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SLVS887B – APRIL 2009 – REVISED OCTOBER 2010
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PWM FREQUENCY AND ADAPTIVE ON-TIME CONTROL
TPS53114 employs adaptive on-time control scheme and does not have a dedicated on board oscillator.
TPS53114 runs with pseudo-constant frequency by using the input voltage and output voltage to set the on-time
one-shot timer. The on-time is inversely proportional to the input voltage and proportional to the output voltage.
Therefore, when the duty ratio is VOUT/VIN, the frequency is constant.
5-VOLT REGULATOR
The TPS53114 has an internal 5-V low-dropout (LDO) Regulator to provide a regulated voltage for all both
drivers and the IC's internal logic. A high-quality 4.7-mF or greater ceramic capacitor from VREG5 to GND is
required to stabilize the internal regular. An internal 10-
resistor from VREG5 filters the regulator output to the
IC's analog and logic input voltage, V5FILT. An additional high-quality 1.0-mF ceramic capacitor is required from
V5FILT to GND to filter switching noise from VREG5.
SOFT START
The TPS53114 has a programmable soft start . When the EN pin becomes high, 2.0-mA current begins charging
the capacitor which is connected SS pin to GND. Smooth control of the output voltage is maintained during start
up.
PRE-BIAS SUPPORT
The TPS53114 supports pre-bias start-up without sinking current from the output capacitor. When enabled, the
low-side driver is held off until the soft start commands a voltage higher than the pre-bias level (internal soft start
becomes greater than feedback voltage (VFB)), then the TPS53114 slowly activates synchronous rectification by
limiting the first DRVL pulses with a narrow on-time. This limited on-time is then incremented on a cycle-by-cycle
basis until it coincides with the full 1-D off-time. This scheme prevents the initial sinking of current from the
pre-bias output, and ensure that the output voltage (VOUT) starts and ramps up smoothly into regulation and the
control loop is given time to transition from pre-biased start-up to normal mode operation.
SWITCHING FREQUENCY SELECTION
The TPS53114 allows the user to select from two different switching frequencies by connecting the FSEL pin to
either GND or V5FILT. Connect FSEL to GND for a switching frequency (fsw) of 350 KHz. Connect FSEL to
V5FILT for a switching frequency of 700 KHz.
OUTPUT DISCHARGE CONTROL
The TPS53114 discharges the outputs when EN is low, or the controller is turned off by the protection functions
(OVP, UVP, UVLO, and thermal shutdown). The device discharges output using an internal 40-
MOSFET which
is connected to VO and PGND. The external low-side MOSFET is not turned on during the output discharge
operation to avoid the possibility of causing negative voltage at the output. This discharge ensures that, on start,
the regulated voltage always initializes from 0 V.
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