Datasheet

V
IT BYP rising
V
IT BYP falling
DC/DC
Stepdown
Mode
Bypass
Operation
Battery
Voltage
ON/BYP
TPS62732, TPS62733
TPS62730
www.ti.com SLVSAC3C –MAY 2011–REVISED DECEMBER 2012
START UP
Once the device is supplied with a battery voltage, the bypass switch is activated. If the ON/BYP pin is set to
high, the device operates in bypass mode until the DC/DC converter has settled and can kick in. During start up,
high peak currents can flow over the bypass switch to charge up the output capacitor and the additional
decoupling capacitors in the system.
AUTOMATIC TRANSITION FROM DC/DC TO BYPASS OPERATION
With pin ON/BYP set to high, the TPS62730 features an automatic transition between DC/DC and bypass mode
to reduce the output ripple voltage to zero. Once the input voltage comes close to the output voltage of the
DC/DC converter, the DC/DC converters operates close to 100% duty cycle operation. At this operating
condition, the switch frequency would start to drop and would lead to increased output ripple voltage. The internal
bypass switch is turned on once the battery voltage at VIN trips the Automatic Bypass Transition Threshold VIT
BYP for falling VIN. The DC/DC regulator is turned off and therefore it generates no output ripple voltage. Due to
the output is connected via the bypass switch to the input, the output voltage follows the input voltage minus the
voltage drop across the internal bypass switch. In this mode the current consumption of the DC/DC converter is
reduced to typically 23µA. Once the input voltage increases and trips the bypass deactivation threshold VIT BYP
for rising VIN, the DC/DC regulator turns on and the bypass switch is turned off.
INTERNAL CURRENT LIMIT
The TPS62730 integrates a High Side and Low Side MOSFET current limit to protect the device against heavy
load or short circuit when the DC/DC converter is active. The current in the switches is monitored by current limit
comparators. When the current in the High Side MOSFET reaches its current limit, the High Side MOSFET is
turned off and the Low Side MOSFET is turned on to ramp down the current in the inductor. The High Side
MOSFET switch can only turn on again, once the current in the Low Side MOSFET switch has decreased below
the threshold of its current limit comparator. The bypass switch doesn't feature a current limit to support lowest
current consumption.
Figure 28. Operation Mode Diagram with ON/BYP = High
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Product Folder Links: TPS62732 TPS62733 TPS62730