DS75361 Datasheet, PDF(5/6 Page) National Semiconductor (TI) – Dual TTL-to-MOS Driver

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DS75361 Datasheet, PDF (5/6 Pages) National Semiconductor (TI) – Dual TTL-to-MOS Driver

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Typical Applications

The fast switching speeds of this device may produce unde-

sirable output transient overshoot because of load or wiring

inductance A small series damping resistor may be used to

reduce or eliminate this output transient overshoot The

optimum value of the damping resistor to use depends on

the specific load characteristics and switching speed A typi-

cal value would be between 10X and 30X (Figure 3)

TL F 7557 â 6

FIGURE 2 Interconnection of DS75361 Devices with 1103 RAM

TL F 7557 â 7

Note RD 10X to 30X (Optional)

FIGURE 3 Use of Damping

Resistor to Reduce or Eliminate

Output Transient Overshoot in

Certain DS75361 Applications

Thermal Information

POWER DISSIPATION PRECAUTIONS

Significant power may be dissipated in the DS75361 driver

when charging and discharging high-capacitance loads over

a wide voltage range at high frequencies The total dissipa-

tion curve shows the power dissipated in a typical DS75361

as a function of load capacitance and frequency Average

power dissipated by this driver can be broken into three

components

PT(AV) e PDC(AV) a PC(AV) a PS(AV)

where PDC(AV) is the steady-state power dissipation with the

output high or low PC(AV) is the power level during charging

or discharging of the load capacitance and PS(AV) is the

power dissipation during switching between the low and

high levels None of these include energy transferred to the

load and all are averaged over a full cycle

The power components per driver channel are

PDC(AV)

e

PLtL

a

T

PHtH

PC(AV) C VC2 f

PS(AV)

e

PLHtLH

a

T

PHLtHL

where the times are defined in Figure 4

PL PH PLH and PHL are the respective instantaneous lev-

els of power dissipation and C is load capacitance

The DS75361 is so designed that PS is a negligible portion

of PT in most applications Except at very high frequencies

tL a tH n tLH a tHL so that PS can be neglected The total

dissipation curve for no load demonstrates this point The

power dissipation contributions from both channels are then

added together to obtain total device power

The following example illustrates this power calculation

technique Assume both channels are operating identically

with C e 200 pF f e 2 MHz VCC1 e 5V VCC2 e 20V and

duty cycle e 60% outputs high (tH T e 0 6) Also assume

VOH e 19 3V VOL e 0 1V PS is negligible and that the

current from VCC2 is negligible when the output is high

On a per-channel basis using data sheet values

J J ( 2 mA

0 mA

PDC(AV) e (5V) 2 a (20V) 2

(0 6) a

J J ( 16 mA

7 mA

(5V)

a (20V)

2

2

(0 4)

PDC(AV) e 47 mW per channel

PC(AV) (200 pF) (19 2V)2 (2 MHz)

PC(AV) 148 mW per channel

For the total device dissipation of the two channels

PT(AV)

PT(AV)

2 (47 a 148)

390 mW typical for total package

FIGURE 4 Output Voltage Waveform

5

TL F 7557 â 8

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