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DUAL HIGH-EFFICIENCY PWM STEP-DOWN DC-DC CONVERTER
Description
The PAM2306D is a dual step-down current mode, DC-DC converter.
At heavy load, the constant-frequency PWM control performs
excellent stability and transient response. To ensure the longest
battery life in portable applications, the PAM2306D provides a
powersaving Pulse-Skipping Modulation (PSM) mode to reduce
quiescent cur rent under light load operation.
The PAM2306D supports a range of input voltages from 2.5V to 5.5V,
allowing the use of a single Li+/Li-polymer cell, multiple Alkaline/NiMH
cell, USB, and other standard power sources. The dual output
voltages are available for adjustment. All versions employ internal
power switch and synchronous rectifier to minimize external part
count and realize high efficiency. During shutdown, the input is
disconnected from the output and the shutdown current is less than
0.1µA. Other key features include under-voltage lockout to prevent
deep battery discharge.
Features
Pin Assignments
Applications
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PAM2306D
Efficiency up to 96%
Only 40μA (Typ per Channel) Quiescent Current
Output Current: Up to 1A per Channel
Internal Synchronous Rectifier
1.5MHz Switching Frequency
Soft-Start
Under-Voltage Lockout
Short Circuit Protection
Thermal Shutdown
Small 12L WDFN3x3 Package
Pb-Free and RoHS Compliant
Typical Applications Circuit
Cellular Phone
Portable Electronics
Personal Information Appliances
Wireless and DSL Modems
MP3 Players
1Rx
VV
1REFOUT
2Rx
PAM2306D
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Pin Descriptions
Pin Number
1 VIN2 Power Input of Channel 2.
2 LX2 Pin for Switching of Channel 2.
3, 9
Exposed Pad
4 FB1 Feedback of Channel 1.
5, 11 NC1, NC2 No Connection
6 EN1
7 VIN1 Power Input of Channel 1.
8 LX1 Pin for Switching of Channel 1.
10 FB2 Feedback of Channel 2.
12 EN2
Pin Name
WDFN3x3-12L
GND
Ground. The exposed pad must be soldered to a large PCB and connected to GND for maximum
power dissipation.
Chip Enable of Channel 1 (Active High). V
Chip Enable of Channel 2 (Active High). V
Functional Block Diagram
Function
≤ V
EN1
≤ V
EN2
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.
IN1
.
IN2
PAM2306D
PAM2306D
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PAM2306D
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.
= +25°C, unless otherwise specified.)
A
Parameter Rating Unit
Input Voltage -0.3 to +6.5 V
EN1, FB1, LX1, EN2, FB2 and LX2 Pin Voltage
-0.3 to (V
+0.3)
IN
V
Maximum Junction Temperature 150 °C
Storage Temperature Range -65 to +150 °C
Soldering Temperature 260, 10sec °C
Recommended Operating Conditions (@T
= +25°C, unless otherwise specified.)
A
Parameter Rating Unit
Supply Voltage 2.5 to 5.5 V
Ambient Temperature Range -40 to +85 °C
Junction Temperature Range -40 to +125 °C
Thermal Information
Parameter Symbol Package Maximum Unit
Thermal Resistance (Junction to Ambient)
Thermal Resistance (Junction to Case)
Power Dissipation
θ
JA
θ
JC
P
D
W-DFN3x3-12
W-DFN3x3-12
W-DFN3x3-12
60 °C/W
8.5 °C/W
1.66 W
Electrical Characteristics
(@TA = +25°C, VIN = 3.6V, VO = 1.8V, CIN = 10µF, CO = 10µF, L = 2.2µH, unless otherwise specified.)
Parameter Symbol Test Conditions Min Typ Max Units
Input Voltage Range
Regulated Feedback Voltage
Reference Voltage Line Regulation
Regulated Output Voltage Accuracy
Peak Indictor Current
V
∆V
V
IN
FB
FB
V
O
I
PK
Output Voltage Line Regulation LNR
Output Voltage Load Regulation LDR
Quiescent Current (per channel)
Shutdown Current (per channel)
Oscillator Frequency
Drain-Source On-State Resistance
SW Leakage Current (per channel)
EN Threshold High
EN Threshold Low
EN Leakage Current
f
R
DS(ON)
I
V
V
I
Q
I
SD
OSC
LSW
EH
EL
I
EN
Over Temperature Protection OTP 150 °C
OTP Hysteresis OTH 30 °C
PAM2306D
Document number: DSxxxxx Rev. 1 - 1
2.5 5.5 V
0.588 0.6 0.612 V
0.3 %/V
I
V
= 10mA
O
= 3V, VFB = 0.5V or VO = 90%
IN
V
= 2.5V to 5V, IO = 10mA
IN
I
= 1mA to 1A
O
-3 +3 %
1.5 A
0.2 0.5 %/V
1.5 %
No load 40 70 µA
VEN = 0V
= 100%
V
O
VFB = 0V or VO = 0V
IDS = 100mA
P MOSFET 0.30 0.45 Ω
N MOSFET 0.35 0.50 Ω
±0.01 1 µA
1.5 V
0.3 V
±0.01 µA
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0.1 1 µA
1.2 1.5 1.8 MHz
500 kHz
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Typical Performance Characteristics (@T
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PAM2306D
= +25°C, CIN = 10µF, CO = 10µF, L = 4.7µH, unless otherwise specified.)
A
PAM2306D
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Typical Performance Characteristics (cont.)
(@TA = +25°C, CIN = 10µF, CO = 10µF, L = 4.7µH, unless otherwise specified.)
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PAM2306D
PAM2306D
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Typical Performance Characteristics (cont.)
(@TA = +25°C, CIN = 10µF, CO = 10µF, L = 4.7µH, unless otherwise specified.)
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PAM2306D
PAM2306D
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PAM2306D
Application Information
The basic PAM2306D application circuit is shown in 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 4.7μH. 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
ripple current as shown in Equation 1. A reasonable starting point for setting ripple current is ∆I
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 1.4A rated inductor should be enough for most applications (1A + 400mA). For better efficiency, choose a low DC-
resistance inductor.
V
O
L 2.2 µH 2.2 µH 2.2 µH 4.7 µH 4.7µH
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
even 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 C
Typically, once the ESR requirement for C
output ripple ∆V
and C
IN
I
1.2V 1.5V 1.8V 2.5V 3.3V
Selection
OUT
required
C
IN
OUT
OUT
.
OUT
1
Lf
is determined by:
1
V
OUTL
II
OMAXRMS
is driven by the required effective series resistance (ESR).
ESR
IV
LOUT
V
OUT
Equation (1)
V
IN
VVV
V
IN
IN
fC8
=2V
1
OUT
, where I
OUT
has been met, the RMS current rating generally far exceeds the I
OUT
OUTINOUT
RMS
2/1
= I
or V
IN
= 400mA (40% of 1A).
L
. To prevent large voltage transients, a low
OUT/VIN
/2. This simple worst-case condition is commonly used for design because
OUT
RIPPLE
also increases the
OUT
(P-P) requirement. The
Where f = operating frequency, C
is highest at maximum input voltage since ∆I
= output capacitance and ∆IL = ripple current in the inductor. For a fixed output voltage, the output ripple
OUT
increases with input voltage.
L
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 PAM2306D. 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:
2
I
is the step-down converter quiescent current. The term tsw is used to estimate the full load step-down converter switching losses.
Q
IP
OD
V
IN
RVVRV
PAM2306D
Document number: DSxxxxx Rev. 1 - 1
L)ON(DSOINH)ON(DSO
t
SW
VIIF
INQOS
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Application Information (cont.)
For the condition where the step-down converter is in dropout at 100% duty cycle, the total device dissipation reduces to:
2
OD
VIRIP
INQH)ON(DS
PAM2306D
Since R
input 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 layers thermal test board, the thermal resistance θ
The maximum power dissipation at T
P
, quiescent current, and switching losses all vary with input voltage, the total losses should be investigated over the complete
DS(ON)
TT
A)MAX(J
P
D
J(MAX)
= (125°C - 25°C)/60°C/W = 1.66W
D
is the maximum allowable junction temperature 125°C. TA is the ambient temperature and θJA is the thermal resistance from the
JA
= +25°C can be calculated by following formula:
A
of WDFN3X3 is 60°C/W.
JA
Selecting the Output Voltage
The internal reference is 0.6V (Typical). The output voltage is calculated as below:
1R
The output voltage is given by Table 1.
Table 1: Resistor selection for output voltage setting.
V
O
V
O
1.2V 100k 100k
1.5V 150k 100k
1.8V 200k 100k
2.5V 380k 120k
3.3V 540k 120k
16.0
2R
R1 R2
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:
V
where R
= VIN - I
OUT
= P-Channel switch ON resistance, I
DS(ON)
LOAD
(R
DS(ON)
+ RL )
= Output Current, RL = Inductor DC Resistance
LOAD
UVLO and Soft-Start
The reference and the circuit remain reset until the VIN crosses its UVLO threshold.
The PAM2306D 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. The soft-start acts as a digital circuit to increase the switch current in several steps to the
P-Channel current limit (1500mA).
Short Circuit Protection
The switch peak current is limited cycle-by-cycle to a typical value of 1500mA. In the event of an output voltage short circuit, the device
operates with a frequency of 400kHz and minimum duty cycle, therefore the average input current is typically 200mA.
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.
PAM2306D
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PAM2306D
Application Information (cont.)
PCB Layout Check List
When laying out the printed circuit board, the following checklist should be used to ensure proper operation of the PAM2306D. These items
are also illustrated graphically in Figure 1. Check the following
in your layout:
1. The power traces, consisting of the GND trace, the SW trace and the V
2. Does the FB pin connect directly to the feedback resistors? The resistive divider R1/R2 must be c onnected between the (+) plate of C
and ground.
3. Does the (+) plate of C
4. Keep the switching node, SW, away from the sensitive FB node.
5. Keep the (–) plates of C
connect to VIN as closely as possible? This capacitor provides the AC current to the internal power MOSFETs.
IN
and C
IN
as close as possible.
OUT
Top Bottom
trace should be kept short, direct and wide.
IN
OUT
Figure 1. PAM2306D Suggested Layout
PAM2306D
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Ordering Information
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PAM2306D
PAM2306DYPv1v2
Part Number Marking Package Type Packaging
2306Dv
X XXYW
1v2
W-DFN3x3-12 3000 Units/ Tape&Reel
Marking Information
PAM2306D
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Package Outline Dimensions (All dimensions in mm.)
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PAM2306D
PAM2306D
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PAM2306D
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INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
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IMPORTANT NOTICE
LIFE SUPPORT
PAM2306D
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