L9907 datasheet(12/49 Pages) STMICROELECTRONICS

12 / 49 page

Functional description

L9907

12/49

DS11800 Rev 5

In case Boost converter is disabled, but voltage at BST_C pin is present, Current Sense

Amplifiers are active but with degraded performances at least in common mode dynamic

range. In order to improve EMC behaviour an external RC series snubber can be added

between BST_L and BGND pins. RC~1/(6.28*fSW_BST).

2.4.1

BstDis (boost disable) function

In case noise-free CSA measuring is needed, a special functionality that temporarily

disables Boost regulator is implemented, with the purpose to reduce PCB coupling between

CSA output and boost PCB metal stripes that can act as antennas. Once BST_DIS pin is

asserted, boost regulator is disabled starting from the next complete boost cycle (maximum

delay T_BOOST_OFF_FILT).

Boost is re-enabled in two ways:



internal timer expired (T_BOOST_OFF_MAX time is reached)



BstDis pin deasserted

In both cases boost starts working again from the beginning of the next complete boost

cycle.

T_BOOST_OFF_MAX = 6*TBOOST = 96*TCK

T_BOOST_OFF_FILT = 3*TCK min, 21*TCK max

Figure 4. Case of T_BOOST_OFF < T_BOOST_OFF_MAX

Figure 5. Case of T_BOOST_OFF > T_BOOST_OFF_MAX

Internal boost control

signal generated by

logic and internal oscillator

21*TCK MAX =

5*TCK filter +

1BOOST period

BOOST DIS PIN

BOOST CLK MASK

BOOST CLK

GAPGPS00836

Internal sync signal

T_BOOST_OFF_MAX =

96*TCK = 6 BOOST periods

BOOST DIS PIN

BOOST CLK MASK

BOOST CLK

GAPGPS00837

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