LTC4230IGN datasheet(8/36 Pages) LINER

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LTC4230

4230f

FB3 (Pin 1): The FB3 (Feedback) pin is an input to the

FBCOMP3 comparator which monitors the VCC3 output

supply voltage through an external resistor divider. If VFB3

< 1.234V, RESET 3 pin pulls low. An internal glitch filter at

FBCOMP3’s output prevents triggering a reset condition

due to negative voltage transients. If VFB3 > 1.237V,

RESET 3 pin goes high after exiting undervoltage lockout.

RESET 3 (Pin 2): An open-drain N-channel device whose

source connects to GND (Pin 14). This pin pulls low if the

voltage at FB3 (Pin 1) falls below the FB3 threshold

(1.234V). This pin requires an external pull-up resistor to

VOUT3. If an undervoltage lockout condition occurs,

RESET 3 pulls low independently of FB3 to prevent false

glitches.

GATE 3 (Pin 3): The output signal at this pin is the high side

gate drive for Channel 3’s external N-channel MOSFET

pass transistor. An internal charge pump produces a 4.5V

(minimum) to 18V (maximum) gate drive voltage for VCC1

supply voltages from 2.7V to 16.5V, respectively.

As shown in the Block Diagram for each channel, an

internal charge pump supplies a 10

µA gate current and

sufficient gate voltage drive to the external MOSFET. The

internal charge pump produces a minimum 4.5V gate

drive for VCC1 < 4.75V. For VCC1 > 4.75V, the minimum

gate voltage drive is 9V. For VCC1 ≥ 12V, the minimum gate

voltage drive is 7V which is set by an internal zener diode

clamp connected between the GATE 3 pin and GND.

SENSE 3 (Pin 4): Circuit Breaker Sense Pin for Channel 3.

With a sense resistor placed in the power path between

VCC3 and SENSE 3, Channel 3’s electronic circuit breaker

trips if the voltage across the sense resistor (VCC3 –

VSENSE3) exceeds the thresholds set internally for SLOW

COMP3 and FAST COMP3, as shown in the Block Diagram.

The threshold for SLOW COMP3 is VCB(SLOW) = 50mV, and

the electronic circuit breaker trips if the voltage across

RSENSE3 exceeds 50mV for 10µs, or for the time delay

programmed by CFILTER. To adjust SLOW COMP3’s delay,

please refer to the section on Adjusting SLOW COMP

n’s

Response Time.

Under transient conditions where large step current

changes can and do occur over shorter periods of time, a

PI FU CTIO S

second (fast) comparator instead trips the electronic

circuit breaker. The threshold for FAST COMP3 is set at

VCB(FAST) = 150mV, and the circuit breaker trips if the

voltage across the RSENSE3 exceeds 150mV for more than

500ns. FAST COMP3’s delay is fixed in the LTC4230 and

cannot be adjusted. To disable Channel 3’s electronic

circuit breaker, connect the VCC3 and SENSE 3 pins

together.

VCC3 (Pin 5): Positive Supply Input for Channel 3. VCC3

operates from 1.7V to 15.5V (VCC3 ≤ VCC1 – 1V) and its

supply current, ICC3, is typically 65µA. The master UVLO

circuit disables all three GATE

n outputs of the LTC4230

until the voltage at VCC3 exceeds 1.19V.

VCC1 (Pin 6): This is the positive supply input to the

LTC4230, the power supply input for Channel 1, and the

power supply input for all three internal charge pumps.

The LTC4230 operates from 2.7V to 16.5V, and the ICC1

supply current is typically 1.8mA. The master UVLO circuit

disables all three GATE

n outputs of the LTC4230 if VCC1 is

less than 2.35V. The internal charge pump outputs are

enabled when VCC1 > 2.35V, VCC2 > 2.15V, and

VCC3 > 1.19V.

SENSE 1 (Pin 7): Circuit Breaker Sense Pin for Channel 1.

With a sense resistor placed in the power path between

VCC1 and SENSE 1, Channel 1’s electronic circuit breaker

trips if the voltage across the sense resistor (VCC1 –

VSENSE1) exceeds the thresholds set internally for SLOW

COMP1 and FAST COMP1, as shown in the Block Diagram.

The threshold for SLOW COMP1 is VCB(SLOW) = 50mV, and

the electronic circuit breaker trips if the voltage across

RSENSE1 exceeds 50mV for 10µs, or for the time delay

programmed by CFILTER. To adjust SLOW COMP1’s delay,

please refer to the section on Adjusting SLOW COMP

n’s

Response Time.

Undertransientconditionswherelargestepcurrentchanges

can and do occur over shorter periods of time, a second

(fast) comparator instead trips the electronic circuit breaker.

The threshold for FAST COMP1 is set at VCB(FAST) = 150mV,

and the circuit breaker trips if the voltage across the

RSENSE1 exceeds 150mV for more than 500ns. FAST

COMP1’s delay is fixed in the LTC4230 and cannot be

adjusted. To disable Channel 1’s electronic circuit breaker,

connect the VCC1 and SENSE 1 pins together.

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