sc1110cstr Semtech Corporation, sc1110cstr Datasheet - Page 7

• Manufacturer Part Number: sc1110cstr
• Description: Sc1110 Sink And Source Dc/dc Controller For Termination Power Supply Applications
• Manufacturer: Semtech Corporation

Soft Start
Initially, SS/ENABLE sources 10µA of current to charge
an external capacitor. The outputs of the error amplifiers
are clamped to a voltage proportional to the voltage on
SS/ENABLE. This limits the on-time of the high-side
MOSFETs, thus leading to a controlled ramp-up of the
output voltages.
R
The current limit threshold is set by connecting an exter-
nal resistor from the V
drop across this resistor is due to the 200µA internal
sink sets the voltage at the pin. This voltage is compared
to the voltage at the PHASE node. This comparison is
made only when the high-side drive is high to avoid false
current limit triggering due to uncontributing measure-
ments from the MOSFET’s off-voltage. When the voltage
at PHASE is less than the voltage at OCSET, an overcurrent
condition occurs and the soft start cycle is initiated. The
POWER MANAGEMENT
Applications Information
DS(ON)
2004 Semtech Corp.
Current Limiting
CC
supply to OCSET. The voltage
7
synchronous switcher turns off and SS/ENABLE starts
to sink 2µA. When SS/ENABLE reaches 0.8V, it then
starts to source 10µA and a new cycle begins.
Hiccup Mode
During power up, the SS/ENABLE pin is internally pulled
low until VCC reaches the undervoltage lockout level of
4.2V. Once V
released and begins to source 10µA of current to the
external soft-start capacitor. As the soft-start voltage
rises, the output of the internal error amplifier is clamped
to this voltage. When the error signal reaches the level
of the internal triangular oscillator, which swings from 1V
to 2V at a fixed frequency of 250 kHz, switching occurs.
As the error signal crosses over the oscillator signal, the
duty cycle of the PWM signal continues to increase until
the output comes into regulation. If an over-current con-
dition has not occurred the soft-start voltage will con-
tinue to rise and level off at about 2.2V.
CC
has reached 4.2V, the SS/ENABLE pin is
SC1110
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