L6204D datasheet(6/10 Pages) STMICROELECTRONICS

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a voltage higher than VS is supplied on pin 20

(Vboot). This bootstrap voltage is not needed for

the lower power DMOS transistor because their

sources are grounded. To produce this voltage a

charge pump method is used and mAde by two

external capacitors and two diodes. It can supply

the 4 driving blocks of the high side drivers. Using

an external capacitor the turn-on speed of the

high side driver is very high; furthermore with dif-

ferent capacitance values it is possible to adapt

the device to different switching frequencies. It is

also possible to operate two or more L6204s us-

ing only 2 diodes and 2 capacitance for all the

ICs; all the Vboot pins are connected to the Cstore

capacitance while the pin 11 (VCP) of just one

L6204 is connect to Cpump, obviously all the

L6204 ICs have to be connected to the same VS.

(see fig. 4)

DEAD TIME

To protect the device against simultaneous con-

duction in both arms of the bridge and the result-

ing rail-to-rail short, the logic circuits provide a

dead time.

THERMAL PROTECTION

A thermal protection circuit has been included

that will disable the device if the junction tempera-

ture reaches 150

°C. When the temperature has

fallen to a safe level the device restarts under the

control of the input and enable signals.

APPLICATION INFORMATION

RECIRCULATION

During recirculation with the ENABLE input high,

the voltage drop across the transistor is RDS(ON).

IL for voltages less than 0.7 V and is clamped at a

voltage depending on the characteristics of the

source-drain diode for greater voltages. Although

the device is protected against cross conduction,

current spikes can appear on the current sense

pin due to charge/discharge phenomena in the in-

trinsic source drain capacitances. In the applica-

tion this does not cause any problems because

the voltage created across the sense resistor is

usually much less than the peak value, although a

small RC filter can be added if necessary.

POWER DISSIPATION (each bridge)

In order to achieve the high performance provided

by the L6204 some attention must be paid to en-

sure that it has an adequate PCB area to dissi-

pate the heat. The first stage of any thermal de-

sign is to calculate the dissipated power in the

application, for this example the half step opera-

tion shown in figure 5 is considered.

RISE TIME Tr

When an arm of the half bridge is turned on cur-

rent begins to flow in the inductive load until the

maximum current IL is reached after a time Tr.

The dissipated energy EOFF/ON is in this case :

EOFF/ON =[RDS(ON)

⋅ IL2 ⋅ Tr] ⋅ 2/3

ON TIME TON

During this time the energy dissipated is due to

the ON resistance of the transistors EON and the

commutation ECOM. As two of the POWER DMOS

transistors are ON EON is given by :

EON =IL

2 ⋅ RDS(ON) ⋅ 2 ⋅ TON

In the commutation the energy dissipated is :

ECOM =VS

⋅ IL ⋅ TCOM ⋅ fSWITCH ⋅ TON

Where :

TCOM = Commutation Time and it is assumed that ;

TCOM =TTURN-ON =TTURN-OFF = 100 ns

fSWITCH = Chopper frequency

FALL TIME Tf

For this example it is assumed that the energy

dissipated in this part of the cycle takes the same

form as that shown for the rise time :

EON/OFF =[RDS(ON)

⋅ IL2⋅ Tf] ⋅ 2/3

Figure 4

Figure 5

L6204

6/10

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