62W TDP too high for sempron 2800+[for 3400+top model]
see below,AMD use top model for power rating.
but Mobile with Cool‘n’Quiet 15W average
so your calculation will be right.

Mobile AMD Sempron™ Processor for Thin and Light Notebooks
Model Number TDP Frequency L2 Cache
3300+ 25W 2.0 GHz 128 KB
3100+ 25W 1.8 GHz 256 KB
3000+ 25W 1.8 GHz 128 KB
2800+ 25W 1.6 GHz 256 KB
2600+ 25W 1.6 GHz 128 KB

Mobile AMD Sempron™ Processors for Full-Size Notebooks
Model Number TDP Frequency L2 Cache
3300+ 62W 2.0 GHz 128 KB
3100+ 62W 1.8 GHz 256 KB
3000+ 62W 1.8 GHz 128 KB
2800+ 62W 1.6 GHz 256 KB
2600+ 62W 1.6 GHz 128 KB