Datasheet LTC3868-1 (Analog Devices) - 8
| Manufacturer | Analog Devices |
| Description | Low IQ, Dual 2-Phase Synchronous Step-Down Controller |
| Pages / Page | 38 / 8 — TYPICAL PERFORMANCE CHARACTERISTICS. Latchoff Thresholds. INTVCC vs Load … |
| File Format / Size | PDF / 475 Kb |
| Document Language | English |
TYPICAL PERFORMANCE CHARACTERISTICS. Latchoff Thresholds. INTVCC vs Load Current. vs Temperature. PIN FUNCTIONS (QFN/SSOP)
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LTC3868-1
TYPICAL PERFORMANCE CHARACTERISTICS Latchoff Thresholds INTVCC vs Load Current vs Temperature
5.20 2.3 VIN = 12V 2.2 5.15 2.1 ARMING THRESHOLD 2.0 1.9 5.10 1.8 EXTV VOLTAGE (V) CC = 0V VOLTAGE (V) 1.7 CC 5.05 CC 1.6 LATCH-OFF THRESHOLD INTV INTV EXTVCC = 8V 1.5 5.00 1.4 1.3 4.95 1.2 0 20 40 60 80 100 120 140 160 180 200 –45 –20 5 30 55 80 105 130 LOAD CURRENT (mA) TEMPERATURE (°C) 38681 G26 38681 G27
PIN FUNCTIONS (QFN/SSOP) SENSE1–, SENSE2– (Pin 2, Pin 8/Pin 4, Pin 10):
The (–) LTC3868-1 operates at light loads. Pulling this pin to Input to the Differential Current Comparators. When greater ground selects Burst Mode operation. An internal 100k than INTVCC – 0.5V, the SENSE– pin supplies current to resistor to ground also invokes Burst Mode operation the current comparator. when the pin is fl oated. Tying this pin to INTVCC forces continuous inductor current operation. Tying this pin to
FREQ (Pin 3/Pin 5):
The Frequency Control Pin for the a voltage greater than 1.2V and less than INTV Internal VCO. Connecting this pin to GND forces the VCO CC – 1.3V selects pulse-skipping operation. to a fi xed low frequency of 350kHz. Connecting this pin to INTVCC forces the VCO to a fi xed high frequency of
SGND (Pin 5, Exposed Pad Pin 29/Pin 7):
Small-signal 535kHz. Other frequencies between 50kHz and 900kHz can ground common to both controllers, must be routed be programmed using a resistor between FREQ and GND. separately from high current grounds to the common (–) An internal 20μA pull-up current develops the voltage to terminals of the CIN capacitors. The exposed pad (QFN be used by the VCO to control the frequency only) must be soldered to the PCB for rated thermal performance.
PLLIN/MODE (Pin 4/Pin 6):
External Synchronization Input to Phase Detector and Forced Continuous Mode
RUN1, RUN2 (Pin 6, Pin 7/Pin 8, Pin 9):
Digital Run Input. When an external clock is applied to this pin, the Control Inputs for Each Controller. Forcing either of these phase-locked loop will force the rising TG1 signal to be pins below 1.26V shuts down that controller. Forcing both synchronized with the rising edge of the external clock. of these pins below 0.7V shuts down the entire LTC3868-1, When not synchronizing to an external clock, this input, reducing quiescent current to approximately 8μA. Do not which acts on both controllers, determines how the fl oat these pins. 38681fd 8
TYPICAL PERFORMANCE CHARACTERISTICS Latchoff Thresholds INTVCC vs Load Current vs Temperature
5.20 2.3 VIN = 12V 2.2 5.15 2.1 ARMING THRESHOLD 2.0 1.9 5.10 1.8 EXTV VOLTAGE (V) CC = 0V VOLTAGE (V) 1.7 CC 5.05 CC 1.6 LATCH-OFF THRESHOLD INTV INTV EXTVCC = 8V 1.5 5.00 1.4 1.3 4.95 1.2 0 20 40 60 80 100 120 140 160 180 200 –45 –20 5 30 55 80 105 130 LOAD CURRENT (mA) TEMPERATURE (°C) 38681 G26 38681 G27
PIN FUNCTIONS (QFN/SSOP) SENSE1–, SENSE2– (Pin 2, Pin 8/Pin 4, Pin 10):
The (–) LTC3868-1 operates at light loads. Pulling this pin to Input to the Differential Current Comparators. When greater ground selects Burst Mode operation. An internal 100k than INTVCC – 0.5V, the SENSE– pin supplies current to resistor to ground also invokes Burst Mode operation the current comparator. when the pin is fl oated. Tying this pin to INTVCC forces continuous inductor current operation. Tying this pin to
FREQ (Pin 3/Pin 5):
The Frequency Control Pin for the a voltage greater than 1.2V and less than INTV Internal VCO. Connecting this pin to GND forces the VCO CC – 1.3V selects pulse-skipping operation. to a fi xed low frequency of 350kHz. Connecting this pin to INTVCC forces the VCO to a fi xed high frequency of
SGND (Pin 5, Exposed Pad Pin 29/Pin 7):
Small-signal 535kHz. Other frequencies between 50kHz and 900kHz can ground common to both controllers, must be routed be programmed using a resistor between FREQ and GND. separately from high current grounds to the common (–) An internal 20μA pull-up current develops the voltage to terminals of the CIN capacitors. The exposed pad (QFN be used by the VCO to control the frequency only) must be soldered to the PCB for rated thermal performance.
PLLIN/MODE (Pin 4/Pin 6):
External Synchronization Input to Phase Detector and Forced Continuous Mode
RUN1, RUN2 (Pin 6, Pin 7/Pin 8, Pin 9):
Digital Run Input. When an external clock is applied to this pin, the Control Inputs for Each Controller. Forcing either of these phase-locked loop will force the rising TG1 signal to be pins below 1.26V shuts down that controller. Forcing both synchronized with the rising edge of the external clock. of these pins below 0.7V shuts down the entire LTC3868-1, When not synchronizing to an external clock, this input, reducing quiescent current to approximately 8μA. Do not which acts on both controllers, determines how the fl oat these pins. 38681fd 8
