CM3708A
3A L
OW
-N
OISE
PWM S
TEP
-D
OWN
R
EGULATOR
GENERAL DESCRIPTION
The CM3708A is a low-noise, pulse-width-modulated (PWM),
DC-DC step-down converter. It powers logic and transmitters
in small wireless systems such as cellular phones,
communicating PDAs, and handy-terminals. The device
features an internal synchronous rectifier for high efficiency; it
requires no external Schottky diode. Excellent noise
characteristics and fixed-frequency operation provide easy
post-filtering. The CM3708A is ideally suited for Li-lon battery
applications. It is also useful for +3V or +5V fixed input
applications.
The device operates in one of four modes. Forced PWM
mode operates at a fixed frequency regardless of the load.
Shutdown mode places the device in standby, reducing
quiescent supply current to under 0.1µA.
The CM3708A can deliver over 3.0A. The output voltage can
be adjusted from VREF to VIN. The input range is from 2.0V
to 5.0V. Other features of the CM3708A include high
efficiency, low dropout voltage. It is available in a
space-saving 16-pin SOP & TSSOP package.
FEATURES
Patent Filed #6,452,366
600KHz switching and synchronization
Dynamic output-voltage adjustment from VREF to VIN
3A Guaranteed Output Current
95% Efficiency
No Schottky Diode Required
16-pin PSOP/PTSSOP power packages
6A Low Noise Current Limit Protection
External Soft Start
Rail to Rail output Buck Converter
APPLICATIONS
Cellular Phone
Cordless Phone
PDAs and Handy-Terminals
AGP Chipset Supplies
CPU I/O Supplies
Notebook Chipset Supplies
Battery Operated Devices
PIN CONFIGURATION
PSOP-16 (PS16) / PTSSOP-16 (PT16)
Top View
1
2
3
4
5
6
7
8
VIN2
PVIN2
LX2
PGND2
AGND
VFB
NC
AGND
16
15
14
13
12
11
10
9
VIN1
PVIN1
LX1
PGND1
AGND
SD
VREF
AGSEN
2004/12/13
Champion Microelectronic Corporation
Page 1
CM3708A
3A L
OW
-N
OISE
PWM S
TEP
-D
OWN
R
EGULATOR
PIN DESCRIPTION
Pin No.
1,16
2,15
3,14
4,13
5,9,12
8
6
Symbol
VIN1, VIN2
PVIN1, PVIN2
LX1, LX2
PGND1, PGND2
AGND
Description
Voltage supply for internal circuits
Voltage supply for output power transistors
Inductor connection to the Drains of the internal
power MOSFETs
Ground for output power transistors
Ground for internal reference voltage divider
Ground for remote sensing
Shutdown active high. CMOS input level
0.75 x
VIN
7
10
11
VREF
NC
VFB
V
OUT
Set Voltage
No Connection
Feedback node for the V
OUT
5
V
0
VIN +
0.3V
VIN
V
V
Min.
2
2
Operating Rating
Typ.
Max.
2.5
2.5
5
5
5
Unit
V
V
V
AGSEN
SD
BLOCK DIAGRAM
NC
10
VIN1
1
VIN2
16
SD
6
PVIN1
2
PVIN2
15
AGND
AGND
AGND
5
9
Oscillator Ramp Generator
12
PW M Controller
Therm al
Protection
MOS
3
14
LX1
LX2
VREF
7
Error Amp
8
AGSEN
11
VFB
4
PGND1
13
PGND2
2004/12/13
Champion Microelectronic Corporation
Page 2
CM3708A
3A L
OW
-N
OISE
PWM S
TEP
-D
OWN
R
EGULATOR
ORDERING INFORMATION
Part Number
CM3708AIT
CM3708AGIT*
CM3708AIS
CM3708AGIS*
*Note:
G : Suffix for Pb Free Product
Temperature Range
-40℃ to 85℃
-40℃ to 85℃
-40℃ to 85℃
-40℃ to 85℃
Package
16-Pin PTSSOP (PT16)
16-Pin PTSSOP (PT16)
16-Pin PSOP (PS16)
16-Pin PSOP (PS16)
ABSOLUTE MAXIMUM RATINGS
Absolute maximum ratings are those values beyond which the
device could be permanently damaged.
PVIN/VIN …………......................................….......-0.3V to 6.0V
Voltage on Any Other Pin ………... GND – 0.3V to VIN + 0.3V
Output Current, Source or Sink ……......…………........…...3.0A
Junction Temperature ...…………………… …………150°C
Storage Temperature ……................……. -65°C to 125°C
Lead Temperature (Soldering, 5 sec)……………….. 260°C
Thermal Dissipation(
θ
JC
)….. ………………….. .50°C/W
OPERATING CONDITIONS
Temperature Range ............................. -40°C to 85°C
P
VIN
Operating Range .........................2.0V to 5.0V
(Unless otherwise stated, these specifications apply T
A
=25°C;
VIN=+3.3V and PVIN=+3.3V)
maximum ratings are stress ratings only and functional device operation is not implied.
(Note 1)
CM3708A
Min.
0
CM3708A
CM3708A
CM3708A
CM3708A
PVIN=5V
VFB = 1.4V
LC unconnected
VFB = 1.4V
LC unconnected
6
150
180
480
Typ.
Max.
VIN
660
3.0
6.0
ELECTRICAL CHARACTERISTICS
Symbol
SWITCHING REGULATOR
V
REF
fsw
I
OUT(RMS)
I
OUT(PEAK)
I
limit
MOSFETs
RDS
(ON)
SUPPLY
I
VIN
I
PVIN
Parameter
Test Conditions
Unit
Adjustable Output Voltage
Switching Frequency
Maximum Output RMS Current
Maximum Output Peak Current
Current limit
Drain to Source on-State Resistance
V
KHz
A
A
A
mΩ
Quiescent Current
Quiescent Current
200
500
µA
µA
Note 1:
Limits are guaranteed by 100% testing, sampling, or correlation with worst case test conditions
Note 2:
VIN, PVIN = 3.3V ±10%
Note 3:
It’s not 100% test
2004/12/13
Champion Microelectronic Corporation
Page 3
CM3708A
3A L
OW
-N
OISE
PWM S
TEP
-D
OWN
R
EGULATOR
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
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.
INPUTS
The input voltage reference pin, VREF determine the output
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.
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.
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
(ON)
is around 100m Ohm each.
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.
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
L1
3.3uH
Vout
J1
1
2
C2
104
C1
220uf/6.3V
10uf/6.3V
C4
104
VIN
C3
PVIN
1
U1 CM3708A
VIN1
PVIN1
LX1
VIN2
PVIN2
LX2
VIN
16
R1
5R1
PVIN
J2
DC-INPUT
1
2
C5
2
C7
104
15
PVIN
C8
104
C6
100uf/6.3V
3
4
5
14
PGND1 PGND2
AGND
SD
VREF
AGSEN
AGND
VFB
NC
AGND
13
12
C9
104
C10
100uf/6.3V
470uf/6.3V
VREF
6
7
8
11
10
9
C11
104
R2 200k
2
1
1
2
R3
1k
C12
102
2004/12/13
Champion Microelectronic Corporation
Page 4
CM3708A
3A L
OW
-N
OISE
PWM S
TEP
-D
OWN
R
EGULATOR
PACKAGE DIMENSION
16-PIN PTSSOP (PT16)
θ
16-PIN PSOP (PS16)
θ
θ
θ
2004/12/13
Champion Microelectronic Corporation
Page 5
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