PM6686 STMicroelectronics, PM6686 Datasheet - Page 36

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

Monitoring and protections
9.5
36/50
Charge pump
The PM6686 can drive an external charge pump circuit whose typical application schematic
is shown in the next figure.
Figure 54. Charge pump application circuit
The charge pump works in 4 phases:
1.
2.
3.
4.
Every diode used to transfer charge introduces a voltage drop that decreases the charge
pump output voltage.
Repeating this cycle several times makes the charge pump output voltage equals to:
Equation 6
Where V
section 1, V
voltage droop of the diodes used in the application.
CP_FB pin must be connected to the output of the charge pump with a resistor divider;
when CP_FB pin droops below 2 V typ., OUT1 controller starts a NA SKIP cycle to boost the
voltage of the charge pump.
LGATE is low. C1 is charged through the D1a diode at OUT1 voltage minus the diode
drop.
LGATE is driven high and C1 transfers the charge to C2. C2 voltage is OUT1 voltage
plus the LGATE voltage minus the voltage drops on D1 and D2.
LGATE is turned low and C2 shares its charge with C3 thought D3.
LGATE becomes high and C3 can charge C4 thought diode D4.
CP
LGATE1
is the charge pump output voltage, V
COU T
is the low-side MOSFET gate driving voltage and V
Vo ut
C2
C4
CP
D1
L
D2
D3
V
D4
Doc ID 15281 Rev 4
CP
=
V
OUT
C1
C3
1
+
2
V
LGATE
OUT1
R 1
1
PHASE
LGAT E
−
4
is the output voltage of the switching
V
CP_F B
DIODE
R 2
DIODE
is the forward
PM6686