PM6686 STMicroelectronics, PM6686 Datasheet - Page 32

• Manufacturer Part Number: PM6686
• Description: Dual Step-down Controller With Adjustable Voltages, Adjustable Ldo And Auxiliary Charge Pump Controller For Notebook
• Manufacturer: STMicroelectronics

Device description
8.1.8
32/50
Figure 52. Current limit circuit block diagram
Table 10.
A negative current control is also implemented: the low-side MOSFET is forced off when the
current exceeds the negative limit. This function prevents the excessive negative inductor
current during the PWM operating mode. The threshold is set approximately at the 120% of
the positive current limit.
Soft-start and soft-end
The two sections have independent enable pins, EN1 and EN2. A not programmable soft-
start procedure takes place when EN pin rises above 2.4 V typ.
To prevent high input inrush currents, the current limit is increased from 25% to 100% with
steps of 25%.
The procedure is not programmable and ends typically in 2.8 ms. The overvoltage protection
is always active while the undervoltage protection is enabled typically 20 ms after the
beginning of the soft-start procedure.
Driving one EN pin below 0.8 V makes the section perform a soft-end: gate driving signals
are pulled low and the output is discharged through an internal MOSFET with R
28 Ω typ.
A power up sequence for the switching sections can be selected connecting one EN pin to
VREF2.
RILIM
Control pin
ILIM1
ILIM2
ILIM
Current limit configuration
5uA
+
-
Doc ID 15281 Rev 4
Control pin voltage
0.2 V = V
V
9R
R
V
ILIM
ILIM
= 5µA * R
= VCC-1 V
ILIM
Generator
= 2 V
+
Ton
ILIM
-
HGATE
PHASE
LGAT E
Threshold SET
V
100 mV
ILIM
/10
DS(on)
PM6686
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