CM3708 Datasheet, PDF (4/6 Pages) List of Unclassifed Manufacturers – 3A LOOW NOISE PWM STEP DOWN REGULATOR

CM3708
3A LOW-NOISE PWM STEP-DOWN REGULATOR
FUNCTIONAL DESCRIPTION
The CM3708 step-down, pulse-width-modulated (PWM),
INPUTS
DC-DC converter has an adjustable output range from VREF The input voltage reference pin, VREF determine the output
to the input voltage (VIN). An internal synchronous rectifier
voltages (LX1, LX2). If a specific voltage is forced at the VREF
improves efficiency and eliminates an external Schottky diode. pin, the output voltage follows the voltage at the VREF pin.
Fixed-frequency operation enables easy post-filtering, thereby
providing excellent noise characteristics. As a result, the
OTHER SUPPLY VOLTAGES
CM3708 is an ideal choice for many small wireless systems. Several inputs are provided for the supply voltages: PVIN and
VIN.
VREF
The PVIN provide the power supply to the power MOSFETs.
The reference voltage could be ranged from 1.1V to VIN.
VIN provides the voltage supply to the logic section and internal
error amplifiers.
OUPUTS
The output voltage pins (LX1, LX2) are tied to the RF power FEEDBACK
amp, via an external inductor. Output voltage is determined by The VFB pin is an input that can be used for closed loop
the VREF inputs.
compensation. This input is derived from the voltage output.
AGND pin is a contact node of internal resistor divider for
remote sense.
APPLICATION CIRCUIT
L1
3.3uH
Vout
J1
1
2
C1
C2
104 220uf/6.3V
10uf/6.3V
C3
C4
104
PVIN
C6
100uf/6.3V
VIN
U1 CM3708
1
VIN1
16
VIN2
2 _{PVIN1 PVIN2} 15
3
C7
LX1
14
LX2
104 4 _{PGND1 PGND2} 13
5
12
AGND AGND
VREF
6 _SD
7 _VREF
VFB ¹¹
NC ¹⁰
8 _{AGSEN AGND} 9
C11
104
R1
VIN _5R1
PVIN
C8
C9
104
104
C10
100uf/6.3V
PVIN
C5
470uf/6.3V
J2
DC-INPUT
1
2
R2 200k
1
2
1
2
R3
C12
1k
102
2004/09/15 Rev. 1.2
Champion Microelectronic Corporation
Page 4