L9352B

Functional description

17/27

4.7

Drift detection (regulated channels only)

The drift detection is used to compare the two regulated channels during regulation. This

“Drift” test compares the output PWM of the regulators. The resistivity of the load influences

the output PWM. The approximated formula for the output current below shows the

dependency of the load resistor to the output PWM. In this formula the energy reduction

during the recirculation is not taken into account. The real output PWM is higher. The

testmode is enabled with IN, EN and TEST high. With an identical 2kHz PWM-Signal

connected to the IN-inputs the output PWM must be in a range of ±14.3%. If the difference

between the two on-times is more than ±14.3% of the expected value an error is detected

and monitored by the status outputs, in the same way as described above, but a drift error

Drift Definition:

Drift = PWM(1+E) - PWM (1-E) = 2PWM E

Drift * 4 < PWM (1+E)

with E >14.3% a drift is detected

E.. not correlated Error of the channels

%PWM ... Corresponding ideal output PWM to a given input PWM

A 7bit output-PWM-register is used for the comparison. The register with the lower value is

subtracted from the higher one. This result is multiplied by four and compared with the

higher value.

4.8

Other test modes

The test pin is also used to test the regulated channels in the production. With a special

sequence on this pin the power stages of the regulated channels can be controlled direct

from the input. No status feedback of the regulated channels is given. The status output is

clocked by the regulator logic. The output sequence is a indication of a proper logic

functionality. The following table shows the functionality of this special test mode.

For more details about the test condition four see timing diagram.

IOUT

VBAT

RL

RON

+

---------------------------- PWM

⋅

=

Table 8.

Special test mode functionality

EN

IN

TEST

OUT

STATUS

Note

1

X

X

X

X

disable test mode

1

1

1

on

1

Drift mode

0

X

off

test pattern

test condition one

0

X

off

test pattern

test condition two

0

X

off

test pattern

test condition three

0

0

off

test pattern

test condition four

0

1

on

test pattern

test condition four