CM3708AGIT Просмотр технического описания (PDF) - Unspecified
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CM3708AGIT Datasheet PDF : 6 Pages
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CM3708A
3A LOW-NOISE PWM STEP-DOWN REGULATOR
FUNCTIONAL DESCRIPTION
The CM3708A 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
CM3708A is an ideal choice for many small wireless systems. Several inputs are provided for the supply voltages: PVIN and
VREF
The reference voltage could be ranged from 0V to VIN.
VIN.
The PVIN provide the power supply to the power MOSFETs.
VIN provides the voltage supply to the logic section and internal
OUPUTS
error amplifiers.
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(ON) is around 100m Ohm each.
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.
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
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
1
2
3
C7
104 4
5
6
VREF
7
8
C11
104
U1 CM3708A
VIN1
VIN2 16
PVIN1 PVIN2 15
LX1
LX2 14
PGND1 PGND2 13
12
AGND AGND
SD
VFB 11
VREF
10
NC
AGSEN AGND 9
R1
VIN 5R1
PVIN
C8
C9
104
104
C10
100uf/6.3V
PVIN
C5
470uf/6.3V
J2
DC-INPUT
1
2
2004/12/13
R2 200k
1
2
1
2
R3
C12
1k
102
Champion Microelectronic Corporation
Page 4
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