Datasheet LTC3858 (Analog Devices) - 8
| Manufacturer | Analog Devices |
| Description | Low IQ, Dual 2-Phase Synchronous Step-Down Controller |
| Pages / Page | 38 / 8 — TYPICAL PERFORMANCE CHARACTERISTICS. INTVCC and EXTVCC. Latch-Off … |
| File Format / Size | PDF / 434 Kb |
| Document Language | English |
TYPICAL PERFORMANCE CHARACTERISTICS. INTVCC and EXTVCC. Latch-Off Threshold Voltages. vs Load Current. vs Temperature
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LTC3858
TYPICAL PERFORMANCE CHARACTERISTICS INTVCC and EXTVCC Latch-Off Threshold Voltages 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) 3858 G26 3858 G27
PIN FUNCTIONS SENSE1–, SENSE2– (Pin 1, Pin 9):
The (–) Input to the
CLKOUT (Pin 4):
Output clock signal available to daisy- Differential Current Comparators. When greater than chain other controller ICs for additional MOSFET driver INTVCC – 0.5V, the SENSE– pin supplies current to the stages/phases. The output levels swing from INTVCC to current comparator. ground.
FREQ (Pin 2):
The Frequency Control Pin for the Internal
PLLIN/MODE (Pin 5):
External Synchronization Input to Voltage-Controlled Oscillator (VCO). Connecting this pin Phase Detector and Forced Continuous Mode Input. When to GND forces the VCO to a fi xed low frequency of 350kHz. an external clock is applied to this pin, the phase-locked Connecting this pin to INTVCC forces the VCO to a fi xed loop will force the rising TG1 signal to be synchronized high frequency of 535kHz. Other frequencies between with the rising edge of the external clock. When not syn- 50kHz and 900kHz can be programmed using a resistor chronizing to an external clock, this input, which acts on between FREQ and GND. An internal 20μA pull-up current both controllers, determines how the LTC3858 operates at develops the voltage to be used by the VCO to control the light loads. Pulling this pin to ground selects Burst Mode frequency operation. An internal 100k resistor to ground also invokes Burst Mode operation when the pin is fl oated. Tying this pin
PHASMD (Pin 3):
Control input to phase selector which to INTV determines the phase relationships between controller 1, CC forces continuous inductor current operation. Tying this pin to a voltage greater than 1.2V and less than controller 2 and the CLKOUT signal. Pulling this pin to INTV ground forces TG2 and CLKOUT to be out of phase 180° CC – 1.3V selects pulse-skipping operation. and 60° with respect to TG1. Connecting this pin to INTVCC
SGND (Pin 6, Exposed Pad Pin 33):
Small-signal ground forces TG2 and CLKOUT to be out of phase 240° and 120° common to both controllers, must be routed separately with respect to TG1. Floating this pin forces TG2 and from high current grounds to the common (–) terminals CLKOUT to be out of phase 180° and 90° with respect to of the CIN capacitors. The exposed pad must be soldered TG1. Refer to the Table 1. to the PCB for rated thermal performance. 3858fc 8
TYPICAL PERFORMANCE CHARACTERISTICS INTVCC and EXTVCC Latch-Off Threshold Voltages 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) 3858 G26 3858 G27
PIN FUNCTIONS SENSE1–, SENSE2– (Pin 1, Pin 9):
The (–) Input to the
CLKOUT (Pin 4):
Output clock signal available to daisy- Differential Current Comparators. When greater than chain other controller ICs for additional MOSFET driver INTVCC – 0.5V, the SENSE– pin supplies current to the stages/phases. The output levels swing from INTVCC to current comparator. ground.
FREQ (Pin 2):
The Frequency Control Pin for the Internal
PLLIN/MODE (Pin 5):
External Synchronization Input to Voltage-Controlled Oscillator (VCO). Connecting this pin Phase Detector and Forced Continuous Mode Input. When to GND forces the VCO to a fi xed low frequency of 350kHz. an external clock is applied to this pin, the phase-locked Connecting this pin to INTVCC forces the VCO to a fi xed loop will force the rising TG1 signal to be synchronized high frequency of 535kHz. Other frequencies between with the rising edge of the external clock. When not syn- 50kHz and 900kHz can be programmed using a resistor chronizing to an external clock, this input, which acts on between FREQ and GND. An internal 20μA pull-up current both controllers, determines how the LTC3858 operates at develops the voltage to be used by the VCO to control the light loads. Pulling this pin to ground selects Burst Mode frequency operation. An internal 100k resistor to ground also invokes Burst Mode operation when the pin is fl oated. Tying this pin
PHASMD (Pin 3):
Control input to phase selector which to INTV determines the phase relationships between controller 1, CC forces continuous inductor current operation. Tying this pin to a voltage greater than 1.2V and less than controller 2 and the CLKOUT signal. Pulling this pin to INTV ground forces TG2 and CLKOUT to be out of phase 180° CC – 1.3V selects pulse-skipping operation. and 60° with respect to TG1. Connecting this pin to INTVCC
SGND (Pin 6, Exposed Pad Pin 33):
Small-signal ground forces TG2 and CLKOUT to be out of phase 240° and 120° common to both controllers, must be routed separately with respect to TG1. Floating this pin forces TG2 and from high current grounds to the common (–) terminals CLKOUT to be out of phase 180° and 90° with respect to of the CIN capacitors. The exposed pad must be soldered TG1. Refer to the Table 1. to the PCB for rated thermal performance. 3858fc 8
