TPS65263_16 Datasheet, PDF (21/46 Pages) Texas Instruments – 4.5- to 18-V Input Voltage, 3-A/2-A/2-A Output Current Triple Synchronous Step-Down Converter With I2C Controlled Dynamic Voltage Scaling

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TPS65263
SLVSCN0A – JUNE 2014 – REVISED SEPTEMBER 2014
Due to the delay in the circuit and current comparator tdly (typical 50 nS at Vin = 12 V), the real peak inductor
current threshold to turn off high-side power MOSFET could shift higher depending on inductor inductance and
input/output voltages. The threshold of peak inductor current to turn off high-side power MOSFET can be
calculated by Equation 6.
IL_PEAK
= 230mA
+
vin - vout
L
´ tdly
(6)
When the charge accumulated on Vout capacitor is more than loading need, COMP pin voltage drops to low
voltage driven by error amplifier. There is an internal comparator at COMP pin. If comp voltage is lower than 0.35
V, power stage stops switching to save power.
230mA
IL_Peak
Inductor Peak Current
Inductor
Current Peak
Current
Sensing
x1
Turn off
high-side Power MOSFET
Current Comparator
Delay: tdly
Figure 30. PSM Current Comparator
9.3.9 Slope Compensation
In order to prevent the sub-harmonic oscillations when the device operates at duty cycles greater than 50%, the
TPS65263 adds built-in slope compensation, which is a compensating ramp to the switch current signal.
9.3.10 Overcurrent 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.
9.3.10.1 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.
9.3.10.2 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 0.5 ms (typical) shown in Figure 31, the device will shut down itself
and restart after the hiccup time of 14 ms (typical). The hiccup mode helps to reduce the device power
dissipation under severe overcurrent condition.
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