OVP

Light

Load

SW

R

R

OCP

Switch

Driver

R

S

R

6

+

-

+

-

Osc/

ramp

-

+

VREF

FB

Boost output

voltage

adjustment

Active Load

Startup

LP8543

www.ti.com

SNVS604D – AUGUST 2009 – REVISED MARCH 2013

User can program the output voltage of the boost converter or use adaptive mode where boost output voltage is

adjusted automatically based on LED driver saturation. In adaptive mode the boost output voltage control steps

are 0.25V. Enabling the adaptive mode is done with <BOOST_AUTO> bit in Boost Control register. If boost is

started with adaptive mode enabled (default) then the initial voltage value is defined with EEPROM bits at

address 29H in order to eliminate long iteration time when the chip is started. If adaptive mode is enabled after

boost startup, then the boost will use register 07H values as initial voltage value. The output voltage control

changes the resistor divider in the feedback loop. The following figure shows the boost topology with the

protection circuitry.

Protection

Four different protection schemes are implemented:

1. Over-voltage protection limit changes dynamically based on output voltage setting

–

Over-voltage protection limit changes dynamically based on output voltage setting.

–

Keeps the output below breakdown voltage.

–

Prevents boost operation if battery voltage is much higher than desired output.

2. SW current limiting, limits the maximum inductor current.

3. Over-current protection enables fault flag and shuts down boost converter in over-current condition.

4. Duty cycle limiting.

Manual Output Voltage Control

User can control the boost output voltage with Boost_output (07H) register when adaptive mode is disabled;

i.e., <BOOST_AUTO> = 0.

Table 7. Boost Output Voltage Controls

VPROG[4:0]

Voltage (typical)

Bin

Dec

Volts

00000

0

10

00001

1

11

00010

2

12

00011

3

13

00100

4

14

...

...

...

11011

27

37

11100

28

38

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