LP5813 datasheet(15/60 Pages) TI

15 / 60 page

9.3.1.5 Boost PWM Mode

The LP5813 uses a quasi-constant 1.0-MHz frequency pulse width modulation (PWM) at moderate to heavy

load current. Based on the input voltage to output voltage ratio, a circuit predicts the required on-time. At the

beginning of the switching cycle, the main switching low-side FET is turned on. The input voltage is applied

across the inductor and the inductor current ramps up. In this phase, the output capacitor is discharged by the

load current. When the on-time expires, the low-side FET is turned off, and the high-side rectifier FET is turned

on. The inductor transfers its stored energy to replenish the output capacitor and supplies the load. The inductor

current declines because the output voltage is higher than the input voltage. When the inductor current hits the

valley current threshold determined by the output of the error amplifier, the next switching cycle starts again.

The LP5813 has a built-in compensation circuit that can accommodate a wide range of input voltage, output

voltage, inductor value, and output capacitor value for stable operation.

9.3.1.6 Boost PFM Mode

The LP5813 works at PFM to improve efficiency at light load. When the load current decreases, the inductor

valley current set by the output of the error amplifier no longer regulates the output voltage. When the inductor

valley current hits the low limit, the output voltage exceeds the setting voltage as the load current decreases

further. When the feedback voltage hits the PFM reference voltage (0.6 V typical), the LP5813 works at PFM.

When the feedback voltage rises and hits the PFM reference voltage, the device continues switching for several

cycles because of the delay time of the internal comparator — then it stops switching. The load is supplied by

the output capacitor, and the output voltage declines. When the feedback voltage falls below the PFM reference

voltage, after the delay time of the comparator, the device starts switching again to ramp up the output voltage.

Figure 9-2 showes the waveform of voltage when the device works at PWM and PFM.

Output

Voltage

VOUT_NOM

1.01 x VOUT_NOM

PFM mode at light load

PWM mode at heavy load

Figure 9-2. Output Voltage in PWM Mode and PFM

9.3.1.7 Pass-Through Mode

When the input voltage is higher than the setting output voltage, the output voltage is higher than the target

regulation voltage. When the output voltage is 101% of the setting target voltage, the LP5813 stops switching

and fully turns on the high-side FET and works in pass-through mode. The output voltage is the input voltage

minus the voltage drop across the DCR of the inductor and the RDS(on) of the high-side FET. When the output

voltage drops below the 97% of the setting target voltage as the input voltage declines or the load current

increases, the LP5813 resumes switching again to regulate the output voltage.

9.3.2 Time-cross-multiplexing (TCM) scheme

The LP5813 integrates 4 high-side PMOS scan switches and 4 constant current sinks. Each OUTx (x = 0, 1, 2,

3) has 1 PMOS scan switch and 1 constant current sink. The source of PMOS switches are connected to the

boost output VOUT. During normal operation at default setting, the switches turn on sequentially from OUT0 to

OUT3. At the same time, only one OUT is selected working as switch, the other 3 OUTs act as constant current

sink. Thus a 4×3 matrix is formed with ¼ multiplexing ratio. The scanning order of OUTs can be configured in

'Dev_config_2' register

www.ti.com

LP5813

SNVSC74 – SEPTEMBER 2023

Submit Document Feedback

Product Folder Links: LP5813

LP5813 Datasheet(PDF) 15 Page - Texas Instruments

LP5813 Datasheet(HTML) 15 Page - Texas Instruments

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Datasheet Download

Link URL