LP5520TL NSC [National Semiconductor], LP5520TL Datasheet - Page 20

• Manufacturer Part Number: LP5520TL
• Description: RGB Backlight LED Driver
• Manufacturer: NSC [National Semiconductor]

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MAGNETIC BOOST DC/DC CONVERTER ELECTRICAL CHARACTERISTICS
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.
I
V
RDS
f
t
t
I
LOAD
PWM
PULSE
STARTUP
MAX
OUT
Symbol
ON
00101
00110
00111
01100
01101
01110
10010
10011
10100
Bin
...
...
Boost Output [7:0]
Register 0DH
Maximum
Continuous Load
Current
Output Voltage
Accuracy
(FB Pin)
Switch ON
Resistance
Frequency
Accuracy
Switch Pulse
Minimum
Width
Startup Time
SW Pin Current
Limit
Parameter
Dec
12
13
14
18
19
20
...
...
5
6
7
2.9V = V
V
2.9V
5.5V
V
I
no load
SW
OUT
OUT
Conditions
= 0.5A
Voltage (typical)
≤
= 20V
= 20V
Boost Output
V
IN
IN
12.0V
13.0V
14.0V
18.0V
19.0V
20.0V
5.0V
6.0V
7.0V
≤
...
...
Min
-1.7
70
−6
−9
20
-5
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.
1100
Typ
0.3
±3
50
20
Max
1.7
+5
+6
+9
Units
mA
mA
ms
ns
%
%
Ω