L9963E datasheet(165/184 Pages) STMICROELECTRONICS

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6.13.1

Requirements for safe cell hotplug

L9963E can safely handle hotplug if the following conditions are met:

•

The recommended components and configurations for cell voltage sensing and balancing are used (refer to

Section 6.3 Cell voltage sensing circuit and Section 6.6.1 Cell balancing with internal MOSFETs)

•

The VBAT, Cx, Sx and Bx_x-1 pin absolute voltage vs AGND during hotplug must not exceed 64 V

Zeners in parallel to each cell are not needed, since the device can withstand very high transient differential

voltages between those pins, as listed in Table 3. Moreover, RLPF resistors in series to Cx pins will limit the

current flowing into the centralized clamp (green paths in Figure 57).

The internal balancing MOSFETs mounted between Bx_x-1 and Sx pins are equipped with zener feedback that

clamps their VDS to VBAL_CLAMP during hotplug (orange paths in Figure 57). The feedback will turn them ON,

allowing the hotplug current to flow through their channel. Balancing resistors (RDIS) will limit the current.

Hotplug current also flows through the body-drain diode of the internal balancing MOSFETs. Also in this case,

current is limited by RDIS balancing resistors (orange paths in Figure 57).

6.13.2

Additional external components for hotplug protection

In case Requirements for safe cell hotplug are not met by the application, additional external components must

be mounted in order to limit the hotplug current flowing in the centralized ESD clamp.

The most critical paths are those involving VBAT and Bx_x-1 pins (red paths in Figure 57), since no series

resistance is present to limit the inrush current in the centralized clamp.

Adding the structure in Figure 57 on the GND path will help withstanding the hotplug by limiting the inrush current

incoming from any L9963E pin connected to the centralized clamp.

Working principle is the following:

•

When L9963E is OFF and no cell is connected, the VTREF/VREG regulator is shut down and MHOT is safely

kept off by the RPD pull down resistor

•

Upon the first hotplug event, inrush current incoming from the centralized clamp is forced to flow into RHOT

resistor, which offers proper limiting in order to not violate the critical point shown in Figure 56

•

Any VDS voltage spike on MHOT during hotplug could be coupled to the gate via the parasitic Miller

capacitance. Unwanted turn-on is safely filtered by CGS, that helps keeping VGS below the threshold

voltage. Hence, MHOT will stay OFF during hotplug.

•

After L9963E powerup and addressing

–

If MHOT is connected to VTREF, MCU has to program VTREF_EN = 1 and VTREF_DYN_EN

= 0 in order to turn on MHOT. Using the option VTREF_EN = 1 and VTREF_DYN_EN = 1 is

not recommended when MHOT is connected to VTREF. If VTREF dynamic enable is required by

application, connect MHOT to VREG instead.

–

If MHOT is connected to VREG, no action is required, since this regulator will turn on autonomously

•

Finally, during L9963E normal operation, MHOT will be ON, guaranteeing a very low impedance path (few

mΩ) on the AGND line.

–

Such a small shift between L9963E GND and battery pack GND will not alter cell measurement at all,

since cell ADCs are fully differential. Hence, both cell and sum of cells measurements will be accurate.

–

Moreover, since L9963E only drains few mA from the battery pack, error introduced on the VBAT stack

measurement via internal voltage divider will be negligible

–

Also the CSA used for Coulomb Counting features a fully differential architecture, being immune to

such a small common mode shift

L9963E

Hotplug

DS13636 - Rev 12

page 165/184

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