L9925 查看數據表（PDF） - STMicroelectronics

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L9925

DMOS DUAL FULL BRIDGE DRIVER

STMicroelectronics 

L9925

THERMAL PROTECTION

A thermalprotection circuit has been included that

will disable the device if the junction temperature

reaches 150°C. When the temperature has fallen

to a safe level the device restarts under the con-

trol of the input and enable signals.

APPLICATION INFORMATION

RECIRCULATION

During recirculationwith the ENALBE input high,

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

for voltages less than 0.6V and is clamped at a

voltages depending on the characteristics of the

source-drain diode for greater voltages. Although

the device is protected against cross conduction.

POWER DISSIPATION each bridge

In order to achieve the high performance provided

by the L9925 some attention must be paid t en-

sure that it has an adequate PCB area to dissi-

pate the heat. The forst 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 Fig. 6 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.

EOFF/ON

=

[RDS(ON)

⋅

IL2

⋅

TR]

⋅

2

3

Figure 6.

Tswitch

IL

TR TON TF TOFF

D99AT435

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 = IL2 ⋅ RDS(ON) ⋅ 2 ⋅ TON

In the commutation the energy dissipated is:

ECON = VS ⋅ IL ⋅ TCOM ⋅ fSWITCH ⋅ TON

Where:

TCOM = Communication Time and it is assumed that:;

TCOM = trise = tfall ≤ 20µs

TSWITCH = 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:

EOFF/ON

=

[RDS(ON)

⋅

IL2

⋅

TF]

⋅

2

3

QUIESCENT ENERGY

The last contribution of the energy dissipation is

due to the quiescrent supply current and is given

by:

EQUIESCENT = IQUIESCENT ⋅ VS ⋅ T

TOTAL ENERGY PER CYCLE

ETOT = (2 ⋅ EOFF/ON + EON + ECOM) bridge1+

+ (2 ⋅ EOFF/ON + EON + ECOM) bridg2 + EQUIESCENT

The total power dissipation PDIS is simply:

TR = Rise time

TON = ON time

TF = Fall time

TOFF = OFF time

T = Period

PDIS

=

Etot

T

T = TR + TON + TF + TOFF

7/9

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