LP3910 Datasheet, PDF (29/72 Pages) Texas Instruments – Power Management IC for Hard-Drive-Based Portable Media Players

www.ti.com
Feature Description (continued)
LP3910
SNVS481M – NOVEMBER 2006 – REVISED DECEMBER 2015
PFM Mode at Light Load
PFET on
until
Ipfm limit
reached
NFET on
drains inductor
until
I inductor=0
High PFM
Voltage
Threshold reached,
go into
sleep mode
Low PFM
Threshold,
turn on
PFET
Low2 PFM
Threshold,
switch back to
PWMmode
Load
current
increases
High PFM Threshold
approx. 1.016 x VOUT
Low1 PFM Threshold
approx. 1.008 x VOUT
Current load increases,
draws VOUT towards
Low2 PFM Threshold
Low2 PFM
Threshold VOUT
PWM Mode at
Moderate to Heavy
Loads
Figure 50. Operation in PFM Mode and Transfer to PWM Mode
8.3.2 Buck-Boost: Synchronous Buck-Boost Magnetic DC-DC Converter
The LP3910 is equipped with a synchronous buck-boost magnetic DC-DC converter to supply power to the hard
drive that has a typical 3.3-V operating voltage. This voltage is lower than the maximum battery (4.2 V typically
for Li-polymer cells) and higher than the minimum battery (typically 2.8 V). Therefore, in order to provide 3.3 V,
regardless of the battery voltage, the Buck-Boost converter either steps down the battery voltage or steps up the
battery voltage. The Buck-Boost automatically switches between PWM and PFM modes depending on the load
and automatically switches between buck and boost modes, depending on the battery voltage.
By setting bit D6 of the Buck-Boost control register, the Buck-Boost is forced to operate using PWM modulation
regardless of the load. By default this bit is cleared.
35
VBBL 1
BUCK/
BOOST
Lbb
2.2 PH
33
VBBL 2
32
VBBOUT
VBBFB
31
Cbb
22 PF
LOAD
Figure 51. Schematic Section for Buck-Boost Operation
8.3.3 Linear Low Dropout Regulators (LDOs)
LDO1 is a regulator that can respond to fast transients and is slated for digital loads and high bandwidth analog
loads. LDO2 is a linear regulator with a similar architecture but has a slower transient response time with a lower
noise performance to supply analog loads. The output voltages of both LDOs are register programmable through
the I²C interface. The default output voltages are factory programmed during final test.
Copyright © 2006–2015, Texas Instruments Incorporated
Product Folder Links: LP3910
Submit Documentation Feedback
29