LTC3834 Linear Technology, LTC3834 Datasheet - Page 11

• Manufacturer Part Number: LTC3834
• Description: Synchronous Step-Down Controller
• Manufacturer: Linear Technology

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OPERATION
When the RUN pin is pulled low to disable the LTC3834, or
when V
of 3.7V, the TRACK/SS pin is pulled low by an internal
MOSFET. When in undervoltage lockout, the controller is
disabled and the external MOSFETs are held off.
Light Load Current Operation (Burst Mode Operation,
Pulse-Skipping or Continuous Conduction)
(PLLIN/MODE Pin)
The LTC3834 can be enabled to enter high effi ciency
Burst Mode operation, constant-frequency pulse-skipping
mode, or forced continuous conduction mode at low load
currents. To select Burst Mode operation, tie the PLLIN/
MODE pin to a DC voltage below 0.8V (e.g., SGND). To
select forced continuous operation, tie the PLLIN/MODE
pin to INTV
PLLIN/MODE pin to a DC voltage greater than 0.8V and
less than INTV
When the LTC3834 is enabled for Burst Mode operation,
the peak current in the inductor is set to approximately
one-tenth of the maximum sense voltage even though the
voltage on the I
age inductor current is lower than the load current, the
error amplifi er EA will decrease the voltage on the I
When the I
signal goes high (enabling “sleep” mode) and both external
MOSFETs are turned off. The I
from the output of the EA and “parked” at 0.425V.
In sleep mode, much of the internal circuitry is turned off,
reducing the quiescent current that the LTC3834 draws to
only 30μA. In sleep mode, the load current is supplied by
the output capacitor. As the output voltage decreases, the
EA’s output begins to rise. When the output voltage drops
enough, the I
EA, the sleep signal goes low, and the controller resumes
IN
drops below its undervoltage lockout threshold
TH
CC
voltage drops below 0.4V, the internal sleep
TH
. To select pulse skipping mode, tie the
CC
TH
pin is reconnected to the output of the
– 0.5V.
pin indicates a lower value. If the aver-
(Refer to Functional Diagram)
TH
pin is then disconnected
TH
pin.
normal operation by turning on the top external MOSFET
on the next cycle of the internal oscillator.
When the LTC3834 is enabled for Burst Mode operation,
the inductor current is not allowed to reverse. The reverse
current comparator (RI
MOSFET just before the inductor current reaches zero,
preventing it from reversing and going negative, thus
operating in discontinuous operation.
In forced continuous operation, the inductor current is
allowed to reverse at light loads or under large transient
conditions. The peak inductor current is determined by the
voltage on the I
mode, the effi ciency at light loads is lower than in Burst
Mode operation. However, continuous operation has the
advantages of lower output ripple and less interference
to audio circuitry. In forced continuous mode, the output
ripple is independent of load current.
When the PLLIN/MODE pin is connected for pulse skip-
ping mode or clocked by an external clock source to
use the phase-locked loop (see Frequency Selection and
Phase-Locked Loop section), the LTC3834 operates in
PWM pulse skipping mode at light loads. In this mode,
constant-frequency operation is maintained down to ap-
proximately 1% of designed maximum output current.
At very light loads, the current comparator ICMP may
remain tripped for several cycles and force the external top
MOSFET to stay off for the same number of cycles (i.e.,
skipping pulses). The inductor current is not allowed to
reverse (discontinuous operation). This mode, like forced
continuous operation, exhibits low output ripple as well as
low audio noise and reduced RF interference as compared
to Burst Mode operation. It provides higher low current
effi ciency than forced continuous mode, but not nearly as
high as Burst Mode operation.
TH
pin, just as in normal operation. In this
CMP
) turns off the bottom external
LTC3834
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