TPS5450 Datasheet, PDF (7/20 Pages) Texas Instruments – 5-A, WIDE INPUT RANGE, STEP-DOWN SWIFT CONVERTER

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APPLICATION INFORMATION
FUNCTIONAL BLOCK DIAGRAM
VIN
VIN
TPS5450
SLVS757 – MARCH 2007
ENA
NC
NC
GND
5 µA
UVLO
ENABLE
Thermal
Protection
1.221 V Bandgap
Reference
VREF
Slow Start
SHDN
SHDN
Boot
Regulator
HICCUP
SHDN
BOOT
Z1
SHDN
SHDN
Error
Amplifier
Z2
Ramp
VIN
Generator Feed Forward
Gain = 25
SHDN
PWM
Comparator
HICCUP
SHDN
Oscillator
Overcurrent
Protection
VSENSE
VSENSE
POWERPAD 112.5% VREF
OVP
Gate Drive
Control
SHDN
SHDN
Gate
Driver
BOOT
PH
VOUT
DETAILED DESCRIPTION
Oscillator Frequency
The internal free running oscillator sets the PWM switching frequency at 500 kHz. The 500 kHz switching
frequency allows less output inductance for the same output ripple requirement resulting in a smaller output
inductor.
Voltage Reference
The voltage reference system produces a precision reference signal by scaling the output of a temperature
stable bandgap circuit. The bandgap and scaling circuits are trimmed during production testing to an output of
1.221 V at room temperature.
Enable (ENA) and Internal Slow Start
The ENA pin provides electrical on/off control of the regulator. Once the ENA pin voltage exceeds the threshold
voltage, the regulator starts operation and the internal slow start begins to ramp. If the ENA pin voltage is pulled
below the threshold voltage, the regulator stops switching and the internal slow start resets. Connecting the pin
to ground or to any voltage less than 0.5 V will disable the regulator and activate the shutdown mode. The
quiescent current of the TPS5450 in shutdown mode is typically 18 µA.
The ENA pin has an internal pullup current source, allowing the user to float the ENA pin. If an application
requires controlling the ENA pin, use open drain or open collector output logic to interface with the pin. To limit
the start-up inrush current, an internal slow-start circuit is used to ramp up the reference voltage from 0 V to its
final value, linearly. The internal slow start time is 8 ms typically.
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