SC2612C Semtech, SC2612C Datasheet - Page 5

• Manufacturer Part Number: SC2612C
• Description: 600kHz/200kHz Step-Down DC/DC Converter
• Manufacturer: Semtech

The SC2612 is a step down DC/DC controller designed
for minimum cost and size without sacrificing accuracy
and protection. Overcurrent protection is implemented
by a simple undervoltage detection scheme and is dis-
abled until soft start has been completed to eliminate
false trips due to output capacitor charging. The SS/EN
pin is held low, as are the DH and DL pins, until the
undervoltage lockout points are exceeded. Once the VCC
and BST pins both rise above their undervoltage lockout
points, the SS capacitor begins to charge, controlling the
duty cycle of the switcher, and therefore slowly ramping
up the switcher output voltage. Once the SS capacitor is
charged, the current limit circuitry is enabled. If a short
circuit is applied , the output will be pulled down below
it’s trip point and shut down. The device may be restarted
by either cycling power, or momentarily pulling SS/EN low.
POWER MANAGEMENT
Theory of Operation
2003 Semtech Corp.
5
OUTPUT INDUCTOR
OUTPUT INDUCTOR
OUTPUT CAP
OUTPUT CAP
OUTPUT INDUCTOR
OUTPUT INDUCTOR
OUTPUT INDUCTOR - A good starting point for output
filter component selection is to choose an inductor value
that will give an inductor ripple current of approximately
20% of max. output current.
Inductor ripple current is given by:-
So choose inductor value from:-
OUTPUT CAP
OUTPUT CAP
OUTPUT CAPA A A A A CIT
be selected to meet output ripple and transient response
criteria. Output ripple voltage is caused by the inductor
ripple current flowing in the output capacitor’s ESR (There
is also a component due to the inductor ripple current
charging and discharging the output capacitor itself, but
this component is usually small and can often be ignored).
Given a maximum output voltage ripple requirement, ESR
is given by:-
Output voltage transient excursions are a function of load
current transient levels, input and output voltages and
inductor and capacitor values.
Capacitance and R
sient condition can be calculated from:-
values for positive and negative transients must be cal-
culated seperately and the worst case value chosen. For
Capacitor values, the calculated value should be doubled
to allow for duty cycle limitation and voltage drop issues.
I
L
R
R
C
where
V
and
V
Component Selection
L
RIPPLE
ESR
ESR
A
A
=
>
=
=
5
2
×
<
<
V
V
×
V
IN
L
V
O
=
V
V
O
I
I
O
T
×
T
for
O
T
-
V
I
×
T
×
2
×
æ
ç ç
è
O
×
V
V
f
1
V
OSC
positive
L
O
×
A
-
RIPPLE
æ
ç ç
è
×
for
1
L
V
f
V
OSC
-
CIT
CIT
IN
CIT
CITOR(S)
×
O
f
negative
V
V
OSC
ö
÷ ÷
ø
×
IN
O
OR(S)
OR(S)
OR(S) - The output capacitors should
æ
ç ç
è
OR(S)
1
transients
ö
÷ ÷
ø
-
ESR
V
V
IN
O
values to meet a required tran-
transients
ö
÷ ÷
ø
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