L5988D datasheet(23/52 Pages) STMICROELECTRONICS

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L5988D

Functional description

Table 9 shows some resistor values to adjust the current limits

Table 9. ILIM-ADJ resistor examples

5.5.3

UVLO

The under-voltage-lockout (UVLO) is adjustable by the multifunction pin (see Section 5.1 on

page 13). It is possible to set two different thresholds:



2.9 V for 3.3 V BUS



8 V for 12 V BUS

5.5.4

Thermal shutdown

When the junction temperature reaches 150 °C the device enters in thermal shutdown. Both

MOSFETs are turned off and the soft-start capacitor is discharged with a current of 22 µA.

The device doesn’t restart until the junction temperature goes down to 120 °C.

5.6

Minimum on time

The L5988D is based on a voltage mode control loop. The advantage of this technique is

the very short conduction time of the power elements thanks to the proper functioning of the

control loop without a current sense (that is challenging with low conduction times), which

instead is required in current mode regulators. The optimized architecture, the design

solutions and the high performance fabrication technique allow power elements to achieve

extremely short conduction times. This allows very high switching frequency operation even

in very low duty cycle applications. Figure 12 shows how the L5988D can easily manage

a minimum conduction time of 200ns. Moreover, thanks to the embedded P-MOS used for

the high-side, no bootstrap capacitor is required. This means that the device is able to

manage a duty cycle of 100%.

R9(k

)ILIM PEAK(A)

ILIM VALLEY(A)

R3(k

)ILIM PEAK(A)

ILIM VALLEY(A)

1.24

1.62

1500

4.2

4.75

1.47

1.87

750

4.38

4.95

1.88

2.31

470

4.6

5.18

2.26

2.71

330

4.8

5.42

2.71

3.18

270

5.0

5.62

120

3.03

3.52

220

5.20

5.82

200

3.43

3.94

180

5.50

6.12

560

3.81

4.35

160

5.70

6.30

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