TPS40190
www.ti.com
SLUS658A–JULY 2005–REVISED AUGUST 2005
Enable Functionality
The TPS40190 has a dedicated ENABLE pin. This simplifies user level interface design since no multiplexed
functions exist. Another benefit is a true low power shutdown mode of operation. When the ENABLE pin is pulled
to GND, the TPS40190 consumes a typical 20-µA of current. A functionally equivalent circuit to the enable
circuitry on the TPS40190 is shown in Figure 4.
VDD
4
200 kΩ
1.5 MΩ
1 kΩ
ENABLE
1
To
Enable
Chip
200 Ω
1 kΩ
300 kΩ
GND
5
UDG−05061
Figure 4. TPS40190 ENABLE Pin Internal Circuitry
If the ENABLE pin is left floating, the chip starts automatically. The pin must be pulled to less than 600 mV to
guarantee that the TPS40190 is in shutdown mode. Note that the ENABLE pin is relatively high impedance. In
some situations, there could be enough noise nearby to cause the ENABLE pin to swing below the 600 mV
threshold and give erroneous shutdown commands to the rest of the device. There are two solutions to this
problem should it arise.
1. Place a capacitor from ENABLE to GND. A side effect of this is to delay the start of the converter while the
capacitor charges past the enable threshold
2. Place a resistor from VDD to ENABLE. This causes more current to flow in the shutdown mode, but does not
delay converter startup. If a resistor is used, the total current into the ENABLE pin should be limited to no
more than 500 µA.
9
TI [ TEXAS INSTRUMENTS ]
