LT1307BIS8#PBF Linear Technology, LT1307BIS8#PBF Datasheet - Page 12

• Manufacturer Part Number: LT1307BIS8#PBF
• Description: IC DC/DC CONV SINGLE CELL 8-SOIC
• Manufacturer: Linear Technology
• Type: Step-Up (Boost)r

Specifications of LT1307BIS8#PBF

• Internal Switch(s): Yes
• Synchronous Rectifier: No
• Number Of Outputs: 1
• Voltage - Output: 3.3V, 5V
• Current - Output: 100mA
• Frequency - Switching: 600kHz
• Voltage - Input: 1 ~ 5 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 8-SOIC (3.9mm Width)
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Power - Output: -

APPLICATIO S I FOR ATIO
LT1307/LT1307B
LAYOUT HINTS
The LT1307 switches current at high speed, mandating
careful attention to layout for proper performance. You will
not get advertised performance with careless layouts.
Figure 12 shows recommended component placement.
Follow this closely in your PC layout. Note the direct path
of the switching loops. Input capacitor C
close (< 5mm) to the IC package. As little as 10mm of wire
or PC trace from C
inability to regulate or oscillation. A 1 F ceramic bypass
capacitor is the only input capacitance required provided
the battery has a low inductance path to the circuit . The
battery itself provides the bulk capacitance the device
requires for proper operation. If the battery is located some
distance from the circuit, an additional input capacitor may
be required. A 100 F aluminum electrolytic unit works well
in these cases. This capacitor need not have low ESR.
Figure 12. Recommended Component Placement. Traces
Carrying High Current Are Direct. Trace Area at FB Pin and V
Pin is Kept Low. Lead Length to Battery Should Be Kept Short
12
OPERATION FROM A LABORATORY POWER SUPPLY
If a lab supply is used, the leads used to connect the circuit
to the supply can have significant inductance at the
LT1307’s switching frequency. As in the previous situa-
tion, an electrolytic capacitor may be required at the circuit
in order to reduce the AC impedance of the input suffi-
ciently. An alternative solution would be to attach the
circuit directly to the power supply at the supply terminals,
without the use of leads. The power supply’s output
capacitance will then provide the bulk capacitance the
LT1307 circuit requires.
R1
R2
R
1
2
3
4
C
C
C
IN
U
LT1307
to V
U
IN
8
7
6
5
will cause problems such as
L
D
V
W
OR LEADS SHORT!
OUT
C
OUT
KEEP TRACES
IN
C
IN
must be placed
GROUND
U
1307 F12
C
COMPONENT SELECTION
Inductors
Inductors appropriate for use with the LT1307 must pos-
sess three attributes. First, they must have low core loss at
600kHz. Most ferrite core units have acceptable losses at
this switching frequency. Inexpensive iron powder cores
should be viewed suspiciously, as core losses can cause
significant efficiency penalties at 600kHz. Second, the
inductor must handle current of 500mA without saturat-
ing. This places a lower limit on the physical size of the unit.
Molded chokes or chip inductors usually do not have
enough core to support 500mA current and are unsuitable
for the application. Lastly, the inductor should have low
DCR (copper wire resistance) to prevent efficiency-killing
I
tors suitable for use with the LT1307. This is not an
exclusive list. There are many magnetics vendors whose
components are suitable for use. A few vendor’s compo-
nents are listed in Table 1.
Table 1. Inductors Suitable for Use with the LT1307
PART
LQH3C100
DO1608-103
CD43-100
CD54-100
CTX32CT-100 10 H
Capacitors
For single cell applications, a 10 F ceramic output capaci-
tor is generally all that is required. Ripple voltage in Burst
Mode can be reduced by increasing output capacitance.
For 2- and 3-cell applications, more than 10 F is needed.
For a typical 2-cell to 5V application, a 47 F to 100 F low
ESR tantalum capacitor works well. AVX TPS series (100%
surge tested) or Sprague (don’t be vague—ask for Sprague)
594D series are both good choices for low ESR capacitors.
Alternatively, a 10 F ceramic in parallel with a low cost
(read high ESR) electrolytic capacitor, either tantalum or
aluminum, can be used instead. For through hole applica-
2
R losses. Linear Technology has identified several induc-
VALUE
10 H
10 H
10 H
10 H
MAX
DCR
0.57
0.16
0.18
0.10
0.50
Murata-Erie
Coiltronics
Coilcraft
Sumida
Sumida
MFR
HEIGHT
(mm)
2.0
3.0
3.2
4.5
2.2
COMMENT
Smallest Size
Best Efficiency
1210 Footprint
1307fa