LT1170 View Datasheet(PDF) - Linear Technology

Part Name

Description

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LT1170

100kHz, 5A, 2.5A and 1.25A High Efficiency Switching Regulators

Linear Technology 

LT1170/LT1171/LT1172

ELECTRICAL CHARACTERISTICS The q denotes the specifications which apply over the full operating tem-

perature range, otherwise specifications are at TA = 25°C. VIN = 15V, VC = 0.5V, VFB = VREF, output pin open, unless otherwise noted.

SYMBOL

∆IIN

∆ISW

f

PARAMETER

Supply Current Increase

During Switch On-Time

Switching Frequency

CONDITIONS

DCMAX

Maximum Switch Duty Cycle

Shutdown Mode

Supply Current

Shutdown Mode

Threshold Voltage

Flyback Sense Delay Time (Note 5)

3V ≤ VIN ≤ VMAX

VC = 0.05V

3V ≤ VIN ≤ VMAX

MIN TYP MAX

25 35

UNITS

mA/A

88 100 112

kHz

q

85

115

kHz

q

85

92 97

%

100 250

µA

100 150 250

mV

q

50

300

mV

1.5

µs

Note 1: Absolute Maximum Ratings are those values beyond which the life

of the device may be impaired.

Note 2: Minimum effective switch “on” time for the LT1170/71/72 (in current

limit only) is ≈ 0.6µs. This limits the maximum safe input voltage during an

output shorted condition. Buck mode and inverting mode input voltage during

an output shorted condition is limited to:

VIN (max, output shorted)

buck and inverting mode

=

15V

+

(R)(IL) +

(t)(f)

Vf

R = Inductor DC resistance

IL = 10A for LT1170, 5A for LT1171, and 2.5A for LT1172

Vf = Output catch diode forward voltage at IL

t = 0.6µs, f = 100kHz switching frequency

Maximum input voltage can be increased by increasing R or Vf.

External current limiting such as that shown in AN19, Figure 39, will

provide protection up to the full supply voltage rating. C1 in Figure 39

should be reduced to 200pF.

Transformer designs will tolerate much higher input voltages because

leakage inductance limits rate of rise of current in the switch. These

designs must be evaluated individually to assure that current limit is well

controlled up to maximum input voltage.

Boost mode designs are never protected against output shorts because

the external catch diode and inductor connect input to output.

Note 3: Measured with VC in hi clamp, VFB = 0.8V. ISW = 4A for LT1170,

2A for LT1171, and 1A for LT1172.

Note 4: For duty cycles (DC) between 50% and 80%, minimum

guaranteed switch current is given by ILIM = 3.33 (2 – DC) for the LT1170,

ILIM = 1.67 (2 – DC) for the LT1171, and ILIM = 0.833 (2 – DC) for the

LT1172.

Note 5: Minimum input voltage for isolated flyback mode is 7V. VMAX =

55V for HV grade in fully isolated mode to avoid switch breakdown.

TYPICAL PERFOR A CE CHARACTERISTICS

Switch Current Limit vs Duty Cycle*

16

12

–55°C

25°C

8

125°C

4

* DIVIDE VERTICAL SCALE BY TWO FOR

LT1171, BY FOUR FOR LT1172.

0

0 10 20 30 40 50 60 70 80 90 100

DUTY CYCLE (%)

1170/1/2 G01

Minimum Input Voltage

2.9

SWITCH CURRENT = IMAX

2.8

2.7

2.6

SWITCH CURRENT = 0A

2.5

2.4

2.3

–75 –50 –25 0 25 50 75 100 125 150

TEMPERATURE (°C)

1170/1/2 G02

Switch Saturation Voltage

1.6

1.4

150°C

1.2

100°C

1.0

0.8

25°C

–55°C

0.6

0.4

0.2

* DIVIDE CURRENT BY TWO FOR

LT1171, BY FOUR FOR LT1172.

0

0 1 2 34 56 78

SWITCH CURRENT (A)*

1170/1/2 G03

4

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