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TPS61252DGST Datasheet(PDF) 15 Page - Texas Instruments

No. de Pieza. TPS61252DGST
Descripción  TPS61252 Tiny 1.5-A Boost Converter With Adjustable Input Current Limit
Descarga  27 Pages
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Fabricante  TI1 [Texas Instruments]
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TPS61252DGST Datasheet(HTML) 15 Page - Texas Instruments

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DC Bias effect: High capacitance ceramic capacitors have a DC Bias effect, which has a
strong influence on the final effective capacitance. Therefore the right capacitor value has
to be chosen very carefully. Package size and voltage rating in combination with dielectric
material are responsible for differences between the rated capacitor value and the
effective capacitance. A 10 V rated 0805 capacitor with 10 µF can have a effective
capacitance of less than 5 µF at an output voltage of 5 V. Checking Loop Stability
The first step of circuit and stability evaluation is to look from a steady-state perspective at the following signals:
Switch node, SW
Inductor current, IL
Output ripple voltage, VOUT(AC)
These are the basic signals that need to be measured when evaluating a switching converter. When the
switching waveform shows large duty cycle jitter or the output voltage or inductor current shows oscillations, the
regulation loop may be unstable. This is often a result of board layout and/or L-C combination.
As the next step in the evaluation of the regulation loop, the load transient response is tested. During the time
between when the load transient takes place and the turn on of the high side switch, the output capacitor must
supply all of the current required by the load. VOUT immediately shifts by an amount equal to ΔI(LOAD) x ESR,
where ESR is the effective series resistance of COUT. ΔI(LOAD) begins to charge or discharge COUT, generating a
feedback error signal used by the regulator to return VOUT to its steady-state value. The results are most easily
interpreted when the device operates in PWM mode.
During this recovery time, VOUT can be monitored for settling time, overshoot or ringing that helps judge the
converter’s stability. Without any ringing, the loop has usually more than 60° of phase margin. Because the
damping factor of the circuitry is directly related to several resistive parameters (for example, MOSFET rDS(on))
that are temperature dependant, the loop stability analysis has to be done over the input voltage range, load
current range, and temperature range.
11.2.3 Application Curves
Load transient response (VIN = 3.6 V, VOUT = 5.0V, ILIM = 500mA, Load change from 20 mA to 300 mA)
Figure 10
Load transient response (VIN = 3.6 V, VOUT = 5.0V, VIN > VOUT, ILIM = 1000mA, Load change from 50 mA to
Figure 11
550 mA)
Startup after enable (VOUT = 5.0 V, VIN = 3.6 V, ILIM = 500mA)
Figure 12
Startup after enable (VOUT = 5.0 V, VIN = 3.6 V, ILIM = 1000mA)
Figure 13
Startup after enable in 500 mA load (VOUT = 5.0 V, VIN = 3.6 V, ILIM = 1000mA)
Figure 14
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