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PAM2325
FAST TRANSIENT 3.5A STEP-DOWN CONVERTER
Description
The PAM2325 is a 3.5A step-down synchronous converter. The
1.2MHz switching frequency enables the use of small external
components. The ultra-small 2mm x 2mm footprint and high efficiency
make the PAM2325 an ideal choice for portable applications.
The PAM2325 delivers 3.5A maximum output current while
consuming only 55µA no load quiescent current. Low R integrated
MOSFETs and 100% duty cycle operation make the PAM2325 the
ideal choice for high output voltage, high current applications which
require a low dropout threshold.
The PAM2325 provides excel lent transient response and output
accuracy across the operating range.
The PAM2325 maintains high efficiency throughout the load range.
The PAM2325 automatically optimizes efficiency during light load
mode (PSM) and maintains constant frequency and low output ripple
during PWM mode.
Over-temperature and short circuit protection safeguard the PAM2325
and system components from damage.
The PAM2325 is available in an ultra-small QFN2x2-12 package. The
product is rated over a temperature range of -40°C to +85°C.
Applications
• Cellular Phone
• Digital Cameras
• Hard Disk Drives
• MP3 Players
• PDAs and Handheld Computers
• Portable Media Players
• USB Devices
• Wireless Network Cards
PAM2325
Document number: DSxxxxx Rev. 2 - 0
Pin Assignments
Features
• 3.5A Maximum Output Current
• Tiny 1.0µH Chip Inductor
• Excellent Transient Response
• Input Voltage: 2.5V to 5.5V
• Adjustable Output Voltage: 1.0V to 4.0V
• High Efficiency with 1.2MHz Switching Frequency
• 55µA No Load Quiescent Current
• 100% Duty Cycle Low-Dropout Operation
• Internal Soft Start
• Power Good Indicator
• Over-Temperature and Current Limit Protection
• Hiccup mode for output short protection
• 1µA Shutdown Current
• -40°C to +85°C Temperature Range
• Available in QFN2x2-12 Package
• RoHS/REACH Compliant
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Typical Applications Circuit
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PAM2325
Pin Descriptions
Pin
Number
1 PVIN Supply Voltage to power FETs. PVIN is connected to VIN internally.
2, 11 SW Switch Output. Pin 2 and 11 can be connected together.
3, 12 PGND Power Ground. Pin 3 and 12 can be connected together.
4 AGND Quiet ground for controller circuits
5 NC Leave this pin open. Do not connect it to ground.
6 OUT Input sense pin for output voltage
7 FB Feedback. An external resistor divider from the output to GND, tapped to the FB pin, sets the output voltage.
8 EN On/Off Control.
9 PG
10 VIN Supply Voltage to internal control circuitry. VIN is connected to PVIN internally.
Pin
Name
Function
Power Good Indicator. The output of this pin is an open drain with internal pull up resistor to VIN. PG is pulled
up to VIN when the FB voltage is within 10% of the regulation level, otherwise it is LOW.
Functional Block Diagram
PAM2325
Document number: DSxxxxx Rev. 2 - 0
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PAM2325
Absolute Maximum Ratings (@T
These are stress ratings only and functional operation is not implied. Exposure to absolute maximum ratings for prolonged time periods may
affect device reliability. All voltages are with respect to ground.
Parameter Rating Unit
Input Voltage -0.3 to +6.5 V
EN, FB Pin Voltage
SW Pin Voltage
Junction Temperature 150 °C
Storage Temperature Range -65 to +150 °C
Soldering Temperature 300, 5sec °C
Recommended Operating Conditions (@T
Parameter Rating Unit
Supply Voltage 2.5 to 5.5 V
Operation Temperature Range -40 to +85
Junction Temperature Range -40 to +125
= +25°C, unless otherwise specified.)
A
-0.3 to V
-0.3 to (V
+0.3)
IN
IN
= +25°C, unless otherwise specified.)
A
V
V
°C
Thermal Information
Parameter Symbol Package Max Unit
Thermal Resistance (Junction to Case)
Thermal Resistance (Junction to Ambient)
θ
JC
θ
JA
PAM2325
Document number: DSxxxxx Rev. 2 - 0
QFN2x2-12 16
QFN2x2-12 80
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°C/W
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PAM2325
Electrical Characteristics
(@TA = +25°C, VIN = 3.3V, V
Parameter Symbol Test Conditions Min Typ Max Units
Input Voltage Range
UVLO Threshold
Output Voltage Accuracy
Regulated Feedback Voltage
PMOS Current Limit
Output Voltage Line Regulation LNR
Output Voltage Load Regulation LDR
Quiescent Current
Shutdown Current
Oscillator Frequency
Drain-Source On-State Resisitance
SW Leakage Current
Start-Up Time
PSM Threshold
EN Threshold High
EN Threshold Low
EN Input Current
Over Temperature Protection OTP 150 °C
OTP Hysteresis OTH 30 °C
Effciency η
Output Ripple Ripple
Output Transient Ripple
PG Pin Trigger Delay 90 µs
PG Pin Threshold (relative to V
PG Open Drain Impedance
(PG = PV
)
IN
PG Open Drain Impedance
(PG = Low)
PAM2325
Document number: DSxxxxx Rev. 2 - 0
= 1.2V, CIN = 20µF, CO = 20µF, L = 1µH, unless otherwise specified.)
OUT
IN
Rising
V
IN
Hysteresis 400 550 mV
-4.0 +4.0 %
No Load 0.591 0.60 0.609 V
FB
V
= 3.3V to 5.5V
IN
I
= 1mA to 2A
O
No Load 55 100 µA
Q
VEN = 0V
IDS = 100mA
1 µA
250 1000 µs
S
P MOSFET 40 70 mΩ
N MOSFET 30 50 mΩ
VIN = 3.3V, VO = 1.2V
1.2 V
EH
0.4 V
EL
VEN = 2V
= 10mA
I
O
V
V
f
R
DS(ON)
I
V
UVLO
OUT
V
I
LIM
I
I
SD
OSC
LSW
t
I
TH
V
V
I
EN
IO = 500mA to 1A
IO = 1.5A
IO = 2A
I
= 10mA
O
IO ≥ 300mA
= 20mA to 1A
I
O
IO = 20mA to 2A
OUT
V
PK-PK
)
±10 %
250K 500K Ω
100 Ω
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2.5 3.3 5.5 V
2.35 2.5 2.65 V
4.8 A
0.5 1 %/V
2 %
1 µA
1.0 1.2 1.6 MHz
250 mA
1.2 4 µA
75 81
85 90
85 90
%
80 89
-5 +5
-2 +2
-10 +10
-12 +12
© Diodes Incorporated
%
%
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Typical Performance Characteristics (@T
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PAM2325
= +25°C, CIN = 20µF, CO = 20µF, VO = 1.2V, unless otherwise specified.)
A
PAM2325
Document number: DSxxxxx Rev. 2 - 0
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Typical Performance Characteristics (cont.) (@T
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PAM2325
= +25°C, CIN = 10µF, CO = 10µF, VO = 1.2V, unless otherwise specified.)
A
PAM2325
Document number: DSxxxxx Rev. 2 - 0
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Typical Performance Characteristics (cont.) (@T
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PAM2325
= +25°C, CIN = 10µF, CO = 10µF, VO = 1.2V, unless otherwise specified.)
A
PAM2325
Document number: DSxxxxx Rev. 2 - 0
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PAM2325
Application Information
The basic PAM2325 application circuit is shown on Page 1. External component selection is determined by the load requirement, selecting L first
and then C
Inductor Selection
For most applications, the value of the inductor will fall in the range of 1μH to 3.3μH. Its value is chosen based on the desired ripple current.
Large value inductors lower ripple current and small value inductors result in higher ripple currents. Higher V
current as shown in equation 3.5A reasonable starting point for setting ripple current is ΔI
The DC current rating of the inductor should be at least equal to the maximum load current plus half the ripple current to prevent core saturation.
Thus, a 4.2A rated inductor should be enough for most applications (3.5A + 0.7A). For better efficiency, choose a low DC-resistance inductor.
CIN and C
In continuous mode, the source current of the top MOSFET is a square wave of duty cycle V
ESR input capacitor sized for the maximum RMS current must be used. The maximum RMS capacitor current is given by:
This formula has a maximum at V
significant deviations do not offer much relief. Note that the capacitor manufacturer's ripple current ratings are often based on 2000 hours of life.
This makes it advisable to further derate the capacitor, or choose a capacitor rated at a higher temperature than required. Consult the
manufacturer if there is any question.
The selection of Cout is driven by the required effective series resistance (ESR).
Typically, once the ESR requirement for C
output ripple ΔV
Where f = operating frequency, C
highest at maximum input voltage since ΔI
Using Ceramic Input and Output Capacitors
Higher values, lower cost ceramic capacitors are now becoming available in smaller case sizes. Their high ripple current, high voltage rating and
low ESR make them ideal for switching regulator applications. Using ceramic capacitors can achieve very low output ripple and small circuit size.
When choosing the input and output ceramic capacitors, choose the X5R or X7R dielectric formulations. These dielectrics have the best
temperature and voltage characteristics of all the ceramics for a given value and size.
Thermal Consideration
Thermal protection limits power dissipation in the PAM2325. When the junction temperature exceeds +150°C, the OTP (Over Temperature
Protection) starts the thermal shutdown and turns the pass transistor off. The pass transistor resumes operation after the junction temperature
drops below 120°C.
For continuous operation, the junction temperature should be maintained below 125°C. The power dissipation is defined as:
is the step-down converter quiescent current. The term tsw is used to estimate the full load step-down converter switching losses.
I
Q
For the condition where the step-down converter is in dropout at 100% duty cycle, the total device dissipation reduces to:
PAM2325
Document number: DSxxxxx Rev. 2 - 0
and C
IN
I
L
OUT
C
IN
Δ
.
OUT
V
OUT
V
IN
⎞
⎟
(1)
⎟
⎠
1
⎛
⎜
1
OUT
−=Δ
⎜
⎝
V
)L)(f(
Selection
[]
()
−
required
is determined by:
OUT
≈
Δ
2
=
IP
OD
2
OD
≅
II
OMAXRMS
=2V
IN
()
LOUT
OUT
+=
VIRIP
, where I
OUT
OUT
fC8/1ESRIV+
OUT
=output capacitance and ΔIL = ripple current in the inductor. For a fixed output voltage, the output ripple is
increases with input voltage.
L
()
−+
V
IN
INQH)ON(DS
VVV
V
IN
RMS
has been met, the RMS current rating generally far exceeds the I
RVVRV
2/1
OUTINOUT
= I
/2. This simple worst -case condition is commonly used for design because even
OUT
L)ON(DSOINH)ON(DSO
()
t
SW
++
VIIF
INQOS
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= 1.4A (40% of 3.5A).
L
. To prevent large voltage transients, a low
OUT/VIN
IN
or V
also increases the ripple
OUT
(P-P) requirement. The
RIPPLE
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PAM2325
Application Information (cont.)
Thermal Consideration (cont.)
Since R
voltage range. The maximum power dissipation depends on the thermal resistance of IC package, PCB layout, the rate of surrounding airflow
and temperature difference between junction and ambient. The maximum power dissipation can be calculated by the following formula:
Where T
junction to the ambient. Based on the standard JEDEC for a two layer thermal test board, the thermal resistance θ
respectively. The maximum power dissipation at T
P
Setting the Output Voltage
The internal reference is 0.6V (Typical). The output voltage is calculated as below:
The output voltage is given by Table 1.
Table 1: Resistor selection for output voltage setting.
Pulse Skipping Mode (PSM) Description
When load current decreases, the peak switch current in Power-PMOS will be lower than skip current threshold and the device will enter into
Pulse Skipping Mode.
In this mode, the device has two states, working state and idle state. First, the device enters into working state control led by internal error
amplifier.When the feedback voltage gets higher than internal reference voltage, the device will enter into low I idle state with most of internal
blocks disabled. The output voltage will be reduced by loading or leakage current. When the feedback voltage gets lower than the internal
reference voltage, the convertor will start a working state again.
100% Duty Cycle Operation
As the input voltage approaches the output voltage, the converter turns the P-Channel transistor continuously on. In this mode the output voltage
is equal to the input voltage minus the voltage drop across the P-Channel transistor:
where R
UVLO and Soft-Start
The reference and the circuit remain reset until the VIN crosses its UVLO threshold. The PAM2325 has an internal soft-start circuit that limits the
in-rush current during start-up.
This prevents possible voltage drops of the input voltage and eliminates the output voltage overshoot.
Hiccup Mode Short Circuit Control
When the converter output is shorted or the device is overloaded,each high-side MOSFET current- limit event turns off the high-side MOSFET and
turns on the low-side MOSFET. An internal counter is used to count the each current-limit event. The counter is reset after consecutive high-side
MOSFETs turn on without reaching current limit. If the current- limit condition persists, the counter fills up. The control logic then stops both high-
side and lowside MOSFETs and waits for a hiccup period, before attemping a new soft-start sequence. The counter bit is decided by V
If V
FB
disable during soft-start time.
PAM2325
Document number: DSxxxxx Rev. 2 - 0
, quiescent current, and switching losses all vary with input voltage, the total losses should be investigated over the complete input
DS(ON)
−
TT
A)MAX(J
=
P
D
J(MAX)
= (125°C - 25°C) /80°C/W = 1.25W
D
V
O
V
O
1.2V 150k 150k
1.5V 150k 100k
1.8V 300k 150k
2.5V 380k 120k
3.3V 680k 150k
DS(ON)
≤ 0 2, the counter is 3-bit counter; if V
θ
is the maximum allowable junction temperature 125°C.T is the ambient temperature and θJA is the thermal resistance from the
⎛
1x6.0
⎜
⎝
= P-Channel switch ON resistance, I
JA
= +25°C can be calculated by following formula:
A
1R
⎞
+=
⎟
2R
⎠
R1 R2
()
+−=
RRIVV
LDSONLOADINOUT
= Output current, RL = Inductor DC resistance.
LOAD
>0.2 the counter is 6-bit counter. The typical hicuup made duty cycle is 1.7%. The hicuup mode is
FB
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of QFN2X2-12 80°C/W
JA
voltage.
FB
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PAM2325
Application Information (cont.)
Thermal Shutdown
When the die temperature exceeds +150°C, a reset occurs and the reset remains until the temperature decrease to +120°C, at which time the
circuit can be restarted.
Ordering Information
Part Number Output Voltage Part Type Standard Package
PAM2325AGPADJ CLVXYW QFN2x2-12 3000 Units/Tape & Reel
Marking Information
PAM2325
Document number: DSxxxxx Rev. 2 - 0
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Package Outline Dimensions (All dimensions in mm.)
QFN2x2-12
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PAM2325
PAM2325
Document number: DSxxxxx Rev. 2 - 0
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PAM2325
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INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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written approval of the Chief Executive Officer of Diodes Incorporated. As used herein:
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1. are intended to implant into the body, or
2. support or sustain life and whose failure to perform when properly used in accordance with instructions for use provided in the
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B. A critical component is any component in a life support device or system whose failure to perform can be reasonably expected to cause the
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Customers represent that they have all necessary expertise in the safety and regulatory ramifications of their life support devices or systems, and
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IMPORTANT NOTICE
LIFE SUPPORT
PAM2325
Document number: DSxxxxx Rev. 2 - 0
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