LT3837EFE#TRPBF Linear Technology, LT3837EFE#TRPBF Datasheet - Page 19

• Manufacturer Part Number: LT3837EFE#TRPBF
• Description: IC CNTRLR SYNC ISO 16TSSOP
• Manufacturer: Linear Technology
• Type: Flybackr

Specifications of LT3837EFE#TRPBF

• Internal Switch(s): No
• Synchronous Rectifier: Yes
• Number Of Outputs: 1
• Frequency - Switching: 50kHz ~ 250kHz
• Voltage - Input: 4.5 ~ 20 V
• Operating Temperature: -40°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: 16-TSSOP Exposed Pad, 16-eTSSOP, 16-HTSSOP
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Current - Output: -
• Voltage - Output: -
• Power - Output: -

APPLICATIONS INFORMATION
dropping the voltage on UVLO. In this manner, hysteresis
is produced.
Referring to Figure 4, the voltage hysteresis at V
equal to the change in bias current times R
procedure is to select the desired V
hysteresis, V
where:
R
If we wanted a V
of hysteresis (on at 8.4V, off at 8.1V):
Even with good board layout, board noise may cause
problems with UVLO. You can fi lter the divider but keep
large capacitance off the UVLO node because it will slow
the hysteresis produced from the change in bias current.
Figure 4c shows an alternate method of fi ltering by split-
ting the R
put more of the resistance on the UVLO side.
V
(4a) UV Turning ON
B
IN
I
R
R
R
R
R
R
is then selected with the desired turn-on voltage:
UVLO
A
B
B
B
A
A
=
=
=
=
UVLO
⎛
⎜
⎝
⎛
⎝ ⎜
= I
V
3 4
0 3
LT3837
I
UVHYS
.
1 24
A
UVLO
V
V
.
8 4
UVLOL
IN ON
.
UVLO
86 6
μA
resistor with the capacitor. The split should
.
I
V
UVLO
UVHYS
(
R
V
.
V V
A
=
)
k
IN
–
88 2
– I
– 1
. Then:
-referred trip point of 8.4V, with 0.3V
1
⎞
⎠ ⎟
(4b) UV Turning OFF
UVLOH
. ,
V
⎞
⎟
⎠
IN
=
k use
R
R
A
B
14 99
Figure 4
.
UVLO
is approximately 3.4μA
LT3837
86 6
k use
,
I
.
UVLO
k
15
IN
k
referred voltage
(4c) UV Filtering
A
C
. The design
UVLO
V
IN
R
R
R
3837 F04
A1
A2
B
IN
UVLO
is
In further contrast to traditional current mode switchers,
V
The dynamic nature of the clamped feedback amplifi er
forms an effective track/hold type response, whereby the
V
held during the subsequent switch-on portion of the next
cycle. This action naturally holds the V
during the current comparator sense action (current mode
switching).
AN19 provides a method for empirically tweaking frequency
compensation. Basically, it involves introducing a load
current step and monitoring the response.
Slope Compensation
This part incorporates current slope compensation. Slope
compensation is required to ensure current loop stability
when the DC is greater than 50%. In some switcher con-
trollers, slope compensation reduces the maximum peak
current at higher duty cycles. The LT3837 eliminates this
need by having circuitry that compensates for the slope
compensation so that maximum current sense voltage is
constant across all duty cycles.
Control Loop Compensation
Loop frequency compensation is performed by connect-
ing a capacitor network from the output of the feedback
amplifi er (V
cause of the sampling behavior of the feedback amplifi er,
compensation is different from traditional current mode
switcher controllers. Normally only C
can be used to add a “zero” but the phase margin improve-
ment traditionally offered by this extra resistor is usually
already accomplished by the nonzero secondary circuit
impedance. C
frequency pole and is usually sized at 0.1 times C
C
C
pin ripple is generally not an issue with the LT3837.
voltage changes during the fl yback pulse, but is then
C
Figure 5. V
VC2
pin) to ground as shown in Figure 5. Be-
can be used to add an additional high
V
9
C
C
Compensation Network
3825 F05
C
VC2
R
VC
C
VC
VC
C
is required. R
voltage stable
LT3837
19
VC
.
3837fc
VC