SP6649 Sipex, SP6649 Datasheet - Page 5

• Manufacturer Part Number: SP6649
• Description: Ultra-low Quiescent Current / High Efficiency Boost DC-DC Regulator
• Manufacturer: Sipex

At light loads (plot A in Figure 3) the charge
cycle will take t
would be:
t
The current built up in the coil during the charge
cycle gets fully discharged (discontinuous con-
duction mode, DCM) When the current in the
coil has reached zero the synchronous rectifier
switch is opened and the voltage across the coil
(from V
eliminate inductive ringing.
With increasing load (plot B in Figure 3) this
inductor damping time becomes shorter (be-
cause the output will drop quicker below its
regulation point due to the heavier load) up to
the point where it becomes zero. If the load
increases further the SP6649 enters continuous
conduction mode (CCM) where there is always
current in the inductor. The charge time is still
t
limit is not reached (plot C in Figure 3). the
inductor peak current limit can be programmed
by trying a resistor R
ground where:
with a maximum recommended I
(or a minimum R
When the peak current limit is reached the
charge time is short-cycled.
Rev:001 Date:11/20/03
ON, MAX
ON,MAX
= K
BATT
as long as the inductor peak current
I
PEAK
ON
to LX) is shorted internally to
= 1400 / R
ON, MAX
/ V
LIM
BATT
SP6649 Ultra-low Quiescent Current, High Efficiency Boost DC-DC Regulator
of 1.17K ).
LIM
µs. For a 1V battery this
= 3.3Vµs / 1V = 3.3µs
from the R
LIM
PEAK
LIM
of 1.2A
pin to
5
Figure 3. Inductor Current vs. Load
In (plot D of Figure 3) the current reaches the
peak current limit during the charge cycle but
full load is still not reached becuse at the end of
the minimum off-time V
its regulation point. Finally in plot E the maxi-
mum load is reached where the discharge time
has shrunk to its minimum allowed value
t
OFF,MIN
Ton Max.
Ton Max.
Ton Max.
.
Ton Max.
Toff Min.
Toff Min.
Ton Max.
Inductor Current vs. Load
Toff Min.
E. Iripple=Toff* (Vo - Vi)/L
D. Toff*= (Vo - Vi)/L<Iripple<Ton*Vi/L
C. Iripple=Ton*Vi/L
B. Iripple=Ton*Vi/L
A. Iripple=Ton*Vi/L
Toff Min.
Toff Min.
© Copyright 2002 Sipex Corporation
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