LTC1421 datasheet(16/24 Pages) LINER

16 / 24 page

LTC4223-1/LTC4223-2

422312f

APPLICATIONS INFORMATION

GATE Pin Voltage

The gate drive at 12VGATE is compatible with any logic

level MOSFET. The guaranteed range of gate drive is 4.5V

to 7.9V, with a typical of 6.2V.

Active Current Loop Compensation

The compensation network consisting of resistor RG and

gate slew rate control capacitor CG stabilizes the internal

active current limit circuit. The value of CG is selected based

on the inrush current allowed. The suggested value for

RG is 47Ω. The value of CG should be ≤330nF and RG is

between 10Ω and 100Ω for optimum performance.

High Side Current Sense

The 12V load current is monitored via the voltage across an

external sense resistor. The LTC4223 features a high side

current sense ampliﬁer that translates the sense voltage

from the positive rail to the negative rail using a resistor

ratio of 33 times. The output voltage at 12IMON pin can

then be fed into an LTC1197L ADC as shown in Figure 10

for data conversion. The current sense information can be

used by the system controller to manage the power budget

allocated to the modules on the card. Full scale input to

the current sense ampliﬁer is 82.5mV, corresponding to

an output of about 2.7V. If the input exceeds 100mV, the

output clamps at 3.2V.

VCC Supply Filtering

The internal circuitry of the LTC4223 is powered from the

VCC pin. Bypass VCC with at least 330nF to ground. If VCC

is derived from the same supply as is AUXIN, include a

decoupling resistor as shown in Figure 11. This RC net-

work allows the VCC pin to ride out supply glitches caused

by short circuits on the auxiliary output or on adjacent

boards, thus preventing an undervoltage lockout condi-

tion on VCC. Since the absolute maximum rating for VCC

is 7V as compared to 10V for AUXIN, select R2 and C2 to

keep the peak voltage seen by VCC below 7V during any

voltage spikes.

FAULT

TIMER

IAUXOUT

12VOUT

VTMR

422312 F08

μA

5 6 7

μA

FAULT PULLS LOW DUE TO AUX

OVERCURRENT FAULT AFTER POWER UP

START OF COOL-OFF CYCLE

START OF

DEBOUNCE CYCLE

RESET FAULT HIGH

FAULT PULLS LOW AND RESTART OF

COOL-OFF CYCLE DURING POWER UP

END OF DEBOUNCE CYCLE

START AUX INTERNAL GATE RAMP WHEN STARTUP CONDITIONS ARE MET

AUX OUTPUT IN CURRENT LIMIT

RESTART OF

DEBOUNCE CYCLE

COOL-OFF CYCLE

DEBOUNCE CYCLE

FILTER DELAY

COOL-OFF CYCLE

μA2μA2μA

μA10μA10μA10μA

AUX INTERNAL GATE REGULATES

Figure 8. Auto-Retry after AUX Overcurrent Fault

LTC1421 Datasheet(PDF) 16 Page - Linear Technology

LTC1421 Datasheet(HTML) 16 Page - Linear Technology

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

Datasheet Download

Link URL