Linear LTC7860 Demo Manual

Description

DEMO MANUAL DC2392A

LTC7860

High Voltage Switching

Surge Stopper

Demonstration circuit 2392A is a high efficiency switching

®

surge stopper featuring the LT C

7860. The board operates

from an input range of 7V to 100V, and provides a 7V to
34V output at 0A to 10A. Its output is current limited. A
soft-start feature controls output voltage slew rate at start­up, reducing current surge and voltage overshoot. The
demonstration board includes an optional reverse polarity
protection MOSFET and has options for an input filter and
diode to attenuate spikes. For a lower output voltage limit
of less than 12V, there is an optional feedback circuit.

The LTC7860 high efficiency surge stopper protects loads
from high voltage transients. High efficiency compared to
linear circuits permits higher currents and smaller solution
sizes. During an input overvoltage event, such as a load
dump in vehicles, the LTC7860 controls the gate of an
external MOSFET to act as a switching DC/DC regulator
(PROTECTIVE PWM mode). This operation regulates the
output voltage to a safe level, allowing the loads to oper

­ate through the input overvoltage event. During normal
operation (SWITCHON mode), the

LTC7860

turns on the
external MOSFET continuously, passing the input voltage
through to the output. An internal comparator limits the

voltage across the current sense resistor and regulates the
maximum output current to protect against overcurrent
faults. An adjustable timer limits the time that the LTC7860
can spend in overvoltage or overcurrent regulation. When
the timer expires, the external MOSFET is turned off until
the LTC7860 restarts after a cool down period. By strictly
limiting the time in PROTECTIVE PWM mode when the
power loss is higher, the components and thermal design
can be optimized for normal operation and safely oper

­ate through high voltage input surges and/or overcurrent
faults. This demo board takes advantage of the LTC7860’s

-centric PMOS architecture to float the control ground

V

IN

allowing operation beyond the controller’s 60V rating.

This board is suitable for a wide range of automotive,
military, telecom, industrial, and other applications. The
LTC7860 is available in a small 12-pin thermally enhanced
MSOP package. For other output requirements, see the
LTC7860 data sheet or contact the LTC factory.

Design files for this circuit board are available at

http://www.linear.com/demo/DC2392A

L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks of Linear
Technology Corporation. All other trademarks are the property of their respective owners.

performance summary

SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS

V

IN

V

OUT

I

OUT

I

LIMIT

I

LIMIT

V

IN-VOUT

F

SW

T

PWM

V

OUT P-P

Input Supply Range Normal Operation 7 32 V

Output Voltage 7 28 35 V

Output Current Range, continuous Free Air 0 10 A

Current Limit VIN = 28V 13 A

Current Limit VIN = 40V 10.5 A

Insertion Loss VIN = 28V, I

Switching (Clock) Frequency 350 kHz

PROTECTIVE PWM Mode Time Limit VIN > 35V 0.85 1.06 1.24 s

Output Ripple VIN = 40V, V

Approximate Size Component Area x Top Component Height 35 × 42 × 10 mm

Specifications are at TA = 25°C

500ms Ride-Through 7 100 V

DC Survival 0 100 V

= 10A 400 mV

OUT

= 17.2V, I

OUT

= 5A (20MHz BW) 100 mV

OUT

P–P

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DEMO MANUAL DC2392A

Quick start proceDure

Demonstration circuit 2392 is easy to set up to evaluate
the performance of the LTC7860. Refer to Figure 1 for
proper measurement equipment setup and follow the
procedure below:

NOTE: When measuring the output voltage ripple, care must
be taken to avoid a long ground lead on the oscilloscope
probe. Measure the output voltage ripple by touching the
probe tip and ground ring directly across the last output
capacitor as shown in Figure 1.

1. Set an input power supply that is capable of 7V to
100V to 10V. Then turn off the supply.

2. With power off, connect the supply to the input termi
nals +VIN and –VIN.

a. Input Voltages lower than 7V can keep the converter

from turning on due to the undervoltage lockout feature
of the LTC7860.

b. A voltmeter with a capability of measuring at least 100V

can be placed across the input terminals in order to
get an accurate input voltage measurement.

3. Turn on the power at the input.

-

5. Once the proper output voltage is established, connect
a variable load capable of sinking 10A at 34V to the
output terminals +V
0A.

a. A Voltmeter with a capability of measuring at least 36V

can be placed across the output terminals in order to
get an accurate output voltage measurement.

6. Turn on the power at the input.

NOTE: If there is no output, temporarily disconnect the

load to make sure that the load is not set too high.

7. Once the proper output voltage is again established,
adjust the load and/or input within the operating range
up to 33V
desired parameters.

8. Now apply an input between 35V and 100V and ob­serve the output voltage and fault timer operation.

9. If desired, you may apply input transient profiles in
the range of 0V
to illustrate operation of the circuit to prevent input
surges from reaching the output.

and observe the output voltage and other

IN

IN

and –V

OUT

to 100VIN and observe the output

. Set the current for

OUT

NOTE: Make sure that the input voltage never exceeds

100V.

4. Check for the proper output voltage of 10V. Turn off
the power at the input.

10. The output limit voltage can be set in accordance
with the feedback notes on the schematic. The first
line shows the complete formula. The second line is
simplified for the use of a 2:1 divider as shown on the
schematic.

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dc2392af

Quick start proceDure

DEMO MANUAL DC2392A

Figure 1. Proper Measurement Equipment Setup

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