ETC PA2312

PAM2312
1A Step-Down DC-DC Converter
Features
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General Description
The PAM2312 is a step-down current-mode, DCDC converter. At heavy load, the constantfrequency P WM control per for ms exc ellent
stability and transient response. To ensure the
longest battery life in portable applications, the
PA M 2 3 1 2 p r o v i d e s a p o w e r - s a v i n g P u l s e Skipping Modulation (PSM) mode to reduce
quiescent current under light load operation to
save power.
Efficiency up to 96%
Only 40 μA(TYP.) Quiescent Current
Output Current: Up to 1A
Internal Synchronous Rectifier
1.5MHz Switching Frequency
Soft Start
Under-Voltage Lockout
Short Circuit Protection
Thermal Shutdown
5-pin Small SOT23-5 Packages
Pb-Free Package
The PAM2312 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
output voltage is adjustable from 0.6V to the input
voltage, while the part number suffix PAM2312XX indicates pre-set output voltage of 3.3V, 2.8V,
2.5V, 1.8V, 1.5V, 1.2V or adjustable. All versions
employ internal power switch and synchronous
rectifierfor 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 1 μA. Other key features
include under-voltage lockout to prevent deep
battery discharge.
Applications
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Cellular Phone
Portable Electronics
Wireless Devices
Cordless Phone
Computer Peripherals
Battery Powered Widgets
Electronic Scales
Digital Frame
The PAM2312 is available in SOT23-5 packages.
Typical Application
Fixed Output Voltage
V IN
CIN
10µF
L
VIN SW
GND
EN
Adjustable Output Voltage
Vo
V IN
Co
10µF
C IN
10µF
VOUT
/FB
L
VIN
Vo
SW
R1
GND
VOUT/FB
CFW
Co
10µF
R2
EN
R1 ö
æ
VO = 0.6 ´ ç 1 +
÷
è R2 ø
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PAM2312
1A Step-Down DC-DC Converter
Block Diagram
1.5M
OSC
SLOPE
COMP
FREQ
SHIFT
OSC
+
IAMP
-
VIN
VOUT/FB
S Q
R1
R Q
RS LATCH
EA
R2
+
VIN
SWITCHING
LOGIC
AND
BLANKING
CIRCUIT
MAIN
SWITCH( PCH)
ANTI SHOOT THRU
COMP
0.6VREF
EN
SW
SYNCHRONOUS
RECTIFIER (NCH )
+
IRCMP
-
SHUTDOWN
GND
Pin Configuration & Marking Information
Top View
SOT23 - 5
EN 1
5 VOUT/FB
GND 2
SW 3
4 VIN
CG: Product Code
of PAM2312
V: Output Voltage
Y: Year
W: Week
X: Internal Code
Pin Description
Name
Function
VIN
Chip main power s upply pin
GND
Ground
EN
Enable control input. Force this pin voltage above 1.5V, enables the chip, and below
0.3V shuts down the device.
VOUT: Output voltage feedback pin, an internal resistive divider divides the output
VOUT/FB
voltage down for comparison to the internal reference voltage.
FB: Feedback voltage to internal error amplifier, the threshold voltage is 0.6V.
SW
The drains of the internal main and synchronous power MOSFET.
NC
No connection
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PAM2312
1A Step-Down DC-DC Converter
Absolute Maximum Ratings
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.
Input Voltage..................................-0.3V to 6.0V
EN, FB Pin Voltage.............................-0.3V to V IN
SW Pi n Voltage......................- 0.3V to ( VIN +0.3V )
Junction Temperature................................150°C
Storage Temperature Range........-65°C to 150°C
Soldering Temperature......................300°C , 5sec
Recommended Operating Conditions
Supply Voltage................................2.5V to 5.5V
Operation Temperature Range.........-40 °C to 85 °C
Junction Temperature Range........-40 °C to 125 °C
Thermal Information
Parameter
Thermal Resistance
(Junc tion to Case)
Thermal Resistance
(Junction to Ambient)
Internal Power Dissipation
Package
Note
SOT23-5
Symbol
Maximum
θJ C
130
Unit
°C/W
SOT23-5
θJA
250
SOT23-5
PD
400
mW
Note:
The maximun output current for SOT23-5 package is limited by internal power dissipation capacity as
described in Application Information hereinafter.
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PAM2312
1A Step-Down DC-DC Converter
Electrical Characteristic
TA =25 °C , VIN =3.6V, VO =1.8V, CIN =10µF, CO =10µF, L=4.7µH, unless otherwise noted.
PARAMETER
SYMBOL
Test Conditions
MIN
Input Voltage Range
VIN
2.5
Regulated Feedback Voltage
V FB
0.588
Reference Voltage Line Regulation
ΔVFB
Regulated Output Voltage Accuary
VO
Peak Inductor Current
IP K
TYP
0.6
MAX
UNITS
5.5
V
0.612
V
0.3
IO = 100mA
-3
V IN= 3V,VFB = 0.5V or
%/V
+3
1.5
V O=90%
%
A
Output Voltage Line Regulation
LNR
V IN = 2.5V to 5V, IO=10mA
0.2
0.5
%/V
Output Voltage Load Regulation
LDR
IO=1mA to 800mA
0.5
1.5
%
40
70
µA
1
µA
1.8
MHz
Quiescent Current
IQ
No load
Shutdown Current
IS D
V EN = 0V
Oscillator Frequency
fOS C
Drain-Source On-State Res istance
SW Leakage Current
High Effic iency
V O = 100%
1.2
V FB = 0V or VO = 0V
1.5
500
k Hz
P MOSFET
0.3
0.45
Ω
N MOSFET
0.35
0.5
Ω
ILSW
±0.01
1
µA
η
96
RDS (O N)
IDS=100mA
%
EN Threshold High
V EH
1.5
V
EN Threshold Low
VE L
EN Leakage Current
IE N
±0.01
µA
Over Temperature Protection
OTP
150
°C
OTP Hysteresis
OTH
30
°C
0.3
V
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PAM2312
1A Step-Down DC-DC Converter
Typical Performance Characteristics
TA =25 °C , CIN =10μF, CO =10μF, L=4.7 μH, unless otherwise noted.
Efficiency vs Output Current (Vo=1.2V)
100
90
80
70
60
50
40
30
20
10
0
Efficiency vs Output Current (Vo=1.5V)
100
90
80
70
60
50
40
Vi n=3.6V
Vi n=5V
1
2.5V
3.6V
4.2V
30
Vi n=4.2V
20
10
100
1000
1
Efficiency vs Output Current (Vo=1.8V )
10 0
100
90
90
80
80
70
70
60
60
50
50
2.5V
3.6V
30
100
100 0
Outp ut Curren t(mA)
Output C urrent(m A)
40
10
4.2V
Efficiency vs Output Current (Vo=2.5V )
40
3V
30
3.6V
4.2V
20
20
1
10
1 00
Output Cu rrent(m A)
1
10 00
10 0
90
80
70
60
50
40
30
20
10
0
90
80
70
60
50
40
3V
30
3.6V
4.2V
20
1
10
100
1000
Output Current(mA)
Efficiency vs Output Current (Vo=2.8V)
10 0
10
1 00
10 00
Eifficiency VS Output Current (Vo=3.3V)
Vin=3.6V
Vin=4.2V
Vin=5V
1
10
1 00
10 00
Ou tpu t Curren t(mA)
Output Cu rrent(m A)
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PAM2312
1A Step-Down DC-DC Converter
Typical Performance Characteristics
TA =25 °C , CIN =10μF, CO =10μF, L=4.7 μH, unless otherwise noted.
Efficiency VS Input Voltage (Vo=1.2V )
100
100
90
90
80
80
70
70
60
60
Efficiency vs Input Voltage ( Vo=1.5V )
50
50
10mA
Io=10mA
40
40
Io=100mA
Io=800mA
30
100mA
800mA
30
3
3.5
4
4 .5
5
2.5
5.5
3
3.5
4
4.5
5
5.5
Input Voltage(V)
Inp ut Volta ge(V)
Efficiency vs Input Voltage ( Vo=1.8V )
100
100
90
90
80
80
70
70
60
60
Efficiency vs Input Voltage ( Vo=2.5V )
50
50
10mA
10mA
40
40
100mA
30
30
2.5
3
100mA
800mA
800mA
3.5
4
4.5
5
3
5.5
3.5
4
5
5.5
Input Voltage(V)
Input Voltage(V)
Eifficiency VS Input Voltage (Vo=3.3V)
Efficiency vs Input Voltage ( Vo=2.8V )
1 00
4.5
100
90
90
80
80
70
70
60
50
60
40
30
20
50
10mA
40
100mA
I o=1 0mA
I o=1 00mA
10
800mA
I o=8 00mA
30
0
3
3.5
4
4 .5
5
3.5
5.5
3.75
4
4.25
4.5
4.75
5
5.25
5.5
Input Voltage(V)
In put Volta ge(V)
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PAM2312
1A Step-Down DC-DC Converter
Typical Performance Characteristics
TA =25 °C , CIN =10μF, CO =10μF, L=4.7 μH, unless otherwise noted.
Output Voltage VS Load Current
Reference Voltage VS Input Voltage
0.602
1.215
0.600
1.210
0.598
1.205
0.596
1.200
0.594
1.195
0.592
1.190
0.590
0.588
I=1 00mA
I=6 00mA
0.586
1.185
Vo=1.2V
1.180
Vin=3.6V
I=8 00mA
1.175
0.584
2
3
4
Input Voltage
5
6
0
400
600
800
Load Current(mA )
Output Voltage VS Temperature
Reference Voltage VS Temperature
0.620
200
1.194
0.615
1.193
0.610
1.192
0.605
1.191
0.600
1.19
0.595
1.189
0.590
1.188
20
Vo=1.2V
Vin=3.6V
Io=100mA
0
50
100
150
40
60
80
100
120
140
Temperatur e(℃）
Temperature(℃）
Reference Voltage VS Load Current
0.604
Output Voltage VS Output Current
1.205
Vo=1.2V
1.203
0.6
1.201
0.596
1.199
0.592
1.197
1.195
0.588
0.584
2.5V
1.193
Vin=2. 7V
3.6V
1.191
Vin=3. 6V
4.2V
Vin=4. 2V
0.58
5V
1.189
0
200
400
600
800
10
Load Current
110
210
310
410
510
610
710
810
Output Current(mA)
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PAM2312
1A Step-Down DC-DC Converter
Typical Performance Characteristics
TA =25 C, CIN =10 μF, CO =10 μF, L=4.7μH, unless otherwise noted.
O
Dynamic Supply Current VS Input Voltage
50
Dynamic Supply Current VS Temperature
60
Vo=1.2V
45
40
50
ILoad=0A
35
40
30
25
30
20
15
20
10
5
10
0
0
Vo=1.2V
Vin=3.6V
ILoad=0A
2.5
3.5
4.5
40
5.5
60
80
R dson VS Input Voltage
0.4
100
120
140
Temperature(℃）
Input Voltage(V )
Rdson VS Temperature
0.6
Vin=3.6V
0.35
0.5
0.3
0.4
0.25
0.3
0.2
0.2
0.15
0.1
0.1
0
Vi n=4.2V
Vi n=3.6V
Vi n=2.7V
2
3
4
Input Voltage
5
6
20
Oscillator Frequency VS Supply Voltage
70
Temperature(℃)
120
Oscillator Frequency VS Temperature
1.8
1.58
Vin=3.6V
1.6
1.4
1.56
1.2
1
1.54
0.8
0.6
1.52
0.4
Vo=1.2V
Vo=1.5V
0.2
1.50
0
2
3
4
5
20
6
40
60
80
100
120
140
Temperature(℃）
Input Voltage (V)
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PAM2312
1A Step-Down DC-DC Converter
Typical Performance Characteristics
TA =25 °C ,CIN =10μF, CO =10μF, L=4.7 μH, unless otherwise noted.
Load Transient
Io=0-500mA, Vo=3.3V, Vin=5V
Load Transient
Io=0-1A, Vo=1.2V, Vin=3.6V
Output
Current
Output
Current
Voltage
Output
Voltage
Output
Start-up from Shutdown
Vo=1.8V, Vin=3.6V
Enable
Voltage
Output
Inductor
Current
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PAM2312
1A Step-Down DC-DC Converter
Application Information
The basic PAM2312 application circuit is shown
in Page 1. External component selection is
determined by the load requirement, selecting L
first and then Cin and Cout.
The selection of Cout is driven by the required
effective series resistance (ESR).
Typically, once the ESR requirement for Cout
has been met, the RMS current rating generally
far exceeds the I RIPPLE (P-P) requirement. The
output ripple △Vout is determined by:
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 IN or Vout also increases the
ripple current as shown in equation 1. A
reasonable starting point for setting ripple
current is △I L = 400mA (40% of 1A).
DIL =
1
æ VOUT ö
V OUT ç1÷
V IN ø
(f )(L )
è
1 ö
æ
V VOUT @VI L ç ESR+
÷
8fCO UT ø
è
Where f = operating frequency, C OUT=output
capacitance and Δ I L = ripple current in the
inductor. For a fixed output voltage, the output
ripple is highest at maximum input voltage since
ΔIL increases with input voltage.
(1)
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.
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-resis tance inductor.
Vo
1.2V
1.5V
1.8V
2.5V
3.3V
L
2.2µH
2.2µH
4.7µH
4.7µH
4.7µH
When choosing the input and output ceramic
capacitors, choose the X5R or X7R dielectric
formulations. These dielectrics have the best
temperature and voltage charac teristics of all
the ceramics for a given value and size.
C IN and C OUT Selection
Thermal consideration
In continuous mode, the source current of the top
MOSFET is a square wave of duty cycle
Vout/Vin. To prevent large voltage transients, a
low ESR input capacitor sized for the maximum
RMS current must be used. The maximum RMS
capacitor current is given by:
éë VOUT (VIN - VO UT )ùû
C IN required IRMS @ IOMAX
VIN
1
Thermal protection limits power dissipation in
the PAM2312. 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.
2
For continuous operation, the junction
temperature should be maintained below 125°C.
The power dissipation is defined as:
This formula has a maximum at V IN =2Vout,
w h e r e IR MS = IOU T / 2 . T h i s s i m p l e w o r s t - c a s e
condition is com monly used for design because
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 manufac turer if there is any question.
PD =IO
2
VORDSONH + (VIN -VO )RDSONL
VIN
+ (tSW FSIO +IQ )VIN
IQ is the step-down converter quiescent current.
The term tsw is used to estimate the full load
step-down converter switching losses.
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PAM2312
1A Step-Down DC-DC Converter
For the condition where the step-down converter
is in dropout at 100% duty cycle, the total device
dis sipation reduces to:
100% Duty Cycle Operation
As the input voltage approaches the output
voltage, the converter turns the P-chan nel
transistor continuously on. In this mode the
output voltage is equal to the input voltage minus
th e voltag e d rop ac ros s the P - c hannel
transistor:
PD =IO2 RDSON H +IQ VIN
Since RDS(ON) , quiescent current, and switching
losses all vary with input voltage, the total losses
should be investigated over the complete input
voltage range. The maximum power dissipation
de pend s on th e ther ma l r esi sta nc e 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:
PD =
V OUT = V IN –I LOAD (R dson + R L )
where Rdson = P-channel switch ON resistance,
IL O A D = O ut pu t c u rr e n t, RL = I nd uc t or DC
resistance
UVLO and Soft-Start
TJ(MAX) -TA
The reference and the circuit remain reset until
the VIN crosses its UVLO threshold.
θJA
Where TJ(max) is the maximum allowable
junction temper ature 125°C.TA is the ambient
temperature and θJA is the thermal resistance
from the junction to the ambient. Based on the
standard JEDEC for a two layers thermal test
board, the thermal resistance θJA of SOT23-5
package is 250°C/W, DFN2X2 102°C/W, and
QFN3X3 68°C/W, respectively. The maximum
power dissipation at T A = 25°C can be calculated
by following formula:
The PAM2312 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 500kHz and minimum duty
cycle, therefore the average input current is
typically 200mA.
P D=(125°C-25°C)/250°C/W=0.4W
Setting the Output Voltage
The internal reference is 0.6V (Typical). The
output voltage is calculated as below:
Thermal Shutdown
æ R1ö
VO=0.6×1+
ç R2 ÷
è
ø
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.
The output voltage is given by Table 1.
Table 1: Resistor selection for output voltage
setting
Vo
R1
R2
1.2V
100k
100k
1.5V
150k
100k
1.8V
200k
100k
2.5V
380k
120k
3.3V
540k
120k
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PAM2312
1A Step-Down DC-DC Converter
PCB Layout Check List
When laying out the printed circuit board, the following checklist should be used to ensure proper operation of
the PAM2312. 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 VIN trace should be kept short, direct
and wide.
2. Does the V FB pin connect directly to the feedback resistors? The resistive divider R1/R2 must be con nected
between the (+) plate of C OUT and ground.
3. Does the (+) plate of CIN connect to VIN as closely as possible? This capacitor provides the AC current to
the internal power MOSFETs.
4. Keep the switching node, SW, away from the sensitive VFB node.
5. Keep the (–) plates of C IN and C OUT as close as possible.
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PAM2312
1A Step-Down DC-DC Converter
Ordering Information
PAM 2312 X X X xxx
Output Voltage
Number of Pins
Package Type
Pin Configuration
Pin Configuration
Package Type
Number of Pins
A: SOT-23
B: 5
330: 3.3V
1. VIN
E: 16
280: 2.8V
2. GND
F: 6
250: 2.5V
A Type
Output Voltage
3. EN
180: 1.8V
4. VOUT/FB
150: 1.5V
5. SW
120: 1.2V
B Type :
ADJ: Adjustable
16 pins
C Type:
1. NC
2. EN
3. VIN
4. SW
5. GND
6 : VOUT/FB
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PAM2312
1A Step-Down DC-DC Converter
Outline Dimensions
SOT23-5
D
e1
θ
L REF.
e
L1 (REF.)
b
REF.
A
A1
A2
c
D
E
E1
L
L1
θ
b
e
e1
Millimeter
Min
Max
1.10 MAX
0
0.10
0.70
1
0.12 REF.
2.70
3.10
2.60
3.00
1.40
1.80
0.45 REF.
0.60 REF.
0º
10º
0.30
0.50
0.95 REF.
1.90 REF.
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