
MAGNETIC BOOST DC/DC CONVERTER ELECTRICAL CHARACTERISTICS
Symbol
Parameter
Maximum
Continuous Load
Current
Output Voltage
Accuracy
(FB Pin)
Conditions
2.9V = V
IN
V
OUT
= 20V
Min
70
Typ
Max
Units
mA
I
LOAD
V
OUT
2.9V
≤
V
IN
≤
5.5V
V
OUT
= 20V
I
SW
= 0.5A
-1.7
-5
1.7
+5
%
RDS
ON
Switch ON
Resistance
Frequency
Accuracy
Switch Pulse
Minimum
Width
Startup Time
0.3
f
PWM
6
9
±3
+6
+9
%
t
PULSE
no load
50
ns
t
STARTUP
I
MAX
20
ms
SW Pin Current
Limit
1100
mA
BOOST CONTROL
User can set the Boost Converter to STANDBY mode by writ-
ing the register bit
<en_boost>
low. When
<en_boost>
is
written high, the converter starts for 50 ms in low current PWM
mode and then goes to normal PWM mode.
User can control the boost output voltage by boost output
boost_output
(05H) register.
Boost Output [7:0]
Register 0DH
Bin
Dec
00101
5
00110
6
00111
7
...
...
01100
12
01101
13
01110
14
...
...
10010
18
10011
19
10100
20
Boost Output
Voltage (typical)
5.0V
6.0V
7.0V
...
12.0V
13.0V
14.0V
...
18.0V
19.0V
20.0V
If register value is lower than 5, then value of 5 is used inter-
nally. If register value is higher than 20, then value of 20 is
used internally.
ADAPTIVE OUTPUT VOLTAGE CONTROL
When automatic boost voltage control is selected using the
<vout_auto>
bit in
Control
(06H) register, the user defined
boost output voltage is ignored. The boost output voltage is
adjusted for sufficient operating headroom by monitoring all
enabled LED driver outputs. The boosted voltage is adjusted
so that the lowest driver voltage is between 0.85 and 1.35V
when the LED output currents are below 30 mA and to 1.0 –
1.5V when any LED current is above 30 mA. The output volt-
age range is from 5.0 to 20V in adaptive mode.
The adaptive voltage control helps saving energy by always
setting the boost voltage to minimum sufficient value. It elim-
inates the need for extra voltage margins due to LED forward
voltage variation or temperature variation. With very small
brightness settings, when the PWM pulses in LED outputs are
very narrow, the adaptive voltage setting will give higher than
necessary boost voltage. This does not harm the overall effi-
ciency, since this happens only when the power used is very
small.
After reset the adaptive control is on by default. In stand-alone
mode the adaptive output voltage is always used.
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