TLV62065

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SLVSAC4 – NOVEMBER 2010

DETAILED DESCRIPTION

OPERATION

The TLV62065 step down converter operates with typically 3MHz fixed frequency pulse width modulation (PWM)

at moderate to heavy load currents. At light load currents the converter can automatically enter Power Save

Mode and operates then in PFM (Pulse Frequency Mode) mode.

During PWM operation the converter use a unique fast response voltage mode controller scheme with input

voltage feed-forward to achieve good line and load regulation allowing the use of small ceramic input and output

capacitors. At the beginning of each clock cycle initiated by the clock signal, the High Side MOSFET switch is

turned on. The current flows now from the input capacitor via the High Side MOSFET switch through the inductor

to the output capacitor and load. During this phase, the current ramps up until the PWM comparator trips and the

control logic will turn off the switch. The current limit comparator will also turn off the switch in case the current

limit of the High Side MOSFET switch is exceeded. After a dead time preventing shoot through current, the Low

Side MOSFET rectifier is turned on and the inductor current ramps down. The current flows now from the

inductor to the output capacitor and to the load. It returns back to the inductor through the Low Side MOSFET

rectifier.

The next cycle will be initiated by the clock signal again turning off the Low Side MOSFET rectifier and turning on

the High Side MOSFET switch.

POWER SAVE MODE

At TLV62065 pulling the Mode pin low enables Power Save Mode. If the load current decreases, the converter

enters Power Save Mode operation automatically. During Power Save Mode the converter skips switching and

operates with reduced frequency in PFM mode with a minimum quiescent current to maintain high efficiency. The

converter positions the output voltage typically +1% above the nominal output voltage. This voltage positioning

feature minimizes voltage drops caused by a sudden load step.

The transition from PWM mode to PFM mode occurs once the inductor current in the Low Side MOSFET switch

becomes zero, which indicates discontinuous conduction mode.

During the Power Save Mode the output voltage is monitored with a PFM comparator. As the output voltage falls

Side MOSFET switch will turn on and the inductor current ramps up. After the On-time expires the switch will be

turned off and the Low Side MOSFET switch will be turned on until the inductor current becomes zero.

The converter effectively delivers a current to the output capacitor and the load. If the load is below the delivered

current the output voltage will rise. If the output voltage is equal or higher than the PFM comparator threshold,

the device stops switching and enters a sleep mode with typ. 18µA current consumption.

In case the output voltage is still below the PFM comparator threshold, further PFM current pulses will be

generated until the PFM comparator threshold is reached. The converter starts switching again once the output

voltage drops below the PFM comparator threshold due to the load current.

The PFM mode is exited and PWM mode entered in case the output current can no longer be supported in PFM

mode.

Copyright © 2010, Texas Instruments Incorporated

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