LTC1044A(Rev0) Просмотр технического описания (PDF) - Linear Technology

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производитель

LTC1044A
(Rev.:Rev0)

12V CMOS Voltage Converter

Linear Technology 

LTC1044A

APPLICATI S I FOR ATIO

V+

(8)

BOOST

7X

(1)

OSC

OSC

(7)

φ

÷2

φ

SW1

C+

(2)

C1

C–

(4)

CLOSED WHEN

LV

V+ > 3V

GND

(6)

(3)

SW2

LTC1044A • 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.

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

discharge current is increased and hence, the frequency is

increased by approximately 7 times. Increasing the

V+

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 0.5µA) 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).

BOOST

(1)

LV

(6)

6I

I

OSC

(7)

~14pF

SCHMITT

TRIGGER

6I

I

LTC1044A • F04

Figure 4. Oscillator

V+

1

8

NC

2

7

3 LTC1044A 6

C1

4

5

100k

REQUIRED FOR

TTL LOGIC

–(V+)

C2

LTC1044A • F05

OSC INPUT

Figure 5. External Clocking

6

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