LTC3787HUFD-PBF Просмотр технического описания (PDF) - Linear Technology

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LTC3787HUFD-PBF

PolyPhase Synchronous Boost Controller

Linear Technology 

TYPICAL PERFORMANCE CHARACTERISTICS

Maximum Current Sense

Threshold vs Duty Cycle

120

ILIM = INTVCC

100

80 ILIM = FLOAT

60

ILIM = GND

40

20

0

0 10 20 30 40 50 60 70 80 90 100

DUTY CYCLE (%)

3787 G25

Charge Pump Charging Current

vs Operating Frequency

80

T = –60°C

70

60

T = –45°C

50

T = 25°C

40

T = 130°C

30

T = 155°C

20

10

0

50 150 250 350 450 550 650 750

OPERATING FREQUENCY (kHz)

3787 G26

LTC3787

Charge Pump Charging Current

vs Switch Voltage

80

FREQ = GND

70

60

FREQ = INTVCC

50

40

30

20

10

0

5 10 15 20 25 30 35 40

SWITCH VOLTAGE (V)

3787 G27

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 INTVCC

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 INTVCC 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 LTC3787 ICs in Multiphase Systems. The

PHASMD pin voltage controls the relationship between BG1

and CLKOUT. This pin swings between SGND and INTVCC.

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, it will force

the controller into forced continuous mode of operation

and the phase-locked loop will force the rising BG1 signal

to be synchronized with the rising edge of the external

clock. When not synchronizing to an external clock, this

input determines how the LTC3787 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 INTVCC forces continuous inductor current operation.

Tying this pin to a voltage greater than 1.2V and less than

INTVCC – 1.3V selects pulse-skipping operation. This can

be done by adding a 100k resistor between the PLLIN/

MODE pin and INTVCC.

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 LTC3787, reducing

quiescent current to approximately 8μA. An external

resistor divider connected to VIN 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.

3787fc

9

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