l6730cqtr STMicroelectronics, l6730cqtr Datasheet - Page 30

• Manufacturer Part Number: l6730cqtr
• Description: Adjustable Step-down Controller With Synchronous Rectification
• Manufacturer: STMicroelectronics

Application details
6
6.1
Figure 25. Inductor current ripple.
30/50
Application details
Inductor design
The inductance value is defined by a compromise between the transient response time, the
efficiency, the cost and the size. The inductor has to be calculated to maintain the ripple current
(∆I
calculated with the following relationship:
Where F
Figure 25.
with Vin = 5V and Vin = 12V at a switching frequency of 400KHz.
Increasing the value of the inductance reduces the current ripple but, at the same time,
increases the converter response time to a load transient. If the compensation network is well
designed, during a load transient the device is able to set the duty cycle to 100% or to 0%.
When one of these conditions is reached, the response time is limited by the time required to
change the inductor current. During this time the output current is supplied by the output
capacitors. Minimizing the response time can minimize the output capacitor size.
L
) between 20% and 30% of the maximum output current. The inductance value can be
8
7
6
5
4
3
2
1
0
SW
0
shows the ripple current vs. the output voltage for different values of the inductor,
is the switching frequency, V
1
O UT P UT V O L T AG E (V )
L
Vin
Fsw
2
Vout
IN
I
L
is the input voltage and V
Vout
3
Vin
(6)
4
V i n = 5 V , L = 5 0 0 n H
V i n = 1 2 V , L = 1 u H
V i n = 5 V , L = 1 . 5 u H
V i n = 1 2 V , L = 2 u H
OUT
is the output voltage.
L6730C - L6730D