L6728ATR STMicroelectronics, L6728ATR Datasheet - Page 10

• Manufacturer Part Number: L6728ATR
• Description: IC CTLR PWM SGL HI FREQ 10VFQFPN
• Manufacturer: STMicroelectronics

Specifications of L6728ATR

• Pwm Type: Voltage Mode
• Number Of Outputs: 1
• Frequency - Max: 660kHz
• Duty Cycle: 67%
• Voltage - Supply: 5 V ~ 12 V
• Buck: Yes
• Boost: No
• Flyback: No
• Inverting: No
• Doubler: No
• Divider: No
• Cuk: No
• Isolated: No
• Operating Temperature: -40°C ~ 125°C
• Package / Case: 10-DFN
• Frequency-max: 660kHz
• Topology: Buck
• Output Voltage: 0.8 V
• Output Current: 1500 mA
• Switching Frequency: 660 KHz
• Duty Cycle (max): 67 %
• Maximum Operating Temperature: + 125 C
• Minimum Operating Temperature: - 40 C
• Synchronous Pin: No
• For Use With: 497-8228 - BOARD EVALUATION W/L6728497-6418 - BOARD EVAL BASED ON L6728
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: 497-8324-2

L6728A
5
5.1
Driver section
The integrated high-current drivers allow using different types of power MOSFET (also
multiple MOSFETs to reduce the equivalent R
The driver for the high-side MOSFET uses BOOT pin for supply and PHASE pin for return.
The driver for low-side MOSFET uses the
The controller embodies an anti-shoot-through and adaptive dead-time control to minimize
low side body diode conduction time, maintaining good efficiency while saving the use of
Schottky diode:
to check high-side MOSFET turn off, PHASE pin is sensed. When the voltage at PHASE pin
drops down, the low-side MOSFET gate drive is suddenly applied;
to check low-side MOSFET turn off, LGATE pin is sensed. When the voltage at LGATE has
fallen, the high-side MOSFET gate drive is suddenly applied.
If the current flowing in the inductor is negative, voltage on PHASE pin will never drop. To
allow the low-side MOSFET to turn-on even in this case, a watchdog controller is enabled: if
the source of the high-side MOSFET doesn't drop, the low side MOSFET is switched on so
allowing the negative current of the inductor to recirculate. This mechanism allows the
system to regulate even if the current is negative.
Power conversion input is flexible: 5 V, 12 V bus or any bus that allows the conversion (See
maximum duty cycle limitations) can be chosen freely.
Power dissipation
L6728A embeds high current MOSFET drivers for both high side and low side MOSFETs: it
is then important to consider the power that the device is going to dissipate in driving them
in order to avoid overcoming the maximum junction operative temperature.
Two main terms contribute in the device power dissipation: bias power and drivers' power.
●
●
External gate resistors helps the device to dissipate the switching power since the same
power P
resulting in a general cooling of the device.
Device bias power (P
supply pins and it is simply quantifiable as follow (assuming to supply HS and LS
drivers with the same
Drivers power is the power needed by the driver to continuously switch on and off the
external MOSFETs; it is a function of the switching frequency and total gate charge of
the selected MOSFETs. It can be quantified considering that the total power P
dissipated to switch the MOSFETs (easy calculable) is dissipated by three main
factors: external gate resistance (when present), intrinsic MOSFET resistance and
intrinsic driver resistance. This last term is the important one to be determined to
calculate the device power dissipation. The total power dissipated to switch the
MOSFETs results:
SW
will be shared between the internal driver impedance and the external resistor
P
SW
DC
=
V
CC
) depends on the static consumption of the device through the
F
P
of the device):
SW
DC
⋅
=
(
Q
V
gHS
CC
V
CC
⋅
⋅
(
DS(on)
V
pin for supply and GND pin for return.
I
CC
BOOT
+
), maintaining fast switching transition.
I
BOOT
+
Q
gLS
)
⋅
V
CC
)
Driver section
SW
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