6

LTC1044A

S

APPLICATI

I FOR ATIO

LV (Pin 6)

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.

discharge current is increased and hence, the frequency is

increased by approximately 7 times. Increasing the

7X

(1)

LV

(6)

(8)

OSC

OSC

(7)

(2)

BOOST

(4)

(5)

GND

(3)

+

C1

C2

LTC1044A • F03

φ

φ

SW1

SW2

CLOSED WHEN

Figure 3. LTC1044A Switched-Capacitor Voltage Converter Block Diagram

Figure 4. Oscillator

BOOST

(1)

LV

(6)

OSC

(7)

6I

I

6I

~14pF

LTC1044A • F04

SCHMITT

TRIGGER

I

frequency will decrease output impedance and ripple for

higher load currents.

Loading pin 7 with more capacitance will lower the fre-

quency. Using the boost (pin 1) in conjunction with exter-

nal 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 0.5

µA) 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).

1

2

3

4

8

7

6

5

LTC1044A

+

C1

NC

OSC INPUT

C2

100k

REQUIRED FOR

TTL LOGIC

LTC1044A • F05

Figure 5. External Clocking