LTC3829 Datasheet, PDF (26/40 Pages) Linear Technology – 3-Phase, Single Output Synchronous Step-Down DC/DC Controller with Diffamp

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.
3829f
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