L6911E datasheet(25/34 Pages) STMICROELECTRONICS

Part #	L6911E

Description	5-Bit programmable step down controller with synchronous rectification

PDF	34 Pages

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Manufacturer	STMICROELECTRONICS [STMicroelectronics]

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25 / 34 page

L6911E

VRM demo board description

25/34

6.1

Efficiency

The measured efficiency versus load current at different output voltages is shown in

Figure 13. In the application two Mosfets STS12NF30L (30V, 8.5m

Ω typ with V

GS = 12V)

connected in parallel are used for the High Side, while three of them are used for the Low

Side.

Figure 13. Efficiency vs. load current

6.2

Inductor design

Since the maximum output current is 28.5A, to have a 20% ripple (5A) the inductor chosen

is 1.5

µH.

6.3

Output capacitor

In the demo six OSCON capacitors, model 6SP680M, are used, with a maximum ESR equal

to 12m

Ω each. Therefore the resultant ESR is of 2mΩ. For load transient of 28.5A in the

worst case the voltage drop is of:

Equation 24

The voltage drop due to the capacitor discharge during load transient, considering that the

maximum duty cicle is equal to 100% results in 46.5mV with 1.85V of programmed output.

Output Current [A]

Vout = 1.825V

Vout = 1.225V

Vout = 1.500V

∆Vout = 28.5 * 0.002 = 57mV

L6911E Datasheet(PDF) 25 Page - STMicroelectronics