5

LTC1574

LTC1574-3.3/LTC1574-5

going into Pin 12 being negligible, the following expres-

sion is used for setting the trip limit:

V

R

R









125 1

4

3

.

difference between the absolute maximum voltage rating

and the output voltage. A maximum of 12V is specified in

that the circuit can operate from a minimum of 4V,

making it ideal for a four NiCd cell application. For a

higher output current circuit, please refer to the Typical

Applications section.

LTC1574

–

+

1.25V

REFERENCE

R4

R3

12

1574 • F02

Figure 2. Low-Battery Comparator

LTC1574 Adjustable Applications

The LTC1574 develops a 1.25V reference voltage between

the feedback terminal (Pin 10) and ground (see Figure 3).

By selecting resistor R1, a constant current is caused to

flow through R1 and R2 to set the overall output voltage.

The regulated output voltage is determined by:

V

R

R









125 1

2

1

.

For most applications, a 30k resistor is suggested for R1.

To prevent stray pickup, a 100pF capacitor is suggested

across R1 located close to the LTC1574.

LTC1574

R2

R1

10

1574 • F03

100pF

Figure 3. LTC1574 Adjustable Configuration

Inverting Applications

The LTC1574 can easily be set up for a negative output

voltage. If – 5V is desired, the LTC1574-5 is ideal for this

application as it requires the least components. Figure 4

shows the schematic for this application. Note that the

output voltage is now taken off the GND pins. Therefore,

the maximum input voltage is now determined by the

+

+

12

LTC1574-5

GND

SHDN

SW

11

6

5

7

10

3, 14

2, 4, 13, 15

50

µH**

–5V

45mA

2

× 47µF*

16V

1574 • F04

*

**

AVX TPSD476K016

COILTRONICS CTX50-4

INPUT VOLTAGE

4V TO 12V

0.1

µF

+

2

× 47µF*

16V

Figure 4. Positive-to-Negative 5V Converter

Figure 5. Low Noise 5V to 3.3V Regulator

L1**

100

µH

100

µF*

10V

1574 • F05

5

2, 4, 13, 15

56k

33k

7

3, 14

10

12

11

6

5V

3.3V

425mA

GND

LTC1574

SHDN

SW

* AVX TPSD107K010

** COILTRONICS CTX100-4

+

100

µF*

10V

C2

6.8nF

+

Low Noise Regulators

In some applications it is important not to introduce any

switching noise within the audio frequency range. Due to

the nature of the LTC1574 during Burst Mode

there is a possibility that the regulator will introduce audio

noise at some load currents. To circumvent this problem,

a feed-forward capacitor can be used to shift the noise

spectrum up and out of the audio band. Figure 5 shows the

low noise connection with C2 being the feed-forward

capacitor. The peak-to-peak output ripple is reduced to

30mV over the entire load range. A toroidal surface mount

Burst Mode is a trademark of Linear Technology Corporation