The LP875701-Q1 device contains a CLKIN input to synchronize switching clock of the buck regulator with the external clock. The block diagram of the clocking and PLL module is shown in Figure 7-4. Depending on the PLL_MODE[1:0] bits (in 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 SYNC_CLK_MASK bit in TOP_MASK1 register. The nominal frequency of the external input clock is set by EXT_CLK_FREQ[4:0] bits (in 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%) for valid clock detection.

The NO_SYNC_CLK interrupt (in INT_TOP1 register) is also generated in cases the external clock is expected but it is not available. These cases are start-up (read OTP-to-STANDBY transition) when PLL_MODE[1:0] = 01 and regulator enable (STANDBY-to-ACTIVE transition) when PLL_MODE[1:0] = 10.

Figure 7-4 Clock and PLL Module