L6751B datasheet(37/58 Pages) STMICROELECTRONICS

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L6751B

Output voltage monitoring and protection

Doc ID 024028 Rev 1

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–CIMON in parallel to RIMON can be added to adjust the averaging interval for the

current reporting and/or adjust the DPM latencies. Additionally, it can be increased

to prevent false total-OC tripping during DVID.

Note:

This is the typical design flow. Custom design and specifications may require different

settings and ratios between the per-phase OC threshold and the total current OC threshold.

Applications with big ripple across inductors may be required to set per-phase OC to values

different than 110%: design flow should be modified accordingly.

Note:

Current reporting precision on IMON may be affected by external layout. The internal ADC is

referenced to the device GND pin: in order to perform the highest accuracy in the current

monitor, RIMON must be routed to the GND pin with dedicated net to avoid GND plane drops

affecting the precision of the measurement.

7.2.2

Overcurrent and power states

When the controller receives an SetPS command through the SVI interface, it automatically

changes the number of working phases. In particular, the maximum number of phases

which L6751B may work in >PS00h is limited to 2 phases regardless of the number N

configured in PS00h.

OC level is then scaled as the controller enters >PS00h, as per Table 14.

7.2.3

Single-phase section

The L6751B performs two different kinds of OC protection for the single-phase section: it

monitors both the total current and the per-phase current and allows an OC threshold to be

set for both.

–

Per-phase OC.

Maximum information current per-phase (ISINFOx) is internally limited to 35 μA.

This end-of-scale current (ISOC_TH) is compared with the information current

generated for each phase (ISINFOx). If the current information for the single-phase

exceeds the end-of-scale current (i.e. if ISINFOx > ISOC_TH), the device turns on the

LS MOSFET until the threshold is re-crossed (i.e. until ISINFOx < ISOC_TH).

–

Total current OC.

The SIMON pin allows a maximum total output current for the system (ISOC_TOT)

to be defined. ISMON current is sourced from the SIMON pin. By connecting a

resistor RSIMON to GND, a load indicator with 1.55 V (VSOC_TOT) end-of-scale can

be implemented. When the voltage present at the SIMON pin crosses VSOC_TOT,

the device detects an OC and immediately latches with all the MOSFETs of all the

sections OFF (HiZ).

Table 14.

Multi-phase section OC scaling and power states

Power state [Hex]

OC level (VOC_TOT)

00h

3 to 6

2.500 V

01h, 02h

1.650 V

1.250 V

1.000 V

0.830 V

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