CM3708AGIT CHAMP [Champion Microelectronic Corp.], CM3708AGIT Datasheet - Page 4

• Manufacturer Part Number: CM3708AGIT
• Description: 3A LOW-NOISE PWM STEP-DOWN REGULATOR
• Manufacturer: CHAMP [Champion Microelectronic Corp.]

FUNCTIONAL DESCRIPTION
The CM3708A 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
CM3708A is an ideal choice for many small wireless systems.
VREF
The reference voltage could be ranged from 0V to VIN.
OUPUTS
The output voltage pins (LX1, LX2) are tied to the RF power
amp, via an external inductor. Output voltage is determined by
the VREF inputs so it can be from 0V to VIN.
Internal Power Switches:
CM3708A has been integrated 2 Power MOSFETs whose
RDS
Low Noise Current Limit:
CM3708A’s current limit is a low noise current limit. It increase
the system loop noise immunity while it is doing the current
limit protection for the system. The current limit is around 6A
for the normal 3A operation.
APPLICATION CIRCUIT
2007/02/13 Rev1.3
(ON)
Vout
J1
is around 100m Ohm each.
1
2
C2
104
220uf/6.3V
C1
L1
3.3uH
C4
104
100uf/6.3V
10uf/6.3V
C3
C6
PVIN
Champion Microelectronic Corporation
1
3A L
VREF
R3
1k
1
R2 200k
C11
104
C7
104
2
VIN
2
1
2
3
4
5
6
7
8
C12
102
OW
VIN1
PVIN1
LX1
PGND1
AGND
SD
VREF
AGSEN
U1 CM3708A
-N
INPUTS
The input voltage reference pin, VREF determine the output
voltages (LX1, LX2). 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.
PGND2
PVIN2
AGND
AGND
VIN2
VFB
OISE
LX2
NC
16
15
14
13
12
11
10
9
PWM S
C8
104
C9
104
PVIN
100uf/6.3V
TEP
C10
VIN
-D
R1
5R1
OWN
PVIN
470uf/6.3V
CM3708A
R
C5
EGULATOR
Page 4
J2
DC-INPUT
1
2