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L6911C
16/20
Inductor selection
Since the maximum output current is equal to 14A, to have a 30% ripple (4A) in worst case a 3
µ
H inductor has
been chosen. So the ripple is 4.1A @ 3.5V with V
IN
=12V and 1.7A @ 3.5V with V
IN
= 5V.
In worst case the peak is equal to 18.1A.
Output Capacitor
In the demo ten Sanyo capacitors, model 6MV1000GX are used, with a maximum ESR equal to 69m
Ω
. There-
fore, the resultant ESR is 69m
Ω
/10 = 1.9m
Ω
. For a load transient of 14A in worst case the drop results:
∆
Vout = 14 * 0.00069 = 96.6mV
The voltage drop due to the capacitor discharge during load transient, considering that the maximum duty cycle
is equal to 100% results in 13mV with 2.5V of programmed output.
Input Capacitor
For I
OUT
= 14A and D = 0.5 (worst case for input ripple current), Irms is equal to 7A. Five Sanyo electrolytic
capacitors 25MV330GX, with a maximum ESR equal to 69m
Ω
, are chosen to sustain the ripple. Therefore, the
resultant ESR is equal to 69m
Ω
/5 = 13.8m
Ω
. So the losses in worst case are:
Over-Current Protection
Substituting the demo board parameters in the relationship reported in the relative section, (I
OCSMIN
= 170
µ
A;
I
P
= 19A; R
DSONMAX
= 9m
Ω
) it results that R
OCS
= 1k
Ω
.
Part List
R2 499k 1% SMD 0805
R3, R7 1k 1% SMD 0805
R4 20 SMD 0805
R5, R8 20k SMD 0805
R9 15k SMD 0805
R12 1K SMD 0805
R13, R14 0 SMD 0805
C1, C2…C5
330
µ SANYO – 25MV330GX Radial 8x20mm
C6, C7…C15 1000µ SANYO – 6MV1000GX Radial 8x20mm
C16, C17, C24, C25 100n Ceramic SMD 0805
C18 2.2n Ceramic SMD 0805
C19 8.2n Ceramic SMD 0805
C20 82n Ceramic SMD 0805
C21, C22 1µ Ceramic SMD 1206
C23 1n Ceramic SMD 0805
L1
1.5
µ T44-52 Core, 7T-18AWG
L2 3µ T50-52B Core, 10T-16AWG
U1 L6911C STMicroelectronics SO20
Q1, Q2…Q6 STS12NF30L STMicroelectronics SO8
D1 1N4148 STMicroelectronics SOT23
D2 STPS3L25U STMicroelectronics SMB
F1 251015A-15° Littlefuse AXIAL
P ESR I
rms
2
⋅
670mW
==
Obsolete Product(s) - Obsolete Product(s)
