LP5523 datasheet(14/56 Pages) TI1

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8-BIT CURRENT

SETTING

0 mA TO 25.5 mA

12-BIT PWM

PATTERN

CONTROL

0% TO 100 %

TIME

PWM FREQUENCY = 312 Hz

CHARGE PUMP

CURRENT

SOURCE

SATURATION

MONITOR

DIGITAL

FILTER

MODE

CONTROL

COMMAND

LOOK-AHEAD

PROGRAM

MEMORY

CONTROL

REGISTERS

COMPARATOR

VOUT

VDD

VOFS

MODE

LP5523

SNVS550D – SEPTEMBER 2009 – REVISED MAY 2013

www.ti.com

Gain Change Hysteresis

Charge pump gain control utilizes digital filtering to prevent supply voltage disturbances (for example, the

transient voltage on the power supply during the GSM burst) from triggering unnecessary gain changes.

Hysteresis is provided to prevent periodic gain changes (which could occur due to LED driver) and charge-pump

voltage drop in 1x mode. The hysteresis of the gain change is user-configurable; default setting is factory-

programmable. Flexible configuration ensures that hysteresis can be minimized or set to desired level in each

application.

LED forward voltage monitoring and gain control block diagram is shown in Figure 17.

Figure 17. Forward Voltage Monitoring and Gain Control Block

LED Driver Operational Description

Overview

LP5523 LED drivers are constant current sources. Output current can be programmed by control registers up to

25.5 mA. The overall maximum current is set by 8-bit output current control registers with 100

μA step size. Each

of the 9 LED drivers has a separate output current control register.

The LED luminance pattern (dimming) is controlled with PWM (pulse width modulation) technique, which has

internal resolution of 12 bits (8-bit control can be seen by user). PWM frequency is 312 Hz. See Figure 18 below.

Figure 18. LED Pattern and Current Control Principle

LED dimming is controlled according to a logarithmic or linear scale, see Figure 19. A logarithmic or linear

scheme can be set for both the program execution engine control and direct PWM control. Note: if the

temperature compensation is active, the maximum PWM duty cycle is limited to 50% at +25°C. This is required

to allow enough headroom for temperature compensation over the whole temperature range

−40 °C to 90°C.

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