LP5520TL NSC [National Semiconductor], LP5520TL Datasheet - Page 19

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

Magnetic High Voltage Boost DC/DC Converter
The LP5520 Boost DC/DC Converter generates a 5 to 20V
supply voltage for the LEDs from single Li-Ion battery (2.9 to
4.5V). The output voltage is controlled with four bits in 18
steps. In adaptive mode the output voltage is automatically
adjusted so that the LED drivers have enough voltage for
The LP5520 Boost Converter uses pulse-skipping elimination
to stabilize the noise spectrum. Even with light load or no load
a minimum length current pulse is fed to the inductor. An ac-
tive load is used to remove the excess charge from the output
capacitor at very light loads. Active load can be disabled with
the <en_autoload> bit. Disabling active load will increase
slightly the efficiency at light loads, but the downside is that
pulse skipping will occur. The Boost Converter should be
stopped when there is no load to minimize the current con-
sumption.
The topology of the magnetic boost converter is called CPM
control, current programmed mode, where the inductor cur-
rent is measured and controlled with the feedback. The user
can program the output voltage of the boost converter. The
output voltage control changes the resistor divider in the feed-
back loop.
The following figure shows the boost topology with the pro-
tection circuitry. Four different protection schemes are imple-
mented:
<en_autoload> (bit 3)
<vout_auto> (bit 2)
<en_boost> (bit 1)
<nstby> (bit 0)
Boost Converter Topology
0
1
0
1
0
1
0
1
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Internal boost converter loader off
Internal boost converter loader on
Manual boost output adjustment
Adaptive boost output adjustment
Boost converter standby mode
Boost converter active mode
LP5520 standby mode
LP5520 active mode
proper operation. The converter is a magnetic switching PWM
mode DC/DC converter with a current limit. Switching fre-
quency is 1 MHz. Boost converter options are controlled with
few bits of Control (06H) register.
1.
2.
3.
4.
Over voltage protection, limits the maximum output
voltage
— Keeps the output below breakdown voltage.
— Prevents boost operation if battery voltage is much
Over current protection, limits the maximum inductor
current
— Voltage over switching NMOS is monitored; too high
Feedback break protection. Prevents uncontrolled
operation if FB pin gets disconnected.
Duty cycle limiting, done with digital control.
higher than desired output.
voltages turn the switch off.
20186120
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