lp5526tlx National Semiconductor Corporation, lp5526tlx Datasheet - Page 8

• Manufacturer Part Number: lp5526tlx
• Description: Lighting Management Unit With High Voltage Boost Converter With Up To 150ma Serial Flash Led Driver
• Manufacturer: National Semiconductor Corporation

www.national.com
Power-Up Sequence
When powering up the device, V
greater than V
Magnetic Boost DC/DC Converter
The LP5526 Boost DC/DC Converter generates an 8…20V
supply voltage for the LEDs from single Li-Ion battery
(3V…4.5V). The output voltage is controlled with an 8-bit
register in 12 steps. The converter is a magnetic switching
PWM mode DC/DC converter with a current limit. Switching
frequency is 1MHz, when timing resistor RT is 82kΩ. Timing
resistor defines the internal oscillator frequency and thus
directly affects boost frequency and RGB timings.
EMI filter (R
suppress EMI caused by fast switching. These components
should be as near as possible to the SW pin to ensure
reliable operation. The LP5526 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 active load is used to remove the
SW
DDIO
and C
to prevent any damage to the device.
SW
) on the SW pin can be used to
DD1
and V
DD2
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Boost Converter Topology
should be
8
excess charge from the output capacitor at very light loads.
Active load can be disabled by writing the EN_AUTOLOAD
bit low. Disabling active load will increase slightly the effi-
ciency at light loads, but the downside is that pulse skipping
will occur. The Boost Converter should be stopped and set to
8V when there is no load to minimize the current consump-
tion.
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
feedback loop. The following figure shows the boost topol-
ogy with the protection circuitry. Four different protection
schemes are implemented:
1. Over voltage protection, limits the maximum output volt-
2. Over current protection, limits the maximum inductor
3. Feedback break protection. Prevents uncontrolled op-
4. Duty cycle limiting, done with digital control.
age
— Keeps the output below breakdown voltage.
— Prevents boost operation if battery voltage is much
current
— Voltage over switching NMOS is monitored; too high
eration if FB pin gets disconnected.
higher than desired output.
voltages turn the switch off.
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