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LM5145 Datasheet(PDF) 30 Page - Texas Instruments |
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LM5145 Datasheet(HTML) 30 Page - Texas Instruments |
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30 / 73 page  RT RSS PFM/SYNC AGND COMP2 VOUT2 ISNS2+ LO2 SW2 HO2 CBOOT2 VIN COMP1 BIAS1/VOUT1 ISNS1+ LO1 SW1 HO1 CBOOT1 VCC FB1 VDDA FB2 SYNCOUT CFNG EN1 EN2 PG2 PG1 LO1 COUT2 CIN1 CVDDA1 LO2 COUT1 RS2 RS1 Q2 Q1 RSS RRT1 RCNFG1 Q4 Q3 CVCC1 CBOOT1 CBOOT2 LM25137 CNTRL1 PRIMARY/SECONDARY VDDA CIN2 RFB CHF RCOMP CCOMP VIN VOUT RT RSS PFM/SYNC AGND COMP2 VOUT2 ISNS2+ LO2 SW2 HO2 CBOOT2 VIN COMP1 BIAS1/VOUT1 ISNS1+ LO1 SW1 HO1 CBOOT1 VCC FB1 VDDA FB2 SYNCOUT CFNG EN1 EN2 PG2 PG1 LO3 COUT4 CIN3 CVDDA2 LO4 COUT3 RS4 RS3 Q6 Q5 RRT2 RCNFG2 Q8 Q7 CVCC2 CBOOT3 CBOOT4 CIN4 VIN PFM: connect FB1 of the secondary to PFM/SYNC of the primary FPWM: connect FB1 to GND LM25137 CNTRL2 SECONDARY Figure 7-9. LM25137 Multiphase Regulator Schematic Configured for Single-Output Interleaved Operation 7.4 Device Functional Modes 7.4.1 Sleep Mode The LM25137 operates with peak current-mode control such that the compensation (COMP) voltage is proportional to the peak inductor current. During no-load or light-load conditions, the output capacitor discharges very slowly. As a result, the COMP voltage does not demand the driver output pulses on a cycle-by-cycle basis. When the LM25137 controller detects 16 missed switching cycles, the device enters sleep mode and switches to a low IQ state to reduce the current drawn from the input. For the LM25137 to go into sleep mode, the device must be programmed for diode emulation (tie PFM/SYNC to VDDA). The typical controller IQ in sleep mode at 12V input is 1.5μA with channels 1 and 2 set to 5V and 3.3V outputs, respectively. PG1/2 are disabled when the LM25137 goes to sleep. 7.4.2 PFM Mode A synchronous buck regulator implemented with a low-side MOSFET rather than a diode has the capability to sink negative current from the output during light-load, overvoltage, and prebias start-up conditions. The LM25137 provides a diode emulation feature that can be enabled to prevent reverse (drain-to-source) current flow in the low-side MOSFET. When configured for diode emulation (DEM), the low-side MOSFET is switched off when reverse current flow is detected by sensing of the applicable SW voltage using a zero-cross comparator. The benefit of this configuration is lower power loss during light-load conditions; the disadvantage being slower light-load transient response. Table 7-6. PFM Settings PFM/SYNC FPWM, PFM VDDA PFM AGND FPWM External clock FPWM Configure the diode emulation feature using the PFM/SYNC pin. To enable diode emulation and thus achieve discontinuous conduction mode (DCM) operation at light loads, connect PFM/SYNC to VDDA. If FPWM or continuous conduction mode (CCM) operation is desired, tie PFM/SYNC to AGND. See Table 7-6. Note that diode emulation is automatically engaged (in both PFM and FPWM modes) to prevent reverse current flow during a prebias start-up. A gradual change from DCM to CCM operation provides monotonic start-up performance. LM25137 SNVSCU4 – OCTOBER 2025 www.ti.com 30 Submit Document Feedback Copyright © 2025 Texas Instruments Incorporated Product Folder Links: LM25137 |
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