SC2603EVB SEMTECH [Semtech Corporation], SC2603EVB Datasheet - Page 4

• Manufacturer Part Number: SC2603EVB
• Description: Simple PWM Boost Controller
• Manufacturer: SEMTECH [Semtech Corporation]

The SC2603 is a versatile, low-cost, voltage-mode PWM
controller designed for DC/DC power supply applications.
In normal condition, the SC2603 operats at a fixed
200KHz. One exception is that when the FB pin voltage
drops to one half, the frequency will be shifted to one
fouth of 200KHz.
SC2603 features include a temperature compensated
voltage reference, triangle wave oscillator, current limit
comparator, frequency shift over-current protection, and
an internally compensated error amplifier. Pulse by pulse
current limiting is implemented by sensing the
differential voltage across an external resistor, or an
appropriately sized PC board trace.
POWER MANAGEMENT
Theory of Operation
© 2005 Semtech Corp.
4
Soft-Start
Soft-start prevents a DC-DC converter from drawing
excessive current from the power source during start up.
If the soft-start time is made sufficiently long, then the
output will enter regulation without overshoot. An external
capacitor is connected from the EN/SS pin to the ground.
After the part’s input voltage surpasses the UVLO, the
EN/SS pin is allowed to charge its capacitor with 60µA.
When 100mV is reached at the EN/SS pin, the internal
comp node is at 0.4V. The SC2603 will start switching,
and the converter output comes into regulation. Because
the FB pin voltage follows EN/SS pin voltage, finally, the
EN/SS pin voltage will be clamped at 1.25V same as the
refernece voltage.
Setting the Output Voltage
An external resistive divider R
tap tied to the FB pin sets the output voltage.
Under Voltage Lockout
The under voltage lockout circuit of the SC2603 assures
that the gate driver output remains in the off state when-
ever the supply voltage drops below set parameters. Lock-
out occurs if V
sumes once V
Application Information
R
1
=
R
2



V
. 1
OUT
25
IN
IN
−
rises above 4.2V.
falls below 3.8V. Normal operation re-
1



1
and R
VOUT
R1
R2
2
with its center
SC2603
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1
SC2603
FB