CM3706
1.5MHz, 600mA Synchronous
Step-Down Regulator
GENERAL DESCRIPTION
The CM3706 is a 1.5MHz constant frequency, slope
compensated current mode PWM step-down converter.
The device integrates a main switch and a synchronous
rectifier for high efficiency without an external Schottky
diode. It is ideal for powering portable equipment that runs
from a single cell lithium-Ion (Li+) battery. The CM3706
can supply 600mA of load current from a 2.5V to 5.5V
input voltage.
The output voltage can be regulated as
low as 0.6V. The CM3706 can also run at 100% duty cycle
for low dropout operation, extending battery life in portable
system. Idle mode operation at light loads provides very
low output ripple voltage for noise sensitive applications.
The CM3706 is offered in a low profile (1mm) 5-pin, thin
TSOT package, and is available in an adjustable version.
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FEATURES
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High Efficiency: Up to 96%
1.5Mhz Constant Switching Frequency
600mA Output Current at V
IN
=3V
Integrated Main switch and synchronous rectifier. No
Schottky Diode Required
2.5V to 5.5V Input Voltage Range
Output Voltage as Low as 0.6V
100% Duty Cycle in Dropout
Low Quiescent Current: 300µA
Slope Compensated Current Mode Control for Excellent Line
and Load Transient Response
Short Circuit Protection
Thermal Fault Protection
<1uA Shutdown Current
Space Saving 5-Pin Thin TSOT23 package
APPLICATIONS
Cellular and Smart Phones
MP3 Players
Portable Instruments
Digital Still and Video Cameras
Microprocessors and DSP Core Supplies
Wireless and DSL Modems
PDAs
TYPICAL APPLICATIONS
IN
2.5V TO
5.5V
Cin
4.7uF
4
3
2.2uH
V
IN
1
SW
634k
OUT
CM3706
RUN GND V
FB
2
316K
5
Cout
10uF
22PF
Figure 1. Basic Application Circuit with CM3706 adjustable version
2006/12/20
Rev. 1.6
Champion Microelectronic Corporation
Page 1
CM3706
1.5MHz, 600mA Synchronous
Step-Down Regulator
PIN CONFIGURATION
TSOT23-5
Top View
5
4
FB
GND
2
RUN
1
BLOCK DIAGRAM
2006/12/20
Rev. 1.6
Champion Microelectronic Corporation
SW
3
VIN
Page 2
CM3706
1.5MHz, 600mA Synchronous
Step-Down Regulator
PIN DESCRIPTION
Pin No.
1
RUN
Symbol
Description
Regulator Enable control input. Drive RUN above 1.5V to turn on the part. Drive RUN
below 0.3V to turn it off.
2
3
4
5
GND
SW
VIN
FB
Ground Pin.
Power Switch Output. It is the Switch note connection to Inductor. This pin connects to the
drains of the internal P-CH and N-CH MOSFET switches.
Supply Input Pin. Must be closely decoupled to GND, Pin 2, with a 2.2µF or greater ceramic
capacitor.
VFB (CM3706): Feedback Input Pin. Connect FB to the center point of the external resistor
divider. The feedback threshold voltage is 0.6V.
In shutdown, all functions are disabled drawing <1µA supply
current. Do not leave RUN floating.
ORDERING INFORMATION
Part Number
CM3706IM25
CM3706GIM25
Voltage
Adj
Adj
Temperature Range
-40
℃
to +85
℃
-40
℃
to +85
℃
Package
TSOT23-5
TSOT23-5
CM3706
X X X
Lead Free
Suffix for
Temperature
I :
-40
℃
to +85
℃
Package
Blank : Normal
G: Lead Free
Package
M25 : TSOT23-5
ABSOLUTE MAXIMUM RATINGS
(Note 1)
Absolute maximum ratings are those values beyond which the
device could be permanently damaged.
Input Supply Voltage...................................................–0.3V to 6.0V Peak SW Sink and Source Current………...…………….. 1.5A
RUN, VFB Voltages ………………………...…– 0.3V to (VIN + 0.3V) Junction Temperature (Note 2) ........... ........................ 125°C
SW Voltage....…………........………..……..… – 0.3V to (VIN + 0.3V) Storage Temperature Range ....................... – 65°C to 150°C
Operating Temperature Range
….…………..…
-40°C to +85°C
Lead Temperature (Soldering, 10 sec)......................... 300°C
OPERATING CONDITIONS
Temperature Range ............................. -40°C to 85°C
Vin Operating Range .........................2.5V to 5.5V
2006/12/20
Rev. 1.6
Champion Microelectronic Corporation
Page 3
CM3706
1.5MHz, 600mA Synchronous
Step-Down Regulator
Thermal Resistance
(Note 3)
:
Package
TSOT23-5
Ө
JA
250°C/W
Ө
JC
110°C/W
Note 1:
Absolute Maximum Ratings are those values beyond which the life of a device may be impaired.
Note 2:
T
J
is calculated from the ambient temperature T
A
and power dissipation P
D
according to the following formula:
CM3706: T
J
= T
A
+ (P
D
)
╳
(
Ө
JA
)
Note 3:
Thermal Resistance is specified with approximately 1 square of 1 oz copper.
(Unless otherwise stated, these specifications apply T
A
=25°C;
VIN=+3.6V)
maximum ratings are stress ratings only and functional device operation is not implied.
ELECTRICAL CHARACTERISTICS
Parameter
Input Voltage Range
Input DC Supply Current
Active Mode
Shutdown Mode
Conditions
MIN
2.5
TYP
MAX
5.5
unit
V
µA
µA
V
V
V
nA
%/V
V
V
V
%/V
%/mA
A
V
FB
=0.5V
V
FB
=0V, V
IN
=4.2V
0.5880
0.5865
0.5850
270
0.08
0.6000
0.6000
0.6000
400
1.0
0.6120
0.6135
0.6150
±30
T
A
= +25°C
Regulated Feedback Voltage T
A
= 0°C
≤
T
A
≤
85°C
T
A
= -40°C
≤
T
A
≤
85°C
V
FB
Input Bias Current
Reference Voltage Line
Regulation
Regulated Output Voltage
Output Voltage Line
Regulation
Output Voltage Load
Regulation
Peak Inductor Current
Oscillator Frequency
R
DS(ON)
of P-CH MOSFET
R
DS(ON)
of N-CH MOSFET
SW Leakage
RUN Threshold
RUN Leakage Current
Thermal Shutdown Trip
Threshold
Output over voltage lockout
V
FB
= 0.65V
V
IN
= 2.5V to 5.5V,
CM3706
-1.2, -40°C
≤
T
A
≤
85°C
CM3706
-1.5, -40°C
≤
T
A
≤
85°C
CM3706
-1.8, -40°C
≤
T
A
≤
85°C
0.11
1.164
1.455
1.746
1.200
1.500
1.800
0.11
0.0015
1.2
1.2
1.5
0.3
0.2
±0.01
0.3
0.45
±0.1
150
0.4
1.236
1.545
1.854
0.40
VIN = 2.5V to 5.5V,I
OUT
=10mA
I
OUT
from 10 to 600mA
V
IN
=3V, V
FB
=0.5V or V
OUT
=90%
Duty Cycle <35%
V
FB
=0.6V or V
OUT
=100%
I
SW
= 300mA
I
SW
= -300mA
V
RUN
= 0V, V
SW
= 0V or 5V, V
IN
= 5V
-40°C
≤
T
A
≤
85°C
1.8
0.50
0.45
±1
1.5
±1
MHz
Ω
Ω
µA
V
µA
℃
mV
∆V
OVL
= V
OVL
– V
FB
60
Note 4:
100% production test at +25°C. Specifications over the temperature range are guaranteed by design and
characterization.
2006/12/20
Rev. 1.6
Champion Microelectronic Corporation
Page 4
CM3706
1.5MHz, 600mA Synchronous
Step-Down Regulator
FUNCTIONAL DESCRIPTION
Operation
CM3706 is a monolithic switching mode Step-Down DC-DC
converter. It utilizes internal MOSFETs to achieve high
efficiency and can generate very low output voltage by using
internal reference at 0.6V. It operates at a fixed switching
frequency, and uses the slope compensated current mode
architecture. This Step-Down DC-DC Converter supplies
600mA output current at VIN = 3V with input voltage range
from 2.5V to 5.5V.
Idle Mode Operation
At very light loads, the CM3706 automatically enters Idle
Mode. In the Idle Mode, the inductor current may reach zero
or reverse on each pulse.
automatically skip pulses to
maintain output regulation. The bottom MOSFET is turned
off by the current reversal comparator, I
ZERO
, and the switch
voltage will ring. This is discontinuous mode operation, and
is normal behavior for the switching regulator.
The PWM control loop will
Current Mode PWM Control
Slope compensated current mode PWM control provides
stable switching and cycle-by-cycle current limit for excellent
load and line responses and protection of the internal main
switch (P-Ch MOSFET) and synchronous rectifier (N-CH
MOSFET). During normal operation, the internal P-Ch
MOSFET is turned on for a certain time to ramp the inductor
current at each rising edge of the internal oscillator, and
switched off when the peak inductor current
is above the error voltage.
limits
the peak inductor current. When the main switch is off, the
synchronous rectifier will be turned on immediately and stay
on until either the inductor current starts to reverse, as
indicated by the current reversal comparator, I
ZERO
, or the
beginning of the next clock cycle.
The OVDET comparator
controls output transient overshoots by turning the main
switch off and keeping it off until the fault is no longer present.
The current comparator, I
COMP
,
Maximum Load Current
The
CM3706
will operate with input supply voltage as
low as 2.5V, however, the maximum load current
decreases at lower input due to large IR drop on the
main switch and synchronous rectifier. The slope
compensation signal reduces the peak inductor current
as a function of the duty cycle to prevent sub-harmonic
oscillations at duty cycles greater than 50%.
Conversely the current limit increases as the duty cycle
decreases.
Note 5:
The duty cycle D of a step-down converter is defined
as:
D
=
T
ON
×
f
OSC
×
100%
≈
frequency (1.5Mhz).
V
OUT
×
100%
V
IN
where T
ON
is the main switch on time, and f
OSC
is the oscillator
Dropout Operation
When the input voltage decreases toward the value of the
output voltage, the CM3706 allows the main switch to remain
on for more than one switching cycle and increases the duty
cycle (Note 5) until it reaches 100%. The output voltage then
is the input voltage
minus the voltage drop across the main switch and the
inductor. At low input supply voltage, the R
DS
(ON) of the
P-Channel MOSFET increases, and the efficiency of the
converter decreases. Caution must be exercised to ensure
the heat dissipated not to exceed the maximum junction
temperature of the IC.
2006/12/20
Rev. 1.6
Champion Microelectronic Corporation
Page 5
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