Datasheet

LTC3829
25
3829fa
For more information www.linear.com/LTC3829
APPLICATIONS INFORMATION
The final load slope is defined by the inductor current
sense resistors and the two external resistors mentioned
above.
In summary, the load slope is:
R
SENSE
•
R
AVP
R
PRE-AVP






V/A
The recommended value for R
AVP
is 90Ω to 100Ω. The
maximum output voltage at AVP is 2.5V. Therefore, for
output higher than 2.5V, AVP function is not supported.
The DIFFP pin, however, should always be connected to the
output even when AVP or diffamp functions are not used.
Programmable Shed Mode
When the MODE pin is tied to INTV
CC
, the LTC3829 enters
shed mode. It means that the second and third channel will
stop switching when I
TH
is below a certain programmed
threshold. The threshold voltage on I
TH
when LTC3829
goes into shed mode, is programmed according to the
following formula:
V
SHED
= 0.5 + (5/3) • (0.5 – V
ISET
)
The valid range of V
ISET
is between 0V to 0.5V and V
ISET
is the voltage on the ISET pin. There is a precision 7.5µA
flowing out of the ISET pin. Connecting a resistor to SGND
sets the V
ISET
voltage. When left floating, V
ISET
voltage
will be at INTV
CC
. The shed mode threshold voltage in this
case will be 0.5V. There is a 50mV hysteresis for the shed
mode threshold comparator.
Programmable Burst Mode Operation
When the MODE pin is floating, the LTC3829 enters Burst
Mode operation. This means that all channels will stop
switching when I
TH
is below a certain threshold.
The Burst Mode clamp, which sets the current limit when
bursting, can be programmed through V
ISET
according to
the following equation:
V
CLAMP
= 0.7 + 0.62 (0.5 – V
ISET
)
The valid range of V
ISET
is between 0.3V to 0.5V and V
ISET
is the voltage on the ISET pin. There is a precision 7.5µA
flowing out of ISET. Connecting a resistor to SGND sets
the V
ISET
voltage. When left floating, the V
ISET
voltage
will be at INTV
CC
. The Burst Mode clamp voltage in this
case will be 0.7V. There is a 50mV hysteresis for the Burst
Mode comparator.
Nonlinear Control Loop
The LTC3829 features a unique control loop that can speed
up transient response dramatically. This feature is enabled
and programmed through the IFAST pin. When IFAST is
tied to INTV
CC
, the nonlinear control loop is disabled. V
IFAST
is the voltage that can be programmed on the IFAST pin.
There is a precision 10µA flowing out of the ISET pin. Con-
necting a resistor to SGND sets the V
IFAST
voltage. When
V
IFAST
is set below 0.5V, the difference of 0.5V and V
IFAST
sets the threshold voltage that triggers nonlinear control.