rb/(Ra+Rb) is true, as a result, the output of comparator is reversed from "H" to
"L", then the output voltage is equal to the GND level. 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