LP8733 datasheet(21/84 Pages) TI

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The LP8733xx device can be configured to give out an interrupt (the I_MEAS_INT bit in the INT_TOP_1 register)

after the load current measurement sequence is finished. The load current measurement interrupt can be

masked with the I_MEAS_MASK bit (TOP_MASK_1 register). The measurement result can be read from the

registers I_LOAD_1 and I_LOAD_2. The register I_LOAD_1 bits BUCK_LOAD_CURRENT[7:0] gives out the

LSB bits, and the register I_LOAD_2 bit BUCK_LOAD_CURRENT[8] gives out the MSB bit. The measurement

result BUCK_LOAD_CURRENT[8:0] LSB is 20 mA, and the maximum code value of the measurement

corresponds to 10.22 A. In dual-phase configuration, the measured current is the total value of the master

and slave phases.

7.3.1.6 Spread-Spectrum Mode

Systems with periodic switching signals may generate a large amount of switching noise in a set of narrowband

frequencies (the switching frequency and its harmonics). The usual solution to reduce noise coupling is to add

EMI-filters and shields to the boards. The LP8733xx has a register-selectable spread-spectrum mode which

minimizes the need for output filters, ferrite beads, or chokes. In spread spectrum mode, the switching frequency

varies around the center frequency, reducing the EMI emissions radiated by the converter and associated

passive components and PCB traces (see Figure 7-4). Spread-spectrum mode is only available when an internal

RC oscillator is used (EN_PLL bit is 0 in PLL_CTRL register), it is enabled with the EN_SPREAD_SPEC bit in

the CONFIG register, and it affects both buck cores.

Frequency

Where a fixed frequency converter exhibits large amounts of spectral energy at the switching frequency, the spread spectrum

architecture of the LP8733xx spreads that energy over a large bandwidth.

Figure 7-4. Spread-Spectrum Modulation

7.3.2 Sync Clock Functionality

The LP8733xx device contains a CLKIN input to synchronize the switching clock of the buck regulators with

the external clock. The block diagram of the clocking and PLL module is shown in Figure 7-5. Depending on

the EN_PLL bit in the PLL_CTRL register and the external clock availability, the external clock is selected and

interrupt is generated as shown in Table 7-2. The interrupt can be masked with the SYNC_CLK_MASK bit in

the TOP_MASK_1 register. The nominal frequency of the external input clock is set by the EXT_CLK_FREQ[4:0]

bits in the PLL_CTRL register, and it can be from 1 MHz to 24 MHz with 1-MHz steps. The external clock must

be inside accuracy limits (–30%/+10%) of the selected frequency for valid clock detection.

The SYNC_CLK_INT interrupt in the INT_TOP_1 register is also generated in cases where the external clock

is expected but is not available. These cases occur when EN_PLL is 1 during start-up (read OTP-to-standby

transition) and during Buck regulator enable (standby-to-active transition).

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LP8733

SNVSBK2A – SEPTEMBER 2019 – REVISED JUNE 2021

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LP8733 Datasheet(PDF) 21 Page - Texas Instruments