HIGH-SIDE DRIVER

PWM FREQUENCY AND ADAPTIVE ON-TIME CONTROL

SOFT START AND PRE-BIASED SOFTSTART

SWITCHING FREQUENCY SELECTION

OUTPUT DISCHARGE CONTROL

CURRENT PROTECTION

W ´

m

trip

trip

V

(mV) = R

(k ) 10( A)

(1)

TPS53114

floating driver, a 5V bias voltage is delivered from VREG5 supply. The average drive current is also calculated by

the gate charge at Vgs=5V times switching frequency. The instantaneous drive current is supplied by the

capacitor between VBST and SW pins. The drive capability is represented by its internal resistance.

The TPS53114 uses an adaptive on-time control scheme and does not have a dedicated on board oscillator;

however, the device runs with pseudo-constant frequency by feed-forwarding the input and output voltage into

the on-time one-shot timer. The on-time control is inversely proportional to the input voltage and proportional to

the output voltage; therefore, the duty ratio is VO/VIN and has the same cycle time.

The TPS53114 has an adjustable soft-start. When the EN pin becomes high, 2.0

µA current begins charging the

capacitor which is connected from SS pin to GND. Smooth control of the output voltage is maintained during start

up.

The TPS53114 contains a unique circuit to prevent current from being pulled from the output during startup in the

condition the output is pre-biased. When the soft-start commands a voltage higher than the pre-bias level

(internal soft-start becomes greater than feedback voltage [VFB]), the controller slowly activates synchronous

rectification by starting the first DRVL pulses with a narrow on-time. It then increments that on-time on a

cycle-by-cycle basis until it coincides with the time dictated by (1-D), where D is the duty cycle of the converter.

This scheme prevents the initial sinking of the pre-bias output, and ensures that the out voltage (VO) 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.

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-

Ω 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 zero volts.

The TPS53114 has cycle-by-cycle over current limiting control. The inductor current is monitored during the OFF

state and the controller retains the OFF state when the inductor current is larger than the over current trip level.

In order to provide both accuracy and cost effective solution, the device supports temperature compensated

The trip level is in the range of 30mV to 200mV over all operational temperatures. The inductor current is

calculated as follows:

Copyright © 2009, Texas Instruments Incorporated

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