Datasheet

Application information PM6644
24/35 Doc ID 023203 Rev 1
Equation 17
where I
LOAD
is the RMS output current.
The minimum I
LOAD
between equation 16 and equation 17, combined with RMS load current
limitation due to valley current limit (Equation 6 ), determines the maximum RMS output
current I
LOADRMS
sustained by the switching regulator:
Equation 18
Example 1
V
IN
= 5 V, FB = VCC (V
OUT
= 3.47 V), ∆I
L
= 68.5 mA (L = 33 uH, Fsw = 470 kHz).
High-side can withstand a load current of I
LOADRMS
= 432 mA.
Low-side can withstand a load current of I
LOADRMS
= 977 mA.
I
LOADRMS
due to valley current limit = 384 mA.
As a result, I
LOADRMS
= 384 mA (limitation determined by the valley current limit).
The PM6644 switching regulator can source 384 mA RMS. 384 mA is also the peak load
current.
Example 2
V
IN
= 25 V, FB = VCC (V
OUT
= 3.47 V), ∆I
L
= 192.5 mA (L = 33 uH, Fsw = 470 kHz).
High-side can withstand a load current of I
LOADRMS
= 2164 mA.
Low-side can withstand a load current of I
LOADRMS
= 344 mA.
I
LOADRMS
due to valley current limit = 446 mA.
As a result, I
LOADRMS
= 344 mA (limitation determined by the low-side RMS max. current).
The PM6644 switching regulator can source 344 mA RMS. The peak load current is 446
mA.
I
RMS LS,
I
LRMS
1D–() I
LOAD
()
2
∆I
L
()
2
12
----------------+⋅ 300mA===
I
LOADRMS
MIN
300mA
D
-------------------
⎝⎠
⎛⎞
2
∆I
L
()
12
-------------
2
–
300mA
1D–
-------------------
⎝⎠
⎛⎞
2
∆I
L
()
12
-------------
2
–
350mA
∆I
L
2
--------+
⎩⎭
⎪⎪
⎪⎪
⎪⎪
⎪⎪
⎨⎬
⎪⎪
⎪⎪
⎪⎪
⎪⎪
⎧⎫
=