CM3718
1.5A L
OW
-N
OISE
PWM S
TEP
-D
OWN
R
EGULATOR
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
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.
INPUTS
The input voltage reference pin, VREF determine the output
voltages (LX). If a specific voltage is forced at the VREF pin, the
improves efficiency and eliminates an external Schottky diode. 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.
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.
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
NOTE:
JP3---->USEING EXTERNAL
VOLTAGE SETING BOARD
(PIN 1,2 SHORT)
1
D1
SK12
JP1
JUMPER
C2 105
1
L1
3.3uH/2A
2
D2
SK12
2
1
J2
VTT
1
2
J3
VREF-OUT
R5
0
C7
104
C6
47uf/6.3V
VREF
GND
VIN
SD
2
R1
100k
2
C3
470
2
1
8
7
6
5
U3
CM3718-8PIN
2
U2 CM-431
1
VCC
3
R7
0
R2
1k
1
R4
470
VCC
VDD
2
1
J1
PWR/IN
C1 100uf/6.3V
5
4
3
TP1
BNC
1
LX
PGND
PVIN
VFB
1
2
3
1
R8
5.1
JUMPER
VDD
JP2
2
105 C4
4
JP3
1
2
3
CON3
C5 104P
2
R3
100k
1
JP4
on/off sw
2006/10/11
Rev. 1.6
Champion Microelectronic Corporation
2
Page 4
CHAMP [ CHAMPION MICROELECTRONIC CORP. ]
