Linear Technology 397 Manuale utente

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 397

2.2MHZ, SOT-23 DC/DC CONVERTER

LT1930A and LT1931A

DESCRIPTION

Demonstration circuit 397 is a multipurpose DC/DC

switching regulator using the LT1930A and LT1931A, the

industry’s fastest and highest power voltage regulator in

a SOT-23 package. The demo board offers three sepa-

rate DC/DC converters for different applications needs.

The boost circuit is designed to convert a 5V input to

12V output at 250mA maximum load. The SEPIC circuit

generates a constant 12V/250mA (max load) output with

a 10V~16V variable input. The inverter circuit is de-

signed for applications requiring negative 12V/250mA

(max load) from a positive 12V input. All three circuits

are designed to demonstrate fast switching frequency

(2.2Mhz), an internal 36V/1A switch, wide input range,

and small circuit size. These circuits are designed for

space-conscious low profile applications such as cellular

phones, palm top computers, digital cameras, and LCD

displays. The 2.2MHz switching frequency, 1A integrated

switch, small circuit size, and low component count

makes the LT1930A and LT1931A also suitable for PC

cards, miniature disk drives, xDSL power supplies, flash

memory products, and local 5V or 12V supplies.

Design files for this circuit board are available. Call

the LTC factory.

QUICK START PROCEDURE

Demonstration circuit 397 is easy to set up to evaluate

the performance of the LT1930A and LT1931A. Refer to

Figure 1, Figure 2 and Figure 3 for proper measurement

equipment setup and follow the procedures below:

NOTE:

When measuring the output ripple, see Figure 4

for proper scope probe technique.

The equipment setup for the three circuits is very simi-

lar. They all have three pins marked “Vin,” “Gnd”, “Vout”

and a jumper marked “on” and “off” for demonstrating

the shutdown function.

BOOST CIRCUIT (LEFT SIDE OF BOARD)

Before turning on the power, connect a 5V, 1A bench

supply to the Vin and Gnd terminals and connect the

output loads (up to 250mA).

When an electronic load is used, connect the load

AFTER turning on the input supply and the output

voltage has stabilized.

Connect the oscilloscope and meters to the Vout and

Gnd terminals, as shown in Figure 1. For the best ac-

curacy it is important to connect true RMS reading

voltmeters directly to the PCB terminals where the in-

put and output voltage are connected. True RMS read-

ing ammeters should be used for current measure-

ments.

Turn on the input power supply and observe the out-

put. The DC397 boost circuit is programmed to gen-

erate 12V from a 5V input. The circuit will deliver up

to 250mA at 12V.

With the 250mA load at the output observe the

switching frequency ripple at the output using the os-

cilloscope. The typical switching frequency is around

2.2MHz. See Figure 4 for proper measurement tech-

nique.

The current limit is tested by increasing the load past

300mA. The current limit will take effect when the

peak switch current becomes higher than ~1A. When

the current limit is exceeded, the output voltage will

drop drastically. Return to normal operation by re-

moving the load.

The SHUTDOWN function is tested by placing the

jumper in the off position. This will short the shut-

down pin to ground and turn off the internal switch of

the LT1930A. Placing the jumper in the on position

will return the circuit to normal operation.

SEPIC CIRCUIT (MIDDLE OF BOARD)

Before turning on the power, connect a 16V, 1A bench

supply to the Vin and Gnd terminals and connect the

output load (up to 250mA).

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 397

2.2MHZ, SOT-23 DC/DC CONVERTER

When an electronic load is used, connect the load

AFTER turning on the input supply and the output

voltage has stabilized.

Connect the oscilloscope and meters to the Vout and

Gnd terminals, as shown in Figure 2. For the best ac-

curacy it is important to connect true RMS reading

voltmeters directly to the PCB terminals where the in-

put and output voltage are connected. True RMS read-

ing ammeters should be used for current measure-

ments.

Turn on the input power supply and observe the out-

put. The DC397 SEPIC Circuit is programmed to gen-

erate 12V from a 10V~16V input. Vary the input volt-

age to test the line regulation. The circuit is design to

deliver up to 250mA at the 12V output.

With the 250mA load at the output, observe the

switching frequency ripple at the output using the os-

cilloscope. The typical switching frequency is around

2.2Mhz. See Figure 4 for proper measurement tech-

nique.

The current limit is tested by increasing the load past

300mA. The current limit will take effect when the

peak switch current becomes higher than ~1A. When

the current limit is exceeded, the output voltage will

drop drastically. Return to normal operation by re-

moving the load.

The SHUTDOWN function is tested by placing the

jumper in the off position. This will short the shut-

down pin to ground and turn off the internal switch of

the LT1930A. Placing the jumper in the on position

will return the circuit to normal operation.

INVERTER CIRCUIT (RIGHT SIDE OF BOARD)

Before turning on the power, connect a 12V, 1A bench

supply to the Vin and Gnd terminals and connect the

output load (up to 250mA).

When an electronic load is used, connect the load

AFTER turning on the input supply and the output

voltage has stabilized.

Connect the oscilloscope and meters to the Vout and

Gnd terminals, as shown in Figure 3. For the best ac-

curacy it is important to connect true RMS reading

voltmeters directly to the PCB terminals where the in-

put and output voltage are connected. True RMS read-

ing ammeters should be used for current measure-

ments.

Turn on the input power supply and observe the out-

put. The DC397 inverter circuit is programmed to

generate –12V from a +12V input. The circuit will de-

liver up to 250mA at –12V.

With the 250mA load at the output, observe the

switching frequency ripple at the output using the os-

cilloscope. The typical switching frequency is around

1.2MHz. See Figure 4 for proper measurement tech-

nique.

The current limit is tested by increasing the load past

300mA. The current limit will take effect when the

peak switch current becomes higher than ~1A. When

the current limit is exceeded, the output voltage will

drop drastically. Return to normal operation by re-

moving the load.

The SHUTDOWN function is tested by placing the

jumper in the off position. This will short the shut-

down pin to ground and turn off the internal switch of

the LT1931A. Placing the jumper in the on position

will return the circuit to normal operation.

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 397

2.2MHZ, SOT-23 DC/DC CONVERTER

–

+–

–

LOAD

POWER

SUPPLY

VinVout Gnd

Off

]

Shdn

LT1930ES5—Demo Circuit 383A

.2MHz, SOT-23 DC/DC Converter

BOOST CIRCUIT: 5V to 12V/300mA

Figure 1.

Proper Measurement Equipment Setup for Boost Circuit

–

+–

–

LOAD

POWER

SUPPLY

VinVout Gnd

Off

]

Shdn

LT1930ES5—Demo Circuit 383A

.2MHz, SOT-23 DC/DC Converter

SEPIC CIRCUIT: 10V to 16Vin/12V/300mA out

Figure 2.

Proper Measurement Equipment Setup for SEPIC Circuit

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 397

2.2MHZ, SOT-23 DC/DC CONVERTER

–

+–

–+

–

LOAD

POWER

SUPPLY

VinVout Gnd

Off

]

Shdn

LT1931ES5—Demo Circuit 383A

.2MHz, SOT-23 DC/DC Converter

INVERTER CIRCUIT: 12V to –12V/300mA

Figure 3.

Proper Measurement Equipment Setup for Inverter Circuit

VIN

GND

Figure 4.

Scope Probe Placement for Measuring Output Ripple

Mouser Electronics

Authorized Distributor

Click to View Pricing, Inventory, Delivery & Lifecycle Information:

Analog Devices Inc.:

DC397A

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