PM6685 STMicroelectronics, PM6685 Datasheet - Page 26

• Manufacturer Part Number: PM6685
• Description: IC CTLR DUAL SYNC STDN 5X5VFQFPN
• Manufacturer: STMicroelectronics

Specifications of PM6685

• Applications: Controller, Notebook Power System
• Voltage - Input: 6 ~ 28 V
• Number Of Outputs: 2
• Voltage - Output: -3.3V, 5V
• Operating Temperature: 0°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 32-VFQFN, 32-VFQFPN
• Output Voltage: 5 V, 3.3 V
• Output Current: 0.1 A
• Input Voltage: 5.5 V to 28 V
• Mounting Style: SMD/SMT
• Maximum Operating Temperature: + 125 C
• Minimum Operating Temperature: - 10 C
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

Device description
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Figure 35. Soft start waveforms
When a switching section is turned off(EN5/EN3 pins low), the controller enters in soft end
mode. The output capacitor is discharged through an internal 16 Ω P-MOSFET switch;
when the output voltage reaches 0.3 V, the low-side MOSFET turns on, keeping the output
to ground. The soft end time also depends on load condition.
Gate drivers
The integrated high-current drivers allow to use different power MOSFETs. The high side
driver MOSFET uses a bootstrap circuit which is indirectly supplied by LDO5 output. The
BOOT and PHASE pins work respectively as supply and return rails for the HS driver.
The low side driver uses the internal LDO5 output for the supply rail and PGND pin as return
rail.
An important feature of the gate drivers is the adaptive anti-cross conduction protection,
which prevents high side and low side MOSFETs from being on at the same time. When the
high side MOSFET is turned off the voltage at the phase node begins to fall. The low side
MOSFET is turned on when the voltage at the phase node reaches an internal threshold.
When the low side MOSFET is turned off, the high side remains off until the LGATE pin
voltage goes approximately under 1 V.
The power dissipation of the drivers is a function of the total gate charge Qg of the external
power MOSFETs and of the switching frequency, as shown in the following equation:
Where V
driver
is the 5 V driver supply.
Doc ID 11674 Rev 8
P
driver
=
V
driver
×
Q
g
×
f
sw
PM6685