LTC3788 Linear Technology, LTC3788 Datasheet - Page 9

• Manufacturer Part Number: LTC3788
• Description: Dual Output Synchronous Boost Controller
• Manufacturer: Linear Technology

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PIN FUNCTIONS
SENSE1
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 fi xed
low frequency of 350kHz. Connecting the pin to INTV
forces the VCO to a fi xed 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 fl oated, tied to SGND, or
tied to INTV
the rising edges of BG1 and BG2, as well as the phase
relationship between BG1 and CLKOUT.
TYPICAL PERFORMANCE CHARACTERISTICS
–
, SENSE2
CC
to program the phase relationship between
120
100
80
60
40
20
0
0
Maximum Current Sense
Threshold vs Duty Cycle
–
(Pin 1, Pin 9): Negative Current Sense
I
I
10
LIM
I
LIM
LIM
= INTV
= FLOAT
20
= GND
30
CC
DUTY CYCLE (%)
40
50
60
70
80
3788 G25
90
100
CC
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
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
Tying this pin to a voltage greater than 1.2V and less than
INTV
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
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.
CC
80
70
60
50
40
30
20
10
0
50
Charge Pump Charging Current
vs Operating Frequency
CC
–1.3V selects pulse-skipping operation. A clock
V
V
SW
BOOST
150
forces continuous inductor current operation.
= 12V
OPERATING FREQUENCY (kHz)
– V
250
SW
= 4.5V
350
450 550
T = 25°C
T = 130°C
T = –45°C
IN
650 750
and sets the thresholds for
3788 G26
LTC3788
CC
9
3788f
.