LP5523 datasheet(18/61 Pages) TI2

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LP5523 INPUT

CURRENT 1 mA/DIV

PWM POWERSAVE

ENABLED

INPUT CURRENT ~50 éA

DURING PWM

POWERSAVE

LED CURRENT 5 mA/DIV

TIME 1 ms/DIV

LP5523

SNVS550E – SEPTEMBER 2009 – REVISED JANUARY 2017

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Device Functional Modes (continued)

7.4.1.1 Automatic Power-Save Mode

Automatic power-save mode is enabled when POWERSAVE_EN bit in register address 36H is 1. Almost all

analog blocks are powered down in power-save if an external clock signal is used. Only the charge-pump

protection circuits remain active. However, if the internal clock has been selected, only charge pump and LED

drivers are disabled during the power save; the digital part of the LED controller needs to stay active. In both

cases the charge pump enters the weak 1× mode. In this mode the charge pump utilizes a passive current

limited keep-alive switch, which keeps the output voltage at the battery level. During the program execution

LP5523 can enter power save if there is no PWM activity in any of the LED driver outputs. To prevent short

power-save sequences during program execution, LP5523 has an instruction look-ahead filter. During program

execution engine 1, engine 2 and engine 3 instructions are constantly analyzed, and if there are time intervals of

more than 50 ms in length with no PWM activity on LED driver outputs, the device enters power save. In power-

save mode program execution continues uninterrupted. When an instruction that requires PWM activity is

executed, a fast internal-startup sequence is started automatically.

7.4.1.2 PWM Power-Save Mode

PWM cycle power-save mode is enabled when register 36 bit [2] PWM_PS_EN is set to 1. In PWM power-save

mode analog blocks are powered down during the "down time" of the PWM cycle. Which blocks are powered

down depends whether the external or internal clock is used. While the Automatic Power-Save Mode (see

above) saves energy when there is no PWM activity at all, the PWM power-save mode saves energy during

PWM cycles. Like the automatic power-save mode, PWM power-save mode also works during program

execution. Figure 18 shows the principle of the PWM power-save technique. An LED on D9 output is driven at

50% PWM, 5-mA current (top waveform). After PWM Power-save enable, the LED-current remains the same, but

the LP5523 input current drops down to an approximately 50-µA level when the LED is OFF, or to an

approximately 200-µA level when the charge-pump-powered output(s) are used.

Figure 18. PWM Power-Save Principle; External Clock, VDD = 3.6 V

LP5523 Datasheet(PDF) 18 Page - Texas Instruments