EVALPM6680 STMicroelectronics, EVALPM6680 Datasheet - Page 29

• Manufacturer Part Number: EVALPM6680
• Description: BOARD EVALUATION FOR PM6680
• Manufacturer: STMicroelectronics

Specifications of EVALPM6680

• Mfg Application Notes: PM6680 Eval Kit, AN2566 App Note
• Main Purpose: DC/DC, Step Down with LDO
• Outputs And Type: 3, Non-Isolated
• Power - Output: 13.25W
• Voltage - Output: 1.05V, 1.5V, 5V
• Current - Output: 5A, 5A, 100mA
• Voltage - Input: 6 ~ 28V
• Regulator Topology: Buck
• Frequency - Switching: 200kHz, 300kHz
• Board Type: Fully Populated
• Utilized Ic / Part: PM6680
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: 497-6241

PM6680
7.8
7.9
When a switching section is turned off (EN1/EN2 pins low), the controller enters in soft end
mode.The output capacitor is discharged through an internal 18 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 of the external
power MOSFETs and the switching frequency, as shown in the following equation:
Equation 11
Where V
Reference voltage and bandgap
The 1.237 V (typ.) internal bandgap voltage is accurate to ± 1 % over the temperature
range. It is externally available (VREF pin) and can supply up to 100 µA and can be used as
a voltage threshold for the multifunction pins FSEL and SKIP to select the appropriate
working mode. Bypass VREF to ground with a 100 nF minimum capacitor.
If VREF goes below 0.87 V (typ.) , the system detects a fault condition and all the circuitry is
turned off. A toggle on the input voltage (power on reset) or a toggle on SHDN pin is
necessary to restart the device.
An internal divider of the the bandgap provides a voltage reference Vr of 0.9 V. This voltage
is used as reference for the linear and the switching regulators outputs. The overvoltage
protection, the undervoltage protection and the power good signals are referred to Vr.
driver
is the 5 V driver supply.
P
driver
=
V
driver
×
Q
g
×
f
sw
Device description
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