SC202 datasheet(14/19 Pages) SEMTECH

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SC202

VOUT -2%

VOUT

VOUT +2.5%

Load

Demand

(

IOUT)

BURST

OFF

VLX

Time

PWM Mode at

Medium/High

Load

PSAVE Mode at

Light Load

PWM Mode at

Medium/High

Load

PSAVE

EXIT

Figure 2 — Transitions Between PWM and PSAVE Modes

Protection Features

The SC202 provides the following protection features:

Soft-Start Operation

Over-Voltage Protection

Current Limit

Thermal Shutdown

Under-Voltage Lockout

Soft-Start

The soft-start sequence is activated after a transition from

an all zeros CTL code to a non-zero CTL code enables the

device. At start-up, the PMOS current limit is stepped

through four levels: 25%, 40%, 60%, and 100%. Each step

is maintained for 60μs following an internal reference start

up of 20μs, resulting in a total nominal start-up period of

260μs. If V

OUT reaches 90% of the target within the first 2

steps, the device continues in PSAVE mode at the end of

soft-start; otherwise, it goes into PWM mode. Note the

OUT ripple in PSAVE mode can be larger than the ripple in

PWM mode.

•

Applications Information (continued)

Over-Voltage Protection

Over-voltage protection ensures the output voltage does

not rise to a level that could damage its load. When V

OUT

exceeds the regulation voltage by 15%, the PWM drive is

disabled. Switching does not resume until V

OUT has fallen

below the regulation voltage by 2%.

Current Limit

The SC202 switching stage is protected by a current limit

function. If the output load exceeds the PMOS current

limit for 32 consecutive switching cycles, the device enters

fold-back current limit mode and the output current is

limited to approximately 150mA. Under these conditions,

the output voltage will be the product of I

FB-LIM and the load

resistance. The load must fall below I

FB-LIM for the device to

exit fold-back current limit mode. This function makes the

device capable of sustaining an indefinite short circuit on

its output under fault conditions.

Thermal Shutdown

The SC202 has a thermal shutdown feature to protect the

device if the junction temperature exceeds 160°C. During

thermal shutdown, the PMOS and NMOS switches are

both disabled, tri-stating the LX output. When the junc-

tion temperature drops by the hysteresis value (20°C), the

device goes through the soft-start process and resumes

normal operation.

Under-Voltage Lockout

UVLO (Under-Voltage Lockout) activates when the supply

voltage drops below the falling UVLO threshold. This pre-

vents the device from entering an ambiguous state in

which regulation cannot be maintained. Hysteresis of

approximately 200mV is included to prevent chattering

near the threshold.

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