PM6680 STMicroelectronics

PM6680 No Rsense dual step-down controller with adjustable voltages for notebook system power Features 6 V to 28 V input voltage range Adjustable output voltages 5 V always voltage available deliver 100 mA peak current 1.237 V 1% reference voltage available VFQFPN-32 5X5 Lossless current sensing using low side MOSFETs R DS(on) Negative current limit Description Soft-start internally fixed at 2ms PM6680 is a dual step-down controller Soft output discharge specifically designed to provide extremely high Latched OVP and UVP efficiency conversion, with lossless current Selectable pulse skipping at light loads sensing technique. The constant on-time architecture assures fast load transient response Selectable minimum frequency (33 kHz) in and the embedded voltage feed-forward provides pulse skip mode nearly constant switching frequency operation. An 4 mW maximum quiescent power embedded integrator control loop compensates Independent power good signals the DC voltage error due to the output ripple. Pulse skipping technique increases efficiency at Output voltage ripple compensation very light load. Moreover a minimum switching frequency of 33kHz is selectable to avoid audio Applications noise issues. The PM6680 provides a selectable switching frequency, allowing three different Notebook computers values of switching frequencies for the two Tablet PC or slates switching sections. The output voltages OUT1 Mobile system power supply and OUT2 can be adjusted from 0.9 V to 5.5 V and from 0.9 V to 3.3 V respectively. 3-4 cells Li+ battery powered devices Table 1. Device summary Order codes Package Packaging PM6680 Tray VFQFPN-32 5mm x 5mm (Exposed pad) PM6680TR Tape and reel January 2008 Rev 7 1/49 www.st.com 49Contents PM6680 Contents 1 Simplified application schematic . 4 2 Electrical data 5 2.1 Maximum rating . 5 2.2 Thermal data . 5 3 Pin settings 6 3.1 Connections 6 3.2 Functions 7 4 Electrical characteristics 10 5 Typical operating characteristics . 13 6 Block diagram . 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 and loop stability . 22 7.4 Pulse skip mode 23 7.5 No-audible skip mode 23 7.6 Current limit . 24 7.7 Soft start and soft end . 26 7.8 Gate drivers . 27 7.9 Reference voltage and bandgap . 27 7.10 Internal linear regulator 28 7.11 Power up sequencing and operative modes . 28 7.12 Monitoring and protections 29 7.12.1 Power good signals 29 7.12.2 Thermal protection . 29 7.12.3 Overvoltage protection 29 7.12.4 Undervoltage protection . 29 2/49