L6280 datasheet(8/26 Pages) STMICROELECTRONICS

8 / 26 page

SYSTEM DESCRIPTION (Refer to the Block Dia-

gram)

The L6280 is a single chip power microsystem

which includes drives for three different loads, the

associated control logic and a Switched Mode

Power Supply (SMPS) at VSS =5V

± 5%.

The IC can be directly connected to a standard

microprocessor because of its common I/O inter-

face architecture. The L6280 can exchange infor-

mation regarding the load driver and the control

method via a 8 bit data bus. The block named mi-

croprocessor interface decodes the first four bits

(A0....A3), which, depending on the content of the

remaining four (D0.......D3) are used to enable the

power DMOS, to activate the PWM loop, and fi-

nally to set the D/A output value.

The power stage can be divided into 3 channels.

Channels1 and 2 have 6 DMOS transistors each

one (2high side drivers with Rdson =1

Ω, 4 low side

drivers with Rdson =2

Ω). Depending on the appli-

cation load, these driver transistors can be con-

nected in different ways. The microprocessor, via

software, must activate the proper control loop to

optimize operation of different loads and output

stage configurations. Because of this program-

mability in the control of the output configurations,

a large variety of different loads can be driven by

the same integrated circuit (see possible configu-

ration for power stage on Figure 5) giving the

greater system flexibility. Current levels up to 1A

are possible from CH1 and CH2, limited primarily

by the power dissipation of the IC.

The third channel has a fixed configuration in-

tended to drive a solenoid. DMOS transistors with

0.5

Ω Rdson are used to provide 4A max load ca-

pability.

All three channels have 3 bit current D/A resolu-

tion. Some auxiliary blocks of diagnostic and pro-

tection (e.g.: The power Fail/Reset and the watch-

dog) are provided to protect the system from

microprocessor failure or power fail.

Step Down Switchmode Power Supply (See

Figure 7).

The step down switchmode power supply con-

tains a DMOS power stage with 1

Ω Rdson (Q1),

control circuitry, diagnostics and protection cir-

cuits; a regulated voltage (VSSout) is used to drive

some of the internal circuit blocks and the exter-

nal microprocessor and memories. Thanks to the

DMOS output stage this regulator can deliver a

continuous output power of 4W (5V; 0.8A) with an

efficiency betler than 90% at a typical frequency

of 80kHz.

The regulation loop uses a classical pulse width

modulation circuit that includes a sawtooth gener-

ator, an error amplifier, a voltage comparator and a

PWM latch. A precision 5V reference is generated

and trimmed on chip to guarantee a 5% tolerance.

This reference is used as voltage reference for the

SMPS and the reference for the DACs.

The IC also provides an extra voltage (VS+VDHS)

for the correct driving of the high side drivers.

These transistors require a gate voltage higher

than the supply voltage Vs to obtain the minimum

ON resistance. Because of the v ery low current

needed to drive DMOS transistors, this auxiliary

voltage is easily obtained from a second winding

on the inductor of the LC output network (see Ap-

plication Information).

An overcurrent protection circuit is included to

turn OFF the power transistor when a current

level of 1.2A is exceeded.

The SMPS block also includes a voltage sensing

circuit to generate a power ON reset signal for the

microprocessor. This Power Fail circuit senses

the input supply voltage and the output regulated

voltage and sets the Reset-out pin to the high

voltage only when both the sensed voltages are

correct.

Finally, the SMPS block is able to deliver fOSC/2

used in the actuation stage for the PWM control

of the current (CH1; CH2 and CH3).

Figure 7: SMPS Block Diagram

L6280

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