L6728AHTR STMicroelectronics, L6728AHTR Datasheet - Page 11

IC CTLR PWM SGL PHASE 10-VFQFPN

L6728AHTR

Manufacturer Part Number
L6728AHTR
Description
IC CTLR PWM SGL PHASE 10-VFQFPN
Manufacturer
STMicroelectronics
Datasheet

Specifications of L6728AHTR

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-VFQFN, 10-VFQFPN
Frequency-max
660kHz
Lead Free Status / RoHS Status
Lead free / RoHS Compliant
Other names
497-8977-2

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L6728AH
6
6.1
Soft-start
L6728AH 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 msec (typ.), in closed loop regulation, linearly
charging the output capacitors to the final regulation voltage. A pre-charged output voltage
will affect the soft-start duration, resulting in a reduction of this period of time (< 4 msec).
During the soft-start process all the protections but the UVP are active: the UVP becomes
active as soon as the soft-start ends up.
The device begins soft-start phase only when
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, L6728AH 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 startup (left) vs. non-LSLess startup (right)
Doc ID 15726 Rev 1
V
CC
power supply is above UVLO threshold
Soft-start
11/33

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