L99LD02 datasheet(26/66 Pages) STMICROELECTRONICS

26 / 66 page

Functional description

L99LD02

26/66

DS12448 Rev 3

4.2

Protections and diagnostic

4.2.1

Temperature warning

The device integrates a temperature warning TW with two thresholds TW1 and TW2.

If the Tj (junction temperature) of the boost controllers rises above TW1 or TW2, the status

bit TWx (x=1 or x=2 stands for the TW1 or TW2) is set on the status registers (see bit <18>

and bit <19> on Table 26: SR#1: Status Register 1). Thermal warning is also reported in the

Global Status Byte register, and in particular, bit 25 (GW) is set.

If the Tj drops below the temperature warning reset threshold 1 (TW1-TW1_HYS),

respectively TW2 – TW2_HYS, the corresponding status bit is automatically reset. As long as

the Tj does not exceed the over temperature shutdown, the device does not latch off the

boost controllers, even if a temperature warning is detected.

Note that, powering the device via the BST_OUT will produce an extra power dissipation

which must be taken into account during the thermal design.

In case the device is supplied from BST_OUT pin, a flag called BST_OUT_SUPPLY is

provided to inform the application. If the junction temperature rises above TW (thermal

warning) threshold, the application can decide to decrease power losses on gate driver

V10V regulator (switching off 1 boost phase or decreasing boost switching frequency),

minimizing the risk of undesired thermal shutdown.

4.2.2

Overcurrent

On top of the normal current regulation loop comparator, the L99LD02 integrates an

additional comparator to clamp the maximum physical current that can flow in the booster

input circuit while the MOSFET is driven. The aim is to protect all the external components

involved (inductor from saturation, diode and MOSFET from overcurrent…).

The protection is active PWM cycle−by−cycle and switches off the MOSFET gate as the

voltage drop across the shunt resistor reaches its maximum threshold (BST_OCP_LIM).

This threshold can be set by SPI / OTPs according to Table 8.

4.2.3

Over-temperature shutdown

If the junction temperature rises above the shutdown temperature TTSD, an over-

temperature event (OVT) is detected. The boost controllers are switched off and the

corresponding bit OVT is set in the status register (see bit <20> on Table 26: SR#1: Status

Table 8. Boost threshold for input current limitation

BITs [1÷0]

BST_OCP_LIM [mV]

115

150

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