Datasheet

TPS61253, TPS61254, TPS61256
TPS61258, TPS61259
www.ti.com SLVSAG8C –SEPTEMBER 2011–REVISED AUGUST 2012
ENABLE
The TPS6125x device starts operation when EN is set high and starts up with the soft-start sequence. For proper
operation, the EN pin must be terminated and must not be left floating.
Pulling the EN and BP pins low forces the device in shutdown, with a shutdown current of typically 1µA. In this
mode, true load disconnect between the battery and load prevents current flow from V
IN
to V
OUT
, as well as
reverse flow from V
OUT
to V
IN
.
Pulling the EN pin low and the BP pin high forces the device in standby mode, refer to the STANDBY MODE
section for more details.
LOAD DISCONNECT AND REVERSE CURRENT PROTECTION
Regular boost converters do not disconnect the load from the input supply and therefore a connected battery will
be discharge during shutdown. The advantage of TPS6125x is that this converter is disconnecting the output
from the input of the power supply when it is disabled (so called true shutdown mode). In case of a connected
battery it prevents it from being discharge during shutdown of the converter.
SOFTSTART
The TPS6125x device has an internal softstart circuit that limits the inrush current during start-up. The first step
in the start-up cycle is the pre-charge phase. During pre-charge, the rectifying switch is turned on until the output
capacitor is charged to a value close to the input voltage. The rectifying switch is current limited (approx. 200mA)
during this phase. This mechanism is used to limit the output current under short-circuit condition.
Once the output capacitor has been biased to the input voltage, the converter starts switching. The soft-start
system progressively increases the on-time as a function of the input-to-output voltage ratio. As soon as the
output voltage is reached, the regulation loop takes control and full current operation is permitted.
UNDERVOLTAGE LOCKOUT
The under voltage lockout circuit prevents the device from malfunctioning at low input voltages and the battery
from excessive discharge. It disables the output stage of the converter once the falling V
IN
trips the under-voltage
lockout threshold V
UVLO
which is typically 2.0V. The device starts operation once the rising V
IN
trips V
UVLO
threshold plus its hysteresis of 100 mV at typ. 2.1V.
THERMAL REGULATION
The TPS6125x device contains a thermal regulation loop that monitors the die temperature during the pre-charge
phase. If the die temperature rises to high values of about 110 °C, the device automatically reduces the current
to prevent the die temperature from increasing further. Once the die temperature drops about 10 °C below the
threshold, the device will automatically increase the current to the target value. This function also reduces the
current during a short-circuit condition.
THERMAL SHUTDOWN
As soon as the junction temperature, T
J
, exceeds 140°C (typ.) the device goes into thermal shutdown. In this
mode, the high-side and low-side MOSFETs are turned-off. When the junction temperature falls below the
thermal shutdown minus its hysteresis, the device continuous the operation.
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