STMicroelectronics PM6686 Datasheet

PM6686

Dual step-down controller with adjustable voltages, adjustable LDO

and auxiliary charge pump controller for notebook

Features

■ 5.5 V to 28 V input voltage range

■ Dual fixed OUT1 = 1.5 V/5 V and OUT2 =

1.05 V / 3.3 V outputs or adjustable OUT1 = 0.7
V to 5.5 V and OUT2 = 0.7 V to 2.5 V outputs,
± 1.5% accuracy over valley regulation

■ Low-side MOSFETs' R

current sensing

DS(on)

and programmable current limit

■ Constant ON-time control

■ Frequency selectable

■ Soft-start internally fixed at 2 ms and soft-stop

■ Selectable pulse skipping at light loads

■ Selectable minimum frequency (33 kHz) in

pulse skip mode

■ Independent Power Good and EN signals

■ Latched OVP and UVP

■ Charge pump feedback

■ Fixed 3.3 V/5.0 V, or adjustable output 0.7 V to

4.5 V, ± 1.5% (LDO): 200 mA

■ 3.3 V reference voltage ± 2.0%: 5 mA

■ 2.0 V reference voltage ± 1.0%: 50 µA

Applications

■ Notebook computers

■ Main (3.3 V/5 V), chipset (1.5 V/1.05 V),

DDR1/2/3, graphic cards power supply

■ PDAs, mobile devices, tablet PC or slates

■ 3-4 cells Li+ battery powered devices

Description

PM6686 is a dual step-down controller specifically
designed to provide extremely high efficiency
conversion, with lossless current sensing
technique. The constant on-time architecture
assures fast load transient response and the
embedded voltage feed-forward provides nearly
constant switching frequency operation. Pulse
skipping technique increases efficiency at very
light load. Moreover a minimum switching
frequency of 33 kHz is selectable to avoid audio
noise issues. The PM6686 provides a selectable
switching frequency, allowing three different
values of switching frequencies for the two
switching sections. The output voltages OUT1
and OUT2 can be programmed to regulate

1.5 V/5 V and 1.05 V/3.3 V outputs respectively or
can deliver two adjustable output voltages. An
optional external charge pump can be monitored.
This device embeds a linear regulator that can
provide 3.3 V/5 V or an adjustable voltage from

0.7 V to 4.5 V output. The linear regulator
provides up to 100 mA output current. LDO can
be bypassed with the switching regulator outputs
or with an external power supply (switchover
function).

VFQFPN-32 5 x 5 mm

When in switchover, the LDO output can source
up to 200 mA.

Table 1. Device summary

July 2009 Doc ID 15281 Rev 4 1/50

Order codes Package Packaging

PM6686

Tr ay

VFQFPN-32L 5 x 5 mm

PM6686TR Tape and reel

www.st.com

50

Contents PM6686

Contents

1 Simplified application schematic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

2 Pin settings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

2.1 Connections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

2.2 Pin descriptions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

3 Electrical data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

3.1 Maximum rating . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

3.2 Thermal data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

4 Recommended operating conditions . . . . . . . . . . . . . . . . . . . . . . . . . . 11

5 Electrical characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

6 Typical operating characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

6.1 Screen shots . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

7 Block diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

8 Device description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

8.1 Switching sections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

8.1.1 Output voltage set up . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

8.1.2 Constant on time control (COT) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

8.1.3 PWM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

8.1.4 SKIP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

8.1.5 Non audible SKIP (NA SKIP) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

8.1.6 Gate drivers and logic supply . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

8.1.7 Current sensing and current limit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

8.1.8 Soft-start and soft-end . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

9 Monitoring and protections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34

9.1 Overvoltage protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34

9.2 Undervoltage protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34

9.3 PVCC monitor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34

2/50 Doc ID 15281 Rev 4

PM6686 Contents

9.4 Linear regulator section . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35

9.5 Charge pump . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36

9.6 Voltage references . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37

9.7 General device fault management . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37

9.7.1 Thermal protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37

10 Application information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38

10.1 External components selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38

10.1.1 Inductor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38

10.1.2 Input capacitor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39

10.1.3 Output capacitor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39

10.1.4 MOSFET . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40

11 Diode selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42

11.1 Freewheeling diode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42

11.2 Charge pump diode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42

11.3 Other important components . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43

11.3.1 VIN filter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43

11.3.2 PVCC and VCC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43

11.3.3 VREF2 and VREF3 capacitors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44

11.3.4 LDO output capacitors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44

11.3.5 Bootstrap circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44

12 PCB design guidelines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45

13 Package mechanical data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47

14 Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49

Doc ID 15281 Rev 4 3/50

List of figures PM6686

List of figures

Figure 1. Simplified application schematic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

Figure 2. Pin connection (through top view) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

Figure 3. Efficiency vs load OUT1 = 5 V, TON = VCC. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

Figure 4. Efficiency vs load OUT2 = 3.3 V, TON = VCC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

Figure 5. Efficiency vs load OUT1 = 1.5 V, TON = VCC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

Figure 6. Efficiency vs load OUT2 = 1.05 V, TON = VCC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

Figure 7. Load regulationOUT1 = 5 V, TON = VCC. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

Figure 8. Load regulationOUT2 = 3.3 V, TON = VCC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

Figure 9. Load regulation OUT1 = 1.5 V, TON = VCC. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

Figure 10. Load regulation OUT2 = 1.05 V, TON = VCC. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

Figure 11. Switching frequency vs load OUT1 = 5 V, TON = VCC . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

Figure 12. Switching frequency vs load OUT2 = 3.3 V, TON = VCC . . . . . . . . . . . . . . . . . . . . . . . . . . 16

Figure 13. Section 1 line regulation OUT1 = 5 V, TON = VCC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

Figure 14. Section 2 line regulation OUT2 = 3.3 V, TON = VCC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

Figure 15. Section 1 line regulation OUT1 = 1,5 V, TON = VCC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

Figure 16. Section 2 line regulation OUT2 = 1,05 V, TON = VCC . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

Figure 17. Stand-by mode input battery current vs input voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

Figure 18. Shut-down mode input battery current vs input voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

Figure 19. PWM no load input currents vs input voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

Figure 20. SKIP no load input currents vs input voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

Figure 21. NA SKIP no load input currents vs input voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

Figure 22. VREF3 load regulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

Figure 23. VREF2 load regulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

Figure 24. LDO = 3,3 V load regulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

Figure 25. LDO = 5 V load regulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

Figure 26. OUT1 soft-start no load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

Figure 27. OUT2 soft-start no load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

Figure 28. OUT1 soft-start 8 A constant current load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

Figure 29. OUT2 soft-start loaded 8 A constant current load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

Figure 30. OUT1 soft-end, no load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

Figure 31. OUT2 soft-end, no load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

Figure 32. OUT1 soft-start, EN2 = VREF2 no loads applied . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

Figure 33. OUT2 soft-start, EN1=VREF2 no loads applied . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

Figure 34. soft-end, EN2 = VREF2 no loads applied . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

Figure 35. soft-end, EN1=VREF2 no loads applied . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

Figure 36. Load transient 0-5 A 2 A/µs OUT1 = 5 V PWM mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

Figure 37. Load transient 0-5 A 2 A/µs OUT1 = 5 V SKIP mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

Figure 38. Load transient 0-5 A 2 A/ µs OUT1 = 1,5 V PWM mode . . . . . . . . . . . . . . . . . . . . . . . . . . 21

Figure 39. Load transient 0-5 A 2 A/ µs OUT1 = 1,5 V SKIP mode . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

Figure 40. Load transient 0-5 A 2 A/µs OUT2 = 3.3 V PWM mode . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

Figure 41. Load transient 0-5 A 2 A/µs OUT2 = 3.3 V SKIP mode . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

Figure 42. Load transient 0-5 A 2 A/ µs OUT2 = 1,05 V PWM mode . . . . . . . . . . . . . . . . . . . . . . . . . 22

Figure 43. Load transient 0-5 A 2 A/ µs OUT2 = 1,05 V SKIP mode . . . . . . . . . . . . . . . . . . . . . . . . . . 22

Figure 44. Functional block diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

Figure 45. Resistor divider to configure the output voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

Figure 46. Constant on time block diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

Figure 47. Inductor current and output voltage in PWM mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

Figure 48. Inductor current and output voltage in SKIP mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

4/50 Doc ID 15281 Rev 4

PM6686 List of figures

Figure 49. Inductor current and output voltage in NA SKIP mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

Figure 50. Internal supply diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

Figure 51. Current waveforms in current limit conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

Figure 52. Current limit circuit block diagram. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

Figure 53. VOUT2 behavior if EN2 is connected to VREF2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

Figure 54. Charge pump application circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36

Figure 55. VIN pin filter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43

Figure 56. VCC and PVCC filters. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43

Figure 57. Bootstrap circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44

Figure 58. Current paths, ground connection and driver traces layout . . . . . . . . . . . . . . . . . . . . . . . . 46

Figure 59. Package dimensions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48

Doc ID 15281 Rev 4 5/50

Simplified application schematic PM6686

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6/50 Doc ID 15281 Rev 4

PM6686 Pin settings

2 Pin settings

2.1 Connections

Figure 2. Pin connection (through top view)

0-

2.2 Pin descriptions

Table 2. Pin descriptions

N° Pin Function

1VREF2

2TON

3 VCC Controller supply voltage input. Bypass to GND with a 1 μF capacitor.

4EN_LDO

5VREF3

6VIN

!-V

Internal 2 V high accuracy voltage reference. It can deliver 50 μA. Loading
VREF2 can affect FB and output accuracy. Bypass to GND with a 100 nF
capacitor.

Frequency selection pin. It provides a selectable switching frequency,
allowing three different values of switching frequencies for the switching
sections.

Enable input for the linear regulator. The LDO is enabled if
EN_LDO is > 1.6 V and is disabled if EN_LDO < 1 V.

Internal 3.3 V high accuracy voltage reference. It can deliver 5 mA if
bypassed to GND with a 10 nF capacitor. If not used, it can be left floating.

Device supply voltage pin. VIN is used in the on-time generators of the two
switching controllers. VIN is also used to power the linear regulator when the
switchover function is not active. Connect VIN to the battery input and
bypass with a 1 µF capacitor.

Doc ID 15281 Rev 4 7/50

Pin settings PM6686

Table 2. Pin descriptions (continued)

N° Pin Function

Linear regulator output. It can provide up to 100 mA peak current. The LDO
regulates at 5 V If LDOREFIN is connected to GND. When the LDO is set at
5 V and LDO_SW is within 5 V switchover threshold, the internal regulator
shuts down and the LDO output pin is connected to LDO_SW through a

7LDO

8 LDOREFIN

9LDO_SW

10 OUT1

0.8 Ω switch. The LDO regulates at 3.3 V if LDOREFIN is connected to
VCC. When the LDO is set at 3.3 V and LDO_SW is within 3.3 V switchover
threshold, the internal regulator shuts down and the LDO output pin is
connected to LDO_SW through a 1.1 Ω switch. Bypass LDO output to GND
with a minimum of 4.7 µF ceramic capacitor.

Feedback of the adjustable linear regulator. Connect LDOREFIN to GND for
fixed 5 V operation. Connect LDOREFIN to VCC for fixed 3.3 V operation.
LDOREFIN can be used to program LDO output voltage from 0.7 V to 4.5 V:
LDO output is two times the voltage of LDOREFIN. The switchover function
is disabled in adjustable mode.

Source of the switchover connection. LDO_SW is the switchover source
voltage for the LDO when LDOREFIN is connected to GND or VCC.
Connect LDO_SW to 5 V if LDOREFIN is tied to GND. Connect LDO_SW to

3.3 V if LDOREFIN is tied to VCC.

Output voltage sense for the switching section 1.This pin must be directly
connected to the output voltage of the switching section. It provides also the
feedback for the switching section 1 when FB1 is tied to GND/VCC.

Feedback input for the switching section 1:
– If this pin is connected to GND, OUT1 operates at 5 V

11 FB1

– If this pin is connected to VCC, OUT1 operates at 1.5 V
– This pin is connected to a resistive voltage-divider from OUT1 to GND to

adjust the output voltage from 0.7 V to 5.5 V.

12 ILIM1

Positive current sense input for the switching section 1. It is possible to set a
threshold voltage that is compared with 1/10

th

of the GND-PHASE1 drop

during the off time.

Power Good output signal for the section 1. This pin is an open drain output

13 PG1

and It is pulled down when the output of the switching section 1 is out of
+/- 10% of its nominal value.

Enable input for the switching section 1.
– If EN1 < 0.8 V the switching section OUT1 is turned off and all faults are

14 EN1

cleared.
– If EN1 > 2.4 V the switching section OUT1 is turned on.
– If EN1 is connected to VREF2, the switching section OUT1 turns on after

the switching section OUT2 reaches regulation.

15 HGATE1 High-side gate driver output for section 1.

16 PHASE1

17 BOOT1

Switch node connection and return path for the high-side driver for the
section 1.It is also used as positive and negative current sense input.

Bootstrap capacitor connection for the switching section 1. It supplies the
high-side gate driver.

18 LGATE1 Low-side gate driver output for the section 1.

19 PVCC

5 V low-side gate drivers supply voltage input. Bypass to PGND with a 1 μF
capacitor.

8/50 Doc ID 15281 Rev 4

PM6686 Pin settings

Table 2. Pin descriptions (continued)

N° Pin Function

The CP_FB is used to monitor the optional external 14 V charge pump.
Connect a resistive voltage-divider from 14 V charge pump output to GND. If

20 CP_FB

21 GND

22 PGND

23 LGATE2 Low-side gate driver output for the section 2.

24 BOOT2

25 PHASE2

26 HGATE2 High-side gate driver output for section 2.

27 EN2

28 PG2

29 SKIP

30 OUT2

31 ILIM2

32 REFIN2

CP_FB drops below the threshold voltage, the device performs a no audible
skip cycle. This charges the charge pump output (driven by LGATE1). Leave
CP_FB floating if the charge pump feedback is not needed.

Signal ground reference for internal logic circuitry and LDO. It must be
connected to the signal ground plan of the power supply and to the exposed
pad. The signal ground plan and the power ground plan must be connected
together in one point near the PGND pin.

Power ground. This pin must be connected to the power ground plan of the
power supply.

Bootstrap capacitor connection for the switching section 2. It supplies the
high-side gate driver.

Switch node connection and return path for the high-side driver for the
section 2. It is also used as positive and negative current sense input.

Enable input for the switching section 2.
– If EN2 < 0.8 V the switching section OUT2 is turned off and all faults are

cleared.
– If EN2 > 2.4 V the switching section OUT2 is turned on.
If EN2 is connected to VREF2, the switching section OUT2 turns on after

the switching section OUT1 reaches regulation.

Power Good output signal for the section 2. This pin is an open drain output
and It is pulled down when the output of the switching section 2 is out of
+ 14% / - 10% of its nominal value.

Pulse skipping mode control input.
– If the pin is connected to VCC the PWM mode is enabled.
– If the pin is connected to GND, the pulse skip mode is enabled.
– If the pin is connected to VREF2 (or floating) the pulse skip mode is

enabled but and the switching frequency is kept higher than 33 kHz (No-

audible pulse skip mode).

Output voltage sense for the switching section 2.This pin must be directly
connected to the output voltage of the switching section. It provides also the
feedback for the switching section 2 when REFIN2 is tied to VREF3/VCC.

Positive current sense input for the switching section 2. It is possible to set a
threshold voltage that is compared with 1/10

th

of the GND-PHASE2 drop

during the off time.

Feedback input for the switching section 2:
– If this pin is connected to VCC, OUT2 operates at 3.3 V
– If this pin is connected to VREF3, OUT2 operates at 1.05 V
– If this pin is connected to an external reference from 0.7 V to 2.5 V, OUT2

works in tracking with this reference. Bypass REFIN2 to GND with a 100

nF capacitor.

Doc ID 15281 Rev 4 9/50

Electrical data PM6686

3 Electrical data

3.1 Maximum rating

Table 3. Absolute maximum ratings

Parameter Value Unit

VIN to PGND -0.3 to 38 V

PHASEx to PGND -0.3 to 38 V

BOOTx to PHASEx -0.3 to 6 V

PVCC to PGND -0.3 to 6 V

HGATEx to PHASEx -0.3 to BOOTx +0.3 V

LGATEx, CP_FB to PGND -0.3 to PVCC +0.3 V

VCC, ENx, SKIP, PGx, LDO, REFIN2, OUTx, VREF3,
LDOREFIN, LDO_SW, TON to GND

FB1, ILIMx to GND -0.3 to VCC+0.3 V

EN_LDO to GND -0.3 to 7 V

-0.3 to 6 V

VREF2 to GND -0.3 to VREF3+0.3 V

PGND to GND -0.3 to +0.3 V

Power dissipation at T

Maximum withstanding voltage range test condition: CDF-AEC­Q100-002- “human body model” acceptance criteria: “normal
performance”

3.2 Thermal data

Table 4. Thermal data

Symbol Parameter Value Unit

R

thJA

T

J

T

STG

Operating ambient temperature range -40 to 85 °C

T

A

Thermal resistance junction to ambient 35 °C/W

Junction operating temperature range -40 to 125 °C

Storage temperature range -50 to 150 °C

= 25 °C 2 W

A

±1250 V

10/50 Doc ID 15281 Rev 4

PM6686 Recommended operating conditions

4 Recommended operating conditions

Table 5. Recommended operating conditions

Val ue

Symbol Parameter

Min Typ Max

VIN Input voltage range, LDO = 5 V in regulation 5.5 - 28 V

VCC VCC operative voltage range 4.5 - 5.5 V

REFIN2

REFIN2 voltage range with OUT2 in
adjustable mode, VIN = 5.5 V to 28 V

0.7 - 2.5 V

OUT1 OUT1 output voltage range 0.70 - 5.50 V

ILIM ILIM voltage range 0.2 - 2 V

Unit

LDOREFIN

LDO DC output current

(switchover function

enabled)

LDO DC output current

(switchover function

disabled)

LDOREFIN setting with LDO = 2 x LDOREFIN
(adjustable mode)

VIN = 5.5 V to 28 V, LDO_SW = 5 V,
LDOREFIN = GND

VIN = 5.5 V to 28 V, LDO_SW = 3.3 V,
LDOREFIN = VCC

VIN = 5.5 V to 28 V, LDO_SW = 0 V,
LDOREFIN = GND, VCC

0.35 - 2.25 V

- 200 mA

- 100 mA

- 100 mA

Doc ID 15281 Rev 4 11/50

Electrical characteristics PM6686

5 Electrical characteristics

VIN = 12 V, no load on LDO, OUT1, OUT2, VREF3, and VREF2. EN2 = EN1 = VCC,
LDO_SW = 5 V, PVCC = 5 V, EN_LDO = 5 V, T

Table 6. Electrical characteristics

Symbol Parameter Test condition Min Typ Max Unit

Switching controller output accuracy

= 25 °C unless otherwise specified)

J

OUT2 Output voltage

OUT1 Output voltage

FB1

Feedback accuracy with
OUT1 in adjustable mode

REFIN2 Accuracy referred to REFIN2

Current limit and zero crossing comparator

ILIM ILIM bias current T

Positive current limit threshold

Zero crossing current
threshold

VIN = 5.5 V to 28 V, REFIN2 = VCC,
SKIP = VCC

VIN = 5.5 V to 28 V,
REFIN2 = VREF3, SKIP = VCC

VIN = 5.5 V to 28 V, FB1 = VCC,
SKIP = VCC

VIN = 5.5 V to 28 V, FB1 = GND,
SKIP = VCC

3.25 3.330 3.397 V

1.038 1.05 1.062 V

1.482 1.500 1.518 V

4.975 5.050 5.125 V

VIN = 5.5 V to 28 V, SKIP = VCC 0.693 0.700 0.707 V

REFIN2 = 0.7 V to 2.5 V,
SKIP = VCC

= +25 °C. 4.5 5 5.5 µA

A

-1 1 %

Adjustable, VILIM = 0.5 V, GND-PHASE 35 50 65 mV

Adjustable, VILIM = 1 V or VCC, GND­PHASE

85 100 115 mV

Adjustable, VILIM = 2 V, GND-PHASE 180 200 220 mV

SKIP = GND, VREF2, or OPEN, GND­PHASE

-1 +11 mV

Switching frequency

OUT1 = 5.125 V

On-time pulse width

OUT2 = 3.368 V TON = GND 0.477 0.561 0.655

Minimum Off-time 350 472

No-audible skip mode
operating frequency

SKIP = VREF2(or OPEN) 25 33 kHz

Soft-start and soft-end

Soft-start ramp time 2 4 ms

12/50 Doc ID 15281 Rev 4

TON = GND or

VREF2

0.908 1.068 1.228

TON = VCC 1.815 2.135 2.455

TON = VCC or

VREF2

0.796 0.936 1.076

µs

PM6686 Electrical characteristics

Table 6. Electrical characteristics (continued)

Symbol Parameter Test condition Min Typ Max Unit

Linear regulator and reference

LDO LDO output voltage

LDO_SW = GND, 5.5 V < VIN < 28 V,
LDOREFIN < 0.3 V, 0 < ILDO < 100 mA

LDO_SW = GND, 5.5 V < VIN < 28 V,
LDOREFIN = VREF3,

4.925 5.000 5.075 V

3.250 3.300 3.350 V

0 < ILDO < 100 mA

LDO accuracy in adjustable
mode

LDO short circuit current
(linear regulator enabled)

LDO_SW LDO_SW switch on threshold

LDO_SW LDO_SW hysteresis

VIN = 5.5 V to 28 V, LDOREFIN = 0.35 V
to 2.25 V, no load

-2.5 +2.5 %

LDO = 4.3 V, LDO_SW = GND 260 320 380 mA

LDO = 5 V, rising edge of LDO_SW,
LDOREFIN = GND

LDO = 5 V, falling edge of LDO_SW,
LDOREFIN = GND

4.64 4.75 4.84 V

200 400 mV

LDO = 5 V, rising edge of LDO_SW,

LDO_SW switch resistance

LDOREFIN = GND,

0.81 1.275 Ω

output current = 200 mA

VREF3 output voltage No load 3.235 3.300 3.365 V

VREF3

VREF3 current limit VREF3 = GND 22 30 mA

VREF2 VREF2 output voltage No load 1.980 2.000 2.02 V

VREF2 load regulation 0 < Load < 50 μA6mV

VREF2 sink current VREF2 > 2.030 V 10 µA

Fault management

VIN shutdown current EN1 and EN2 low, EN_LDO low 49 70 µA

VIN standby current

Operating power consumption
(VCC and VIN pins
consumption)

EN1 and EN2 low, EN_LDO high,
LDOREFIN = GND

Switching regulators on,
FB1 = SKIP = GND, REFIN2 = VCC,
LDOREFIN = GND,
OUT1 = LDO_SW = 5.3V, OUT2 = 3.5 V

132 180 µA

4,3 6,5 mW

Rising edge of PVCC 4.33 V

PVCC UVLO threshold

Falling edge of PVCC 4 V

Referred to FB1 nominal regulation point +11 %

Overvoltage trip threshold

Referred to REFIN2 nominal regulation
point. worst case:REFIN2 = 0.7 V

+14 %

PG threshold Lower threshold -13 -10 -7 %

PG low voltage ISink = 4 mA 159 235 405 mV

PG leakage current PG = 5 V 1 µA

Doc ID 15281 Rev 4 13/50

Electrical characteristics PM6686

Table 6. Electrical characteristics (continued)

Symbol Parameter Test condition Min Typ Max Unit

Output undervoltage
shutdown threshold

Inputs and outputs

FB1 FB1 logic level

REFIN2 REFIN2 logic level

LDOREFIN LDOREFIN logic level

SKIP SKIP logic level

TON TON logic level

EN1,2 EN level

Referred to FB1, REFIN2 nominal
regulation point

67 70 73 %

fixed OUT1 = 5 V 0.528 V

fixed OUT1 = 1.5 V 4.1 V

fixed OUT2 = 1.05 V, VCC = 5 V

fixed OUT 2= 3.3 V, VCC = 5 V

VREF3

VCC-

0.838

fixed LDO = 5 V 0.4 V

fixed LDO = 3.3 V 2.43 V

Pulse skip mode 0.8 V

No audible skip mode (VREF2 or floating)

VREF2 V

PWM mode 2.4 V

Low level 0.8 V

Middle level

VREF2

High level 2.4 V

Switching regulators off level 0.8 V

Delay start level

VREF2 V

Switching regulators on level 2.4 V

V

V

V

EN_LDO EN_LDO level

Input leakage current FB1 = 0.7 V -1 +1 µA

Internal bootstrap diode

Diode forward voltage PVCC = -BOOT, Idiode = 10 mA 0.2 V

Diode Leakage current BOOT= 30 V, PHASE = 28 V, PVCC = 5 V 500 nA

High-side and low-side gate drivers

HGATE driver on-resistance

LGATE driver on-resistance

Linear regulator off level 0.905 1.00 1.050 V

Linear regulator on level 1.500 1.6 1.650 V

REFIN2 = 2.5 V 12

HGATEx high state (pull-up)
Isource = 100 mA

HGATEx low state (pull-down)
Isink = 100 mA

LGATEx high state (pull-up)
Isource = 100 mA

LGATEx low state (pull-down)
Isink = 100 mA

1.8

1.3 1.9

1.3

0.6 0.8

Ω

14/50 Doc ID 15281 Rev 4

PM6686 Typical operating characteristics

6 Typical operating characteristics

(TON = VCC (200 / 300 kHz), SKIP = GND (skip mode), LDOREFIN = SGND (LDO = 5 V),
LDO_SW = OUT1, PVCC connected to LDO, V
load unless specified). Measures performed on the demonstration kit (PM6686_SYSTEM
and PM6686_CHIPSET)

Efficiency traces: Green: VIN = 7 V, red: VIN = 12 V, blue: VIN = 19 V.

= 12 V, EN1-EN2-EN_LDO are high, no

IN

Figure 3. Efficiency vs load

OUT1 = 5 V, T

= VCC

ON

Figure 5. Efficiency vs load

OUT1 = 1.5 V, T

ON

= VCC

Figure 4. Efficiency vs load

OUT2 = 3.3 V, TON = VCC

Figure 6. Efficiency vs load

OUT2 = 1.05 V, TON = VCC

A-PWM
B-SKIP
A-NASKIP

A-PWM
B-SKIP
A-NASKIP

Doc ID 15281 Rev 4 15/50