Datasheet

LTC4223-1/LTC4223-2
16
422312f
APPLICATIONS INFORMATION
GATE Pin Voltage
The gate drive at 12V
GATE
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 R
G
and
gate slew rate control capacitor C
G
stabilizes the internal
active current limit circuit. The value of C
G
is selected based
on the inrush current allowed. The suggested value for
R
G
is 47Ω. The value of C
G
should be ≤330nF and R
G
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 amplifi er 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 amplifi er is 82.5mV, corresponding to
an output of about 2.7V. If the input exceeds 100mV, the
output clamps at 3.2V.
V
CC
Supply Filtering
The internal circuitry of the LTC4223 is powered from the
V
CC
pin. Bypass V
CC
with at least 330nF to ground. If V
CC
is derived from the same supply as is AUXIN, include a
decoupling resistor as shown in Figure 11. This RC net-
work allows the V
CC
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 V
CC
. Since the absolute maximum rating for V
CC
is 7V as compared to 10V for AUXIN, select R2 and C2 to
keep the peak voltage seen by V
CC
below 7V during any
voltage spikes.
FAULT
TIMER
I
AUXOUT
12V
OUT
V
TMR
V
TMR
V
TMR
V
TMR
422312 F08
10μA
12 34 5678 9 10
2μA
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
2μA2μA2μA10μA10μA10μA10μA
AUX INTERNAL GATE REGULATES
Figure 8. Auto-Retry after AUX Overcurrent Fault