LT1767EMS8-1.8#TR Linear Technology, LT1767EMS8-1.8#TR Datasheet - Page 9

• Manufacturer Part Number: LT1767EMS8-1.8#TR
• Description: IC SW REG STEP-DOWN 1.8V 8-MSOP
• Manufacturer: Linear Technology
• Type: Step-Down (Buck)r

Specifications of LT1767EMS8-1.8#TR

• Internal Switch(s): Yes
• Synchronous Rectifier: No
• Number Of Outputs: 1
• Voltage - Output: 1.8V
• Current - Output: 1.5A
• Frequency - Switching: 1.25MHz
• Voltage - Input: 3 ~ 25 V
• Operating Temperature: -40°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: 8-MSOP, Micro8™, 8-uMAX, 8-uSOP,
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Power - Output: -
• Other names: LT1767EMS8-1.8TR; LT1767EMS81.8TR

APPLICATIONS
2. Calculate peak inductor current at full load current to
3. Decide if the design can tolerate an “open” core geom-
Table 3
PART NUMBER
Coiltronics
TP1-2R2
TP2-2R2
TP3-4R7
TP4- 100
Murata
LQH1C1R0M04
LQH3C1R0M24
LQH3C2R2M24
LQH4C1R5M04
Sumida
CD73- 100
CDRH4D18-2R2
CDRH5D18-6R2
CDRH5D28-100
saturation of the inductor. In these applications, the
soft-start circuit shown in Figure 10 should be used.
ensure that the inductor will not saturate. Peak current
can be significantly higher than output current,
especially with smaller inductors and lighter loads, so
don’t omit this step. Powdered iron cores are forgiving
because they saturate softly, whereas ferrite cores
saturate abruptly. Other core materials fall somewhere
in between.
V
f = Switching frequency, 1.25MHz
etry like a rod or barrel, which have high magnetic field
radiation, or whether it needs a closed core like a toroid
to prevent EMI problems. This is a tough decision
because the rods or barrels are temptingly cheap and
small and there are no helpful guidelines to calculate
when the magnetic field radiation will be a problem.
IN
I
PEAK
= Maximum input voltage
VALUE (uH)
I
OUT
2.2
2.2
4.7
1.0
1.0
2.2
1.5
2.2
6.2
10
10
10
U
V
OUT
INFORMATION
2
U
I
SAT
L f V
V
0.51
0.79
1.44
1.32
(Amps)
1.3
1.5
1.5
1.5
1.0
1.0
1.4
1.3
IN
V
IN
W
OUT
DCR ( ) HEIGHT (mm)
0.188
0.111
0.181
0.146
0.080
0.058
0.071
0.048
0.28
0.06
0.09
0.1
U
1.8
2.2
2.2
3.0
1.8
2.0
2.0
2.6
3.5
1.8
1.8
2.8
LT1767-2.5/LT1767-3.3/LT1767-5
4. After making an initial choice, consider the secondary
CATCH DIODE
The suggested catch diode (D1) is a UPS120 Schottky, or
its Motorola equivalent, MBRM120LTI/MBRM130LTI. It
is rated at 2A average forward current and 20V/30V
reverse voltage. Typical forward voltage is 0.5V at 1A. The
diode conducts current only during switch off time. Peak
reverse voltage is equal to regulator input voltage. Average
forward current in normal operation can be calculated
from:
BOOST PIN
For most applications, the boost components are a 0.1 F
capacitor and a CMDSH-3 diode. The anode is typically
connected to the regulated output voltage to generate a
voltage approximately V
stage. The output driver requires at least 2.7V of head-
room throughout the on period to keep the switch fully
saturated. However, the output stage discharges the boost
capacitor during the on time. If the output voltage is less
than 3.3V, it is recommended that an alternate boost
supply is used. The boost diode can be connected to the
input, although, care must be taken to prevent the 2x V
boost voltage from exceeding the BOOST pin absolute
maximum rating. The additional voltage across the switch
driver also increases power loss, reducing efficiency. If
available, an independent supply can be used with a local
bypass capacitor.
A 0.1 F boost capacitor is recommended for most appli-
cations. Almost any type of film or ceramic capacitor is
I
things like output voltage ripple, second sourcing, etc.
Use the experts in the Linear Technology’s applica-
tions department if you feel uncertain about the final
choice. They have experience with a wide range of
inductor types and can tell you about the latest devel-
opments in low profile, surface mounting, etc.
D AVG
I
OUT
V
IN
V
LT1767/LT1767-1.8/
IN
OUT
V
OUT
above V
IN
to drive the output
sn1767 1767fas
9
IN