TPS62692 Datasheet, PDF (20/29 Pages) Texas Instruments – 800-mA , 3-MHz HIGH-EFFICIENCY STEP-DOWN CONVERTER

TPS62692, TPS62693
TPS62694, TPS62698
SLVSAZ1 – DECEMBER 2012
www.ti.com
With:
I_OUTmax = Maximum output current, plus inductor ripple current.
R_DS(on)max = Maximum P-channel MOSFET R_DS(on).
R_L = Inductor DC resistance.
V_OUTmax = Nominal output voltage, plus maximum output voltage tolerance.
ENABLE
The TPS62692 device starts operation when EN is set high and starts up with the soft start as previously
described. For proper operation, the EN pin must be terminated and must not be left floating.
Pulling the EN pin low forces the device into shutdown, with a shutdown quiescent current of typically 0.2 μA. In
this mode, the P and N-channel MOSFETs are turned off, the internal resistor feedback divider is disconnected,
and the entire internal-control circuitry is switched off.
The TPS62692 device can actively discharge the output capacitor when it turns off. The integrated discharge
resistor has a typical resistance of 100 Ω. The required time to discharge the output capacitor at the output node
depends on load current and the output capacitance value.
SOFT START
The TPS62692 has an internal soft-start circuit that limits the inrush current during start-up. This limits input
voltage drops when a battery or a high-impedance power source is connected to the input of the converter.
In the TPS62692, the soft start is implemented as a digital circuit increasing the switch current in steps of
typically 300 mA, 700 mA, 1000 mA, and the typical switch current limit of 1250 mA. During the first phase the
soft-start system progressively increases the on-time from a minimum pulse-width of 35 ns as a function of the
output voltage, resulting in an current limit of approximately 300mA in this phase. The current limit transitions to
the next step every 256 clocks (≈ 88us). To be able to switch from 700 mA to 1000 mA current limit step, the
output voltage needs to be higher than 0.6 V (otherwise the parts keeps operating at 700 mA current limit).
After the soft-start time has exceeded and the output voltage settled at its nominal value, the converter supports
the full load curent.
UNDERVOLTAGE LOCKOUT
The undervoltage lockout circuit prevents the device from misoperation at low input voltages. It prevents the
converter from turning on the switch or rectifier MOSFET under undefined conditions. The TPS62692 device has
an UVLO threshold set to 2.05V (typical). Fully functional operation is permitted down to 2.1 V input voltage.
SHORT-CIRCUIT PROTECTION
The TPS62692 integrates a P-channel MOSFET current limit to protect the device against heavy load or short
circuits. When the current in the P-channel MOSFET reaches its current limit, the P-channel MOSFET is turned
off and the N-channel MOSFET is turned on. The regulator continues to limit the current on a cycle-by-cycle
basis.
As soon as the output voltage falls below ca. 0.4 V, the converter current limit is reduced to half of the nominal
value. Because the short-circuit protection is enabled during start-up, the device does not deliver more than half
of its nominal current limit until the output voltage exceeds approximately 0.5 V. This needs to be considered
when a load acting as a current sink is connected to the output of the converter.
THERMAL SHUTDOWN
As soon as the junction temperature, T_J, exceeds typically 140°C, the device goes into thermal shutdown. In this
mode, the P- and N-channel MOSFETs are turned off. The device continues its operation when the junction
temperature again falls below typically 130°C.
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