LT1738EG#TRPBF Linear Technology, LT1738EG#TRPBF Datasheet - Page 11

• Manufacturer Part Number: LT1738EG#TRPBF
• Description: IC DC/DC CONTRLR LOW NOIS 20SSOP
• Manufacturer: Linear Technology
• Type: Step-Up (Boost), Cuk, Flybackr

Specifications of LT1738EG#TRPBF

• Internal Switch(s): No
• Synchronous Rectifier: No
• Number Of Outputs: 1
• Voltage - Output: 5 ~ 100 V
• Frequency - Switching: 20kHz ~ 250kHz
• Voltage - Input: 2.55 ~ 20 V
• Operating Temperature: -40°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: 20-SSOP
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Current - Output: -
• Power - Output: -

OPERATIO
APPLICATIO S I FOR ATIO
Table 1. Safety and Protection Features
FEATURE
Maximum Current Fault
Short-Circuit Fault
Overvoltage Fault
GCL Clamp
Gate Drive
Undervoltage Lockout
Thermal Shutdown
V
Gate Drive Source and Sink Current Limit
V5 Source/Sink Current Limit
Shutdown
Reducing EMI from switching power supplies has tradi-
tionally invoked fear in designers. Many switchers are
designed solely on efficiency and as such produce wave-
forms filled with high frequency harmonics that then
propagate through the rest of the system.
The LT1738 provides control over two of the more impor-
tant variables for controlling EMI with switching inductive
loads: switch voltage slew rate and switch current slew
rate. The use of this part will reduce noise and EMI over
conventional switch mode controllers. Because these
variables are under control, a supply built with this part will
exhibit far less tendency to create EMI and less chance of
encountering problems during production.
It is beyond the scope of this data sheet to get into EMI
fundamentals. Application Note 70 contains much infor-
mation concerning noise in switching regulators and
should be consulted.
Oscillator Frequency
The oscillator determines the switching frequency and
therefore the fundamental positioning of all harmonics.
The use of good quality external components is important
IN
Undervoltage Lockout
U
U
U
W
FUNCTION
Turn Off FET at Maximum
Switch Current (V
Turn Off FET and Reset V
for Short-Circuit (V
Turn Off Driver If FB > V
(Output Overvoltage)
Set Max Gate Voltage to Prevent
FET Gate Breakdown
Disable Gate Drive When V
Is Too Low. Set Via GCL Pin
Turn Off Driver If Chip
Temperature Is Too Hot
Disable Part When V
Limit Gate Drive Current
Limit Current from V5
Disable Part When SHDN <1.3V
U
SENSE
SENSE
IN
= 0.1)
REG
2.55V
C
= 0.22)
IN
+ 0.22V
to ensure oscillator frequency stability. The oscillator is of
a sawtooth design. A current defined by external resistor
R
discharge rate is approximately ten times the charge rate.
By allowing the user to have control over both compo-
nents, trimming of oscillator frequency can be more easily
achieved.
The external capacitance C
where f is the desired oscillator frequency in kHz. For R
equal to 16.9k, this simplifies to:
Nominally R
temperature coefficient should be selected to compliment
the capacitor. Ideally, both should have low temperature
coefficients.
T
e.g., C
is used to charge and discharge the capacitor C
C nF
C nF
T
T
EFFECT on GATE DRIVER
Immediately Goes Low
Immediately Goes Low
Immediately Goes Low
Limits Max Voltage
Immediately Goes Low
Immediately Goes Low
Immediately Goes Low
Limit Drive Current
None
( )
( )
T
= 1.29nF for f = 100kHz
T
f kHz R k
f kHz
should be 16.9k. Since it sets up current, its
(
(
129
2180
)•
)
T
(
T
SLEW CONTROL EFFECT on V
Overridden
Overridden
Overridden
None
Overridden
Overridden
Overridden
None
None
)
is chosen by:
None
Discharge V
to GND
None
None
None
None
None
None
None
LT1738
11
T
C
C
, SS
. The
, SS
1738fa
T