BD9757MWV_10 Datasheet, PDF (14/24 Pages) Rohm – Switching Regulator IC

BD9757MWV
Technical Note
●CH8 Modulated light function explanation
HS78H
OCP
VCCOUT
Load
SW
INV8
INV8I
UPIC8
To SCP
-
+
1.0V
+
ERRAMP 8V
VREGA1
I/O
(schmitt)
VREGA_D
counter for
tone setting
reaches 31
(5bit)
1Fh(Fixed)
S
E
COUNT[4:0] L
5->6bit
decode
latch
DAC
DACIN[5:0]
UVLO
EN
LOGIC
RESET
GEN
EN ^UVLO
STBY
-
+
+
ERRAMP 8I
EN
SOFT
START
SS_CLK
OSC
Detect CounterDetect Counter
for H Section for L Section
(6bit)
(6bit)
+
+
-
PWM COMP8
VCCOUT
N-ch
DRIVER
HS78H
VBAT
HS8L
Lx8
Vo8(Feed Back ch8)
PGND678
INV8I
LED
LED Current
setting resister R
P&R area
Fig.28 CH8 block diagram
○Description of CH8 operation
EN, the signal for getting CH8 operated, is turned to H (EN=H) by maintaining the H interval that is shown by T_EN and
from UPIC8 terminal (refer to Fig.29 EN start-up-G) .
EN signal is turned to L and CH8 is turned OFF by maintaining the L interval that is shown by T_OFF and from UPIC8
terminal (refer to Fig.29 EN start-up-K ~ L) .
Moreover, UPIC8 terminal will not become L ever since EN starting-up, and if the H interval shown by T_ON is passed, then
the DAC input data (DACIN [4:0]) for setting of INV8I output voltage is started up by the state of MAX voltage setting (1Fh)
(refer to Fig.29 FULLON Mode-H ~ I).
As for the method to set the values except MAX voltage as INV8I voltage, first fix the UPIC8 terminal on interval L shown
by T_CLR and then reset the counter for tone setting, before inputting only the number of times equivalent to the tone
intended for setting the UPIC8 terminal’s rising edge. Right after that, if it is fixed on interval H shown by T_ON, then the
number of count is latched, transmitted to DAC, and the voltage of INV8I is switched to the set voltage. At the time of
setting again, please repeat this operation (procedure). For the frequency of pulse inputted to UPIC8 terminal, please
follow the rules of T_H and T_L. (refer to Fig.29 Normal mode-K ~ N, and refer to P.2 for the rules).
Once the counter for tone setting reaches 31, 1Fh remains unchanged no matter how many times it is counted. If the
counter for tone setting needs to be cleared, please input the interval L of T_CLR.
If the pulses less than T_CLR is continued to be inputted to UPIC8 terminal after EN becomes H (EN=H) at the time of
starting up, then the value of counter for tone setting is undetermined, and DAC for INV8I output voltage setting is turned
OFF, therefore, please determine the set value with the time shown by T_SET .
Furthermore, for the possible setting range of INV8I output voltage value, please refer to P.16(Fig.30 LED current value
setting).
○Points for attention at the time of CH8 starting up
Soft start is started when light control setting signal is inputted from UPIC8 terminal. At this moment it is necessary to
make any one of STB1 ~ 7 to be H, if OSC does not start oscillating after VREGA is started and UVLO is released, then
CH8 does not start up.
At the time of starting up there is no voltage enough for turning ON the LED, so the feedback on the side of INV8I does
not return,and it is soft-started by the voltage feedback from Vo8 to INV8.
Before the soft start internal is ended, the feedback (return) based on any current setting which is according to light
control setting is started. After soft-starting, any current setting is performed by changing the light control setting signal.
CH8 is turned off by making UPIC8 terminal to be L for a certain period of time.
Moreover, the interval of about 5.4mS from the time of UPIC8 terminal’s rising is taken as the soft start interval, and the
soft start is applied according to the current value originally set by light control from UPIC8 terminal. The change of light
control setting excepting turning off during this interval is not reflected.
○Recommended method of setting at the time of INV8I output voltage setting
If INV8I output setting value is made larger than previous setting value during all intervals but soft start interval (at the
time of starting up), it is recommended that the value of voltage is increased step by step with the smallest possible width
of step after fully evaluating the restriction at the soft side that controls rush current and switching and the vision of
brightness etc. in terms of set application.
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14/20
2010.11 - Rev.A