TPS54526

SLVSB84 – MAY 2012

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VREG5

VREG5 is an internally generated voltage source used by the TPS54526. It is derived directly from the input

voltage and is nominally regulated to 5.5 V when the input voltage is above 5.6 V. The output of the VREG5

regulator is the input to the internal UVLO function. VREG5 must be above the UVLO wake up threshold voltage

(3.6 V typical) for the TPS54526 to function. Connect a 1.0 µF capacitor between pin 3 of the TPS54526 and

power ground for proper regulation of the VREG5 output. The VREG5 output voltage is available for external

use. It is recommended to use no more than 5 mA for external loads. The VREG5 output is disabled when the

TPS54526 EN pin is open or pulled low.

Output Discharge Control

TPS54526 discharges the output when EN is low, or the controller is turned off by the protection functions (OVP,

UVP, UVLO and thermal shutdown). The output is discharged by an internal 50-

Ω MOSFET which is connected

from VO to PGND. The internal low-side MOSFET is not turned on during 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.

above the voltage proportional to the current limit. Then, the device constantly monitors the low-side FET switch

voltage, which is proportional to the switch current, during the low-side on-time.

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.

There are some important considerations for this type of overcurrent protection. The load current one half of the

peak-to-peak inductor current higher than the overcurrent threshold. Also when the current is being limited, the

output voltage tends to fall as the demanded load current may be higher than the current available from the

converter. This may cause the output under-voltage protection circuit to be activated. When the overcurrent

condition is removed, the output voltage will return to the regulated value. This protection is non-latching.

Over/Under Voltage Protection

TPS54526 monitors a resistor divided feedback voltage to detect over and under voltage. When the feedback

voltage becomes higher than 125% of the target voltage, the OVP comparator output goes high and the circuit

latches as the high-side MOSFET driver turns off and the low-side MOSFET turns on. When the feedback

voltage becomes lower than 65% of the target voltage, the UVP comparator output goes high and an internal

UVP delay counter begins. After 250

μs, the device latches off both internal top and bottom MOSFET. This

function is enabled approximately 1.7 x softstart time.

UVLO Protection

than UVLO threshold voltage, the TPS54526 is shut off. This is protection is non-latching.

Thermal Shutdown

TPS54526 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.

SPACER

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Product Folder Link(s) :TPS54526