SC195 datasheet(14/20 Pages) SEMTECH

14 / 20 page

SC195

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 SC195 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.

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

•

Applications Information (continued)

disabled. Switching does not resume until V

OUT has fallen

below the regulation voltage by 2%.

Current Limit

The SC195 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 SC195 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

Under-Voltage Lockout (UVLO) activates when the supply

voltage drops below the UVLO threshold. This prevents

the device from entering an ambiguous state in which

regulation cannot be maintained. Hysteresis of approxi-

mately 200mV is included to prevent chattering near the

threshold.

Inductor Selection

The SC195 is designed to operate with a 1µH inductor

between the LX pin and the OUT pin. Other values may

lead to instability, malfunction, or out-of-specification

performance. The specified current levels for PSAVE entry,

PSAVE exit, and current limit are dependent on the induc-

tor value.

The SC195 converter has internal loop compensation. The

compensation is designed to work with a specific single-

SC195 Datasheet(PDF) 14 Page - Semtech Corporation

SC195 Datasheet(HTML) 14 Page - Semtech Corporation

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

Datasheet Download

Link URL