AS1326
Datasheet - Application Information
Setting the Switch Current Limit
The ISET pin is used to adjust the inductor current limit and to implement the soft-start feature.
With pin ISET connected to pin REF, the inductor current limit is set to 1.6A. With ISET connected to a resistor-divider
network from pin REF to GND, the current limit is calculated as:
VISET
1,25V
⎛
⎝
⎞
⎠
---------------
ILIMIT = 1,6A ⋅
(EQ 2)
Soft Start
The soft-start feature can be implemented by placing a resistor between pin ISET and pin REF (see Figure 21) and a
capacitor between pin ISET and GND.
Figure 21. Circuit for Soft-Start with Maximum Switch Current Limit
2
REF
10nF
RSS
≥220kΩ
AS1326A/
AS1326B
1
ISET
CSS
ILIMIT = 1.6A
tSS = Rss x CSS
At power-up, ISET is 0V and the LX current is zero. As the capacitor voltage rises, the current increases and the output
voltage rises. The soft-start time constant is:
tSS = RSS x CSS
(EQ 3)
Where:
RSS ≥ 220kΩ.
Note: Placing a capacitor across the lower resistor of the current-limiting resistor-divider network enables both the
current-limit and soft-start (see Figure 22).
Figure 22. Application Circuit for Soft-Start with Reduced Switch Current Limit
2
REF
10nF
RSS
≥220kΩ
AS1326A/
AS1326B
1
ISET
RSS2
CSS
Rss2
Rss1 + Rss2
ILIMIT = 1.6A
(
)
tSS = (Rss1 || Rss2) CSS
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