SC32300ASLASHB.EVB datasheet(10/18 Pages) SEMTECH

10 / 18 page

SC32300B

Application Information

Overview

The SC32300B is a high-side and low-side N-channel

MOSFET driver. The driver receives a ground-referenced

PWM signal with fast slew rate to drive two N-channel

MOSFETs in a synchronous buck converter or any

other application with two MOSFETs in a half-bridge

configuration. The SmartDriveTMfunction at the turn-on of

the high-side MOSFET reduces the voltage ringing on the

low-side switch and also reduces the EMI. Tying the FCCM

pin to ground offers diode emulation mode operation to

achieve high efficiency at light load. The Under-Voltage-

Lock-Out (UVLO) threshold ensures a reliable drive

voltage for the external MOSFETs. The over temperature

shutdown feature is also included to prevent the driver

from overheating.

For a synchronous buck converter application, the

SC32300B takes the PWM signal from the buck controller

as the input, and outputs drive signals on the DH pin

and the DL pin to drive the external MOSFETs. The buck

controller senses and regulates the output voltage of the

converter as shown in Figure 5 on page 13.

The SC32300B can also be used together with the

SC32300A to drive a DC motor or similar load. Figure 7 on

page 15 shows one typical application for driving the DC

motor in an electronic tool. The SC32300A and SC32300B

are controlled by PWM signals from the microcontroller.

The SC32300A takes its input from the battery and

regulates a 5.25V output on its VDD pin. This 5.25V is

used to bias the internal control circuitry and the low-

side driver. The 5.25V LDO output is also connected to

the VDD pin of the SC32300B to bias its internal circuitry

and low-side driver, and functions as the input for a 3.3V

LDO in the SC32300B. The 3.3V LDO can then be used to

power the microcontroller. The feature of programming

the dead-time offers the flexibility to design the switch

clamp circuitry for more reliable system operation.

Under Voltage Lockout

The SC32300B has an under voltage lockout (UVLO)

circuit which keeps the driver off when the input voltage

is not high enough to drive the external MOSFETs reliably.

During power on, the driver outputs (DH and DL) are low

until the input voltage reaches the UVLO rising threshold.

Once the UVLO threshold is reached, the driver outputs

are determined by the signals on the PWM pin and FCCM

pin. The UVLO falling threshold is about 0.2V lower which

prevents the driver from turning on and off due to a slow

input slew rate.

Tri-State PWM Input

The SC32300B features a tri-state PWM input pin. When

the PWM signal is less than 1V (typical), it is considered as

a logic low while the signal is taken as a logic high when

it is higher than 2.1V (typical). 1V to 2.1V is the tri-state

window for the PWM signal. These thresholds make it

work well for both 3.3V logic and 5V logic PWM signals.

If the PWM pin is left floating, the internal resistor divider

sets the voltage on the PWM pin to 1.45V which is within

the tri-state window. For a synchronous buck converter

application, pre-biased output startup is supported if the

buck controller features a tri-state PWM output pin.

Programmable Dead Time Control

The dead time control is to prevent shoot-through of

the high-side MOSFET and the low-side MOSFET. Shoot-

through can cause poor efficiency and even cause the

MOSFET to blow up. The dead time control circuitry of a

MOSFET driver is thus very important in real applications.

An adaptive dead time control function is implemented

in the SC32300B by sensing the DH and DL signals. The

SC32300B has a DT pin which offers an option to program

the dead time with a ceramic capacitor from this pin to

the GND pin. A ceramic capacitor with tight tolerance

such as Murata C0G material capacitor should be used for

this purpose. The dead time is 20ns typical with the DT

pin floated.

For DC motor drive in electronic tool applications, the

system designer generally will add clamp circuitry for

each external MOSFET as shown in Figure 7. In order to

make the clamp circuitry work, an external gate resistor

with value up to 20Ω is needed. The MOSFET drivers

with traditional adaptive dead time control will not work

with such a big external gate resistor added. The ability

of programming the dead time from SC32300B is a good

fit for this kind of application to provide the freedom to

adjust the dead time based upon the added gate resistor

to ensure reliable operation.

SC32300A/B.EVB Scheda tecnica(PDF) 10 Page - Semtech Corporation

SC32300A/B.EVB Scheda tecnica(HTML) 10 Page - Semtech Corporation

Html Pages

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

Scheda tecnica Scarica

Link URL