LTC3722EGN-1#PBF Linear Technology, LTC3722EGN-1#PBF Datasheet - Page 18

• Manufacturer Part Number: LTC3722EGN-1#PBF
• Description: IC CTLR PWM CURRENT-MODE 24SSOP
• Manufacturer: Linear Technology

Specifications of LTC3722EGN-1#PBF

• Pwm Type: Current Mode, Full Bridge
• Number Of Outputs: 1
• Frequency - Max: 1MHz
• Duty Cycle: 98.5%
• Voltage - Supply: 3.8 V ~ 10.3 V
• Buck: No
• Boost: No
• Flyback: No
• Inverting: No
• Doubler: No
• Divider: Yes
• Cuk: No
• Isolated: Yes
• Operating Temperature: -40°C ~ 85°C
• Package / Case: 24-SSOP
• Frequency-max: 1MHz
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

LTC3722-1/LTC3722-2
operaTion
3. Slope compensation is required for most peak current

mode controllers in order to prevent subharmonic
oscillation of the current control loop. In general, if the
system duty cycle exceeds 50% in a fixed frequency,
continuous current mode converter, an unstable con-
dition exists within the current control loop. Any
perturbation in the current signal is amplified by the
PWM modulator resulting in an unstable condition.
Some common manifestations of this include alternate
pulse nonuniformity and pulse width jitter. Fortunately,
this can be addressed by adding a corrective slope to
the current sense signal or by subtracting the same
slope from the current command signal (error am-
plifier output). In theory, the current doubler output
configuration does not require slope compensation
since the output inductor duty cycles only approach
50%. However, transient conditions can momentarily
cause higher duty cycles and therefore, the possibility
for unstable operation.
The exact amount of required slope compensation is
easily programmed by the LTC3722-1/LTC3722-2 with
the addition of a single external resistor (see Figure 9).
The LTC3722-1/LTC3722-2 generates a current that
is proportional to the instantaneous voltage on C
(33µA/V(C
approximately 74µA and is output from the CS pin. A
resistor connected between CS and the external current
sense resistor sums in the required amount of slope
compensation. The value of this resistor is dependent
on several factors including minimum V
ing frequency, current sense resistor value and output
inductor value. An illustrative example with the design
equation for current doubler secondary follows.
Example:
V
V
I
L = 2.2µH
OUT
IN
OUT
= 36V to 72V
= 40A
= 3.3V
T
)). Thus, at the peak of C
T
IN
, this current is
, V
OUT
, switch-
T
,
Transformer turns ratio (N) =
R
R
to account for tolerances in I
R
V
f
=
f
SW
SW
CS
SLOPE
IN MIN
2
SL
3 3
(
.
= 0.05Ω
O O PE
=
C
=
T
V
300
150
= 338Ω, choose the next higher standard value
)
Figure 9. Slope Compensation Circuitry
•
=
•
2
V
kHz i e transformer f
kHz
( •
O
2
DC
• .
LTC3722
•
33k
, . .,
2 2 H H
I =
V
MAX
( • •
OUT
2
V(C
µ
33k
T
L f
)
)
•
0 05
=
300
.
SW
CS
SLOPE
ADDED
5
R
CURRENT SENSE
k
CS
SLOPE
WAVEFORM
•
•
R
74
SLOPE
74
µA N
, R
µA
• )
CS
=
•
, N and L.
5
372212 F09
R
BRIDGE
CURRENT
CS
372212fa