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參數資料
| 型號： | TPS5420MDREP |
| 廠商： | TEXAS INSTRUMENTS INC |
| 元件分類： | 穩壓器 |
| 英文描述： | 5.2 A SWITCHING REGULATOR, 600 kHz SWITCHING FREQ-MAX, PDSO8 |
| 封裝： | GREEN, PLASTIC, MS-012AA, SOIC-8 |
| 文件頁數： | 21/23頁 |
| 文件大小： | 658K |
| 代理商： | TPS5420MDREP |
www.ti.com
Undervoltage Lockout (UVLO)
Boost Capacitor (BOOT)
Output Feedback (VSENSE)
Internal Compensation
Voltage Feed Forward
FeedForwardGain=
VIN
Ramppk-pk
(1)
Pulse-Width-Modulation (PWM) Control
Overcurrent Protection
SLVS717 – DECEMBER 2006
APPLICATION INFORMATION (continued)
The TPS5420 incorporates an undervoltage lockout circuit to keep the device disabled when VIN (the input
voltage) is below the UVLO start voltage threshold. During power up, internal circuits are held inactive until VIN
exceeds the UVLO start threshold voltage. Once the UVLO start threshold voltage is reached, device start-up
begins. The device operates until VIN falls below the UVLO stop threshold voltage. The typical hysteresis in the
UVLO comparator is 330 mV.
Connect a 0.01-
F low-ESR ceramic capacitor between the BOOT pin and PH pin. This capacitor provides the
gate drive voltage for the high-side MOSFET. X7R or X5R grade dielectrics are recommended due to their
stable values over temperature.
The output voltage of the regulator is set by feeding back the center point voltage of an external resistor divider
network to the VSENSE pin. In steady-state operation, the VSENSE pin voltage should be equal to the voltage
reference 1.221 V.
The TPS5420 implements internal compensation to simplify the regulator design. Since the TPS5420 uses
voltage mode control, a type 3 compensation network has been designed on chip to provide a high crossover
frequency and a high phase margin for good stability. See the Internal Compensation Network in the
applications section for more details.
The internal voltage feed forward provides a constant dc power stage gain, despite any variations with the input
voltage. This greatly simplifies the stability analysis and improves the transient response. Voltage feed forward
varies the peak ramp voltage inversely with the input voltage so that the modulator and power stage gain are
constant at the feed forward gain:
The typical feed-forward gain of TPS5420 is 25.
The regulator employs a fixed-frequency pulse-width-modulator (PWM) control method. First, the feedback
voltage (VSENSE pin voltage) is compared to the constant voltage reference by the high-gain error amplifier and
compensation network to produce a error voltage. Then, the error voltage is compared to the ramp voltage by
the PWM comparator. In this way, the error voltage magnitude is converted to a pulse width that is the duty
cycle. Finally, the PWM output is fed into the gate drive circuit to control the on time of the high-side MOSFET.
Overcurrent protection is implemented by sensing the drain-to-source voltage across the high-side MOSFET.
The drain to source voltage is then compared to a voltage level representing the overcurrent threshold limit. If
the drain-to-source voltage exceeds the overcurrent threshold limit, the overcurrent indicator is set true. The
system ignores the overcurrent indicator for the leading-edge blanking time at the beginning of each cycle to
avoid any turn-on noise glitches.
Once overcurrent indicator is set true, overcurrent protection is triggered. The high-side MOSFET is turned off
for the rest of the cycle after a propagation delay. The overcurrent protection scheme is called cycle-by-cycle
current limiting.
7
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