Datasheet

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IND(ripple)
IN OUT OUT
OCL
EXT EXT X SW IN
I
V V V
25mV 25mV 1
I
R 2 R 2 L f V
TPS51219
SLUSAG1B – MARCH 2011– REVISED OCTOBER 2011 www.ti.com
Overcurrent limiting using resistor sensing is shown in Equation 9.
where
• I
IND(ripple)
is inductor ripple current
• R
EXT
is the external current sense resistance (9)
In an overcurrent condition, the current to the load exceeds the current to the output capacitor, thus the output
voltage tends to fall down. Eventually, it crosses the undervoltage protection threshold and shuts down.
Overvoltage and Undervoltage Protection
The TPS51219 sets the overvoltage protection (OVP) when VSNS voltage reaches a level 20% (typ) higher than
the REFIN voltage. When an OV event is detected, the controller changes the output target voltage to 0 V. This
usually turns off DH and forces DL to be on. When the inductor current begins to flow through the low-side
MOSFET and reaches the negative OCL, DL is turned off and DH is turned on, for a minimum on-time.
After the minimum on-time expires, DH is turned off and DL is turned on again. This action minimizes the output
node undershoot due to LC resonance. When the VSNS reaches 0 V, the driver output is latched as DH off, DL
on.
The undervoltage protection (UVP) latch is set when the VSNS voltage remains lower than 68% (typ) of the
REFIN voltage for 1 ms or longer. In this fault condition, the controller latches DH low and DL low and discharges
the V
OUT
. UVP detection function is enabled after 1.2 ms of SMPS operation to ensure startup.
To release the OVP and UVP latches, toggle EN or adjust the V5 voltage down and up beyond the undervoltage
lockout threshold.
V5 Undervoltage Lockout Protection
TPS51219 has a 5-V supply undervoltage lockout protection (UVLO) threshold. When the V5 voltage is lower
than UVLO threshold voltage, typically 3.9 V, V
OUT
is shut off. This is a non-latch protection.
Thermal Shutdown
TPS51219 includes an internal temperature monitor. If the temperature exceeds the threshold value, 140°C (typ),
V
OUT
is shut off. The state of V
OUT
is open at thermal shutdown. This is a non-latch protection and the operation
is restarted with soft-start sequence when the device temperature is reduced by 10°C (typ).
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