TPS65283_15 Datasheet, PDF (19/42 Pages) Texas Instruments – TPS65283/-1 4.5- to 18-V Input Voltage, Maximum 3.5-A/2.5-A Current, Synchronous Dual Buck Converter With Power Distribution Switch

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TPS65283, TPS65283-1
SLVSCL3C – JUNE 2014 – REVISED AUGUST 2014
9.3.2.8 Short Circuit Protection
The device is protected from overcurrent conditions by cycle-by-cycle current limiting on both the high-side
MOSFET and the low-side MOSFET.
9.3.2.8.1 High-Side MOSFET Overcurrent Protection
The device implements current mode control, which uses the COMP pin voltage to control the turn off of the
high-side MOSFET and the turn on of the low-side MOSFET on a cycle by cycle basis. Each cycle the switch
current and the current reference generated by the COMP pin voltage are compared, when the peak switch
current intersects the current reference the high-side switch is turned off.
9.3.2.8.2 Low-Side MOSFET Overcurrent Protection
While the low-side MOSFET is turned on, its conduction current is monitored by the internal circuitry. During
normal operation, the low-side MOSFET sources current to the load. At the end of every clock cycle, the low-side
MOSFET sourcing current is compared to the internally-set low-side sourcing current limit. If the low-side
sourcing current is exceeded, the high-side MOSFET is not turned on and the low-side MOSFET stays on for the
next cycle. The high-side MOSFET is turned on again when the low-side current is below the low-side sourcing
current limit at the start of a cycle.
The low-side MOSFET may also sink current from the load. If the low-side sinking current limit is exceeded, the
low-side MOSFET is turned off immediately for the rest of that clock cycle. In this scenario, both MOSFETs are
off until the start of the next cycle.
Furthermore, if an output overload condition (as measured by the COMP pin voltage) has lasted for more than
the hiccup wait time, which is programmed for 4 ms, the device shuts down and restarts after the hiccup time of
64 ms. The hiccup mode helps to reduce the device power dissipation under severe overcurrent conditions
Vout
Current limit threshold
IL
4 ms
VLX
64 ms
Figure 28. DC-DC Overcurrent Protection
9.3.2.9 Bootstrap Voltage (BST) and Low Dropout Operation
The device has an integrated boot regulator and requires a small ceramic capacitor between the BST and LX
pins to provide the gate drive voltage for the high-side MOSFET. The boot capacitor is charged when the BST
pin voltage is less than VIN and BST-LX voltage is below regulation. The value of this ceramic capacitor should
be 47 nF. TI recommends a ceramic capacitor with an X7R or X5R grade dielectric with a voltage rating of 10 V
or higher because of the stable characteristics over temperature and voltage. To improve dropout, the device is
designed to operate at 100% duty cycle as long as the BST to LX pin voltage is greater than the BST-LX UVLO
threshold, which is typically 2.1 V. When the voltage between BST and LX drops below the BST-LX UVLO
threshold, the high-side MOSFET is turned off and the low-side MOSFET is turned on allowing the boot capacitor
to be recharged.
Copyright © 2014, Texas Instruments Incorporated
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