PM6680A STMicroelectronics

PM6680A Dual synchronous step-down controller with adjustable output voltages plus LDO Features 6 V to 36 V input voltage range Adjustable output voltages 5V LDO delivers 100 mA peak current 1.237 V 1 % reference voltage available externally VFQFPN-32 5X5 Current sensing using low side MOSFETs R DS(on) Valley current sensing Description Soft-start internally fixed at 2ms PM6680A is a dual step-down controller Soft output discharge specifically designed to provide extremely high Latched OVP and UVP efficiency conversion, with loss less 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 5mW 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 Thermal shutdown frequency of 33 kHz is selectable to avoid audio noise issues. The PM6680A provides a selectable Applications switching frequency, allowing three different values of switching frequencies for the two Embedded computer system switching sections. The output voltages OUT1 FPGA system power and OUT2 can be adjusted from 0.9 V to 5 V and from 0.9 V to 3.3 V respectively. Industrial applications on 24 V High performance and high density DC/DC modules Table 1. Device summary Order codes Package Packaging PM6680A Tube VFQFPN-32 5X5 (exposed pad) PM6680ATR Tape and reel December 2007 Rev 2 1/48 www.st.com 48Contents PM6680A Contents 1 Block diagram 3 2 Pin settings 4 2.1 Connections 4 2.2 Functions 5 3 Electrical data 8 3.1 Maximum rating . 8 3.2 Thermal data . 8 4 Electrical characteristics . 9 5 Typical operating characteristics . 12 6 Application schematic 17 7 Device description . 18 7.1 Constant On time PWM control 18 7.2 Constant On time architecture . 20 7.3 Output ripple compensation and loop stability . 21 7.4 Pulse skip mode 22 7.5 No-audible skip mode 23 7.6 Current limit . 24 7.7 Soft start and soft end . 25 7.8 Gate drivers . 26 7.9 Reference voltage and bandgap . 27 7.10 Internal linear regulator 27 7.11 Power up sequencing and operative modes . 28 8 Monitoring and protections 29 2/48