LTC3210
operation
4.6
sources and charge pump until the die has cooled by
about 15°C. This thermal cycling will continue until the
fault has been corrected.
V
V
= 3V
BAT
CPO
= 4.8V
4.4
C2 = C3 = C4 = 2.2µF
4.2
4.0
3.8
3.6
3.4
3.2
Mode Switching
The LTC3210 will automatically switch from 1x mode
to 1.5x mode and subsequently to 2x mode whenever
a dropout condition is detected at an LED pin. Dropout
occurs when a current source voltage becomes too low
for the programmed current to be supplied. The time
from drop-out detection to mode switching is typically
0.4ms.
–15
10
35
85
–40
60
TEMPERATURE (˚C)
3210 F04
Figure 4. Typical 2x ROL vs Temperature
The part is reset back to 1x mode when the part is shut
down (ENM = ENC = Low) or on the falling edge of ENC.
An internal comparator will not allow the main switches to
Thermal Protection
The LTC3210 has built-in overtemperature protection.
At internal die temperatures of around 150°C thermal
shutdown will occur. This will disable all of the current
connect V and CPO in 1x mode until the voltage at the
CPO pin has decayed to less than or equal to the voltage
BAT
at the V pin.
BAT
applications inFormation
V , CPO Capacitor Selection
BAT
The output ripple in 2x mode is very small due to the fact
that load current is supplied on both cycles of the clock.
ThestyleandvalueofthecapacitorsusedwiththeLTC3210
determineseveralimportantparameterssuchasregulator
controlloopstability,outputripple,chargepumpstrength
and minimum start-up time.
Bothstyleandvalueoftheoutputcapacitorcansignificantly
affect the stability of the LTC3210. As shown in the Block
Diagram, the LTC3210 uses a control loop to adjust the
strength of the charge pump to match the required output
current.Theerrorsignaloftheloopisstoreddirectlyonthe
output capacitor. The output capacitor also serves as the
dominant pole for the control loop. To prevent ringing or
instability,itisimportantfortheoutputcapacitortomaintain
at least 1.3µF of capacitance over all conditions.
To reduce noise and ripple, it is recommended that low
equivalentseriesresistance(ESR)ceramiccapacitorsare
used for both CV
and C . Tantalum and aluminum
BAT
CPO
capacitors are not recommended due to high ESR.
The value of C directly controls the amount of output
CPO
ripple for a given load current. Increasing the size of C
CPO
In addition, excessive output capacitor ESR >100mΩ will
tend to degrade the loop stability. Multilayer ceramic chip
capacitorstypicallyhaveexceptionalESRperformanceand
when combined with a tight board layout will result in very
will reduce output ripple at the expense of higher start-up
current. The peak-to-peak output ripple of the 1.5x mode
is approximately given by the expression:
IOUT
(3f0SC •CCPO
good stability. As the value of C
controls the amount of
controls the amount of
CPO
VRIPPLE(P−P)
=
(3)
)
output ripple, the value of CV
BAT
ripple present at the input pin(V ). The LTC3210’s input
currentwillberelativelyconstantwhilethechargepumpis
either in the input charging phase or the output charging
BAT
Wheref istheLTC3210oscillatorfrequencyortypically
OSC
800kHz and C
is the output storage capacitor.
CPO
3210fb
ꢀꢀ
Linear Systems [ Linear Systems ]
