LTC3560
2.25MHz, 800mA
Synchronous Step-Down
Regulator in ThinSOT
DESCRIPTION FEATURES High Efficiency: Up to 95%
Low Output Ripple (1μF) supply bypass capacitors. The
discharged bypass capacitors are effectively put in parallel with COUT, causing a rapid drop in VOUT. No regulator
can deliver enough current to prevent this problem if
the load switch resistance is low and it is driven quickly.
The only solution is to limit the rise time of the switch
drive so that the load rise time is limited to approximately
(25 • CLOAD). Thus, a 10μF capacitor charging to 3.3V
would require a 250μs rise time, limiting the charging
current to about 130mA. where TA is the ambient temperature. PC Board Layout Checklist As an example, consider the LTC3560 in dropout at an
input voltage of 2.7V, a load current of 800mA and an
ambient temperature of 70°C. From the typical performance graph of switch resistance, the RDS(ON) of the
P-channel switch at 70°C is approximately 0.31Ω. Therefore, power dissipated by the part is: When laying out the printed circuit board, the following
checklist should be used to ensure proper operation of
the LTC3560. These items are also illustrated graphically
in Figures 4 and 5. Check the following in your layout: PD = ILOAD2 • RDS(ON) = 198mW
For the SOT-23 package, the θJA is 250°C/ W. Thus, the
junction temperature of the regulator is:
TJ = 70°C + (0.198)(250) = 120°C 1. The power traces, consisting of the GND trace, the SW …