LTC3784_15 Datasheet, PDF (8/38 Pages) Linear Technology – 60V PolyPhase Synchronous Boost Controller

LTC3784
Pin Functions (QFN/SSOP)
FREQ (Pin 1/Pin 4): Frequency Control Pin for the Internal
VCO. Connecting the pin to GND forces the VCO to a fixed
low frequency of 350kHz. Connecting the pin to INTV_CC
forces the VCO to a fixed high frequency of 535kHz. The
frequency can be programmed from 50kHz to 900kHz
by connecting a resistor from the FREQ pin to GND. The
resistor and an internal 20μA source current create a volt-
age used by the internal oscillator to set the frequency.
Alternatively, this pin can be driven with a DC voltage to
vary the frequency of the internal oscillator.
PHASMD (Pin 2/Pin 5): This pin can be floated, tied to
SGND, or tied to INTV_CC to program the phase relationship
between the rising edges of BG1 and BG2, as well as the
phase relationship between BG1 and CLKOUT.
CLKOUT (Pin 3/Pin 6): A Digital Output Used for Daisy-
chaining Multiple LTC3784 ICs in Multiphase Systems. The
PHASMD pin voltage controls the relationship between BG1
and CLKOUT. This pin swings between SGND and INTV_CC.
PLLIN/MODE (Pin 4/Pin 7): External Synchronization
Input to Phase Detector and Forced Continuous Mode
Input. When an external clock is applied to this pin, the
phase-locked loop will force the rising edge of BG1 to be
synchronized with the rising edge of the external clock.
When an external clock is applied to this pin, the OVMODE
pin is used to determine how the LTC3784 operates at light
load. When not synchronizing to an external clock, this
input determines how the LTC3784 operates at light loads.
Pulling this pin to ground selects Burst Mode operation.
An internal 100k resistor to ground also invokes Burst
Mode operation when the pin is floated. Tying this pin
to INTV_CC forces continuous inductor current operation.
Tying this pin to a voltage greater than 1.2V and less than
INTV_CC – 1.3V selects pulse-skipping operation. This can
be done by adding a 100k resistor between the PLLIN/
MODE pin and INTV_CC.
SGND (Pin 5/Pin 8): Signal Ground. All small-signal
components and compensation components should
connect to this ground, which in turn connects to PGND
at a single point.
RUN (Pin 6/Pin 9): Run Control Input. Forcing this pin
below 1.28V shuts down the controller. Forcing this pin
below 0.7V shuts down the entire LTC3784, reducing
quiescent current to approximately 4µA. An external
resistor divider connected to V_IN can set the threshold
for converter operation. Once running, a 4.5µA current is
sourced from the RUN pin allowing the user to program
hysteresis using the resistor values.
SS (Pin 7/Pin 10): Output Soft-Start Input. A capacitor to
ground at this pin sets the ramp rate of the output voltage
during start-up.
SENSE2^– , SENSE1^– (Pin 8, Pin 28/Pin 11, Pin 3): Nega-
tive Current Sense Comparator Input. The (–) input to the
current comparator is normally connected to the negative
terminal of a current sense resistor connected in series
with the inductor.
SENSE2⁺, SENSE1⁺ (Pin 9, Pin 27/Pin 12, Pin 2): Posi-
tive Current Sense Comparator Input. The (+) input to the
current comparator is normally connected to the positive
terminal of a current sense resistor. The current sense resis-
tor is normally placed at the input of the boost controller in
series with the inductor. This pin also supplies power to the
current comparator. The common mode voltage range on
SENSE⁺ and SENSE^– pins is 2.3V to 60V (65V abs max).
VFB (Pin 10/Pin 13): Error Amplifier Feedback Input. This
pin receives the remotely sensed feedback voltage from
an external resistive divider connected across the output.
ITH (Pin 11/Pin 14): Current Control Threshold and Error
Amplifier Compensation Point. The voltage on this pin sets
the current trip threshold.
3784fb
8
For more information www.linear.com/LTC3784