PM6685TR STMicroelectronics

PM6685 Dual step-down main supply controller with auxilary voltages for notebook system power Features 6 V to 28 V input voltage range Fixed 5 V - 3.3 V output voltages 5 V and 3.3 V voltage always available to deliver 100 mA of peak current 1.230 V 1% reference voltage available VFQFPN-32 (5mm x 5mm) Lossless current sensing using low side MOSFETs R DS(on) Negative current limit Description Soft-start internally fixed at 2 ms PM6685 is a dual step-down controller specifically Soft output discharge designed to provide extremely high efficiency conversion with loss-less current sensing Latched OVP and UVP technique. The constant on-time architecture Selectable pulse skipping at light loads assures fast load transient response and the Selectable minimum frequency (33 kHz) in embedded voltage feed-forward provides nearly pulse skip mode constant switching frequency operation. 4 mW maximum quiescent power An embedded integrator control loop compensates the DC voltage error due to the Independent power good signals output ripple. The pulse skipping technique Output voltage ripple compensation increases efficiency for very light loads. Moreover, a minimum switching frequency of 33kHz is Applications selectable in order to avoid audio noise issues. Notebook computers The PM6685 provides a selectable switching frequency, allowing either 200 kHz/300 kHz, 300 Tablet PC or slates kHz/400 kHz, or 400 kHz/500 kHz operation of Mobile system power supply the 5 V/3.3 V switching sections. 3 and -4 Cells Li+ battery-powered devices Table 1. Device summary Order code Package Packaging PM6685 Tube VFQFPN-32 (5 mm x 5 mm) PM6685TR Tape and reel March 2011 Doc ID 11674 Rev 8 1/48 www.st.com 48Contents PM6685 Contents 1 Block diagram 4 2 Pin settings 5 2.1 Connections 5 2.2 Functions 6 3 Electrical data 8 3.1 Maximum rating . 8 3.2 Thermal data . 8 4 Electrical characteristics . 9 5 Typical operating characteristics . 13 6 Application schematic 18 7 Device description . 19 7.1 Constant on time PWM control . 19 7.2 Constant on time architecture . 21 7.3 Output ripple compensation . 21 7.4 Pulse skip mode 22 7.5 No-audible skip mode 23 7.6 Current limit . 23 7.7 Soft start and soft end . 25 7.8 Gate drivers . 26 7.9 Reference voltage and bandgap . 27 7.10 Internal linear regulators . 27 7.11 Power up sequencing and operative modes . 28 8 Monitoring and protections 29 8.1 Power good signals . 29 8.2 Thermal protection 29 8.3 Overvoltage protection . 29 2/48 Doc ID 11674 Rev 8