TK75050 データシートの表示（PDF） - Toko America Inc

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TK75050

SMART MOSFET DRIVER

Toko America Inc  

TK75050

PIN DESCRIPTION

SUPPLY VOLTAGE PIN (VCC)

This pin is connected to the supply voltage. Regardless of

the state of the other pins, the IC is always in a low-current

standby mode when the supply voltage is below the lower

threshold of the undervoltage lockout circuit. The IC enters

normal mode when two conditions are met simultaneously:

1) the supply voltage exceeds the upper threshold of the

undervoltage lockout circuit, and 2) a "first" pulse arrives at

the input.

That first pulse "wakes up" the IC ( i.e., it enables the high-

speed internal circuitry). The First Pulse Wake-Up is a

proprietary feature of theTK75050. The feature is

proprietary, but use is granted for use with the IC. That

feature is indispensable in off-line self-biased power-

supply applications where the start-up current is provided

by a large-value resistor connected between the rectified

line and the IC (see Figure 1). Without the First Pulse

Wake-up, the starting current would be equal to the normal

supply current, which is prohibitively large for a self-biased

start.

1.3 V. The hysteresis ensures that noise riding on the input

signal does not cause spurious response at the output.

POWER GROUND/CURRENT SENSE PIN (PGND/CS)

This pin has two distinct functions: 1) it provides a separate,

fully floating return path for the turnoff drive current of the

output stage and, thus, reduces the internal noise of the IC;

2) by connecting the pin to a current-sense resistor, the IC

acts as a fast cycle-by-cycle current limiter.

When the voltage between the power-ground pin (PGND/

CS) and the signal-ground pin (GND) exceeds the 0.95 V

current-limit threshold, the drive signal is terminated for

the remainder of the time while the input signal is high.

Once the input signal returned to zero, the latch that stored

the information about the presence of the overcurrent is

reset, and the IC is ready to acquire another overcurrent

event in the next cycle.

GROUND PIN (GND)

This pin provides ground return connection for the small-

signal portion of the IC. The return of the output stage is not

connected here, but to the floating power GND pin.

OUTPUT PIN

This pin drives the external MOSFET using a totem pole

output stage. The peak drive source or sink current is

typically 2 A into a 10,000 pF equivalent load. The UVLO

circuity ensures that the high-level output voltage will

never be less than about 7 V. In standby mode, the output

stage is equivalent to a pull-down resistor of about 3 kΩ

value, eliminating the need for an external gate to source

resistor. Normally, there is no need to add a Schottky diode

between the output and ground. In applications, however,

with heavy capacitive load located far from the IC or when

the IC drives a transformer, the Schottky diode may

become necessary.

INPUT PIN

The input pin receives the signal to be buffered. The

incoming signal is processed by a comparator with a

600 mV hysteresis centered around a threshold of about

January 1999 TOKO, Inc.

Page 7

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