LP5569 datasheet(17/93 Pages) TI2

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LP5569

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SNVSAP8A – JULY 2017 – REVISED SEPTEMBER 2017

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8.3.1.2.4

EN/PWM Input Timeout

The EN/PWM input timeout feature has two operating modes as follows:

•

STANDBY state: EN/PWM low for > 15 ms shuts down the LP5569 device and returns to the DISABLED

state (see Figure 20).

8.3.2 Charge Pump

8.3.2.1 Overview

The LP5569 device includes a pre-regulated switched-capacitor charge pump with a programmable voltage

multiplication of 1× or 1.5×. In 1.5× mode, by combining the principles of a switched-capacitor charge pump and

a linear regulator, a regulated 4.5-V output is generated from the VIN input within its normal voltage range. A

two-phase non-overlapping clock, generated internally, controls the operation of the charge pump. During the

charge phase, both flying capacitors (CFLY1 and CFLY2) are charged from input voltage. In the pump phase that

follows, the flying capacitors are discharged to the output. A traditional switched-capacitor charge pump

operating in this manner uses switches with very low on-resistance, ideally 0 Ω, to generate an output voltage

that is 1.5× the input voltage. The LP5569 device regulates the output voltage by controlling the resistance of the

input-connected pass-transistor switches in the charge pump.

8.3.2.2 Pre-Regulation

The very low input-current ripple of the LP5569 device, resulting from internal pre-regulation, adds minimal noise

to the input line. The core of the LP5569 device is very similar to that of a basic switched-capacitor charge pump:

it is composed of switches and two flying capacitors (external). Regulation is achieved by controlling the current

through the switches connected to the VIN pin (one switch in each phase). The regulation occurs before the

voltage multiplication, giving rise to the term pre-regulation. It is pre-regulation that eliminates most of the input-

current ripple that is a typical and undesirable characteristic of a many switched-capacitor converters.

8.3.2.3 Input Current Limit

The LP5569 device contains current-limit circuitry that protects the device in the event of excessive input current

and/or output shorts to ground. The input current is limited to 600 mA (typical) when the output is shorted directly

to ground. When the LP5569 device is current limiting, power dissipation in the device is likely to be quite high. In

this event, thermal cycling should be expected.

8.3.2.4 Output Discharge

The LP5569 device provides a feature to discharge the charge-pump output capacitor. The charge-pump output

pulldown is not enabled when the MISC2 register (address 33h) CP_DIS_DISCH bit = 1. The charge pump

output pulldown is enabled when the CP_DIS_DISCH bit = 0. The pulldown draws a minimal current from the

output capacitor (300 μA typical) when in the SHUTDOWN and STANDBY states.

8.3.2.5 Controlling the Charge Pump

The charge pump is controlled with two CP_MODE bits in the MISC register (address 2Fh). When both of the

bits are low, the charge pump is disabled, and output voltage is pulled down as described in Output Discharge.

The charge pump can be forced to the bypass mode, so the battery voltage is connected directly to the current

source; in 1.5× mode the output voltage is boosted to 4.5 V. In automatic mode, the charge-pump operation

mode is determined by saturation of the constant-current drivers described in LED Forward Voltage Monitoring.

8.3.2.6 LED Forward Voltage Monitoring

When the charge-pump automatic-mode selection is enabled, voltages on the LED current sinks LED0 to LED8

are monitored. If the current sinks do not have enough headroom, the charge pump gain is set to 1.5× and

remains in 1.5× mode until one of the following occurs:

•

The LP5569 device enters the SHUTDOWN state and goes through the INITIALIZATION or STARTUP state.

•

The charge-pump mode is forced to 1× mode via the MISC register.

•

The LP5569 device exits power save when the charge pump is in automatic mode (CP_MODE bits = 3h).

A current-sink saturation monitor is selectable to one of four fixed voltage thresholds. The charge-pump gain is

set to 1× when the battery voltage is high enough to supply all LEDs. Note: forward-voltage monitoring is

disabled when the LEDx_CONTROL (addresses 07h–0Fh) register EXTERNAL_POWERx bit = 1.

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