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TPS54628DDAR Datasheet(PDF) 8 Page - Texas Instruments

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Part No. TPS54628DDAR
Description  4.5V to 18V Input, 6-A Synchronous Step-Down Converter with Eco-mode™
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Manufacturer  TI [Texas Instruments]
Direct Link  http://www.ti.com
Logo TI - Texas Instruments

TPS54628DDAR Datasheet(HTML) 8 Page - Texas Instruments

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TPS54628
SLVSBW5 – APRIL 2013
www.ti.com
Output Discharge Control
TPS54628 discharges the output when EN is low, or the controller is turned off by the UVLO protection. The
internal low-side MOSFET is not turned on for the output discharge operation to avoid the possibility of causing
negative voltage at the output.
Current Protection
The output overcurrent protection (OCP) is implemented using a cycle-by-cycle valley detect control circuit. The
switch current is monitored by measuring the low-side FET switch voltage between the SW pin and GND. This
voltage is proportional to the switch current. To improve accuracy, the voltage sensing is temperature
compensated.
During the on time of the high-side FET switch, the switch current increases at a linear rate determined by VIN,
VOUT, the on-time and the output inductor value. During the on time of the low-side FET switch, this current
decreases linearly. The average value of the switch current is the load current IOUT. The TPS54628 constantly
monitors the low-side FET switch voltage, which is proportional to the switch current, during the low-side on-time.
If the measured voltage is above the voltage proportional to the current limit, an internal counter is incremented
per each SW cycle and the converter maintains the low-side switch on until the measured voltage is below the
voltage corresponding to the current limit at which time the switching cycle is terminated and a new switching
cycle begins. In subsequent switching cycles, the on-time is set to a fixed value and the current is monitored in
the same manner. If the over current condition exists for 7 consecutive switching cycles, the internal OCL
threshold is set to a lower level, reducing the available output current. When a switching cycle occurs where the
switch current is not above the lower OCL threshold, the counter is reset and the OCL limit is returned to the
higher value.
There are some important considerations for this type of over-current protection. The peak current is the average
load current plus one half of the peak-to-peak inductor current. The valley current is the average load current
minus one half of the peak-to-peak inductor current. Since the valley current is used to detect the over-current
threshold, the load current is higher than the over-current threshold. Also, when the current is being limited, the
output voltage tends to fall. When the VFB voltage becomes lower than 65% of the target voltage, the UVP
comparator detects it. If the under-voltage condition persists for 250 µs, the device will shut down and re-start in
hiccup mode after 7 times the SS period. When the over current condition is removed, the output voltage will
return to the regulated value. This protection is non-latching.
Over Voltage Protection
TPS54628 detects over and under voltage conditions by monitoring the feedback voltage (VFB). This function is
enabled after approximately 1.7 x times the soft start time. When the feedback voltage becomes higher than
125% of the target voltage, the OVP comparator output goes high and both the high-side MOSFET driver and
the low-side MOSFET driver turn off. This function is non-latch operation.
UVLO Protection
Undervoltage lock out protection (UVLO) monitors the voltage of the VREG5 pin. When the VREG5 voltage is lower
than UVLO threshold voltage, the TPS54628 is shut off. This protection is non-latching.
Thermal Shutdown
TPS54628 monitors the temperature of itself. If the temperature exceeds the threshold value (typically 165°C),
the device is shut off. This is non-latch protection.
8
Copyright © 2013, Texas Instruments Incorporated
Product Folder Links :TPS54628


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