LT1766EFE#TRPBF Linear Technology, LT1766EFE#TRPBF Datasheet - Page 11

• Manufacturer Part Number: LT1766EFE#TRPBF
• Description: IC REG SW HV 1.5A 200KHZ 16TSSOP
• Manufacturer: Linear Technology
• Type: Step-Down (Buck)r

Specifications of LT1766EFE#TRPBF

• Internal Switch(s): Yes
• Synchronous Rectifier: No
• Number Of Outputs: 1
• Voltage - Output: 1.2 ~ 54 V
• Current - Output: 1.5A
• Frequency - Switching: 200kHz
• Voltage - Input: 5.5 ~ 60 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
• Power - Output: -

APPLICATIONS INFORMATION
divider impedance is not critical, caution should be used if
resistors are increased beyond the suggested values and
short-circuit conditions occur with high input voltage. High
frequency pickup will increase and the protection accorded
by frequency and current foldback will decrease.
CHOOSING THE INDUCTOR
For most applications, the output inductor will fall into
the range of 15μH to 100μH. Lower values are chosen to
reduce physical size of the inductor. Higher values allow
more output current because they reduce peak current
seen by the LT1766 switch, which has a 1.5A limit. Higher
values also reduce output ripple voltage.
When choosing an inductor you will need to consider
output ripple voltage, maximum load current, peak induc-
tor current and fault current in the inductor. In addition,
other factors such as core and copper losses, allowable
component height, EMI, saturation and cost should also
be considered. The following procedure is suggested
as a way of handling these somewhat complicated and
confl icting requirements.
Output Ripple Voltage
Figure 3 shows a typical output ripple voltage wave-
form for the LT1766. Ripple voltage is determined by
ripple current (I
frequency impedance of the output capacitor. The fol-
lowing equations will help in choosing the required
LP-P
) through the inductor and the high
LT1766
V
C
Q2
GND
AMPLIFIER
ERROR
TO SYNC CIRCUIT
Figure 2. Frequency and Current Limit Foldback
TO FREQUENCY
SHIFTING
+
–
1.4V
1.2V
R3
1k
BUFFER
Q1
R4
2k
inductor value to achieve a desirable output ripple volt-
age level. If output ripple voltage is of less importance,
the subsequent suggestions in Peak Inductor and Fault
Current and EMI will additionally help in the selection of
the inductor value.
Peak-to-peak output ripple voltage is the sum of a triwave
(created by peak-to-peak ripple current (I
and a square wave (created by parasitic inductance (ESL)
and ripple current slew rate). Capacitive reactance is as-
sumed to be small compared to ESR or ESL.
40mV/DIV
0.5A/DIV
V
RIPPLE
Figure 3. LT1766 Ripple Voltage Waveform
V
V
L = 47μH
C = 100μF, 10V, 0.1Ω
IN
OUT
=
V
= 40V
SW
FB
(
= 5V
I
LP P
-
L1
)(
ESR
2.5μs/DIV
R1
R2
5k
LT1766/LT1766-5
+
)
+
1766 F02
C1
(
ESL
OUTPUT
5V
)
dt
dI
1766 F03
LP-P
V
V
INDUCTOR CURRENT
AT I
INDUCTOR CURRENT
AT I
OUT
OUT
OUT
OUT
) times ESR)
AT I
AT I
= 1A
= 0.1A
OUT
OUT
11
= 1A
= 0.1A
1766fc