Datasheet UM3502QA Rev01

UM3502QA
Low-Profile, 600mA, Synchronous Step-Down Converter
with Integrated Inductor
UM3502QA QFN24 4.0×4.0
General Description
The UM3502QA is a complete power conversion solution requiring only two low cost ceramic
MLCC caps. Inductor, MOSFETs, synchronous rectifier and control IC are integrated into a tiny
4mm×4mm×1.05mm QFN package. The UM3502QA is engineered to simplify design and to
minimize layout constraints. It is an ideal choice to be used to replace less efficient LDO to
achieve improved efficiency in space restricted applications. The UM3502QA is capable of
delivering 600mA output current over a wide input voltage range from 2.5V to 5.5V.
The UM3502QA is a high-efficiency, step-down DC-DC converter with a constant PWM
frequency, current mode architecture. The UM3502QA automatically turns off the synchronous
rectifier while the inductor current is low, and enters pulse skipping mode at light load condition.
This can increase efficiency. The operation frequency is set to 1.2MHz at normal load condition.
The UM3502QA enters shutdown mode and consumes less than 0.1µA when EN pin is pulled
low.
Applications
Features
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Cellular and Smart Phones
MCU, DSP and FPGA Core Supplies
Wireless and DSL Modems
Portable Game Consoles and
Instruments
PDAs, GPS
Bluetooth Headsets
Battery-Powered Devices
Ultra Small QFN Package 4.0×4.0×1.05
Integrated Inductor
No Schottky Diode Required
High Efficiency: Up to 90%
600mA Output Current
0.6V Minimum Output Voltage
2.5V to 5.5V Input Voltage Range
<1µA Shutdown Current
Pulse Skipping Mode Operation
Thermal Fault Protection
Typical Application Circuit
Light Load Efficiency
Light Load Efficiency vs. Input Voltage
VIN 2.5V to 5.5V
PVIN
100
VOUT
VOUT
90
1.8V
AVIN
EN
CIN
4.7µF
(CA)*
AGND
(CFF)*
80
R2
634K
FB
PGND
R1
316K
COUT
10µF
Ef f iciency (%)
UM3502QA
70
60
50
40
30
ILOAD=0.5mA
ILOAD=0.5mA
ILOAD=0.8mA
ILOAD=0.8mA
ILOAD=1.0mA
ILOAD=1.0mA
20
10
* CA and CFF are optional.
VOUT=1.8V
0
2.9
3.1
3.3
3.5
3.7
3.9
Input Voltage (V)
4.1
4.3
4.5
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UM3502QA
Pin Configurations
Top View
VOUT
PGND
PGND
PGND
PVIN
PVIN
(Top View)
24
23
22
21
20
19
1
18
PVIN
2
17
PVIN
VOUT
3
16
PVIN
NC
4
UM3502QA
15
AVIN
13
EN
7
8
9
10
11
12
FB
6
NC(PGND)
NC(SW)
NC
NC
AGND
14
NC(SW)
5
NC(SW)
NC(SW)
3502
VOUT
VOUT
M
M: Month Code
UM3502QA
QFN24 4.0×4.0
Pin Description
Pin Number
Symbol
1-3, 24
VOUT
4, 9, 14
NC
5-8
NC(SW)
10
AGND
21-23
PGND
11
NC(PGND)
12
FB
13
EN
15
AVIN
16-20
PVIN
Function
Regulated output voltage. Must be closely placed a 10μF or
greater ceramic capacitor. These pins are connected together
inside the package.
Not connected.
Not connected — These pins are internally connected to the
common switching node of the internal MOSFETs. NC(SW) pins
are not to be electrically connected to any external signal, ground,
or voltage. However, they must be soldered to the PCB.
Analog ground. This is the ground for the internal control
circuitry, and the ground return for external feedback voltage
divider. It must be connected to the quiet point of the ground.
Power ground. Connect this pin to the ground electrode of the
input and output filter capacitors closely.
This pin has been connected with PGND inside the package. No
other connection is needed in use.
Feedback input pin. Connect FB to the center point of the external
resistor divider.
Chip enable control. Drive EN above 1.0V to turn on the part.
Drive EN below 0.4V to turn it off. Do not leave EN floating.
Input power supply for the controller circuitry. Connect to VIN
at a quiet point. This pin is usually connected to the positive
electrode of CIN.
Power input for the MOSFET switches. Must be closely
decoupled to GND with a 4.7μF or greater ceramic capacitor.
These pins are connected together inside the package.
Ordering Information
Part Number
Packaging Type
Marking Code
UM3502QA
QFN24 4.0×4.0
3502
Shipping Qty
3000pcs/13Inch
Tape & Reel
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UM3502QA
Absolute Maximum Ratings (Note 1)
Symbol
Parameter
Value
Unit
-0.3 to +6.0
V
VIN, VOUT
Input and Output Voltages
VEN, VFB
EN, FB Voltages
-0.3 to VIN+0.3
V
VSW
SW Voltage
-0.3 to VIN+0.3
V
ISW
Peak SW Sink and Source Current
1.5
A
TO
Operating Temperature
-40 to +85
°C
TSTG
Storage Temperature Range
-65 to +150
°C
Reflow Temperature,
TREFLOW
260
°C
MSL3 JEDEC J-STD-020C, 10 Sec
Note 1: Stresses greater than those listed under Maximum Ratings may cause permanent damage
to the device. This is a stress rating only and functional operation of the device at these or any
other conditions above those indicated in the operational sections of this specification is not
implied. Exposure to absolute maximum rating conditions for extended periods may affect
reliability.
Electrical Characteristics (Note 2)
(VIN=VEN=3.6V, TA=+25°C, CIN=4.7μF, COUT=10μF, unless otherwise noted)
Symbol
Parameter
VIN
Input Voltage Range
VOUT
Output Voltage Range
IO(max)
Maximum Output Current
IQ
(Active)
IQ
(Shutdown)
Input DC Supply Current
(Active Mode)
Input DC Supply Current
(Shutdown Mode)
VFB
Feedback Voltage
IFB
FB Input Bias Current
Reference Voltage Line
Regulation
Output Voltage Line
Regulation
Output Voltage Load
Regulation
f
Oscillator Frequency
RDS(ON) of P-CH MOSFET
RDS(ON)
RDS(ON) of N-CH MOSFET
Test Conditions
Min
Max
Unit
2.5
5.5
V
0.6
5
V
VIN≥3V, VOUT=1.8V
600
VIN=2.5V, VOUT=1.8V
300
mA
Peak Inductor Current
μA
VFB=0.6V, ILOAD=0A
60
VEN=0V
0.1
1.0
0.6000
0.6000
0.6120
0.6150
±30
nA
0.11
0.40
%/V
0.11
0.40
%/V
TA=-40~85°C
VFB=0.65V
0.5880
0.5830
2.5V≤VIN≤5.5V,
VOUT=VFB (R2=0)
2.5V≤VIN≤5.5V,
IOUT=10mA
100mA≤IOUT≤600mA
VFB=0.6V or
VOUT=100%
VIN=3.6V,
ISW=100mA
VIN=3.6V,
ISW=-100mA
Internal Inductor DCR
IP
Typ
VIN=3.0V, VFB=0.5V
or VOUT=90%,
Duty Cycle<35%
0.90
μA
V
0.0015
%/mA
1.2
MHz
0.45
0.55
Ω
0.30
0.40
Ω
0.18
0.23
Ω
1.20
1.60
A
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UM3502QA
Electrical Characteristics (Continued)
(VIN=VEN=3.6V, TA=+25°C, CIN=4.7μF, COUT=10μF, unless otherwise noted)
Symbol
ISWL
VH
VL
IENL
η(max)
Parameter
Test Conditions
Min
SW Leakage
VEN=0V, VIN=5V,
VSW=0V or 5V
EN High-Level
Threshold
EN Low-Level
Threshold
EN Leakage Current
-40ºC≤TA≤85ºC
Max. Efficiency
Thermal Shutdown
Temperature
Thermal Shutdown
Trip Point Hysteresis
VIN=3.6V, VOUT=2.5V
Typ
Max
Unit
±0.01
±1
μA
1.0
V
-40ºC≤TA≤85ºC
±0.1
0.4
V
±1
μA
90
%
160
ºC
25
ºC
Note2: 100% production test at +25ºC. Specifications over the temperature range are guaranteed
by design and characterization.
Typical Performance Characteristics
(VIN=3.6V, VOUT=1.8V, CIN=4.7μF, COUT=10μF, TA=+25°C, unless otherwise noted.)
Efficiency vs Load Current
100
90
90
80
80
70
70
Efficiency (%)
Efficiency (%)
Efficiency vs Load Current
100
60
50
40
30
10
1
10
100
40
20
VOUT=1.2V
V
OUT=1.2V
V
OUT=1.8V
VOUT=1.8V
10
VIN=5.5V
0
50
30
V
IN=2.5V
VIN=2.5V
V
IN=3.6V
VIN=3.6V
VIN=4.2V
VIN=4.2V
VIN=5.5V
20
60
0
1
1000
10
100
1000
Output Current (mA)
Output Current (mA)
Efficiency vs Input Voltage
Output Voltage vs Load Current
100
1.81
90
1.80
Output Voltage(V)
Efficiency (%)
80
70
60
50
40
30
20
10
VOUT=1.8V
0
2.5
3.5
ILOAD=200mA
ILOAD=200mA
ILOAD=400mA
ILOAD=400mA
ILOAD=600mA
ILOAD=600mA
4.5
Input Voltage (V)
1.79
1.78
1.77
VIN=2.5V
VIN=2.5V
VIN=3.6V
VIN=3.6V
VVIN=4.2V
IN=4.2V
1.76
5.5
1.75
1
10
100
1000
Output Current (mA)
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UM3502QA
Typical Performance Characteristics (Continued)
(VIN=3.6V, VOUT=1.8V, CIN=4.7μF, COUT=10μF, TA=+25°C, unless otherwise noted.)
Output Voltage vs Input Voltage
Output Voltage vs Temperature
1.810
1.810
1.805
1.800
Output Voltage(V)
Output Voltage(V)
1.805
1.795
1.790
1.785
1.780
ILOAD=200mA
ILOAD=200mA
ILOAD=400mA
ILOAD=400mA
ILOAD=600mA
ILOAD=600mA
1.775
3.5
4.5
Input Voltage(V)
1.785
1.780
1.775
1.770
1.765
1.760
ILOAD=100mA
Iload=100mA
1.755
1.750
1.770
2.5
1.800
1.795
1.790
-50
5.5
1600
70
1400
60
1200
50
40
30
75
100
200
4.5
5
ILOAD=100mA
600
10
2.5
5.5
3
Supply Voltage(V)
3.5
4
4.5
5
5.5
Supply Voltage(V)
Load Transient Response
(VIN=3.5V, IOUT=100mA to 450mA)
Line Transient Response
(VIN=3.5V to 4.5V, IOUT=300mA)
VIN
2V/div
IOUT
200mA/div
VOUT
VOUT
100mV/div
125
800
400
4
50
1000
20
3.5
25
Frequency vs Input Voltage
Frequency(kHz)
Supply Current(uA)
Supply Current vs Input Voltage
3
0
Temperature(℃)
80
2.5
-25
50μs/div
100mV/div
100μs/div
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6
UM3502QA
Typical Performance Characteristics (Continued)
(VIN=3.6V, VOUT=1.8V, CIN=4.7μF, COUT=10μF, TA=+25°C, unless otherwise noted.)
Pulse Skipping Mode Operation
(IOUT=1mA)
SW
Normal Operation
(IOUT=100mA)
SW
1V/div
100µs/div
1V/div
Ripple and HF Noise
(IOUT=300mA)
500ns/div
Ripple and HF Noise
(IOUT=300mA)
BW=200MHz
BW=20MHz
VOUT
VOUT
5mV/div
5mV/div
1µs/div
Ripple and HF Noise
(IOUT=300mA)
1µs/div
Ripple and HF Noise
(IOUT=300mA)
VIN=5.0V, BW=200MHz
VIN=5.0V, BW=20MHz
VOUT
VOUT
5mV/div
1µs/div
5mV/div
1µs/div
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UM3502QA
Typical Performance Characteristics (Continued)
(VIN=3.6V, VOUT=1.8V, CIN=4.7μF, COUT=10μF, TA=+25°C, unless otherwise noted.)
Ripple
(IOUT=20mA)
Ripple
(IOUT=20mA)
VIN=5.0V, BW=20MHz
BW=20MHz
VOUT
VOUT
20mV/div
10µs/div
20mV/div
10µs/div
Start-up from Shutdown
(IOUT=300mA)
VOUT
1V/div
VRUN
1V/div
20µs/div
Block Diagram
SLOPE
COMP
OSC
ISENSE
AMP
PVIN
+
0.6V
+
EA
-
_
S
_
R
Q
_
Q
RS LATCH
NC(SW)
PWM
LOGIC
NONOVERLAP
CONTROL
FB
ICOMP
+
DRV
VOUT
AVIN
+
AGND
REF
0.6V
-
EN
PGND
IZERO
COMP
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UM3502QA
Function Description
Integrated Inductor
The UM3502QA utilizes a low loss, multilayer inductor. The DCR of the integrated inductor is
180mΩ and the inductor is about 2.2µH. The use of an internal inductor localizes the noise
associated with the output loop currents. The proprietary integrated inductor construction reduces
the area of the converter’s large current loop that can reduce the radiated noise coupled into the
traces of the circuit board. Furthermore, the package layout is optimized to reduce the electrical
path length for the AC ripple currents that are a major source of radiated emissions from DC-DC
converters. The integrated inductor significantly reduces parasitic effects that can harm loop
stability, and makes layout very simple. All these lead to lower output noise and fewer influences
on the input power.
Current Mode PWM Control and Current Limit
The UM3502QA uses constant frequency, current mode step-down architecture. Both the main
(P-channel MOSFET) and synchronous (N-channel MOSFET) switches are internal. From the
block diagram, a comparator ICOMP is used to realize current limit protection. Lossless current
sensing converts the peak current signal to a voltage to sum in with the internal slope
compensation. This summed signal is compared to the error amplifier output to provide a peak
current control command for the PWM. The cycle-by-cycle current limit is set at 1200mA
(typical). During normal operation, the internal top power MOSFET is turned on each cycle when
the oscillator sets the RS latch, and turned off when the current comparator ICOMP, resets the RS
latch. The peak inductor current at which ICOMP resets the RS latch, is controlled by the output
of error amplifier EA. When the load current increases, it causes a slight decrease in the feedback
voltage, FB, relative to the 0.6V reference, which in turn, causes the EA amplifier’s output
voltage to increase until the average inductor current matches the new load current. While the top
MOSFET is off, the bottom MOSFET is turned on until either the inductor current starts to
reverse, as indicated by the current reversal comparator IZERO, or the beginning of the next clock
cycle.
When the output is shorted to ground, the inductor current may exceed the maximum inductor
peak current if not allowed enough time to decay. To prevent the inductor current from running
away, the bottom N-channel MOSFET is allowed to stay on for more than one cycle, thereby
allowing the inductor current time to decay.
Pulse Skipping Mode Operation
At very light loads, the UM3502QA automatically enters Pulse Skipping Mode. In the Pulse
Skipping Mode, the inductor current may reach zero or reverse on each pulse. The PWM control
loop will automatically skip pulses to maintain output regulation. The bottom MOSFET is turned
off by the current reversal comparator, IZERO, and the switch voltage will ring. This is
discontinuous mode operation, and is normal behavior for the switching regulator.
Enable
The EN pin provides a means to shut down the converter or enable normal operation. A logic low
will disable the converter and cause it to shut down. A logic high will enable the converter into
normal operation. In shutdown mode, the device quiescent current will be less than 1μA. The EN
pin must not be left floating.
Thermal Shutdown
When excessive power is dissipated in the chip, the junction temperature rises. Once the junction
temperature exceeds the thermal shutdown temperature, the thermal shutdown circuit turns off the
converter output voltage thus allowing the device to cool. When the junction temperature
decreases by 25°C, the device will go through the normal startup process.
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UM3502QA
Applications Information
Output Voltage Setting
The output voltage is set by a resistive divider according to the following formula:
2
1
The value of R1 should be less than 500kΩ, so that the input current on FB pin can reduce its
influence on the accuracy of the output voltage. The CFF capacitor is used to compensate the gain
of the loop for improved stability and the value of the capacitor is usually 4.7pF to 22pF, but it is
optional.
 =0.6V 1 +
Capacitor Selection
The input capacitor reduces the surge current drawn from the input and switching noise from the
device. The input capacitor impedance at the switching frequency shall be less than input source
impedance to prevent high frequency switching current passing to the input. Ceramic capacitors
with X5R or X7R dielectrics are highly recommended because of their low ESR and small
temperature coefficients. For most applications, a 4.7µF capacitor is sufficient.
The AVIN is separate from the PVIN in the chip. A CA capacitor can be used to decouple alone. The
AVIN can also be directly connected to the positive electrode of the CIN to decouple.
The output capacitor keeps output voltage ripple small and ensures regulation loop stable. The
output capacitor impedance shall be low at the switching frequency. Ceramic capacitor with X5R
or X7R dielectrics are recommended. For most applications, a 10µF capacitor is sufficient. For
smaller output voltage ripple, you can choose a bigger output capacitor.
Exposed Metal on the Bottom of the Package
The UM3502QA utilizes the lead frame as part of the electrical circuit. The lead frame offers
many advantages in thermal performance, in reduced electrical lead resistance and in overall foot
print. However, it does require some special considerations.
As part of the package assembly process, lead frame construction requires that for mechanical
support, some of the lead-frame metal be exposed at the point where wire-bond or internal
passives are attached. This results in several small pads being exposed on the bottom of the
package.
The “grayed-out” area in Figure 1 represents the area that should be clear of any metal (traces,
vias, or planes) on the top layer of the PCB.
1
Keep Out Area on
the Top Layer of
the PCB
Figure 1. Exposed Metal of the Package
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UM3502QA
Layout Guidance
The package of the UM3502QA has been optimized that makes it easy for layout. It is an ideal
choice to be used to replace less efficient LDO to achieve improved efficiency in space restricted
applications.
When laying out the PC board, the following suggestions should be taken to ensure higher
performance of the UM3502QA.
1. PCB with at least two planes is recommended. Keep the GND plane under the converter as
complete as possible.
2. Connect the input capacitor CIN to the PVIN and PGND pins, the output capacitor COUT to the
VOUT and PGND pins as closely as possible to get good power filter effect.
3. The power traces, including the PGND trace, the PVIN trace and VOUT trace should be kept
short, direct and wide to allow large current flow.
4. Connect AVIN and AGND to a quiet point. The AGND pin is usually connected to the
GND plane by vias. The AVIN pin should be directly connected to the positive electrode
of CIN. A 0.1µF capacitor can also be used to decouple for better performance.
5. Keep the SW pin away from the sensitive FB node. This pin should also not be electrically
connected to any external signal, ground, or voltage.
6. Do not trace signal line under the chip.
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UM3502QA
Package Information
UM3502QA: QFN24 4.0×4.0
Outline Drawing
D
Symbol
E
Pin #1 ID
Top View
N24
E1
K
K1
K3
D5
M3
E6
D2
1
N1
D6
M4
E3
D1
H1
M2
E5
H
E4
E2
M1
D3
D4
L
K2
N13
M
b
e
N7
A
A1
A3
Bottom View
Side View
A
A1
A3
b
D
E
D1
E1
D2
E2
D3
E3
D4
E4
D5
E5
D6
E6
e
H
H1
K
K1
K2
K3
L
M
M1
M2
M3
M4
DIMENSIONS
MILLIMETERS
Min
Typ
1.00
1.05
0.00
0.02
0.152REF
0.20
0.25
3.90
4.00
3.90
4.00
0.40
0.50
0.25
0.35
0.75
0.85
1.92
2.02
1.37
1.47
0.45
0.55
1.37
1.47
0.67
0.77
0.84
0.94
0.25
0.35
0.10
0.20
0.25
0.35
0.40
0.50
0.125REF
0.25REF
0.20
0.30
0.25
0.35
0.25
0.35
0.25
0.35
0.25
0.30
0.28
0.38
0.60
0.70
0.28
0.38
0.53
0.63
0.33
0.43
Max
1.10
0.05
0.30
4.10
4.10
0.60
0.45
0.95
2.12
1.57
0.65
1.57
0.87
1.04
0.45
0.30
0.45
0.60
0.40
0.45
0.45
0.45
0.35
0.48
0.80
0.48
0.73
0.53
Land Pattern
4.00
4.00
0.60
Keep Out Area
4.60
4.60
0.50
0.30
NOTES:
1. Compound dimension: 4.00×4.00;
2. Unit: mm;
3. General tolerance ±0.05mm unless otherwise
specified;
4. The layout is just for reference.
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UM3502QA
Tape and Reel Orientation
3502
M
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UM3502QA
GREEN COMPLIANCE
Union Semiconductor is committed to environmental excellence in all aspects of its
operations including meeting or exceeding regulatory requirements with respect to the use
of hazardous substances. Numerous successful programs have been implemented to
reduce the use of hazardous substances and/or emissions.
All Union components are compliant with the RoHS directive, which helps to support
customers in their compliance with environmental directives. For more green compliance
information, please visit:
http://www.union-ic.com/index.aspx?cat_code=RoHSDeclaration
IMPORTANT NOTICE
The information in this document has been carefully reviewed and is believed to be
accurate. Nonetheless, this document is subject to change without notice. Union assumes
no responsibility for any inaccuracies that may be contained in this document, and makes
no commitment to update or to keep current the contained information, or to notify a
person or organization of any update. Union reserves the right to make changes, at any
time, in order to improve reliability, function or design and to attempt to supply the best
product possible.
Union Semiconductor, Inc
Add: Unit 606, No.570 Shengxia Road, Shanghai 201210
Tel: 021-51093966
Fax: 021-51026018
Website: www.union-ic.com
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