CM3718

FUNCTIONAL DESCRIPTION

The CM3718 step-down, pulse-width-modulated (PWM),

DC-DC converter has an adjustable output range from VREF

to the input voltage (VIN). An internal synchronous rectifier

improves efficiency and eliminates an external Schottky diode.

Fixed-frequency operation enables easy post-filtering, thereby

providing excellent noise characteristics. As a result, the

CM3718 is an ideal choice for many small wireless systems.

VREF

The reference voltage could be ranged from 1.1V to VIN.

OUPUTS

The output voltage pins (LX) are tied to the RF power amp,

via an external inductor. Output voltage is determined by the

VREF inputs.

INPUTS

The input voltage reference pin, VREF determine the output

voltages (LX). If a specific voltage is forced at the VREF pin, the

output voltage follows the voltage at the VREF pin.

OTHER SUPPLY VOLTAGES

Several inputs are provided for the supply voltages: PVIN and

VIN.

The PVIN provide the power supply to the power MOSFETs.

VIN provides the voltage supply to the logic section and internal

error amplifiers.

FEEDBACK

The VFB pin is an input that can be used for closed loop

compensation. This input is derived from the voltage output.

AGND pin is a contact node of internal resistor divider for

remote sense.

APPLICATION CIRCUIT

TP1

BNC

1

3

4

VCC

R4

470

2

1

L1

3.3uH/2A

C2 105

R5

0

R3

100k

2

1

U3

CM3718-8PIN

VDD

JP1

JUMPER

C3

470

D1

SK12

VCC

JP2

JUMPER

J3

VREF-OUT

1

2

R7

0

2

1

JP3---->USEING EXTERNAL

VOLTAGE SETING BOARD

(PIN

1,2 SHORT)

C4

105

VDD

J2

VTT

1

2

NOTE:

J1

PWR/IN

1

2

R1

100k

2

1

C7

104

C6

47uf/6.3V

C5 104P

JP3

CON3

3

2

1

JP4

on/off sw

U2 CM-431

1

3

R2

1k

2

1

C1 100uf/6.3V

D2

SK12

R8

5.1

2

1

Champion Microelectronic Corporation

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