LTC3788 Datasheet, PDF (9/32 Pages) Linear Technology – 2-Phase, Dual Output Synchronous Boost Controller

TYPICAL PERFORMANCE CHARACTERISTICS
LTC3788
Maximum Current Sense
Threshold vs Duty Cycle
120
100 ^{ILIM = INTVCC}
80 ILIM = FLOAT
60
I_LIM = GND
40
20
0
0 10 20 30 40 50 60 70 80 90 100
DUTY CYCLE (%)
3788 G25
Charge Pump Charging Current
vs Operating Frequency
80
V_SW = 12V
70 ^{VBOOST – VSW = 4.5V}
T = –45°C
60
T = 25°C
50
40
T = 130°C
30
20
10
0
50 150 250 350 450 550 650 750
OPERATING FREQUENCY (kHz)
3788 G26
PIN FUNCTIONS
SENSE1^–, SENSE2^– (Pin 1, Pin 9): Negative Current Sense
Comparator Input. The (–) input to the current comparator
is normally connected to the negative terminal of a cur-
rent sense resistor connected in series with the inductor.
The common mode voltage range on these pins is 2.5V
to 38V (abs max).
FREQ (Pin 2): The 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 3): 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 4): A Digital Output Used for Daisychaining
Multiple LTC3788 ICs in Multiphase Systems. The PHASMD
pin voltage controls the relationship between BG1, BG2 and
CLKOUT. This pin swings between SGND and INTV_CC.
PLLIN/MODE (Pin 5): Forced Continuous Mode, Burst
Mode or Pulse-Skipping Mode Selection Pin and External
Synchronization Input to Phase Detector Pin. Pulling this
pin to ground selects Burst Mode operation. 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. A clock
on the pin will force the controller into pulse-skipping
mode of operation and synchronize the internal oscillator.
SGND (Pin 6): Signal Ground. All small-signal components
and compensation components should connect to this
ground, which in turn connects to PGND at a single point.
RUN1, RUN2 (Pin 7, Pin 8): Run Control Input. An external
resistor divider connects to V_IN and sets the thresholds for
converter operation with a threshold of 1.28V. Once running,
a 4.5μA current is sourced from the RUN pin allowing the
user to program hysteresis using the resistor values.
3788f
9