SC4624AEVB-MLPQ datasheet(11/19 Pages) SEMTECH

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SC4624A

POWER MANAGEMENT

Application Information

Overview

The SC4624A is a programmable high switching frequency,

integrated 4A MOSFET, synchronous step down regulator.

This reduces external component count and makes it

effective for applications which are low in cost and sized

small. A non-overlap protection is provided for the gate

drive signals to prevent shoot through of the internal

MOSFET pair.

The SC4624A is capable of producing an output voltage as

low as 0.5V and Its operation frequency is programmable

up to 2MHz by an external resistor. It features lossless

current sensing of the voltage drop across the internal

drain to source resistance of the high side MOSFET during

its conduction period.

The quiescent supply current in shutdown mode is

typically lower than 1µA. An external soft start is provided

to prevent output voltage overshoot during start-up. Over

Temperature Protection, Power Good Indicator, External

Clock Synchronization are some of the internal added

features.

Enable

The SC4624A is enabled by applying a voltage greater

than 2V (typical) to the V

CC and SYNC/EN pin. The voltage

on the V

CC pin determines the operation of the SC4624A.

As V

CC increases during start up, the UVLO block senses

CC and keeps the high side and low side MOSFETs off and

the internal soft start voltage low until V

CC reaches 2V. If

no faults are present, the SC4624A will initiate a soft start

when V

CC exceeds 2V. A typical 120mV hysteresis in the

UVLO comparator provides noise immunity during its start

up. (refer to Figures 1 & 2).

Shutdown

The SC4624A is disabled when V

CC falls below 1.88V (typi-

cal) or shutdown mode operation is invoked by clamping

the SYNC/EN pin to a voltage below 0.8V. During the shut-

down mode, A typical 0.2µA current draw through the V

pin, the internal soft start voltage is held low and the inter-

nal MOSFETs are turned off. (refer to Figures 3 & 4).

Soft Start

The soft start function is required for step down controllers

to prevent excess in-rush current through the DC bus

during start up. An external capacitor is necessary for

the soft start function and is connected from SS pin to

AGND.

During start up or restart, A typical 4µA sourcing current

charges the capacitor and then the voltage of capacitor

ramp up the error amp reference slowly. The closed

loop creates narrow width driver pulses while the output

voltage is low and allows these pulses to increase to their

steady state duty cycle as the output voltage reaches

its regulated value. The duration of the soft start in the

SC4624A is controlled by an external capacitor.

The SC4624A starts up in asynchronous mode before SS

voltage reaches to 0.5V, and the bottom FET diode is used

for circulating current during the top FET off time. Ths SS

voltage level is clamped at V

CC finally.

Oscillator

The FS pin is used to set the PWM oscillator frequency

through an external resistor that is connected from the

FS pin to the AGND. The internal ramp is a triangle at the

PWM frequency with a peak voltage of 1.25V and a valley

voltage of 0.25V. The approximate operating frequency is

determined by the value of an external resistor as shown

in Figure 15.

105

115

125

135

145

200

400

600

800

1000

1200

1400

1600

1800

2000

5VIN

2.5VIN

The operation frequency can be programmed up to 2MHz,

but there is a minimum on-time limitation which is around

110ns.Usersshouldtakecareofminimumlimitationonthe

operating duty cycle under high frequency application.

Figure 15. Switching Frequency vs. R

Switching Frequency Setting

osc (kHz)

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