TPS62080 Datasheet, PDF (14/28 Pages) Texas Instruments – 1.2A High Efficient Step Down Converter in 2x2mm SON Package

TPS62080, TPS62080A
TPS62081, TPS62082
SLVSAE8B – SEPTEMBER 2011 – REVISED MARCH 2012
www.ti.com
R_DS(on) = High side FET on-resistance
R_L = Inductor ohmic resistance
ENABLING / DISABLING THE DEVICE
The device is enabled by setting the EN input to a logic HIGH. Accordingly, a logic LOW disables the device. If
the device is enabled, the internal power stage will start switching and regulate the output voltage to the
programmed threshold. The EN input must be terminated with a resistance less than 1MΩ pulled to VIN or GND.
OUTPUT DISCHARGE
The output gets discharged by the SW pin with a typical discharge resistor of R_DIS whenever the device shuts
down. This is the case when the device gets disabled by enable, thermal shutdown trigger, and undervoltage
lockout trigger.
SOFT START
After enabling the device, an internal soft-start circuitry monotonically ramps up the output voltage and reaches
the nominal output voltage during a soft start time (100µs, typical). This avoids excessive inrush current and
creates a smooth output voltage rise slope. It also prevents excessive voltage drops of primary cells and
rechargeable batteries with high internal impedance.
If the output voltage is not reached within the soft start time, such as in the case of heavy load, the converter will
enter regular operation. Consequently, the inductor current limit will operate as described below. The TPS6208x
is able to start into a pre-biased output capacitor. The converter starts with the applied bias voltage and ramps
the output voltage to its nominal value.
POWER GOOD
The TPS6208x has a power good output going low when the output voltage is below its nominal value. The
power good keeps high impedance once the output is above 95% of the regulated voltage, and is driven to low
once the output voltage falls below typically 90% of the regulated voltage. The PG pin is a open drain output and
is specified to sink typically up to 0.5mA. The power good output requires a pull up resistor that is recommended
connecting to the device output. When the device is off due to disable, UVLO or thermal shutdown, the PG pin is
at high impedance.
The PG signal can be used for sequencing of multiple rails by connecting to the EN pin of other converters.
Leave the PG pin unconnected when not used.
UNDER VOLTAGE LOCKOUT
To avoid mis-operation of the device at low input voltages, an under voltage lockout is implemented, that shuts
down the device at voltages lower than V_UVLO with a V_{HYS_UVLO} hysteresis.
THERMAL SHUTDOWN
The device goes into thermal shutdown once the junction temperature exceeds typically T_JSD. Once the device
temperature falls below the threshold the device returns to normal operation automatically.
INDUCTOR CURRENT LIMIT
The Inductor Current Limit prevents the device from high inductor current and drawing excessive current from the
battery or input voltage rail. Excessive current might occur with a shorted/saturated inductor or a heavy
load/shorted output circuit condition.
The incorporated inductor peak current limit measures the current during the high side and low side power
MOSFET on-phase in PWM mode. Once the high side switch current limit is tripped, the high side MOSFET is
turned off and the low side MOSFET is turned on to reduce the inductor current. Until the inductor current drops
down to low side switch current limit, the low side MOSFET is turned off and the high side switch is turned on
again. This operation repeats until the inductor current does not reach the high side switch current limit. Due to
the internal propagation delay, the real current limit value can exceed the static current limit in the electrical
characteristics table.
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