ETC ID8255

iDESYN
Preliminary
iD8255
Dual 1.5MHz, 800mA
Synchronous Step-Down Converter
General Description
Applications
The iD8255 is a dual PWM step-down converter
„
TV Tuner/Box
containing two independent 1.5MHz constant
„
Portable Instrument
frequency, and current mode outputs. Each channel
„
DataCom
integrates a main switch and a synchronous rectifier
„
PDAs
for high efficiency with no external Schottky diode
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iD8255 - □□ □□□ □ 伟
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needed. The iD8255 is suitable for powering portable
Features
equipment that operates from a single cell Lithium-Ion
„
800mA Output Current on Each Channel
(Li+) battery to 5.5V power source. Each converter can
„
2.5V to 5.5V Input Voltage Range
supply 800mA of load current from a 2.5V to 5.5V input
„
1.5MHz Constant Frequency Operation
voltage. The iD8255 can also run at 100% duty cycle
„
Low Dropout Operation at 100% Duty Cycle
for low dropout applications.
„
Synchronous Topology
„
0.6V Low Reference Voltage
„
Typically 0.1 μA Shutdown Current
„
Current Mode Operation
„
Over Temperature Protection
„
Over Current Protection
„
Up to 95% Efficiency
„
Internally Compensated
„
Lead Free and Green Devices Available
Ordering Information
Taping
Package
R: Tape and Reel
F3A:DFN-10 (3x3)
(RoHS / Green Compliant)
Output Voltage Voltage Code
Adjustable
AD
Marking Information
For marking information, please contact our sales
representative directly or through distributor around
your location.
Jan. 2010
1
V0.1
iDESYN
Preliminary
iD8255
Typical Application Circuit
(Adjustable Operation)
VIN1/IN2 2.5V ~5.5V
CIN1
4.7μF
8
R5
100KΩ
3
R6
100KΩ
IN2
IN1
CIN2
4.7μF
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1
OFF ON
VOUT1
1.8V
800mA
COUT1
10μF
L1
2.2μH
10
C3 22pF
R1
300KΩ
EN1
2
EN2
SW2
SW1
FB1
R2
150KΩ
FB2
GND1
Supply Voltage VIN
6V
Power Dissipation, PD @ TA=25°C
DFN -10(3x3)
2.083W
Lead Temperature
Storage Temperature
Jan. 2010
OFF ON
L2
2.2μH
C4 22pF
7
R3
680KΩ
VOUT2
3.3V
800mA
COUT2
10μF
R4
150KΩ
4
Recommended Operating Conditions
Input Voltage VIN
2.5V to 5.5V
EN Input Voltage
0V to VIN
Junction Temperature
Thermal Resistance, θja
DFN -10(3x3)
5
GND2
9
Absolute Maximum Ratings (Note 1)
6
Ambient Operating Temperature
-40°C to 125°C
-40°C to 85°C
48°C/W
260°C
-65°C to 150°C
2
V0.1
iDESYN
Preliminary
iD8255
Pin Configurations (Top View)
(Top View)
DFN-10 (3mm x 3mm)
EN1
1
10
SW1
FB1
2
9
GND1
IN2
3
8
IN1
GND2
4
7
FB2
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SW2
5
6
EN2
Exposed pad
on backside
Pin Description
Number
Name
Description
1
EN1
Channel 1 Enable Control Input. Drive EN1 above 1.5V to turn on the Channel 1. Drive EN1
below 0.3V to turn off. In shutdown situation, all functions are disabled to decrease the
supply current below 1μA.There is no pull high or pull low ability inside.
2
FB1
Channel 1 Feedback Input. Connect FB1 to the center point of the external resistor divider.
The feedback voltage is 0.6V.
3
IN2
Channel 2 Supply Input. Bypass to GND with a 4.7μF or greater ceramic capacitor.
4
GND2
5
SW2
Channel 2 Power Switch Output. Inductor connection to drains of the internal PMOSFET
and NMOSFET switches.
6
EN2
Channel 2 Enable Control Input. Drive EN2 above 1.5V to turn on the Channel 2. Drive EN2
below 0.3V to turn it off. In shutdown situation, all functions are disabled to decrease the
supply current below 1μA.There is no pull high or pull low ability inside.
7
FB2
Channel 2 Feedback Input. Connect FB2 to the center point of the external resistor divider.
The feedback voltage is 0.6V.
8
IN1
Channel 1 Supply Input. Bypass to GND with a 4.7μF or greater ceramic capacitor.
9
GND1
10
SW1
Jan. 2010
Ground 2. Connected the exposed pad to GND2.
Ground 1. Connected the exposed pad to GND1.
Channel 1 Power Switch Output. Inductor connection to drains of the internal PMOSFET
and NMOSFET switches.
3
V0.1
iDESYN
Preliminary
iD8255
Functional Block Diagram
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Jan. 2010
4
V0.1
iDESYN
Preliminary
iD8255
Electrical Characteristics
(Unless otherwise specified VIN=5.0V, FOSC=1.5MHz, TA=25oC)
Parameters
Condition
Min
Typ
Max
Units
Reference Voltage VFB
Quiescent Current
Shutdown Current
Under Voltage Lockout Threshold
Operating Voltage Range
–40°C ≤ TA ≤ +85°C
VEN = VIN = 5V, VFB=0.65V
VEN = 0V ; VIN = 5V
VEN pull high; VIN falling
0.582
0.600
50
0.1
1.60
0.618
100
1.0
1.88
5.5
V
μA
μA
V
V
PMOSFET ON Resistance RON
IOUT=200mA
NMOSFET ON Resistance RON
1.0
2.5
VIN=3.6V
0.37
VIN=2.5V
0.45
VIN=3.6V
VIN=2.5V
VOUT = VIN = 5V ; VEN = 0V
VSW = 0V or 5V
VIN = 2.5V to 5.5V
VIN = 2.5V to 5.5V
VEN = VIN = 5V
-40oC ≦ TA ≦ +85oC
VEN = 0V to 5.5V
Ω
0.55
0.63
IOUT=200mA
Ω
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SW Leakage Current
Current Limit
Oscillation Frequency
Thermal Shutdown Threshold
EN Threshold Voltage
EN Input Current
Maximum Duty Cycle
0.01
1
1.2
0.3
1.5
165
0.96
0.01
100
1.0
μA
1.8
1.8
A
MHz
o
C
V
μA
%
1.5
1.0
Note 1: Stresses listed as the above "Absolute Maximum Ratings" may cause permanent damage to the device. These are for
stress ratings. Functional operation of the device at these or any other conditions beyond those indicated in the operational
sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended periods may remain
possibility to affect device reliability.
Jan. 2010
5
V0.1
iDESYN
Preliminary
iD8255
Typical Performance Characteristics
(Unless otherwise specified TA=25℃).
Efficiency vs. Output Current
100%
100%
90%
90%
80%
80%
Efficiency
Efficiency
Efficiency vs. Output Current
70%
70%
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60%
VIN = 5.0V
60%
VIN = 4.2V
VIN = 5.0V
50%
50%
VIN = 4.2V
VEN = VIN, VOUT = 3.3V, L = 2.2μH
40%
0
100
200
300
400
500
600
700
VIN = 3.3V
VIN = 2.5V
VEN = VIN, VOUT = 1.2V, L = 2.2μH
40%
800
0
100
200
300
400
500
600
700
800
Output Current (mA)
Output Current (mA)
Feedback Voltage vs. Output Current
Feedback Voltage vs. Temperature
0.63
0.63
VIN = 4.2V
0.62
VIN = 3.3V
VIN = 2.5V
0.61
0.60
0.59
0.58
VEN = VIN, L = 2.2μH
0.57
0
100
200
300
400
500
600
700
0.62
0.61
0.60
0.59
0.58
800
-40 -25 -10
20 35 50 65 80 95 110 125
Temperature (℃)
Frequency vs. Input Voltage
Frequency vs. Temperature
1.80
1.70
1.70
1.60
1.50
1.40
1.30
VEN = VIN, IOUT = 800mA
1.20
3
3.5
4
4.5
5
1.60
1.50
1.40
1.30
VEN = VIN = 5.0V, IOUT = 800mA
1.20
-40 -25 -10
5.5
Input Voltage (V)
Jan. 2010
5
Output Current (mA)
1.80
2.5
VEN = VIN = 5.0V, IOUT = 800mA
0.57
Frequency (MHz)
Frequency (MHz)
Feedback Voltage (V)
Feedback Voltage (V)
VIN = 5.0V
5
20 35 50 65 80 95 110 125
Temperature (℃)
6
V0.1
iDESYN
Preliminary
iD8255
Standby Current vs. Temperature
120
120
100
100
Standby Current (μA)
Standby Current (μA)
Standby Current vs. Input Voltage
80
60
40
80
60
40
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20
20
VEN1 = VEN2 = VIN, No Load
VEN1 = VEN2 = VIN =5.0V, No Load
0
0
3
3.5
4
4.5
5
5.5
-40
-20
0
20
40
100 120 140
Quiescent Current vs. Input Voltage
Quiescent Current vs. Temperature
60
50
50
40
30
20
10
VEN1 = VEN2 = VIN, No Switching
0
40
30
20
10
VEN1 = VEN2 = VIN =5.0V, No Switching
0
2.5
3
3.5
4
4.5
5
5.5
-40
-20
0
20
40
60
80
100 120 140
Input Voltage (V)
Temperature (℃)
Shutdown Current vs. Input Voltage
Shutdown Current vs. Temperature
0.1
0.96
VEN1 = VEN2 = GND
Shutdown Current (μA)
VEN1 = VEN2 = GND
Shutdown Current (μA)
80
Temperature (℃)
60
0.08
0.06
0.04
0.02
0
0.80
0.64
0.48
0.32
0.16
0.00
2.5
3
3.5
4
4.5
5
5.5
-40
Input Voltage (V)
Jan. 2010
60
Input Voltage (V)
Quiescent Current (μA)
Quiescent Current (μA)
2.5
-20
0
20
40
60
80
100 120 140
Temperature (℃)
7
V0.1
iDESYN
Preliminary
iD8255
Current Limit vs. Input Voltage
P-MOS RDS(ON) vs. Input Voltage
1.8
0.7
0.6
P-MOS RDS(ON) (Ω)
Current Limit (A)
1.6
1.4
1.2
0.5
0.4
0.3
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1.0
0.2
ILOAD = 800mA
VIN = VEN, VFB = 0V ILOAD = 400mA
VEN1 = VEN2 = VIN
0.8
0.1
2.5
3.0
3.5
4.0
4.5
5.0
5.5
2.5
Input Voltage (V)
3
3.5
4
4.5
5
5.5
Input Voltage (V)
Enable Threshold Voltage vs. Input Voltage
UVLO
Enable Threshold Voltage (V)
0.9
ON
OFF
0.8
VIN (DC)
(2V/Div)
0.7
0.6
VSW (DC)
(2V/Div)
0.5
0.4
0.3
2.5
3.0
3.5
4.0
4.5
5.0
VIN = 5.0V, VOUT = 1.2V, L = 2.2μH, IOUT = 100mA
5.5
Input Voltage (V)
Time (10ms/Div)
Steady State Operating
Steady State Operating
VSW (DC)
(5V/Div)
VSW (DC)
(5V/Div)
VOUT (AC)
(20mV/Div)
VOUT (AC)
(20mV/Div)
ISW (DC)
(500mA/Div)
ISW (DC)
(500mA/Div)
Jan. 2010
VIN = 5.5V, VOUT = 1.2V, L = 2.2μH, IOUT = 400mA
VIN = 5.5V, VOUT = 3.3V, L = 2.2μH, IOUT = 400mA
Time (500ns/Div)
Time (1μs/Div)
8
V0.1
iDESYN
Preliminary
iD8255
Steady State Operation
Steady State Operation
VSW (DC)
(5V/Div)
VSW (DC)
(5V/Div)
VOUT (AC)
(20mV/Div)
VOUT (AC)
(5mV/Div)
ISW (DC)
(500mA/Div)
ISW (DC)
(500mA/Div)
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VIN = 5.5V, VOUT = 1.2V, L = 2.2μH, IOUT = 800mA
VIN = 5.5V, VOUT = 3.3V, L = 2.2μH, IOUT = 800mA
Time (500ns/Div)
Time (500ns/Div)
Cross Regulation
Cross Regulation
SW1 (DC)
(5V/Div)
SW1 (DC)
(5V/Div)
VOUT1 (AC)
(20mV/Div)
VOUT1 (AC)
(20mV/Div)
SW2 (DC)
(5V/Div)
SW2 (DC)
(5V/Div)
VOUT2 (AC)
(20mV/Div)
VOUT2 (AC)
(20mV/Div)
Time (500ns/Div)
Time (500ns/Div)
VIN = 5.5V,
VIN = 5.5V,
VOUT1 = 1.2V, L1 = 2.2μH, IOUT1 = 400mA ,
VOUT2 = 3.3V, L2 = 2.2μH, IOUT2 = 400mA
VOUT1 = 1.2V, L1 = 2.2μH, IOUT1 = 800mA ,
VOUT2 = 3.3V, L2 = 2.2μH, IOUT2 = 800mA
Load Transient Response
Load Transient Response
VOUT1 (AC)
(100mV/Div)
VOUT1 (AC)
(100mV/Div)
IOUT1 (DC)
(500mA/Div)
IOUT1 (DC)
(500mA/Div)
VOUT2 (AC)
(100mV/Div)
VOUT2 (AC)
(100mV/Div)
IOUT2 (DC)
(500mA/Div)
IOUT2 (DC)
(500mA/Div)
Time (200μs/Div)
Time (200μs/Div)
VIN = 5.0V,
VIN = 5.0V,
VOUT1 = 1.2V, C3=22pF, L1 = 2.2μH, IOUT1 = 100mA~600mA,
VOUT2 = 3.3V, C4=220pF, L2 = 2.2μH, IOUT2 = 100mA~600mA
VOUT1 = 1.2V, C3=220pF, L1 = 2.2μH, IOUT1 = 400mA~800mA,
VOUT2 = 3.3V, C4=220pF, L2 = 2.2μH, IOUT2 = 400mA~800mA
Jan. 2010
9
V0.1
iDESYN
Preliminary
Power On from VIN
iD8255
Power On from VIN
VIN (DC)
(5V/Div)
VIN (DC)
(5V/Div)
VOUT (DC)
(1V/Div)
VOUT (DC)
(2V/Div)
IIN (DC)
(1A/Div)
IIN (DC)
(500mA/Div)
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(Resistive Load)
VIN = 5.5V, VOUT = 1.2V, L = 2.2μH, IOUT = 800mA
(Resistive Load)
VIN = 5.5V, VOUT = 3.3V, L = 2.2μH, IOUT = 800mA
Time (250μs/Div)
Time (500μs/Div)
Power On from EN
Power On from EN
VEN (DC)
(5V/Div)
VEN (DC)
(5V/Div)
VOUT (DC)
(500mV/Div)
VOUT (DC)
(2V/Div)
IIN (DC)
(500mA/Div)
IIN (DC)
(200mA/Div)
(Resistive Load)
VIN = 5.5V, VOUT = 1.2V, L = 2.2μH, IOUT = 800mA
(Resistive Load)
VIN = 5.5V, VOUT = 3.3V, L = 2.2μH, IOUT = 800mA
Time (100μs/Div)
Jan. 2010
Time (100μs/Div)
10
V0.1
iDESYN
Preliminary
iD8255
Functional Description
the main switch is held on continuously to deliver
The iD8255 is a constant frequency current mode
current to the output up to the PFET current limit. The
PWM step-down converter. The iD8255 is optimized
output voltage then is the input voltage minus the
for low voltage, Li-Ion battery powered applications
voltage drop across the main switch and the inductor.
where high efficiency and small size are critical. The
Short Circuit Protection
iD8255 uses an external resistor divider to set the
The iD8255 has a short circuit protection. When the
output voltage from 0.6V to 6V. The device integrates
output is shorted to ground, the oscillator frequency is
both a main switch and a synchronous rectifier, which
reduced to prevent the inductor current from increasing
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provides high efficiency and eliminates an external
beyond the PFET current limit. The PFET current limit
Schottky diode. The iD8255 can achieve 100% duty
is also reduced to lower the short circuit current. The
cycle. The duty cycle D of a step-down converter is
frequency and current limit will return to the normal
defined as:
values once the short circuit condition is removed and
D = TON × f OSC × 100% ≈
the feedback voltage reaches 0.6V.
VOUT
× 100%
VIN
Maximum Load current
where TON is the main switch on time, and fOSC is the
The iD8255 can operate down to 2.2V input voltage,
oscillator frequency 1.5MHz.
however the maximum load current decreases at lower
Current Mode PWM Control
input due to large IR drop on the main switch and
Slope compensated current mode PWM control
synchronous rectifier. The slope compensation signal
provides stable switching and cycle-by-cycle current
reduces the peak inductor current as a function of the
limit for superior load and line response and protection
duty cycle to prevent sub-harmonic oscillations at duty
of the internal main switch and synchronous rectifier.
cycles greater than 50%. Conversely the current limit
The iD8255 switches at a constant frequency and
increases as the duty cycle decreases.
regulates the output voltage. During each cycle the
Output Voltage Setting
PWM comparator modulates the power transferred to
The external resistor divider sets the output voltage.
the load by changing the inductor peak current based
The feedback resistor R1 also sets the feedback loop
on the feedback error voltage. During normal operation,
bandwidth with the internal compensation capacitor.
the main switch is turned on for a certain time to ramp
Choose R1 around 300kΩ for optimal transient
the inductor current at each rising edge of the internal
response. R2 is then given by:
oscillator, and switched off when the peak inductor
current is above the error voltage. When the main
⎡ V
⎞ - 1⎤
R2 = R1/ ⎢⎛⎜ OUT
⎟ ⎥
0.6
⎠ ⎦
⎣⎝
switch is off, the synchronous rectifier will be turned on
Inductor Selection
immediately and stay on until either the next cycle
A 1μH to 10μH inductor with DC current rating at least
starts.
25% higher than the maximum load current is
The iD8255 allows the main switch to remain on for
recommended
more than one switching cycle and increases the duty
efficiency, the inductor DC resistance shall be <200mΩ.
cycle while the input voltage is dropping close to the
For most designs, the inductance value can be derived
output voltage. When the duty cycle reaches 100%,
from the following equation:
Jan. 2010
11
for
most
applications.
For
best
V0.1
iDESYN
L=
Preliminary
VOUT × (VIN - VOUT )
VIN × ΔI L × f OSC
iD8255
PD ( MAX ) =
(T (
J MAX )
− TA )
θ JA
where ΔIL is Inductor Ripple Current. Choose inductor
Where TJ(MAX) is the maximum operation junction
ripple current approximately 30% of the maximum load
temperature 125°C, TA is the ambient temperature and
current, 600mA. The maximum inductor peak current is:
the θJA is the junction to ambient thermal resistance.
I L(MAX) = I LOAD +
ΔI L
2
For recommended operating conditions specification of
iD8255 where TJ(MAX) is the maximum junction
Under light load conditions below 100mA, larger
temperature of the die (125°C) and TA is the maximum
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inductance is recommended for improved efficiency.
ambient temperature. The junction to ambient thermal
Input Capacitor Selection
resistance θJA is layout dependent. For DFN-10(3x3)
The input capacitor reduces the surge current drawn
packages, the thermal resistance θJA is 48°C/W on the
from the input and switching noise from the device.
standard JEDEC 51-7 four-layers thermal test board.
The input capacitor impedance at the switching
The maximum power dissipation at TA = 25°C can be
frequency shall be less than input source impedance to
calculated by following formula:
prevent high frequency switching current passing to
PD(MAX) = (125°C − 25°C ) / (48°C/W) = 2.083W
the input. Ceramic capacitors with X5R or X7R
for DFN-10(3x3) packages. The maximum power
dielectrics are highly recommended because of their
dissipation depends on operating ambient temperature
low ESR and small temperature coefficients. For most
for fixed TJ(MAX) and thermal resistance θJA. For iD8255
applications, a 4.7μF capacitor is sufficient. Output
packages, the Figure of de-rating curves allows the
Capacitor Selection The output capacitor keeps output
designer to see the effect of rising ambient
voltage ripple small and ensures regulation loop stable.
temperature on the maximum power allowed.
The output capacitor impedance shall be low at the
switching frequency. Ceramic capacitors with X5R or
Maximum Power Dissipation
ΔVOUT is approximately:
ΔVOUT
⎤
V × (VIN - VOUT ) ⎡
1
≤ OUT
× ⎢ESR +
⎥
VIN × f OSC × L
8 × f OSC × C3 ⎦
⎣
Thermal Considerations
For continuous operation, do not exceed the maximum
operation junction temperature 125°C. The maximum
power dissipation depends on the thermal resistance
of IC package, PCB layout, the rate of surroundings
Maximum Power Dissipation (W)
X7R dielectrics are recommended. The output ripple
2.5
2
1.5
1
0.5
0
0
25
50
75
100
125
Ambient Temperature(˚C)
airflow and temperature difference between junctions
to ambient. The maximum power dissipation can be
calculated by following formula:
Jan. 2010
12
V0.1
iDESYN
Preliminary
iD8255
Layout Considerations
When laying out the printed circuit board, the following checklist should be used to ensure proper operation of the
iD8255. These items are also illustrated graphically in layout diagram. Check the following in your layout:
1. The power traces, consisting of the GND trace, the SW trace and the IN trace should be kept short, direct and
wide.
2. Does the FB pin connect directly to the VOUT?
The R1 resistance must be connected between the (+) plate of COUT1.
The R3 resistance must be connected between the (+) plate of COUT2.
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3. Does the (+) plate of CIN connect to IN pin as closely as possible?
This capacitor avoided the AC current to the internal power MOSFETs.
4. Keep the switching node “SW” away from the sensitive FB node.
5. Keep the (–) plates of CIN1 and COUT1 as close as possible.
6. Keep the (–) plates of CIN2 and COUT2 as close as possible.
COUT must be
near iD8255.
The resistor divider, R1 and R2,
must be connected between the
(+) plate of COUT and a ground line
terminated near GND.
FB node copper area
should be minimized
and keep far away
from noise sources
(SW, IN).
COUT1
L1
SW should be connected
to Inductor by wide and
short trace, keep
sensitive compontents
away from this trace.
iD8255
R2
R1
CR1
EN1
1
10 SW1
FB1
2
9
GND1
IN2
3
8
IN1
GND2
4
7
FB2
CIN2
CIN must be placed
between IN and GND
as closer as Possible.
GND
CIN1
CR3 R3 R4
SW2
5
6
EN2
L2
Top layer
Bottom layer
COUT2
The exposed pad and GND
should be connected to a strong
ground plane for heat sinking
and noise prevention.
PCB Layout Guide
Jan. 2010
13
V0.1
iDESYN
Preliminary
iD8255
Packaging
DFN-10 (3mm x 3mm)
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SYMBOLS
A
A1
A3
b
D
D1
E
E1
e
L
θ
Jan. 2010
DIMENSIONS IN MILLIMETERS
MIN
0.80
0.00
--0.18
2.95
--2.85
----0.30
-12°
NOM
0.90
0.01
0.2 REF
0.23
3.0 BSC
2.2 BSC
3.0 BSC
1.6 BSC
0.5BSC
0.40
---
MAX
1.00
0.03
--0.28
3.03
--3.15
----0.50
0°
14
DIMENSIONS IN INCH
MIN
0.031
0.000
--0.0071
0.116
--0.116
----0.012
-12°
NOM
0.035
0.0004
0.008
0.009
0.118
0.087
0.118
0.063
0.020
0.016
---
MAX
0.039
0.0012
--0.011
0.119
--0.119
----0.020
---
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iDESYN
Preliminary
iD8255
Footprint
DFN-10 (3mm x 3mm)
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Jan. 2010
Package
Number of PIN
DFN-10 (3x3)
10
Footprint Dimension (mm)
P
A
B
C
D
Sx
Sy
M
0.50 3.80 2.10 0.85 0.30 2.50 1.50 2.30
15
Tolerance
±0.030
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