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L6928STN/a1886avaiHigh efficiency monolithic synchronous step down regulator
L6928Q1TRSTN/a5895avaiHigh efficiency monolithic synchronous step down regulator


L6928Q1TR ,High efficiency monolithic synchronous step down regulatorAbsolute maximum ratingsSymbol Parameter Value UnitV Input voltage -0.3 to 6 V6V Output switching v ..
L6932D1.2 ,HIGH PERFORMANCE 2A ULDO LINEAR REGULATORapplicationsreducing the power dissipation.■ MOTHERBOARDSL6932 is available in 1.8V, 2.5V and adj v ..
L6932D1.2 ,HIGH PERFORMANCE 2A ULDO LINEAR REGULATORAPPLICATIONStween 2.5V and 1.8V at 2A in portable
L6932D1.2TR ,HIGH PERFORMANCE 2A ULDO LINEAR REGULATORapplicationsreducing the power dissipation.■ MOTHERBOARDSL6932 is available in 1.8V, 2.5V and adj v ..
L6932D1.8 ,HIGH PERFORMANCE 2A ULDO LINEAR REGULATORABSOLUTE MAXIMUM RATINGSSymbol Parameter Value UnitV VIN and Pgood 14.5 VinEN, OUT and ADJ -0.3 to ..
L6932D1.8 ,HIGH PERFORMANCE 2A ULDO LINEAR REGULATORapplicationsreducing the power dissipation.■ MOTHERBOARDSL6932 is available in 1.8V, 2.5V and adj v ..
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L6928-L6928Q1TR
High efficiency monolithic synchronous step down regulator
December 2011 Doc ID 11051 Rev 7 1/16
L6928

High efficiency monolithic synchronous step down regulator
Features
2 V to 5.5 V battery input range High efficiency: up to 95% Internal synchronous switch No external Schottky required Extremely low quiescent current 1 µA max shutdown supply current 800 mA max output current Adjustable output voltage from 0.6 V Low dropout operation: up to 100% duty cycle Selectable low noise/low consumption mode at
light load Power Good signal ± 1% output voltage accuracy Current-mode control 1.4 MHz switching frequency Externally synchronizable from 1 MHz to 2
MHz OVP Short-circuit protection
Applications
Battery-powered equipment Portable instruments Cellular phones PDAs and hand held terminals DSC GPS
Description

The device is DC-DC monolithic regulator
specifically designed to provide extremely high
efficiency. L6928 supply voltage can be as low as
2 V allowing its use in single Li-Ion cell supplied
applications. Output voltage can be selected by
an external divider down to 0.6 V. Duty cycle can
saturate to 100% allowing low dropout operation.
The device is based on a 1.4 MHz fixed
frequency, current mode architecture. Low
consumption mode operation can be selected at
light load conditions, allowing switching losses to
be reduced. L6928 is externally synchronizable
with a clock which makes it useful in noise
sensitive applications. Other features like Power
Good, overvoltage protection, short-circuit
protection and thermal shutdown (150 °C) are
also present.
Figure 1. Application test circuit
Contents L6928
2/16 Doc ID 11051 Rev 7
Contents Pin settings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 Maximum ratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 Electrical characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 Operation description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

4.1 Modes of operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
4.1.1 Low consumption mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
4.1.2 Low noise mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
4.1.3 Synchronization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
4.2 Short circuit protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
4.3 Slope compensation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
4.4 Loop stability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 Additional features and protections . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
5.1 DROPOUT operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
5.2 PGOOD (Power Good output) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
5.3 Adjustable output voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
5.4 OVP (Overvoltage protection) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
5.5 Thermal shutdown . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 Package mechanical data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 Order codes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
L6928 Pin settings
Doc ID 11051 Rev 7 3/16
1 Pin settings
Figure 2. Pin connection (top view)


Table 1. Pin description
Maximum ratings L6928
4/16 Doc ID 11051 Rev 7
2 Maximum ratings

Table 2. Absolute maximum ratings
Table 3. Thermal data
L6928 Electrical characteristics
Doc ID 11051 Rev 7 5/16
3 Electrical characteristics

TJ = 25 °C, VIN = 3.6 V unless otherwise specified.
.Table 4. Electrical characteristics(1)
Electrical characteristics L6928
6/16 Doc ID 11051 Rev 7 Specification referred to TJ from -40°C to +125°C. Specification over the -40 to +125°C TJ temperature range are assured
by design, characterization and statistical correlation. Guaranteed by design.
Table 4. Electrical characteristics (continued)(1)
L6928 Operation description
Doc ID 11051 Rev 7 7/16
4 Operation description

The main loop uses slope compensated PWM current mode architecture. Each cycle the
high side MOSFET is turned on, triggered by the oscillator, so that the current flowing
through it (the same as the inductor current) increases. When this current reaches the
threshold (set by the output of the error amplifier E/A), the peak current limit comparator
PEAK_CL turns off the high side MOSFET and turns on the low side one until the next clock
cycle begins or the current flowing through it goes down to zero (ZERO CROSSING
comparator). The peak inductor current required to trigger PEAK_CL depends on the slope
compensation signal and on the output of the error amplifier.
In particular, the error amplifier output depends on the VFB pin voltage. When the output
current increases, the output capacitor is discharged and so the VFB pin decreases. This
produces increase of the error amplifier output, so allowing a higher value for the peak
inductor current. For the same reason, when due to a load transient the output current
decreases, the error amplifier output goes low, so reducing the peak inductor current to
meet the new load requirements.
The slope compensation signal allows the loop stability also in high duty cycle conditions
(see related section).
Figure 3. Device block diagram
4.1 Modes of operation

Depending on the SYNC pin value the device can operate in low consumption or low noise
mode. If the SYNC pin is high (higher than 1.3 V) the low consumption mode is selected
while the low noise mode is selected if the SYNC pin is low (lower than 0.5 V).
Operation description L6928
8/16 Doc ID 11051 Rev 7
4.1.1 Low consumption mode

In this mode of operation, at light load, the device operates discontinuously based on the
COMP pin voltage, in order to keep the efficiency very high also in these conditions. While
the device is not switching the load discharges the output capacitor and the output voltage
goes down. When the feedback voltage goes lower than the internal reference, the COMP
pin voltage increases and when an internal threshold is reached, the device starts to switch.
In these conditions the peak current limit is set approximately in the range of 200 mA - 400
mA, depending on the slope compensation (see related section).
Once the device starts to switch the output capacitor is recharged. The feedback pin
increases and, when it reaches a value slightly higher than the reference voltage, the output
of the error amplifier goes down until a clamp is activated. At this point, the device stops to
switch. In this phase, most of the internal circuitries are off, so reducing the device
consumption down to a typical value of 25 µA.
4.1.2 Low noise mode

If for noise reasons, the very low frequencies of the low consumption mode are undesirable,
the low noise mode can be selected. In low noise mode, the efficiency is a little bit lower
compared with the low consumption mode in very light load conditions but for medium-high
load currents the efficiency values are very similar.
Basically, the device switches with its internal free running frequency of 1.4 MHz. Obviously,
in very light load conditions, the device could skip some cycles in order to keep the output
voltage in regulation.
4.1.3 Synchronization

The device can also be synchronized with an external signal from 1 MHz up to 2 MHz.
In this case the low noise mode is automatically selected. The device will eventually skip
some cycles in very light load conditions. The internal synchronization circuit is inhibited in
short-circuit and overvoltage conditions in order to keep the protections effective (see
relative sections).
4.2 Short circuit protection

During the device operation, the inductor current increases during the high side turn ON
phase and decrease during the high side turn off phase based on the following equations:
Equation 1
Equation 2

In strong overcurrent or short-circuit conditions the V OUT can be very close to zero. In this
case ΔION increases and ΔI OFF decreases. When the inductor peak current reaches the ONINV OUT– ()-------------- --------------------TON⋅= OFF OUT()-------------------T OFF⋅=
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