L6728TR STMicroelectronics, L6728TR Datasheet - Page 11

• Manufacturer Part Number: L6728TR
• Description: IC PWM CTLR 1PH PWRGOOD 10DFN
• Manufacturer: STMicroelectronics

Specifications of L6728TR

• Pwm Type: Voltage Mode
• Number Of Outputs: 1
• Frequency - Max: 330kHz
• Duty Cycle: 80%
• Voltage - Supply: 4.5 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: 330kHz
• Output Voltage: 0.8 V
• Output Current: 30 A
• Input Voltage: 1.5 V to 13.2 V
• Mounting Style: SMD/SMT
• Maximum Operating Temperature: + 125 C
• Minimum Operating Temperature: - 40 C
• 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: 497-6274-2

L6728
7
7.1
Soft-start
L6728 implements a soft-start to smoothly charge the output filter avoiding high in-rush
currents to be required from the input power supply. The device gradually increases the
internal reference from 0 V to 0.8 V in 4.5 ms (typ.), in closed loop regulation, linearly
charging the output capacitors to the final regulation voltage.
In the event of an over current triggering during soft start, the over current logic will override
the soft start sequence and will shut down the PWM logic and both the high side and low
side gates. This condition is latched, cycle VCC to recover.
The device begins soft start phase only when VCC power supply is above UVLO threshold
and over current threshold setting phase has been completed.
Low-side-less start up (LSLess)
In order to avoid any kind of negative undershoot and dangerous return from the load during
start-up, L6728 performs a special sequence in enabling LS driver to switch: during the soft-
start phase, the LS driver results disabled (LS = OFF) until the HS starts to switch. This
avoid the dangerous negative spike on the output voltage that can happen if starting over a
pre-biased output.
If the output voltage is pre-biased to a voltage higher than the final one, the HS would never
start to switch. In this case, at the end of soft start time, LS is enabled and discharge the
output to the final regulation value.
This particular feature of the device masks the LS turn-on only from the control loop point of
view: protections by-pass this turning ON the LS MOSFET in case of need.
Figure 4.
LSLess start up (left) vs non-LSLess start up (right)
Soft-start
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