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LTC1044A

12V CMOS Voltage Converter

Linear Technology 

LTC1044A

Applications Information

BOOST

7X

(1)

OSC

OSC

(7)

LV

(6)

V+

(8)

φ

÷2

φ

SW1

C+

(2)

C1

C–

(4)

CLOSED WHEN

V+ > 3V

GND

(3)

SW2

1044a F03

VOUT

(5)

C2

Figure 3. LTC1044A Switched-Capacitor Voltage Converter Block Diagram

LV (Pin 6)

The internal logic of the LTC1044A runs between V+ and

LV (pin 6). For V+ greater than or equal to 3V, an internal

switch shorts LV to GND (pin 3). For V+ less than 3V, the

LV pin should be tied to GND. For V+ greater than or equal

to 3V, the LV pin can be tied to GND or left floating.

OSC (Pin 7) and Boost (Pin 1)

The switching frequency can be raised, lowered, or driven

from an external source. Figure 4 shows a functional

diagram of the oscillator circuit.

V+

BOOST

(1)

6I

I

Loading pin 7 with more capacitance will lower the

frequency. Using the boost (pin 1) in conjunction with

external capacitance on pin 7 allows user selection of the

frequency over a wide range.

Driving the LTC1044A from an external frequency source

can be easily achieved by driving pin 7 and leaving the boost

pin open as shown in Figure 5. The output current from

pin 7 is small (typically 0.5µA) so a logic gate is capable

of driving this current. The choice of using a CMOS logic

gate is best because it can operate over a wide supply

voltage range (3V to 15V) and has enough voltage swing

to drive the internal Schmitt trigger shown in Figure 4. For

5V applications, a TTL logic gate can be used by simply

adding an external pull-up resistor (see Figure 5).

V+

OSC

(7)

~14pF

SCHMITT

TRIGGER

6I

I

LV

1044a F04

(6)

Figure 4. Oscillator

By connecting the boost pin (pin 1) to V+, the charge and

discharge current is increased and hence, the frequency

is increased by approximately seven times. Increasing the

frequency will decrease output impedance and ripple for

higher load currents.

NC 1

8

2

7

3 LTC1044A 6

C1

4

5

100k

REQUIRED FOR

TTL LOGIC

–(V+)

C2

Figure 5. External Clocking

For more information www.linear.com/LTC1044A

OSC INPUT

1044a F05

1044afa

7

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