LP3936SL National Semiconductor, LP3936SL Datasheet - Page 13

• Manufacturer Part Number: LP3936SL
• Manufacturer: National Semiconductor

Specifications of LP3936SL

• Operating Supply Voltage (typ): 3.3/5V
• Number Of Segments: 6
• Operating Temperature (min): -40C
• Operating Temperature (max): 85C
• Operating Temperature Classification: Industrial
• Package Type: LAM CSP
• Pin Count: 32
• Mounting: Surface Mount
• Operating Supply Voltage (min): 3V
• Operating Supply Voltage (max): 6V
• Lead Free Status / Rohs Status: Compliant

Magnetic Boost DC/DC Converter
The LP3936 Boost DC/DC Converter generates a 4.1V–5.3V supply voltage for the LEDs from single Li-Ion battery (3V … 4.5V).
The output voltage is controlled with an 8-bit register in 9 steps. The converter is a magnetic switching PFM/PWM mode DC/DC
converter with a current limit. The converter has a 1 MHz switching frequency when timing resistor RT is 82 kΩ.
The topology of the magnetic boost converter is called CPM control, current programmed mode, where the inductor current is
measured and controlled with the feedback. The user can program the output voltage of the boost converter. The control changes
the resistor divider in the feedback loop.
The following figure shows the boost topology with the protection circuitry. Three different protection schemes are implemented:
1) Over voltage protection, limits the maximum output voltage
2) Over current protection, limits the maximum inductor current
3) Duty cycle limiting, done with digital control.
Boost Output Voltage Control
User can control the boost output voltage by boost output 8-bit register.
a. Keeps the output below breakdown voltage.
b. Prevents boost operation if battery voltage is much higher than desired output.
a. Voltage over switching NMOS is monitored; too high voltages turn the switch off.
0000 0000
0000 0001
0000 0011
0000 0111
0000 1111
0001 1111
0011 1111
0111 1111
1111 1111
Binary
Register 0Dh
Boost[7:0]
Hex
FF
00
01
03
07
0F
1F
3F
7F
BOOST Output
4.55 Default
(typical)
Voltage
4.10
4.25
4.40
4.70
4.85
5.00
5.15
5.30
13
Boost Output Voltage Control
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