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www.fairchildsemi.com
REV. 1.0.10 5/3/04
Features
Wide input voltage range (2 to 24V) for Mobile systems
Excellent dynamic response with Voltage Feed-Forward
and Average Current Mode control
Lossless current sensing on low-side MOSFET or
precision over-current using sense resistor
VCC Under-voltage Lockout
Power-Good Signal
Light load Hysteretic mode maximizes efficiency
QSOP16, TSSOP16
300Khz or 600Khz operation
Applications
Mobile PC regulator
Hand-Held PC power
General Description
The FAN5234 PWM controller provides high efficiency and
regulation with an adjustable output from 0.9V to 5.5V that
are required to power I/O, chip-sets, memory banks or
peripherals in high-performance notebook computers, PDAs
and Internet appliances. Synchronous rectification and
hysteretic operation at light loads contribute to a high
efficiency over a wide range of loads. The hysteretic mode of
operation can be disabled if PWM mode is desired for all
load levels. Efficiency is even further enhanced by using
MOSFET's R
DS(ON)
as a current sense component.
Feed-forward ramp modulation, average current mode
control, and internal feedback compensation provide fast
response to load transients. The FAN5234 monitors these
outputs and generates a PGOOD (power good) signal when
the soft-start is completed and the output is within 10% of
its set point. A built-in over-voltage protection prevents the
output voltage from going above 120% of the set point.
Normal operation is automatically restored when the over-
voltage conditions go away. Under-voltage protection latches
the chip off when the output drops below 75% of its set value
after the soft-start sequence is completed. An adjustable
over-current function monitors the output current by sensing
the voltage drop across the lower MOSFET.
Typical Application
Figure 1. 1.8V Output Regulator (see Table 2, page 12 for BOM)
SW
FAN5234
10
C6
L1
Q1B
14
ILIM
1
4
R1
R2
11
VCC
+5
D1
+5
15
13
R3
12
C4
8
R5
PGOOD
2
+5
9
ISNS
PGND
Q1A
6
VSEN
LDRV
HDRV
BOOT
VIN
C5
C1
1.8V@ 3.5A
R4
VIN (BATTERY)
= 2 to 24V
C2
AGND
EN
3
SS1
7
C3
16
FPWM
VOUT
5
FAN5234
Mobile-Friendly PWM/PFM Controller
FAN5234
PRODUCT SPECIFICATION
REV. 1.0.10 5/3/04
2
Pin Configurations
Pin Definitions
Pin
Number
Pin Name
Pin Function Description
1
VIN
Input Voltage.
Connect to main input power source (battery). Also used to program
operating frequency for low input voltage operation. See Table 1.
2
PGOOD
Power Good Flag.
An open-drain output that will pull LOW when VSEN is outside of a
10% range of the 0.9V reference.
3
EN
ENABLE
. Enables operation when pulled to logic high. Toggling EN will also reset the
regulator after a latched fault condition. This is a CMOS inputs whose state is
indeterminate if left open.
4
ILIM
Current Limit.
A resistor from this pin to GND sets the current limit.
5
VOUT
Output Voltage.
Connect to output voltage. Used for regulation to ensure a smooth
transitions during mode changes. When VOUT is expected to exceed VCC, tie this pin to
VCC.
6
VSEN
Output Voltage Sense.
The feedback from the output. Used for regulation as well as
PGOOD, under-voltage, and over-voltage protection and monitoring.
7
SS
Soft Start.
A capacitor from this pin to GND programs the slew rate of the converter
during initialization. During initialization, this pin is charged with a 5
A current source.
8
AGND
Analog Ground.
This is the signal ground reference for the IC. All voltage levels are
measured with respect to this pin.
9
PGND
Power Ground.
The return for the low-side MOSFET driver. Connect to source of low-
side MOSFET.
10
LDRV
Low-Side Drive.
The low-side (lower) MOSFET driver output. Connect to gate of low-side
MOSFET.
11
VCC
VCC.
This pin powers the chip as well as the LDRV buffers. The IC starts to operate when
voltage on this pin exceeds 4.6V (UVLO rising) and shuts down when it drops below 4.3V
(UVLO falling).
12
ISNS
Current Sense input.
Monitors the voltage drop across the lower MOSFET or external
sense resistor for current feedback.
13
SW
Switching node.
Return for the high-side MOSFET driver and a current sense input.
Connect to source of high-side MOSFET and low-side MOSFET drain.
14
HDRV
High-Side Drive.
High-side (upper) MOSFET driver output. Connect to gate of high-side
MOSFET.
15
BOOT
BOOT.
Positive supply for the upper MOSFET driver. Connect as shown in Figure 2.
16
FPWM
Forced PWM mode.
When logic HIGH, inhibits the regulator from entering hysteretic
mode.
VIN
PGOOD
EN
ILIM
VOUT
VSEN
SS
AGND
FAN5234
1
2
3
4
5
6
7
8
16
15
14
13
12
11
10
9
FPWM
BOOT
HDRV
SW
ISNS
VCC
LDRV
PGND
QSOP-16 or TSSOP-16
JA
= 112
C/W
FAN5234
PRODUCT SPECIFICATION
REV. 1.0.10 5/3/04
3
Absolute Maximum Ratings
Absolute maximum ratings are the values beyond which the device may be damaged or have its useful life
impaired. Functional operation under these conditions is not implied.
Recommended Operating Conditions
Parameter
Min.
Typ.
Max.
Units
VCC Supply Voltage:
6.5
V
VIN
27
V
BOOT, SW, ISNS, HDRV
33
V
BOOT to SW
6.5
V
All Other Pins
0.3
VCC+0.3
V
Junction Temperature (T
J
)
10
150
C
Storage Temperature
65
150
C
Lead Soldering Temperature, 10 seconds
300
C
Parameter
Conditions
Min.
Typ.
Max.
Units
Supply Voltage VCC
4.75
5
5.25
V
Supply Voltage VIN
5
24
V
Ambient Temperature (T
A
)
10
85
C
PRODUCT SPECIFICATION
FAN5234
4
REV. 1.0.10 5/3/04
Electrical Specifications
Recommended operating conditions, unless otherwise noted.
Parameter
Conditions
Min.
Typ.
Max.
Units
Power Supplies
VCC Current
LDRV, HDRV Open, VSEN forced
above regulation point
850
1300
A
Shut-down (EN=0)
5
15
A
VIN Current - Sinking
VIN pin = input voltage source
10
20
30
A
VIN Current - Sourcing
VIN pin = GND
7
15
20
A
VIN Current - Shut-down
1
A
UVLO Threshold
Rising VCC
4.3
4.55
4.75
V
Falling
4.1
4.27
4.5
V
Hysteresis
0.1
0.5
V
Oscillator
Frequency
VIN > 5V
255
300
345
KHz
VIN = 0V
510
600
690
KHz
Ramp Amplitude, pkpk
VIN = 16V
2
V
Ramp Amplitude, pkpk
VIN < 5V
1.25
V
Ramp Offset
0.5
V
Ramp / VIN Gain
VIN > 3V
125
mV/V
Ramp / VIN Gain
1V < VIN < 3V
250
mV/V
Reference and Soft Start
Internal Reference Voltage
0.891
0.9
0.909
V
Soft Start current (I
SS
)
at start-up
5
A
Soft Start Complete Threshold
1.5
V
PWM Converter
Load Regulation
I
OUT
from 0 to 3A, VIN from 2 to 24V
-1
+1
%
VSEN Bias Current
50
80
120
nA
VOUT pin input impedance
40
55
65
K
Under-voltage Shutdown
as % of set point. 2
S noise filter
70
75
80
%
I
SNS
Over-Current threshold
R
ILIM
= 68.5K
. See Figure 4
115
144
172
A
Over-voltage threshold
as % of set point. 2
S noise filter
113
120
%
Output Driver
HDRV Output Resistance
Sourcing
8
15
Sinking
3.2
4
LDRV Output Resistance
Sourcing
8
15
Sinking
1.5
2.4
PGOOD (Power Good Output) and Control pins
Lower Threshold
as % of set point, 2
S noise filter
86
92
%
Upper Threshold
as % of set point, 2
S noise filter
110
115
%
PGOOD Output Low
I
PGOOD
= 4mA
0.5
V
Leakage Current
V
PULLUP
= 5V
1
A
Soft Start Voltage when PGOOD
Enabled
1.5
V
EN, FPWM Inputs
Input High
2
V
Input Low
0.8
V
FAN5234
PRODUCT SPECIFICATION
REV. 1.0.10 5/3/04
5
Figure 2. IC Block Diagram
REF2
PGOOD
EN
C
BOOT
Q1
Q2
5V
VDD
ADAPTIVE
GATE
CONTROL LOGIC
CURRENT PROCESSING
HDRV
SW
LDRV
PGND
BOOT
VDD
HYST
ISNS
VIN
C
OUT
VOUT
PWM/HYST
PWM
S/H
ILIM
R
ILIM
R
SENSE
ILIM det.
HYST
SS
SS
DUTY
CYCLE
CLAMP
PWM
S
R
Q
RAMP
MODE
OSC
I
OU T
RAMP
CLK
OVP
POR/UVLO
Reference and
Soft Start
FPWM
L
OU T
VREF
EA
PWM/HYST
VSEN
FPWM
VIN
Circuit Description
Overview
The FAN5234 is a PWM controller intended for low voltage
power applications in modern notebook, desktop, and
sub-notebook PCs. The output voltage of the controller can
be set in the range of 0.9V to 5.5V by an external resistor
divider.
The synchronous buck converter can operate from either an
unregulated DC source (such as a notebook battery) with
voltage ranging from 2V to 24V, or from a regulated system
rail. In either mode of operation the IC is biased from a +5V
source. The PWM modulator uses an average current mode
control with input voltage feed-forward for simplified feed-
back loop compensation and improved line regulation. The
controller includes integrated feedback loop compensation
that dramatically reduces the number of external compo-
nents.
Depending on the load level, the converter can operate either
in fixed frequency PWM mode or in a hysteretic mode.
Switch-over from PWM to hysteretic mode improves the
converters' efficiency at light loads and prolongs battery run
time. In hysteretic mode, a comparator is synchronized to the
main clock that allows seamless transition between the oper-
ational modes and reduced channel-to-channel interaction.
The hysteretic mode of operation can be inhibited indepen-
dently using the FPWM pin if variable frequency operation is
not desired.
Oscillator
Table 1. Converter Operating modes
When VIN is from the battery, the oscillator's ramp ampli-
tude is proportional to VIN, providing voltage feed-forward
control for improved loop response. When in either of the
Fixed modes, oscillator's ramp amplitude is fixed. The oper-
ating frequency is then determined according to the connec-
tion on the VIN pin (Table 1).
Initialization and Soft Start
Assuming EN is high, FAN5234 is initialized when VCC
exceeds the rising UVLO threshold. Should VCC drop below
the UVLO threshold, an internal Power-On Reset function
disables the chip.
Mode
F
SW
(Khz)
Converter
Power
VIN Pin
Battery
300
2 to 24V
Battery (>5V)
Fixed
300
300
< 5.5V Fixed
100K
to GND
Fixed
600
600
< 5.5V Fixed
GND