LTC3723EGN-2 Linear Technology, LTC3723EGN-2 Datasheet - Page 14

• Manufacturer Part Number: LTC3723EGN-2
• Description: IC CTRLR PWM SYNC PUSHPLL 16SSOP
• Manufacturer: Linear Technology

Specifications of LTC3723EGN-2

• Pwm Type: Voltage Mode
• Number Of Outputs: 1
• Frequency - Max: 1MHz
• Duty Cycle: 50%
• Buck: No
• Boost: No
• Flyback: Yes
• Inverting: No
• Doubler: No
• Divider: No
• Cuk: No
• Isolated: Yes
• Operating Temperature: -40°C ~ 85°C
• Package / Case: 16-SSOP
• Frequency-max: 1MHz
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Voltage - Supply: -

OPERATIO
LTC3723-1/LTC3723-2
The LTC3723-1 derives a compensating slope current
from the oscillator ramp waveform and sources this
current out of CS. This function is disabled in the
LTC3723-2. The desired level of slope compensation is
selected with an external resistor connected between CS
and the external current sense resistor, (Figure 11).
Current Sensing and Overcurrent Protection
Current sensing provides feedback for the current mode
control loop and protection from overload conditions. The
LTC3723-1/LTC3723-2 are compatible with either resis-
tive sensing or current transformer methods. Internally
connected to the LTC3723-1/LTC3723-2 CS pin are two
comparators that provide pulse-by-pulse and overcurrent
shutdown functions respectively, (Figure 12).
14
R
CS
CS
300mV
600mV
PULSE BY PULSE
Figure 12. Current Sense/Fault Circuitry Detail
CURRENT LIMIT
CURRENT LIMIT
OVERLOAD
Figure 11. Slope Compensation Circuitry
+
–
+
–
C
T
PWM
ENABLE
UVLO
U
LTC3723
33k
I =
V(C
LATCH
33k
PWM
S
T
Q
)
R
S Q
PWM
LOGIC
CS
SLOPE
ADDED
CURRENT SENSE
WAVEFORM
R
UVLO
ENABLE
SLOPE
372312 F11
R
–
–
SWITCH
CURRENT
S Q
R
+
+
Q
CS
0.4V
4.1V
Q
H = SHUTDOWN
OUTPUTS
13µA
372312
SS
C
F12
SS
The pulse-by-pulse comparator has a 300mV nominal
threshold. If the 300mV threshold is exceeded, the PWM
cycle is terminated. The overcurrent comparator is set
approximately 2x higher than the pulse-by-pulse level. If
the current signal exceeds this level, the PWM cycle is
terminated, the soft-start capacitor is quickly discharged
and a soft-start cycle is initiated. If the overcurrent condi-
tion persists, the LTC3723-1/LTC3723-2 halts PWM op-
eration and waits for the soft-start capacitor to charge up
to approximately 4V before a retry is allowed. The soft-
start capacitor is charged by an internal 13µA current
source. If the fault condition has not cleared when soft-
start reaches 4V, the soft-start pin is again discharged and
a new cycle is initiated. This is referred to as hiccup mode
operation. In normal operation and under most abnormal
conditions, the pulse-by-pulse comparator is fast enough
to prevent hiccup mode operation. In severe cases, how-
ever, with high input voltage, very low R
and a shorted output, or with saturating magnetics, the
overcurrent comparator provides a means of protecting
the power converter.
Leading Edge Blanking
The LTC3723-1/LTC3723-2 provides programmable lead-
ing edge blanking to prevent nuisance tripping of the
current sense circuitry. Leading edge blanking relieves the
filtering requirements for the CS pin, greatly improving the
response to real overcurrent conditions. It also allows the
use of a ground referenced current sense resistor or
transformer(s), further simplifying the design. With a
single 10k to 100k resistor from R
times of approximately 40ns to 320ns are programmed. If
not required, connecting R
edge blanking. Keep in mind that the use of leading edge
blanking will slightly reduce the linear control range for the
pulse width modulator.
LEB
to V
REF
LEB
can disable leading
to GND, blanking
DS(ON)
MOSFETs
372312f