Si9174
Vishay Siliconix
High Performance Step-Down DC-DC Converter
With Dynamically Adjustable Output Voltage
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FEATURES
2-MHz PWM Operation
Integrated MOSFET Switches
2.6-V to 6.0-V Input Voltage Range
Minimal Number of External Components
Up to 96% conversion efficiency
600-mA Load Capability
100% Duty Cycle Allows Low Dropout
Integrated Compensation Circuit
Over-Current Protection
Shutdown Current < 2
mA
Thermal Shutdown
Integrated UVLO
10-Pin MSOP and Space Saving MLP33 Packaging
DAC Input for Dynamic Output Voltage Adjustment
D
Synchronizable to13-MHz Clock
D
User Selectable PWM, PSM, or AUTO Mode
D
PSM Frequency
w20
kHz for Inaudible
Harmonics
APPLICATIONS
D
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W-CDMA Cell Phone
PDAs/Palmtop PCs
LCD Modules
Portable Image Scanners
GPS Receivers
Smart Phones
MP3 Players
3G Cell Phone
Digital Cameras
DESCRIPTION
The Si9174 is a high efficiency 600-mA step down converter
with internal low on resistance power MOSFET switch and
synchronous rectifier transistors. It is designed to convert one
cell LiIon battery or three cell alkaline battery voltages to a
dynamically adjustable dc output. The voltage on the DAC pin
controls the output voltage. The output voltage is adjustable
between 0.4 V and the input voltage V
IN
less a small dropout
voltage and settles in <30
ms.
minimize system noise, the switching frequency can be
synchronized to an external 13-MHz clock.
PSM mode provides increased efficiency at light loads. In PSM
mode the oscillator frequency is kept above 20 kHz to avoid
audio band interference. When operating in Auto mode, the
converter automatically selects operating in either PWM or
PSM mode according to load current demand.
The Si9174 is available in the10-pin MSOP and the even
smaller MLP33 package and is specified to operate over the
industrial temperature range of –40_C to 85_C. The Si9174
packaged in the MLP33 package is available in both standard
and lead (Pb)-free.
In order to insure efficient conversion throughout the entire
load range, PWM (pulse width modulation), PSM (pulse
skipping mode) or Auto mode can be selected. In PWM mode,
2-MHz switching permits use of small external inductor and
capacitor sizes allowing
one of the smallest solutions.
To
TYPICAL APPLICATIONS CIRCUIT
BATTERY
C
IN
10
mF
V
IN
V
DD
LX
2.2
mH
V
OUT
Si9174
PGND
13 MHz
DAC
ENABLE
PWM/PSM/AUTO
SYNC
DAC
SD
MODE
AGND
FB
C
OUT
4.7
mF
R
1
R
2
Document Number: 71668
S-41148—Rev. C, 14-jun-04
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1
Si9174
Vishay Siliconix
ABSOLUTE MAXIMUM RATINGS
Voltages Referenced to AGND = 0 V
V
IN,
V
DD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6.2 V
Lx, SD, MODE, FB, DAC, SYNC
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
−0.3
to 6.2 V
(or to V
DD
)0.3
V whichever is less)
GND
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
−0.3
to +0.3 V
ESD Rating
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2 kV
Storage Temperature
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
−65
to 125_C
Operating Junction Temperature
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
150_C
Power Dissipation (Package)
a
10-pin MSOP
b . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
481 mW
10-pin MLP33
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
915 mW
Thermal Impedance (Q
JA
)
10-Pin MSOP
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
135_C/W
10-Pin MLP33
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
71_C/W
Peak Inductor Current
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1.8 A
Notes
a. Device mounted with all leads soldered or welded to PC board.
b. Derate 7.4 mW/_C above 85_C.
c. Derate 14 mW/_C above 85_C.
Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and 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 affect device reliability.
RECOMMENDED OPERATING RANGE
V
IN
Range . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.6 V to 5.5 V
C
IN
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
mF
Ceramic
C
OUT
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.7
mF
Ceramic
Inductor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.2
mH
Operating Load Current PWM Mode . . . . . . . . . . . . . . . . . . . . . . 0 to 600 mA
Operating Load Current PSM Mode . . . . . . . . . . . . . . . . . . . . . . . 0 to 150 mA
SPECIFICATIONS
Parameter
Mode
f
Symbol
Test Conditions Unless Specified
−40_C
to 85_C V
IN
= V
DD
V
DAC
= 1 215 V C
IN
= 10
mF
40_C 85_C,
1.215 V,
mF,
DD,
C
OUT
= 4.7
mF,
L = 2.2
mH,
2.6 V
v
V
IN
v
5.5 V
R
1
= 11.3 kW, R
2
= 20 kW
Limits
Min
a
Typ
b
Max
a
Unit
Under Voltage Lockout (UVLO)
Under Voltage Lockout (turn-on)
Hysteresis
V
IN
rising
2.3
0.1
2.5
V
Shutdown (SD)
Logic HIGH
Logic LOW
Delay to Output
c
Pull Down
V
SDH
V
SDL
t
en
I
SD
Settle Within
$2%
accuracy SD rising
t
r
< 1
ms
Input at V
IN
R
L
= 3.3
W
R
L
= 51
W
100
1.6
0.4
100
V
ms
mA
Mode Selection Tri-Level Logic (MODE)
MODE Pin HIGH
MODE Pin LOW
Mode Pin Input Current
PWM
Auto
MODE = GND
MODE = V
IN
−5
5
V
IN
−0.4
V
IN
0.4
V
mA
Oscillator
Frequency
f
OSC
1.6
2
2.4
MHz
External Clock Synchronization (SYNC)
Frequency
Ac Coupled Sinewave
SYNC Input = 500 mV
p-p
Frequency = 13 MHz
0.2
13
0.8
MHz
V
p-p
Error Amplifier (FB, DAC Pin)
FB Voltage Accuracy
DAC Input Voltage Range
Input Bias Current FB, DAC
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I
FBDAC
V
IN
> 2.6, V
IN
−
V
DAC
> 0.5 V
V
FB
= 1.25 V
V
DAC
−20
0.28
−1
0.01
V
DAC
+20
2.45
1
mV
V
mA
2
Document Number: 71668
S-41148—Rev. C, 14-jun-04
Si9174
Vishay Siliconix
SPECIFICATIONS
Parameter
Mode
f
Converter Operation
Maximum Output
Current
Maximum Output
Current
Dropout Voltage
e
Closed Loop Bandwidth
Load Regulation
c
Line Regulation
PWM
PSM
PWM
PSM
I
AUpk
I
Lpk
Negative Transition on V
DAC
r
DS( )
DS(on)
V
IN
= 3 6 V
3.6
0.05
0 05
W
C
OUT(ESR)
V
IN
= 3.6 V, V
OUT
= 3 3 V
36V
3.3
I
OUT
w
30 mA
I
OUT
= 600 mA
I
OUT
= 30 mA
I
OUT
= 600 mA
I
OUT
= 30 mA
20
PWM
PSM
I
LOAD
I
LOAD
V
DD
BW
V
IN
= 3.6 V
V
OUT
= 1.9 V @ 25_C
I
OUT
= 30 mA to 600 mA
I
OUT
= 30 mA to 75 mA
V
IN
= 3.6 V
V
IN
= 3.6 V
V
IN
= 2.6 V, I
OUT
= 600 mA
190
300
0.5
0.25
"0.1
"0.1
200
1500
1500
250
250
60
80
90
80
mW
mV
p-p
%
kHz
mA
600
150
300
mA
mA
mV
kHz
%
%/V
Test Conditions Unless Specified
Symbol
−40_C
to 85_C, V
IN
= V
DD,
V
DAC
= 1.215 V, C
IN
= 10
mF,
C
OUT
= 4.7
mF,
L = 2.2
mH,
2.6 V
v
V
IN
v
5.5 V
R
1
= 11.3 kW, R
2
= 20 kW
Limits
Min
a
Typ
b
Max
a
Unit
V
OUT
= 3.0 V, V
IN
= 3 5 V to 5 5 V
30V
3.5
5.5
PWM/PSM Switch Threshold Current
Maximum Inductor Peak Current Limit
Maximum NMOS
Transistor Current Sink
On Resistance
Output Ripple Voltage
Efficiency
Frequency
PWM
P-Channel
N-Channel
PWM
PSM
PWM
PSM
PSM
Supply Current
Input Supply Current
Shutdown Supply Current
PWM
PSM
I
SUPPLY
(V
DD
&
V
IN
)
I
SD
I
OUT
= 0 mA V
IN
= 3 6 V (not switching FB = GND)
mA,
3.6
switching,
SD = Low
500
400
2
800
mA
Thermal Shutdown
Thermal Shutdown Temperature
c
Thermal
Hysteresis
c
T
J(S/D)
165
20
_C
Notes
a. The algebraic convention whereby the most negative value is a minimum and the most positive a maximum, is used in this data sheet.
b. Typical values are for DESIGN AID ONLY, not guaranteed or subject to production testing.
c. Guaranteed by design.
d. Settling times, t
s
, apply after t
en
.
e. Bypass is a device mode of operation, in which, the device is in 100% duty cycle. Bypass operation is possible in either PWM or PSM.
f.
Operating modes are controlled with the MODE pin where Auto mode = MODE = LOW, PWM Mode = MODE = HIGH, and PSM mode = MODE = OPEN.
Document Number: 71668
S-41148—Rev. C, 14-jun-04
www.vishay.com
3
Si9174
Vishay Siliconix
PIN CONFIGURATION
MSOP-10
L
X
AGND
FB
V
DD
DAC
1
2
3
4
5
10
9
8
7
6
MLP33
PGND
V
IN
SYNC
SD
MODE
L
X
AGND
FB
V
DD
DAC
10
9
8
7
6
PGND
V
IN
SYNC
SD
MODE
2
3
4
5
Top View
Top View
PIN DESCRIPTION
Pin Number
1
2
3
4
5
Name
L
X
AGND
FB
V
DD
DAC
Inductor connection
Low power analog ground
Output voltage feedback
Input supply voltage for the analog circuit.
Voltage from external DAC to adjust output voltage.
Used to select switching mode of the buck converter
PWM/PSM Pin Logic:
Function
6
MODE
MODE Pin
V
IN
Open
GND
Operating Mode
PWM
PSM
AUTO
7
8
9
10
SD
SYNC
V
IN
PGND
Logic low disables IC and reduces quiescent current to below 2
mA
Converter switching frequency can be synchronized to
1
/
6
of the clock frequency at this pin.
Input supply voltage
Low impedance power ground
ORDERING INFORMATION
MSOP-10
Standard
Part Number
Si9174DH-T1
MLP33
Temperature
−40
to 85_C
Marking
9174
Standard
Part Number
Si9174DM-T1
Lead (Pb)-Free
Part Number
Si9174DM-T1—E3
Marking
9174
Temperature
−40
to 85_C
Additional voltage options are available.
Eval Kit
Si9174DB
Temperature Range
−40
to 85_C
Board
Surface Mount
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Document Number: 71668
S-41148—Rev. C, 14-jun-04
Si9174
Vishay Siliconix
FUNCTIONAL BLOCK DIAGRAM
V
DD
Si9174
V
IN
PMOS
Current Sense
Error
Amplifier
−
+
Clamp
−
+
FB
DAC
PWM
Comparator
PWM and
Pulse
Skipping
Logic
L
X
To IC Bias
Voltage
Reference
UVLO
B6
2 MHz
Oscillator
NMOS
Current Sense
AGND
SYNC
MODE
SD
PGND
DETAIL DESCRIPTION
General
The Si9174 is a high efficiency synchronous dc-dc converter
that is ideally suited for lithium ion battery or three cell alkaline
applications, as well as step-down of 3.3-V or 5.0-V supplies.
It is design to provide power to the power amplifier in WCDMA
cell phones, but can utilized in any applications requiring a
dynamically adjustable 600-mA power supply. The major
blocks of the Si9174 are shown in the Functional Block
Diagram. The 0.25-W internal MOSFETs switching at a
frequency of 2-MHz minimize PC board space while providing
high conversion efficiency and performance. The high
frequency error-amplifier with built-in loop compensation
minimizes external components and provides rapid output
settling times of <30
ms.
Sensing of the inductor current for
control is accomplished internally without power wasting
resistors. The switching frequency can be synchronized to an
external 13-MHz clock signal.
Start-Up
When voltage is applied to V
IN
and V
DD
, the under-voltage
lockout (UVLO) circuit prevents the oscillator and control
circuitry from turning on until the voltage on the exceeds 2.4 V.
With a typical UVLO hysteresis of 0.1 V, the converter
operates continuously until the voltage on V
IN
drops below
2.3 V, whereupon the converter shuts down. This hysteresis
Document Number: 71668
S-41148—Rev. C, 14-jun-04
prevents false start-stop cycling as the input voltage
approaches the UVLO switching threshold. Start-up is always
accomplished in PWM mode to ensure start-up under all load
conditions. Switching to other modes of operation occurs
according to the state of the MODE pin and the load current.
The start-up sequence occurs after SD switches from LOW to
HIGH with V
IN
applied, or after V
IN
rises above the UVLO
threshold and SD is a logic HIGH.
Mode Control (MODE)
The MODE pin allows the user to control the mode of operation
or to enable the Si9174 to automatically optimize the mode of
operation according to load current. There are three different
modes of operation as controlled by the MODE pin. Switching
waveforms are shown in the
Typical Switching Waveform
sections, page 9.
PWM Mode (MODE pin = HIGH)
With the MODE pin in the logic HIGH condition, the Si9174
operates as a 2-MHz fixed frequency voltage mode converter.
A NMOS synchronous rectification MOSFET transistor
provides very high conversion efficiency for large load currents
by minimizing the conduction losses. PWM mode provides low
output ripple, fast transient response, and switching frequency
synchronization. Output load currents can range from 0 to
600 mA.
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