R1211N002A_06 Datasheet, PDF (12/40 Pages) RICOH electronics devices division – STEP-UP DC/DC CONTROLLER

R1211x
TIMING CHART
• R1211x002A/R1211x002C
EXT
VOUT
VREF
+
VFB
-
DTC
SS
AMPOUT
-
--
+
EXT
R1
R2
OP AMP
PWM Comparator
• R1211x002B/R1211x002D
EXT
VOUT
VREF
+
VFB
-
DTC
SS
-
AMPOUT
-
-
+
EXT
R1
R2
OP AMP
PWM Comparator
<Soft-start Operation>
Soft-start operation is starting from power-on as follows:
(Step1)
The voltage level of SS is rising gradually by constant current circuit of the IC and a capacitor. VREF level which
is input to OP AMP is also gradually rising. VOUT is rising up to input voltage level just after the power-on,
therefore, VFB voltage is rising up to the setting voltage with input voltage and the ration of R1 and R2. AMPOUT
is at "L", and switching does not start.
(Step2)
When the voltage level of SS becomes the setting voltage with the ration of R1 and R2 or more, switching
operation starts. VREF level gradually increases together with SS level. VOUT is also rising with balancing VREF and
VFB. Duty cycle depends on the lowest level among AMPOUT, SS, and DTC of the 4 input terminals in the PWM
comparator.
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