MIC2224
High Efficiency 2MHz PWM Buck
Converter with DAC Input and 40m
Bypass Switch
Preliminary
Micrel, Inc. 2180 Fortune Drive San Jose, Ca 95131 USA tel +1 (408) 944-0800 fax +1 (408) 474-1000 http://www.micrel.com
2005January 2005
M9999-012705
www.micrel@micrel.com
General Description
The MIC2224 is a high efficiency 2MHz PWM
synchronous buck switching regulator optimized for
powering 2.5G and 3G CDMA RF Power Amplifiers.
The output voltage of MIC2224 can be dynamically
adjusted with an external DAC to maximize PA
efficiency versus required output power. When the
PA requires the highest power, the DAC can be
used to enable a low on-resistance, 40m
, bypass
switch that powers the PA directly from the battery.
The 2MHz PWM operation of MIC2224 allows the
smallest possible components. It also allows the
device to easily meet stringent W-CDMA V
OUT
response specifications.
The MIC2224 operates from a 2.7V to 5.5V input,
making it ideal for single cell Li-Ion applications.
The device features built-in power MOSFETs that
can supply up to 600mA of output current in PWM
mode, or over 1A in bypass mode. The MIC2224
can operate with a maximum duty cycle of 100% for
use in low-dropout conditions.
The MIC2224 has a junction temperature range of
40
C to +125
C and is available in a 3mm x 3mm
MLF
TM
-10L package.
Features
2.7V to 5.5V input voltage range
DAC-adjustable output voltage down to 0.3V
600mA output current in PWM mode
Internally protected 40m
bypass switch
Allows direct connection of battery to
load
Over 95% efficient
Fully integrated MOSFET switches
Constant 2MHz PWM operation
Internal
soft-start
1% line and load regulation
<1
A shutdown current
Under-voltage
lockout
Thermal shutdown and current limit
protection
40
C to +125
C junction temperature range
Applications:
Cellular
phones
PDAs
____________________________________________________________________________________________________
Typical Application
MIC2224
VIN
AVIN
ENABLE
DAC
DAC
V
IN
2.6V to 5.5V
GND
GND
V
OUT
C1
1F
C2
1F
L1
4.7H
AGND
PGND
VOUT
SW
2, 3
5
4
6
7
10
8, 9
1
2MHz PWM Converter with DAC input and 40m
Bypass Switch
Micrel
MIC2224
January 2005
2
M9999-012705
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Ordering Information
Part Number
Output
Voltage
(1)
Junction Temp. Range
Package
Lead Finish
MIC2224YML
Adj.
40 to +125C
3x3 MLF-10L
Pb-free
Pin Configuration
SW
VIN
VIN
EN
PGND
VOUT
VOUT
AGND
1
2
3
4
10
9
8
7
5
6
AVIN
DAC
EP
3mm x 3mm MLF-10L (ML)
Pin Description
Pin
Pin Name
Pin Function
1
SW
Switch (Output): Internal power MOSFET output switches.
2, 3
VIN
Supply Voltage (Input): Requires bypass capacitor to GND.
4 EN
A low level EN will power down the device, reducing the quiescent current to under 5uA
( typ 1uA )
5
AVIN
Supply Voltage (Input): Requires bypass capacitor to GND.
6 DAC
DAC Control Input. Provides control of output voltage. The output voltage is 3 X the
DAC voltage. (Ex. 0.5V
DAC
=1.5V
out
) Bypass mode is enabled when the DAC voltage
exceeds 1.2V.
7
AGND
Signal Ground of chip
8, 9
VOUT
Source of Internal P-Channel MOSFET and Feedback of internal PWM regulator.
10
PGND
Power Ground of chip.
EP
Exposed Pad
Connect to ground.
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MIC2224
January 2005
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Absolute Maximum Rating (Note 1)
Supply Voltage (V
IN
) ..................................... 0V to 6V
Output Switch Voltage (V
SW
) ................................. 6V
DAC Input Voltage (V
DAC
) ................... 0V to V
in
+0.3V
Output Switch Current (I
SW
) ................................ 2.5A
Logic Input Voltage (V
EN
).................... 0V to V
IN
+0.3V
Storage Temperature (T
S
) ............... -65
C to +150
C
Operating Ratings
Supply Voltage (V
IN
)................................2.7V to 5.5V
Output Voltage (V
OUT
) ................................0V to 5.5V
DAC Input Voltage (V
DAC
) ......................... 0.1V to V
in
Junction Temperature Range (T
J
) .. -40
C to +125
C
Thermal Resistance
JA
MLF .................................................... 60
C/W
Electrical Characteristics
(4)
V
IN
= V
EN
= 3.6V;V
DAC
=0.6V; L = 4.7
H; C
OUT
= 1
F; T
A
= 25C, unless noted. Bold values indicate 40C< T
J
< +125C
Parameter Condition
Min
Typ
Max
Units
Supply Voltage Range
2.7
5.5
V
Total Quiescent Current
V
DAC
= 0.6V V
OUT
= 2.4V
(regulator on, not switching)
360
450
A
Shutdown Current
V
EN
= 0V (regulator off)
1
5
A
Maximum Duty Cycle
100
%
Regulation
Output Voltage
V
DAC
= 0.6V, I
LOAD
=0mA
1.746
1.8
1.854
V
Output Voltage Line Regulation
3.0V
V
IN
4.5, I
LOAD
= 10mA
0.05
0.5 %/V
Output Voltage Load Regulation
0mA < I
OUT
< 500mA
0.2
%
Output
Switch On-Resistance
I
SW
= -100mA, High-Side Switch
I
SW
= 100mA , Low-Side Switch
0.55
0.6
0.75
0.85
Current limit (Peak SW Current)
0.65
0.85
1.6
A
Oscillator
Frequency
1.8
2
2.2
MHz
Enable / UVLO
Enable Pin Threshold
0.5
0.9
1.3
V
Enable Pin Hysteresis
30
mV
Enable Pin Input Current
0.01
1
A
EN high to 90% V
OUT
25
50
s
Under-Voltage Lockout Threshold
(turn-on)
2.6
2.7
V
UVLO Hysteresis
85
mV
DAC Input
DAC Input Current
0.15
2
A
Output Voltage/DAC Voltage
(internally set)
3
V/V
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MIC2224
January 2005
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Parameter Condition
Min
Typ
Max
Units
Bypass Switch
Bypass Switch Threshold
DAC Voltage required to enable bypass mode
1.176
1.2
1.224
V
Bypass Switch Hysteresis
35
mV
Bypass Transition Time
Delay from V
DAC
= 1.2V to V
OUT
= 0.90V
IN
10
s
Bypass Switch On-Resistance
V
IN
= 3.0V, I
BYPASS
= 100mA
40
m
Bypass Switch Leakage
V
DAC
< 1.2V
5
A
Bypass Over-Current Limit
1
1.4
2.5
A
Current Limit Retry Time
32
s
Current Limit Retry Duty Cycle
12.5
%
Over Temperature Shutdown
Shutdown Temperature
160
C
Over Temperature Shutdown
Hysteresis
20
C
Notes:
1. Exceeding the absolute maximum rating may damage the device.
2. The device is not guaranteed to function outside its operating rating.
3. Devices are ESD sensitive. Handling precautions recommended. Human body model: 1.5k
in series with 100pF.
4. Specification for packaged product only.
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MIC2224
January 2005
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Typical Characteristics
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MIC2224
January 2005
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Typical Characteristics (cont.)
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MIC2224
January 2005
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Function Characteristics
Bypass Mode Transient
Time 10 s
DA
C
V
o
l
ta
g
e
(
500m
V/di
v)
Output
V
o
l
t
ag
e
(2
V
/
d
i
v)
V
IN
= 4.2V
L = 4.7H
C
OUT
= 1F
0V
0V
Bypass Mode Transient
Time 10 s
DA
C
V
o
l
ta
ge
(
500m
V/di
v)
Output
V
o
l
t
ag
e
(2
V
/
d
i
v)
V
IN
= 4.2V
L = 4.7H
C
OUT
= 1F
0V
0V
Current Limit Transient (Bypass Mode)
Time 2ms
Output C
u
r
r
ent
(
500m
A/di
v)
Output
V
o
l
t
ag
e
(2
V
/
d
i
v)
V
IN
= 3.6V
VDAC = 1.3V
L = 4.7H
C
OUT
= 1F
0mA
0V
Current Limit Transient (PWM Mode)
Time 100s
Output C
u
r
r
ent
(
500m
A/di
v)
Output
V
o
l
t
ag
e
(2
V
/
d
i
v)
V
IN
= 3.6V
VDAC = 1.3V
L = 4.7H
C
OUT
= 1F
0mA
0V
Enable Transient
Time 10s
Enabl
e
V
ol
tag
e
(1
V
/
d
i
v)
Output
V
o
l
t
ag
e
(1
V
/
d
i
v)
V
IN
= 3.6V
VDAC = 0.6V
L = 4.7H
C
OUT
= 1F
0V
0V
Load Transient
Time 10s
Output C
u
r
r
ent
(
100m
A/di
v)
Output
V
o
l
t
ag
e
(
100m
V/di
v)
V
IN
= 3.6V
VDAC = 0.6V
L = 4.7H
C
OUT
= 1F
0mA
Micrel
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January 2005
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Functional Characteristics (cont.)
Output Voltage Transient
Time 10s
DA
C
V
o
l
ta
ge
(
500m
V/di
v)
Output
V
o
l
t
ag
e
(1
V
/
d
i
v)
V
IN
= 3.6V
L = 4.7H
C
OUT
= 1F
0V
0V
Output Voltage Transient
Time 10s
DA
C
V
o
l
ta
g
e
(
500m
V/di
v)
Output
V
o
l
t
ag
e
(1
V
/
d
i
v)
V
IN
= 3.6V
L = 4.7H
C
OUT
= 1F
0V
0V
Switch Voltage - Output Ripple
Time 400ns
Sw
i
t
ch
V
o
l
t
ag
e
(2
V
/
d
i
v)
Output
V
o
l
t
age R
i
ppl
e
AC
C
oupl
ed
(
10m
V/di
v)
V
IN
= 3.6V
VDAC = 0.6V
I
OUT
= 600mA
L = 4.7H
C
OUT
= 1F
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MIC2224
January 2005
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Functional Block Diagram
1.2V
DRIVER
AVIN
VIN
DAC
EN
80k
40k
AGND
PGND
SW
VOUT
MIC2224 Block Diagram
Micrel
MIC2224
January 2005
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Functional Description
VIN
VIN provides power to the MOSFETs for the switch
mode regulator section, along with the current
limiting sensing. Due to the high switching speeds, a
1
F capacitor is recommended close to VIN and the
power ground (PGND) pin for bypassing.
AVIN
Analog V
IN
(AVIN) provides power to the internal
reference and control section. AVIN and VIN must
be tied together. Careful layout should be
considered to ensure high frequency switching noise
caused by VIN is reduced before reaching AVIN.
DAC
The DAC pin is the control pin that sets the output
voltage. The Output voltage is 3X the voltage set on
the DAC pin. When 1.2V or greater is applied to the
DAC pin, the MIC2224 enters bypass mode. In
bypass mode, the input supply is connected to the
output through a 40mOhm P-Channel MOSFET.
EN
The enable pin provides a logic level control of the
output. In the off state, supply current of the device
is greatly reduced (typically <1
A). Also, in the off
state, the output drive and bypass switch are placed
in a "tri-stated" condition, where both the high side
P-channel Mosfet and the low-side N-channel are in
an off or non-conducting state. Do not drive the
enable pin above the supply voltage.
VOUT
The VOUT pin connects the internal bypass drain
and the feedback signal to the output. The bypass
applies the input voltage through a low resistance
(40mOhm typical) P-Channel MOSFET switch.
The feedback signal provides the control path to set
the output at 3X the DAC voltage.
SW
The switch (SW) pin connects directly to the inductor
and provides the switching current necessary to
operate in PWM mode. Due to the high speed
switching on this pin, the switch node should be
routed away from sensitive nodes.
PGND
Power ground (PGND) is the ground path for the
high current PWM mode. The current loop for the
power ground should be as small as possible and
separate from the Analog ground (AGND) loop.
AGND
Signal ground (AGND) is the ground path for the
biasing and control circuitry. The current loop for the
signal ground should be separate from the Power
ground (PGND) loop.
Applications Information
The MIC2224 is a 600mA PWM power supply that
utilizes a dynamically adjustable output voltage for
powering RF power amplifiers. By dynamically
adjusting the output power as necessary, battery life
can be dramatically improved in battery powered RF
applications. For instances where high power is
required, the MIC2224 also has a bypass mode.
Bypass mode is enabled by driving the DAC pin
above 1.2V. This bypasses the input supply directly
to the output through a highly efficient, short circuit
protected, 40mOhm P channel MOSFET.
Input Capacitor
A minimum 1
F ceramic is recommended on the
VIN pin for bypassing. X5R or X7R dielectrics are
recommended for the input capacitor. Y5V
dielectrics lose most of their capacitance over
temperature and are therefore not recommended.
A minimum 1
F is recommended close to the VIN
and PGND pins for high frequency filtering. Smaller
case size capacitors are recommended due to their
lower ESR and ESL.
Output Capacitor
The MIC2224 is optimized for a 1
F ceramic output
capacitor. The MIC2224 utilizes type III internal
compensation and utilizes internal high frequency
zeros to compensate for the double pole roll off of
the LC filter. For this reason, larger output capacitors
can create instabilities. X5R or X7R dielectrics are
recommended for the output capacitor. Y5V
dielectrics lose most of their capacitance over
temperature and are therefore not recommended.
In addition to a 1
F, a small 10nF is recommended
close to the load for high frequency filtering. Smaller
case size capacitors are recommended due to there
lower ESR and ESL.
Inductor Selection
The MIC2224 is designed for use with a 4.7
H
inductor. Proper selection should ensure the
inductor can handle the maximum average and peak
currents required by the load. Maximum current
ratings of the inductor are generally given in two
methods; permissible DC current and saturation
current. Permissible DC current can be rated either
for a 40C temperature rise or a 10% to 20% loss in
Micrel
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January 2005
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inductance. Ensure the inductor selected can handle
the maximum operating current. When saturation
current is specified, make sure that there is enough
margin that the peak current will not saturate the
inductor. Peak inductor current can be calculated as
follows:
L
f
2
V
V
1
V
I
I
IN
OUT
OUT
OUT
PK
-
+
=
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January 2005
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Bill of Materials
MIC2224
VIN
AVIN
ENABLE
DAC
DAC
V
IN
2.7V to 5.5V
GND
GND
V
OUT
C1
1F
C2
1F
L1
4.7H
AGND
PGND
VOUT
SW
2, 3
5
4
6
7
10
8, 9
1
Ref Part
Number
Description
Manufacturer
Qty
C1,C2 06036D105MAT2
1uF Ceramic Capacitor X5R, 6.3V 0603
AVX
C1608X5R0J105K
1uF Ceramic Capacitor X5R, 6.3V 0603
TDK
GRM185R60J105KE21D 1uF Ceramic Capacitor X5R, 6.3V 0603
Murata
2
L1 LQH32CN4R7M53K
4.7uH
3.2mmx2.5mmx1.55mm
Murata
CDRH2D14-4R7
4.7uH Inductor 94mOhm 3.2mmx3.2mmx1.55mm
Sumida
1
GLF201208T4R7M
(1)
4.7uH Inductor 660mOhm
(1)
TDK
(1)
1
(1)
U1 MIC2224YML
2MHz Dynamically Controlled PWM Regulator
Micrel Semiconductor
1
Notes:
1.
For maximum load currents less than 200mA
Micrel
MIC2224
January 2005
13
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Package Information
10-Lead MLFTM (ML)
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