SC196 datasheet(7/18 Pages) SEMTECH

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SC196 Detailed Description

The SC196 is a synchronous step-down Pulse Width

Modulated (PWM), DC-DC converter utilizing a 1MHz

ﬁxed-frequency current mode architecture. The device

is designed to operate in a ﬁxed-frequency PWM mode

across the full load range and can enter Power Save Mode

(PSAVE), utilizing Pulse Frequency Modulation (PFM) at

light loads to maximize efﬁciency.

Operation

During normal operation, the PMOS MOSFET is activated

on each rising edge of the internal oscillator. Current

feedback for the switching regulator uses the PMOS

current path, and it is ampliﬁed and summed with

the internal slope compensation network. The voltage

feedback loop uses an external feedback divider. The on-

time is determined by comparing the summed current

feedback and the output of the error ampliﬁer. The period

is set by the onboard oscillator or by an external clock

attached to the SYNC/PWM pin.

The SC196 has an internal synchronous NMOS rectiﬁer

and does not require a Schottky diode on the LX pin.

Output Voltage Selection

The output voltage can be programmed using a resistor

network connected from VOUT to ADJ to GND. The

combined resistance of the divider chain should be

greater than 10KΩ and less than 1MΩ. Table 1 lists

appropriate resistors which limit the bias current required

of the external feedback resistor chain and ensuring good

noise immunity.

The output voltage can be adjusted between less than

0.8V and V

IN. The output voltage formula is:

OUT

OUT = output voltage (V)

FB1 = feedback resistor from VOUT to ADJ (Ω)

FB2 = feedback resistor from ADJ to GND (Ω)

Resistors with 1% or better tolerance are recommended

to ensure voltage accuracy.

Table 1 — Recommended ADJ Resistor Combinations

OUT(V)

FB2(kΩ)RFB1(kΩ)

200

1.1

200

240

1.2

200

280

1.3

200

320

1.5

178

357

1.6

200

442

1.7

178

432

1.8

178

464

1.875

178

487

2.5

200

806

2.8

178

820

178

887

3.3

100

560

3.6

100

620

3.8

100

665

Continuous Conduction & Oscillator Synchronization

The SC196 is designed to operate in continuous

conduction, ﬁxed-frequency mode. When the SYNC/PWM

pin is tied high the part runs in PWM mode using the

internal oscillator. The part can be synchronized to an

external clock by driving a clock signal into the SYNC/

PWM pin. The part synchronizes to the rising edge of the

clock.

Protection Features

The SC196 provides the following protection features:

• Thermal Shutdown

• Current Limit

• Over-Voltage Protection

• Soft-Start

Thermal Shutdown

The device has a thermal shutdown feature to protect the

SC196 if the junction temperature exceeds 145°C. In

thermal shutdown, the on-chip power devices are disabled,

effectively tri-stating the LX output. Switching will resume

when the temperature drops by 10°C. During this time,

Applications Information

www.semtech.com

SC196

PRELIMINARY

POWER MANAGEMENT

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