L6920D ,1V HIGH EFFICIENCY SYNCHRONOUS STEP UP CONVERTERABSOLUTE MAXIMUM RATINGSSymbol Parameter Value UnitV V to GND 6 Vccmax ccLBI, SHDN, FB to GND 6 VV ..
L6920DB ,Synchronous rectifier step up converterfeatures■ 0.8V start up input voltage■ Up to 5.5V operating input voltage■ Internal synchronous rec ..
L6920DBTR ,Synchronous rectifier step up converterElectrical characteristics . . . . . 54 Typical performance . 65 Detailed description ..
L6920DBTR ,Synchronous rectifier step up converterApplicationsto the selected output voltage.■ Conversion from 1 to 3 alkaline,The minimum output vol ..
L6920DCTR ,Synchronous rectifier step up converterElectrical characteristics . . . . . 54 Typical performance . 65 Detailed description ..
L6920DTR ,1V HIGH EFFICIENCY SYNCHRONOUS STEP UP CONVERTERFeatures■ 0.6 TO 5.5V OPERATING INPUT VOLTAGE■ 1V START UP INPUT VOLTAGE■ INTERNAL SYNCHRONOUS RECT ..
LC4128B-10TN100I , 3.3V/2.5V/1.8V In-System Programmable SuperFAST High Density PLDs
LC4128B-75T128C , 3.3V/2.5V/1.8V In-System Programmable SuperFAST High Density PLDs
LC4128B-75TN100C , 3.3V/2.5V/1.8V In-System Programmable SuperFAST High Density PLDs
LC4128C-75T100C , 3.3V/2.5V/1.8V In-System Programmable SuperFAST High Density PLDs
LC4128C-75T100C , 3.3V/2.5V/1.8V In-System Programmable SuperFAST High Density PLDs
LC4128C-75T100I , 3.3V/2.5V/1.8V In-System Programmable SuperFAST High Density PLDs
L6920D
1V HIGH EFFICIENCY SYNCHRONOUS STEP UP CONVERTER
1/12
L6920January 2003 0.6 TO 5.5V OPERATING INPUT VOLTAGE 1V START UP INPUT VOLTAGE INTERNAL SYNCHRONOUS RECTIFIER ZERO SHUT DOWN CURRENT 3.3V AND 5V FIXED OR ADJUSTABLE
OUTPUT VOLTAGE (2V UP TO 5.2V) 120mΩ INTERNAL ACTIVE SWITCH LOW BATTERY VOLTAGE DETECTION REVERSE BATTERY PROTECTION
Applications ONE TO THREE CELL BATTERY DEVICES PDA AND HAND HELD INSTRUMENTS CELLULAR PHONES - DIGITAL CORDLESS
PHONE PAGERS GPS DIGITAL CAMERAS
DESCRIPTIONThe L6920 is a high efficiency step-up controller re-
quiring only three external components to realize the
conversion from the battery voltage to the selected
output voltage.
The start up is guaranteed at 1V and the device is op-
erating down to 0.6V.
Internal synchronous rectifier is implemented with a
120mΩ P-channel MOSFET and, in order to improve
the efficiency, a variable frequency control is imple-
mented.
1V HIGH EFFICIENCY SYNCRONOUS STEP UP CONVERTER
APPLICATION CIRCUIT
L6920 2/12
PIN DESCRIPTION
PIN CONNECTION (Top view)
ABSOLUTE MAXIMUM RATINGS
THERMAL DATA
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L6920
ELECTRICAL CHARACTERISTCS (Vin = 2V, FB = GND, Tamb = -40°C to 85°C and Tj < 125°C unless other-wise specified))
L6920 4/12
Figure 1. Efficiency vs. Output Current
Figure 2. Efficiency vs. Output Current
Figure 3. Startup Voltage vs Output Current
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L6920
DETAILED DESCRIPTIONThe L6920 is a high efficiency, low voltage step-up DC/DC converter particularly suitable for 1 to 3 cells (Li-Ion/
polymer, NiMH respectively) battery up conversion.
These performances are achieved via a strong reduction of quiescent current (10μA only) and adopting a syn-
chronous rectification, that implies also a reduced cost in the application (no external diode required).
Operation is based on maximum ON time - minimum OFF time control, tailored by a current limit set to 1A. A
simplified block diagram is shown here below.
Figure 4. Simplified Block Diagram
PRINCIPLE OF OPERATIONIn L6920 the control is based on a comparator that continuously checks the status of output voltage.
If the output voltage is lower than the expected value, the control function of the L6920 directs the energy stored
in the inductor to be transferred to the load. This is accomplished by alternating between two basic steps:
- TON phase: the energy is transferred from the battery to the inductor by shorting LX node to ground via the N-
channel power switch. The switch is turned off if the current flowing in the inductor reaches 1A or after a max-
imum on time set to 5μs.
- TOFF phase: the energy stored in the inductor is transferred to the load through the synchronous switch for at
least a minimum off time equal to 1μs. After this, the synchronous switch is turned off as soon as the output
voltage goes lower than the regulated voltage or the current flowing in the inductor goes down to zero.
So, in case of light load, the device works in PFM mode, as shown in figure 5.
L6920 6/12
Figure 5.1. PFM mode Condition: Vout = 5V; Vin
=1.5V. Trace1: Vout (50mV~/div) Trace
4: IL (100mA/div) Time div.: 5μs/div
Figure 5.2. Heavier load - Train pulses overlapping.
Trace1: Vout (100mV~/div) Trace 4: IL
(200mA/div) Time div.: 10 μs/div
Figure 5.3. Heavy load - Inductor current ripples
below Ilim Trace1: Vout (100mV~/div)
Trace 4: IL (200mA/div) Time div.: 20 μs/div
Figure 5.4. Heavy load and High ESR. Regulation
falls in continuous mode of operation.
Trace1: Vout (100mV~/div) Trace 4: IL
(200mA/div). Time div.: 5 μs/divWhen Iload is heavier, the pulse trains are overlapped. Figures 5.2 - 5.4 show some possible behaviors.
Considering that current in the inductor is limited to 1A, the maximum load current is defined by the following
relationship:
eq. (1)
Where η is the efficiency and Ilim =1A.
Of course, if Iload is greater than Iload_lim the regulation is lost (figure 6). load_liminout
----------- IlimT off min– Vout Vin–⋅----------- ---------------⋅ η⋅⋅=
