Datasheet
TPS65735
SLVSAI6–JUNE 2011
www.ti.com
2.9.2 Boost Load Disconnect
When the boost is disabled (BST_EN = LOW), the H-bridge is automatically placed into the OFF state. In
the OFF state the high side H-bridge switches are open and the low side switches of the H-bridge are
closed. The OFF state grounds and discharges the load, potentially prolonging the life of the LC shutters
by eliminating any DC content (see Section 2.10.1 for more information regarding the H-bridge states).
The disconnection of the load is done with the H-Bridge and can be seen in the next figure (Figure 2-10).
Figure 2-10. Boost Load Disconnect
An advantage to this topology for disconnecting the load is that the boost output capacitor is charged to
approximately the SYS voltage level, specifically V
SYS
- V
DIODE(BST)
, when the boost is disabled. This
design ensures that there is not a large in-rush current into the boost output capacitor when the boost is
enabled. The boost operation efficiency is also increased because there is no load disconnect switch in
the boost output path, such a switch would decrease efficiency because of the resistance that it would
introduce.
2.10 Full H-Bridge Analog Switches
The TPS65735 has two integrated full H-bridge analog switches that can be connected to GPIOs of a host
microcontroller. There is an internal level shifter that takes care of the input signals to the H-Bridge
switches.
2.10.1 H-Bridge Switch Control
The H-Bridge switches are controlled by an external microcontroller for system operation - specifically to
control charge polarity on the LCD shutters. Depending on the state of the signals from the
microcontroller, the H-Bridge will be put into 4 different states. These states are:
• OPEN: All Switches Opened
• CHARGE+: Boost Output Voltage Present on Pins LCLP or LCRP
• CHARGE-: Boost Output Voltage Present on Pins LCLN or LCRN
• GROUNDED: High side switches are opened and low side switches are closed
20 POWER MANAGEMENT CORE Copyright © 2011, Texas Instruments Incorporated
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