LT1339ISW#PBF Linear Technology, LT1339ISW#PBF Datasheet - Page 10

• Manufacturer Part Number: LT1339ISW#PBF
• Description: IC DC/DC CONTROLLER HIPWR 20SOIC
• Manufacturer: Linear Technology
• Type: Step-Up (Boost)r

Specifications of LT1339ISW#PBF

• Internal Switch(s): No
• Synchronous Rectifier: Yes
• Number Of Outputs: 1
• Current - Output: 65mA
• Frequency - Switching: 150kHz
• Voltage - Input: Up to 60V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 20-SOIC (7.5mm Width)
• Primary Input Voltage: 60V
• No. Of Outputs: 1
• Output Voltage: 54V
• Output Current: 65mA
• No. Of Pins: 20
• Operating Temperature Range: -40°C To +85°C
• Msl: MSL 1 - Unlimited
• Rohs Compliant: Yes
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Voltage - Output: -
• Power - Output: -

LT1339
APPLICATIONS
R
R
inductor current for use by the LT1339 current sense
amplifier. The value of R
load current. The average current limit function has a
typical threshold of 120mV/R
Operation with V
may slightly degrade current limit accuracy. See Average
Current Limit Threshold Tolerance vs Common Mode
Voltage curve in the Typical Performance Characteristics
section for more information.
Output Voltage Programming
Output voltage is programmed through a resistor feed-
back network to V
inverting input of the error amplifier, which is internally
referenced to 1.25V. The divider is ratioed to provide
1.25V at the V
The output voltage is thus set following the relation:
when an external resistor divider is connected to the
output as shown in Figure 1.
10
If high value feedback resistors are used, the input bias
current of the V
increase in output voltage. A Thevenin resistance at the
V
Oscillator Components R
The LT1339 oscillator creates a modified sawtooth wave
at its timing node (CT) with a slow charge, rapid discharge
characteristic. The rapid discharge time corresponds to
SENSE
SENSE
FB
R
V
OUT
SENSE
pin of <5k is recommended.
Selection for Output Current
Figure 1. Programming LT1339 Output Voltage
generates a voltage that is proportional to the
= 1.25(1 + R2/R1)
= 120mV/I
FB
FB
pin when the output is at its desired value.
SENSE
pin (1 A maximum) could cause a slight
FB
U
(Pin 9) on the LT1339. This pin is the
LT1339
LIMIT
SGND
common mode voltage below 4.5V
8
INFORMATION
SENSE
U
CT
V
FB
and C
SENSE
9
is based on the required
V
OUT
CT
, or:
W
R2
R1
1339 • F01
U
the minimum off-time of the PWM controller. This limits
maximum duty cycle (DC
This relation corresponds to the minimum value of the
timing resistor (R
to the following relation (R
the Typical Performance Characteristics section):
Values for R
90%. Given a timing resistor value, the value of the timing
capacitor (C
ating frequency (f
A plot of Operating Frequency vs R
Figure 2. Typical 100kHz operational values are C
1000pF and R
Average Current Limit
The average current limit function is implemented using
an external capacitor (C
that forms a single pole integrator with the 50k output
DC
R
C
CT(MIN)
CT
MAX
Figure 2. Oscillator Frequency vs R
= 1 – (t
R
160
140
120
100
CT
CT
CT
80
60
40
20
0
[(0.8)(10
CT
) can then be determined for desired oper-
0
/ .
> 15k yield maximum duty cycles above
1 85
= 16.9k.
CT
C
DISCH
O
CT
) using the relation:
), which can be determined according
5
= 3.3nF
C
1
CT
TIMING RESISTOR (k )
)(f
/
AVG
–3
= 2.2nF
f
10
O
O
MAX
)(1 – DC
2 5 10
) connected from I
)
CT
.
C
CT
) to:
15
vs DC
100 10
= 1.0nF
C
MAX
20
CT
CT
3
MAX
= 1.5nF
1 75
and C
)]
.
25
graph appears in
–1
LT1339 • F02
9
CT
3 375
.
, C
CT
30
AVG
CT
is shown in
sn1339 1339fas
/
to SGND
R
CT
CT
=