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Электронный компонент: FAN5308

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FAN5308 Rev. 1.0.1
1
www.fairchildsemi.com
April 2005
2005 Fairchild Semiconductor Corporation
F
AN5308 800mA High-Efficienc
y Step-Do
wn DC-DC Con
ver
ter
FAN5308
800mA High-Efficiency Step-Down DC-DC Converter
Features
96% Efficiency, Synchronous Operation
Adjustable Output Voltage Options from 0.8V to V
IN
2.5V to 5.5V Input Voltage Range
Up to 800mA Output Current
Fixed Frequency 1.3MHz PWM Operation
High Efficiency Power Save Mode
100% Duty Cycle Low Dropout Operation
Soft Start
Output Over-Voltage Protection
Dynamic Output Voltage Positioning
25
A Quiescent Current
Thermal Shutdown and Short Circuit Protection
Pb-Free 3x3mm 6-Lead MLP Package
Applications
Pocket PCs, PDAs
Cell Phones
Battery-Powered Portable Devices
Digital Cameras
Hard Disk Drives
Set-Top-Boxes
Point-of-Load Power
Notebook Computers
Communications Equipment
Description
Designed for use in battery-powered applications, the FAN5308
is a high-efficiency, low-noise synchronous PWM current mode
and Pulse Skip (Power Save) mode DC-DC converter. It can
provide up to 800mA of output current over a wide input range
from 2.5V to 5.5V. The output voltage can be externally adjusted
over a wide range of 0.8V to 5.5V by means of an external volt-
age divider.
At moderate and light loads, pulse skipping modulation is used.
Dynamic voltage positioning is applied, and the output voltage is
shifted 0.8% above nominal value for increased headroom dur-
ing load transients. At higher loads the system automatically
switches over to current mode PWM control, operating at 1.3
MHz. A current mode control loop with fast transient response
ensures excellent line and load regulation. To achieve high effi-
ciency and ensure long battery life, the quiescent current is
reduced to 25A in Power Save mode, and the supply current
drops below 1A in shut-down mode. The FAN5308 is available
in a 3x3mm 6-lead MLP package.
Typical Application
Figure 1. Typical Application
2 x 10
F
10
F
V
OUT
EN
SW
C
IN
C
OUT
1.2V (800mA)
1
2
3
6
5
4
FB
PGND
V
IN
NC
P1
(AGND)
3.3
H
R1
10K
5K
R2
2
www.fairchildsemi.com
FAN5308 Rev. 1.0.1
F
AN5308 800mA High-Efficienc
y Step-Do
wn DC-DC Con
ver
ter
Pin Assignment
Figure 2. Pin Assignment
Pin Description
Pin No.
Pin Name
Pin Description
P1
AGND
Analog Ground.
P1 must be soldered to the PCB ground.
1
V
IN
Supply Voltage Input.
2
PGND
Power Ground.
This pin is connected to the internal MOSFET switches. This pin must be
externally connected to AGND.
3
EN
Enable Input.
Logic high enables the chip and logic low disables the chip, reducing the supply
current to less than 1A. Do not float this pin.
4 FB
Feedback
Input.
Adjustable voltage option, connect this pin to the resistor divider.
5
NC
No Connection Pin.
6
SW
Switching Node.
This pin is connected to the internal MOSFET switches.
V
IN
PGND
EN
FB
SW
NC
1
2
3
6
5
4
P1
(AGND)
Top View
3x3mm 6-Lead MLP
3
www.fairchildsemi.com
FAN5308 Rev. 1.0.1
F
AN5308 800mA High-Efficienc
y Step-Do
wn DC-DC Con
ver
ter
Absolute Maximum Ratings
(Note1)
Recommended Operating Conditions
Notes:
1. Stresses above those listed under "Absolute 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 section of this specification is not implied. Exposure
to absolute maximum rating conditions for extended periods may affect device reliability. Absolute maximum ratings apply individually only, not in
combination. Unless otherwise specified, all other voltages are referenced to AGND.
2. Junction to ambient thermal resistance,
JA
, is a strong function of PCB material, board thickness, thickness and number of copper planes, number of
via used, diameter of via used, available copper surface, and attached heat sink characteristics.
3. Using Mil Std. 883E, method 3015.7(Human Body Model) and EIA/JESD22C101-A (Charge Device Model).
4. Refer to the applications section for further details.
Parameter
Min
Max
Unit
V
IN
-0.3
7
V
Voltage On Any Other Pin
-0.3
V
IN
V
Lead Soldering Temperature (10 seconds)
260
C
Junction Temperature
150
C
Storage Temperature
-65
150
C
Thermal Resistance-Junction to Tab
(
JC
)
,
3x3mm 6-lead MLP (Note 2)
8
C/W
Electrostatic Discharge Protection (ESD) Level (Note 3)
HBM
4
kV
CDM
1
Parameter
Min
Typ
Max
Unit
Supply Voltage Range
2.5
5.5
V
Output Voltage Range, Adjustable Version
0.8
V
IN
V
Output Current
800
mA
Inductor (Note 4)
3.3
H
Input Capacitor (Note 4)
10
F
Output Capacitor (Note 4)
2 x 10
F
Operating Ambient Temperature Range
-40
+85
C
Operating Junction Temperature Range
-40
+125
C
4
www.fairchildsemi.com
FAN5308 Rev. 1.0.1
F
AN5308 800mA High-Efficienc
y Step-Do
wn DC-DC Con
ver
ter
Electrical Characteristics
Notes:
5. Refer to the application section for further details.
6. For output voltages
1.2V a 40
F output capacitor value is required to achieve a maximum output accuracy of 3% while operating in power save mode
(PFM mode).
V
IN
= V
OUT
+ 0.6V(min. 2.5V) to 5.5V, I
OUT
= 350mA, V
OUT
=1.2V, EN = V
IN
, T
A
= -40C to +85C, Unless
otherwise noted. Typical values are at T
A
= 25C.
Symbol
Parameter
Conditions
Min.
Typ.
Max.
Units
V
IN
Input Voltage
0 mA
I
OUT
800 mA
2.5
5.5
V
I
Q
Quiescent Current
I
OUT
= 0mA, Device is not switching
20
35
A
I
OUT
= 0mA, Device is
switching (Note 5)
R2 =10K
50
A
R2 =100K
25
A
Shutdown Supply Current
EN = GND
0.1
1
A
Undervoltage Lockout
Threshold
V
IN
Rising
1.9
2.1
2.3
V
Hysteresis
150
mV
V
ENH
Enable High Input Voltage
1.3
V
V
ENL
Enable Low Input Voltage
0.4
V
I
EN
EN input bias current
EN = V
IN
or GND
0.01
0.1
A
R
DS-ON
PMOS On Resistance
V
IN
= V
GS
= 5.5V
250
350
m
V
IN
= V
GS
= 2.5V
300
400
NMOS On Resistance
V
IN
= V
GS
= 5.5V
200
300
m
V
IN
= V
GS
= 2.5V
250
350
I
LIM
P-channel current limit
2.5V < V
IN
< 5.5V
1300
1500
2000
mA
Oscillator frequency
1000
1300
1500
KHz
I
lkg_(N)
N-channel leakage current
V
DS
= 5.5V
0.1
1
A
I
lkg_(P)
P-channel leakage current
V
DS
= 5.5V
0.1
1
A
Line regulation
I
OUT
= 10 mA
0.16
%/V
Load regulation
350 mA
I
OUT
800 mA
0.15
%
Vref
Reference Voltage
0.8
V
Output DC Voltage Accuracy
(Note 6)
0 mA
I
OUT
800 mA
-3
+3
%
Over-Temperature Protection
PWM Mode Only
350 mA
I
OUT
800 mA
Rising
Temperature
150
C
Hysteresis
20
C
Start-Up Time
I
OUT
= 800mA, C
OUT
= 20F
800
S
5
www.fairchildsemi.com
FAN5308 Rev. 1.0.1
F
AN5308 800mA High-Efficienc
y Step-Do
wn DC-DC Con
ver
ter
Typical Performance Characteristics
T
A
= 25C, C
IN
= 10F, C
OUT
= 20F, L = 3.3H, R
2
= 10K
, unless otherwise noted.
1
10
100
1000
60
65
70
75
80
85
90
95
100
V
IN
= 5V
V
OUT
= 3.3V
V
IN
= 3.6V
V
OUT
= 1.2V
V
IN
= 3.6V
V
OUT
= 3V
0.1
1
10
100
1000
35
40
45
50
55
60
65
70
75
80
85
90
95
100
V
IN
= 5.5V
V
OUT
= 3.3V
V
IN
= 3.9V
0.1
1
10
100
1000
30
40
50
60
70
80
90
100
Load Current (mA)
Load Current (mA)
Load Current (mA)
Load Current (mA)
Efficiency (%)
Efficiency (%)
Efficiency (%)
Efficiency vs. Load Current
Efficiency vs. Load Current
Efficiency vs. Load Current
V
OUT
= 1.2V
V
IN
= 5.5V
V
IN
= 3. 6V
V
IN
= 2.5V
0
200
400
600
800
1000
1.192
1.194
1.196
1.198
1.200
1.202
1.204
1.206
1.208
1.210
1.212
1.214

Output Voltage (V)

Quiescent Current (
A)

Oscillator Frequency (kHz)
V
IN
= 5V
Output Voltage vs. Load Current
2.5
3.0
3.5
4.0
4.5
5.0
5.5
0
10
20
30
40
50
60
70
80
Input Voltage (V)
R
2
= 100K
R
2
= 10K
Quiescent Current vs. Input Voltage
-40
-20
0
20
40
60
80
100
1200
1220
1240
1260
1280
1300
1320
1340
1360
1380
1400
Temperature (
C)
Frequency vs. Temperature
V
IN
= 2.5V
V
IN
= 3.6V
V
IN
= 5.5V
V
OUT
= 1. 2V
R
2
= 100K
R
2
= 100K
6
www.fairchildsemi.com
FAN5308 Rev. 1.0.1
F
AN5308 800mA High-Efficienc
y Step-Do
wn DC-DC Con
ver
ter
Typical Performance Characteristics
(Contd.)
T
A
= 25C, C
IN
= 10F, C
OUT
= 20F, L = 3.3H, R
2
= 10K
, unless otherwise noted.
PWM Mode
Power Save Mode
Time (1
s/div)
SW
Node
(2
V
/
di
v
)
Vo
l
t
ag
e
In
du
cto
r
(2
00
mA/
div
)
Cu
rrent
Outpu
t
(5m
V/d
iv)
Vo
l
t
ag
e
Time (5
s/div)
SW Node
(2V
/div
)
Vo
l
t
ag
e
Out
put
(2
0m
V/d
iv)
Vo
l
t
ag
e
In
du
cto
r
(2
00
mA/
div
)
Cu
rrent
Time (10
s/div)
Load Transient Response
Ou
tput
(5
0m
V/d
i
v)
Vo
l
t
a
g
e
Ind
uc
tor
(50
0
m
A
/d
iv)
Current
600mA
100mA
Load Transient Response
Time (10
s/div)
Outp
ut
(50
m
V
/
div
)
Vo
l
t
ag
e
Ind
uc
tor
(50
0
m
A
/d
iv)
Current
Vo
l
t
ag
e a
t
En
a
b
le Pin
600mA
100mA
V
OUT
= 1.2V
Start-Up Response
Ou
tput
(
500
mV
/div
)
Vo
l
t
a
g
e
Ind
uc
tor
(20
0
m
A
/d
iv)
Current
Time (100
s/div)
(5
V/
Div
)
Loa
d C
u
rren
t
St
e
p
Lo
ad
Curre
nt
St
e
p
Start-Up Response
Time (200
s/div)
Outp
ut
(50
0
m
V
/d
iv)
Vo
l
t
ag
e
In
du
cto
r
(4
00
mA/
d
iv
)
Cu
rrent
Vo
l
t
a
g
e at
Enable Pin
(5V/Div)
V
OUT
= 1.2V
V
OUT
= 1.2V
I
OUT
= 10mA
V
OUT
= 1.2V
I
OUT
= 800mA
7
www.fairchildsemi.com
FAN5308 Rev. 1.0.1
F
AN5308 800mA High-Efficienc
y Step-Do
wn DC-DC Con
ver
ter
Block Diagram
Figure 3. Block Diagram
Detailed Operation Description
The FAN5308 is a step-down converter operating in a current-
mode PFM/PWM architecture with a typical switching frequency
of 1.3MHz. At moderate to heavy loads, the converter operates
in pulse-width-modulation (PWM) mode. At light loads the con-
verter enters a power-save mode (PFM pulse skipping) to keep
the efficiency high.
PWM Mode
In PWM mode, the device operates at a fixed frequency of
1.3MHz. At the beginning of each clock cycle, the P-channel
transistor is turned on. The inductor current ramps up and is
monitored via an internal circuit. The P-channel switch is turned
off when the sensed current causes the PWM comparator to trip
when the output voltage is in regulation or when the inductor
current reaches the current limit (set internally to typically
1500mA). After a minimum dead time the N-channel transistor
is turned on and the inductor current ramps down. As the clock
cycle is completed, the N-channel switch is turned off and the
next clock cycle starts.
PFM (Power Save) Mode
As the load current decreases and the inductor current reaches
negative value, the converter enters pulse-frequency-modula-
tion (PFM) mode. The transition point for the PFM mode is given
by the equation:
The typical output current when the device enters PFM mode is
150mA for input voltage of 3.6V and output voltage of 1.2V. In
PFM mode the device operates with a variable frequency and
constant peak current, thus reducing the quiescent current to
minimum. Consequently, the high efficiency is maintained at
light loads. As soon as the output voltage falls below a thresh-
old, set at 0.8% above the nominal value, the P-channel transis-
tor is turned on and the inductor current ramps up. The P-
channel switch turns off and the N-channel turns on as the peak
inductor current is reached (typical 450mA).
The N-channel transistor is turned off before the inductor cur-
rent becomes negative. At this time the P-channel is switched
on again starting the next pulse. The converter continues these
pulses until the high threshold (typical 1.6% above nominal
value) is reached. A higher output voltage in PFM mode gives
additional headroom for the voltage drop during a load transient
from light to full load. The voltage overshoot during this load
transient is also minimized due to active regulation during turn
on of the N-channel rectifier switch. The device stays in sleep
mode until the output voltage falls below the low threshold. The
FAN5308 enters the PWM mode as soon as the output voltage
can no longer be regulated in PFM with constant peak current.
100% Duty Cycle Operation
As the input voltage approaches the output voltage and the duty
cycle exceeds the typical 95%, the converter turns the P-chan-
nel 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
OUT
= V
IN
I
LOAD
(R
dsON
+ R
L
), where
R
dsON
=
P-channel switch ON resistance
I
LOAD
=
Output current
R
L
=
Inductor DC resistance
FB
ERROR
AMP
NEG.
LIMIT
COMP
PFM
COMP
LOGIC
CONTROL
OVER
VOLTAGE
COMP
UNDER-VOLTAGE
LOCKOUT
MOSFET
DRIVER
OSC
SLOPE COMPENSATION
REF
FB
REF
IS
IS
CURRENT
SENSE
NEG.
LIMIT
SENSE
DIGITAL
SOFT START
IS
GND
SW
V
IN
EN
GND
0.8V
COMP
I
OUT
V
OUT
1
V
OUT
V
IN
/
(
)
2
L
f
------------------------------------------
=
8
www.fairchildsemi.com
FAN5308 Rev. 1.0.1
F
AN5308 800mA High-Efficienc
y Step-Do
wn DC-DC Con
ver
ter
UVLO and Soft Start
The reference and the circuit remain reset until the V
IN
crosses
its UVLO threshold.
The FAN5308 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 is implemented as a digital circuit
increasing the switch current in four steps to the P-channel cur-
rent limit (1500mA). Typical start-up time for a 20F output
capacitor and a load current of 800mA is 800s.
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 150C, a reset occurs and
will remain in effect until the die cools to 130C, at that time the
circuit will be allowed to restart.
Applications Information
Setting the Output Voltage
The internal reference is 0.8V (Typical). The output voltage is
divided by a resistor divider, R1 and R2 to the FB pin. The out-
put voltage is given by:
Where R
1
+ R
2
< 800K
.
According to this equation, and assuming desired output volt-
age of 1.5096V, and given R2 = 10K
, the calculated value of
R1 is 8.87K
. If quiescent current is a key design parameter a
higher value feedback resistor can be used (e.g. R2 = 100K
)
and a small bypass capacitor of 10pF is required in parallel with
the upper resistor as shown in Figure 4.
Figure 4. Setting the Output Voltage
Inductor Selection
The inductor parameters directly related to the device's perfor-
mances are saturation current and dc resistance. The FAN5308
operates with a typical inductor value of 3.3H. The lower the dc
resistance, the higher the efficiency. For saturation current, the
inductor should be rated higher than the maximum load current
plus half of the inductor ripple current.
This is calculated as follows:
where:
I
L
= Inductor Ripple Current
f = Switching Frequency
L = Inductor Value
Some recommended inductors are suggested in the table
below:
Table 1: Recommended Inductors
Capacitors Selection
For best performances, a low ESR input capacitor is required. A
ceramic capacitor of at least 10F, placed as close to the V
IN
and AGND pins of the device is recommended. The output
capacitor determines the output ripple and the transient
response.
Table 2: Recommended Capacitors
PCB Layout Recommendations
The recommended PCB layout is shown in Figure 5. The inher-
ently high peak currents and switching frequency of power sup-
plies require a careful PCB layout design.
Figure 5. Recommended PCB Layout
I
OUT
V
OUT
1
V
OUT
V
IN
/
(
)
2
L
f
------------------------------------------
=
2 x 10
F
10
F
V
OUT
EN
SW
C
IN
C
OUT
1.2V (800mA)
1
2
3
6
5
4
FB
PGND
V
IN
NC
P1
(AGND)
C
f
3.3
H
R1
10K
5K
R2
Inductor Value
Vendor
Part Number
3.3H
Panasonic
ELL6PM3R3N
3.3H
Murata
LQS66C3R3M04
Capacitor
Value
Vendor
Part Number
10F
Taiyo Yuden
JMK212BJ106MG
JMK316BJ106KL
TDK
C2012X5ROJ106K
C3216X5ROJ106M
Murata
GRM32ER61C106K
I
L
V
OUT
1
V
OUT
V
IN
/
(
)
L
f
-----------------------------------------
=
9
www.fairchildsemi.com
FAN5308 Rev. 1.0.1
F
AN5308 800mA High-Efficienc
y Step-Do
wn DC-DC Con
ver
ter
Therefore, use wide traces for high current paths and place the
input capacitor, the inductor, and the output capacitor as close
as possible to the integrated circuit terminals. In order to mini-
mize voltage stress to the device resulting from ever present
switching spikes, use an input bypass capacitor with low ESR.
Note that the peak amplitude of the switching spikes depends
upon the load current; the higher the load current, the higher the
switching spikes. The resistor divider that sets the output volt-
age should be routed away from the inductor to avoid RF cou-
pling. The ground plane at the bottom side of the PCB acts as
an electromagnetic shield to reduce EMI.
For more board layout recommendations download the applica-
tion note "PCB Grounding System and FAN2001/FAN2011 High
Performance DC-DC Converters" (AN-42036).
10
www.fairchildsemi.com
FAN5308 Rev. 1.0.1
F
AN5308 800mA High-Efficienc
y Step-Do
wn DC-DC Con
ver
ter
Mechanical Dimensions
3x3mm 6-Lead MLP
Ordering Information
Product Number
Output Voltage
Package Type
Order Code
FAN5308
Adjustable
3x3mm 6-Lead MLP
FAN5308MPX
11
www.fairchildsemi.com
FAN5308 Rev. 1.0.1
F
AN5308 800mA High-Efficienc
y Step-Do
wn DC-DC Con
ver
ter
DISCLAIMER
FAIRCHILD SEMICONDUCTOR RESERVES THE RIGHT TO MAKE CHANGES WITHOUT FURTHER NOTICE TO ANY
PRODUCTS HEREIN TO IMPROVE RELIABILITY, FUNCTION OR DESIGN. FAIRCHILD DOES NOT ASSUME ANY LIABILITY
ARISING OUT OF THE APPLICATION OR USE OF ANY PRODUCT OR CIRCUIT DESCRIBED HEREIN; NEITHER DOES IT
CONVEY ANY LICENSE UNDER ITS PATENT RIGHTS, NOR THE RIGHTS OF OTHERS.
TRADEMARKS
The following are registered and unregistered trademarks Fairchild Semiconductor owns or is authorized to use and is
not intended to be an exhaustive list of all such trademarks.
LIFE SUPPORT POLICY
FAIRCHILD'S PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORT
DEVICES OR SYSTEMS WITHOUT THE EXPRESS WRITTEN APPROVAL OF FAIRCHILD SEMICONDUCTOR CORPORATION.
As used herein:
1. Life support devices or systems are devices or
systems which, (a) are intended for surgical implant into
the body, or (b) support or sustain life, or (c) whose
failure to perform when properly used in accordance
with instructions for use provided in the labeling, can be
reasonably expected to result in significant injury to the
user.
2. A critical component is any component of a life
support device or system whose failure to perform can
be reasonably expected to cause the failure of the life
support device or system, or to affect its safety or
effectiveness.
PRODUCT STATUS DEFINITIONS
Definition of Terms
Datasheet Identification
Product Status
Definition
Advance Information
Preliminary
No Identification Needed
Obsolete
This datasheet contains the design specifications for
product development. Specifications may change in
any manner without notice.
This datasheet contains preliminary data, and
supplementary data will be published at a later date.
Fairchild Semiconductor reserves the right to make
changes at any time without notice in order to improve
design.
This datasheet contains final specifications. Fairchild
Semiconductor reserves the right to make changes at
any time without notice in order to improve design.
This datasheet contains specifications on a product
that has been discontinued by Fairchild semiconductor.
The datasheet is printed for reference information only.
Formative or
In Design
First Production
Full Production
Not In Production
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2
CMOSTM
EnSignaTM
FACTTM
FACT Quiet SeriesTM
POPTM
Power247TM
PowerEdgeTM
PowerSaverTM
PowerTrench
QFET
QSTM
QT OptoelectronicsTM
Quiet SeriesTM
RapidConfigureTM
RapidConnectTM
SerDesTM
SILENT SWITCHER
SMART STARTTM
SPMTM
StealthTM
SuperFETTM
SuperSOTTM-3
SuperSOTTM-6
SuperSOTTM-8
SyncFETTM
TinyLogic
TINYOPTOTM
TruTranslationTM
UHCTM
UltraFET
UniFETTM
VCXTM
Across the board. Around the world.TM
The Power Franchise
Programmable Active DroopTM