TPS82740A, TPS82740B

SLVSCE3A – JUNE 2014 – REVISED JUNE 2014

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Feature Description (continued)

voltage and superior load transient regulation, combined with very low output voltage ripple, minimizing

interference with RF circuits. At high load currents, the converter operates in quasi fixed frequency PWM mode

operation and at light loads in PFM (Pulse Frequency Modulation) mode to maintain highest efficiency over the

full load current range. In PFM Mode, the device generates a single switching pulse to ramp up the inductor

current and recharge the output capacitor, followed by a sleep period where most of the internal circuits are

shutdown to achieve the lowest quiescent current. During this time, the load current is supported by the output

capacitor. The duration of the sleep period depends on the load current and the inductor peak current.

During the sleep periods, the quiescent current of the TPS82740 is reduced to 360nA. This low quiescent current

consumption is achieved by an ultra low power voltage reference, an integrated high impedance (typ. 50M

Ω)

feedback divider network and an optimized DCS-Control™ block.

10.3.2 LOAD Switch

The LOAD pin can be used to power an additional, temporarily used sub-system. If the CTRL pin is set high, the

LOAD pin is connected to the VOUT pin via an integrated load switch. The load switch is slew rate controlled to

support soft switching and not impacting the regulated output VOUT. If the CTRL pin is set to low, the LOAD pin

is disconnected from the VOUT pin and internally connected to GND by an internal discharge switch. The CTRL

pin can be controlled by a micro controller and must be terminated. With CTRL pin high, the quiescent current is

increased to improve the transient response.

10.3.3 Output Voltage Selection (VSEL1, VSEL2, VSEL3)

The TPS82740 provides an integrated, high impedance (typ. 50M

Ω) feedback resistor divider network which is

programmed by the pins VSEL1-3. The TPS82740A supports an output voltage range of 1.8V to 2.5V in 100mV

steps, while the TPS82740B supports an output voltage range from 2.6V to 3.3V in 100mV steps. The output

voltage can be changed during operation and supports a simple dynamic output voltage scaling, shown in

Figure 44. The output voltage is programmed according to Table 2 and Table 3.

10.3.4 Output Discharge Function (VOUT and LOAD)

Both the VOUT pin and the LOAD pin feature a discharge circuit to connect each rail to GND, once they are

disabled. This feature prevents residual charge voltages on capacitors connected to these pins, which may

impact proper power up of the main- and sub-system. With the CTRL pin pulled low, the discharge circuit at the

LOAD pin activates. With the EN pin pulled low, the discharge circuit at the pin VOUT activates.

10.3.5 Internal Current Limit

The TPS82740 integrates a current limit in the high side, as well as in the low side MOSFETs to protect the

device against overload or short circuit conditions. The peak current in the switches is monitored cycle by cycle.

If the high side MOSFET current limit is reached, the high side MOSFET is turned off and the low side MOSFET

is turned on until the current decreases below the low side MOSFET current limit.

10.4 Device Functional Modes

10.4.1 Enable / Shutdown

The TPS82740 is activated when the EN pin is set high. For proper operation, the pin must be terminated and

must not be left floating. With the EN pin set low, the device enters shutdown mode with less than typ. 70nA

current consumption.

10.4.2 Softstart

expired, the device enters softstart, starts switching and ramps up the output voltage. During softstart, the device

expired or the nominal output voltage is reached.

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