FAIRCHILD FAN5232

www.fairchildsemi.com
FAN5232
Adjustable PWM Buck Controller for LCD PCs
Features
Description
• Three outputs: Adjustable Buck, 3.3V-Always,
5V-Always
• Adjustable synchronous switcher, 5V – 80% Vin
• 1% internal reference precision
• Current mode with voltage feed-forward
• Precision current limit option
• Charge pump works at all loads
• No shoot-through current
• Independent shutdown pins for ACPI
• Power Good, input UVLO, output OV
• 5.6V to 24V input voltage range
The FAN5232 is a high efficiency and high precision DC/DC
controller for PCs. It has a synchronous switcher whose
output can be adjusted from 5V up to 80% of Vin. It also has
two linear regulators for standby, 3.3V and 5V. The PWM
utilizes both input and output voltage feedback in a
current-mode control, allowing for fast and stable loop
response over a wide range of input and output variations.
Synchronous switching provides best efficiency over a wide
range of loads. Current sense based on MOSFET RDS,on
gives maximum efficiency, while also permitting use of an
optional sense resistor for high precision.
Applications
The FAN5232 is available in a 14 pin TSSOP package.
• LCD PCs
• Notebook PCs and PDAs
• Hand-held portable instruments
Block Diagram
Vin = 16–22V
1
14
3.3V-Always
2
13
5V-Always
3
12
FAN5232
4
11
SDWN
5
10
SDNADJ
6
9
PWRGD
7
8
12V @ 8A
+
REV. 1.1.1 10/7/02
FAN5232
PRODUCT SPECIFICATION
Pin Assignments
VBATT
3V_ALWAYS
5V_ALWAYS
AGND
SDWN
SDNADJ
PWRGD
1
2
3
4
5
6
7
14
13
12
11
10
9
8
CPUMP
HSD
ISNS
SW
LSD
PGND
VFB
Pin Description
Pin Number
Pin Name
Pin Function Description
1
VBATT
2
3V_ALWAYS
3.3V-ALWAYS Linear Regulator. Total load current on pins 2 and 3 together
must not exceed 50mA.
Battery Voltage. Battery voltage sensor.
3
5V_ALWAYS
5V-ALWAYS Linear Regulator. Total load current on pins 2 and 3 together
must not exceed 50mA.
4
AGND
Analog Ground.
5
SDWN
IC Shutdown. Puts entire chip into shutdown. OFF=0. ON=1.
6
SDNADJ
Shutdown and Softstart for the Switcher. OFF=0. ON=1.
7
PWRGD
Switcher Output OK. An open collector output that will be low if the switcher
output is out of spec.
Voltage Feedback for the Switcher.
8
VFBSW
9
PGND
Ground for the Switcher. Connect by the shortest possible path to the source
of the low side MOSFET.
10
LSD
Low Side FET Driver for the Switcher. Connect this pin through a resistor to
the gate of an N-channel MOSFET.
11
SW
High Side FET Source and Low Side FET Drain Switching Node.
12
ISNS
Current Feedback for the Switcher. Connect by the shortest possible path to
a resistor connected to the drain of the low side MOSFET.
13
HSD
High Side FET Driver for the Switcher. Connect this pin through a resistor to
the gate of an N-channel MOSFET.
14
CPUMP
Charge Pump for the Switcher. Generates gate drive voltage for the high-side
MOSFET.
Absolute Maximum Ratings1
Parameter
VBATT Pin
PHASE, IFB, SDWN Pins
Conditions
Min.
Typ.
Max.
Units
-0.3
29
V
-5
29
V
CPUMP, HSD Pins
-0.3
34
V
All Other Pins
-0.3
6.5
V
Thermal Resistance, θJ-A
θJ-C
100
32
Junction Temperature
Storage Temperature
Lead Temperature, Soldering 10 sec.
-65
°C/W
°C/W
150
°C
150
°C
300
°C
Note:
1. Functional operation under any of these conditions is NOT implied. Performance and reliability are guaranteed only if
Operating Conditions are not exceeded.
2
REV. 1.1.1 10/7/02
PRODUCT SPECIFICATION
FAN5232
Recommended Operating Conditions
Parameter
Conditions
Min.
Typ.
Max.
Units
VBATT Voltage
5.6
24
V
Ambient Temperature
-20
85
°C
Electrical Specifications
(VBATT = 16V, TA = -20 to 85°C, circuit of Figure 1, unless otherwise specified.)
Parameter
Conditions
Min.
Typ.
Max.
Units
H/LSD Open
1.4
mA
Stand-by
60
µA
Supply
VCC Input Quiescent Current
Shut-down
VCC Input UVLO Threshold
10
µA
Rising
4.3
4.5
5.1
V
Falling
4.0
4.3
4.7
0.1 ≤I ≤ 5.5A, 7.2 ≤ VBATT ≤ 24V
4.900
5
5.100
I ≤ 100mA, 5.6 ≤ VBATT ≤ 24V
4.900
5
5.100
255
Switcher
Output Voltage Precision, VFB
Oscillator Frequency, fOSC
V
300
345
KHz
Gate Drive On-Resistance for
all Sources and HSD Sinks
6
12
Ω
Gate Drive On Resistance for
LSD Sink
1.5
8
Ω
100
mV
HSD On Output, VCPUMP-VGS
I = 10µA
HSD Off Output, VGS
I = -10µA
100
mV
LSD On Output, V5V-Always-VGS I = 10µA
100
mV
LSD Off Output, VGS
100
mV
I = -10µA
Ramp Amplitude, pk-pk
2
V
Ramp Offset
0.5
V
Ramp Gain from VBATT
125
mV/V
3
MHz
Error Amplifier GBW
Current Limit Threshold
R3 = 1KΩ
135
150
165
mV
Over Voltage Threshold
2µs delay
110
115
120
%VO
Under Voltage Threshold
2µs delay
70
75
80
%VO
Max Duty Cycle
80
%
Min HSD On-time
200
VFBSW, ISNS Input Leakage
Current
100
SDN/SS Full On Voltage Min.
nsec
200
4.2
nA
V
SDN/SS Full Off Voltage Max.
800
mV
-3.3
2
%
50
mA
180
mA
80
%
5V and 3.3V Always
Linear Regulator Accuracy
5.6V ≤VBATT≤ 22V,
0 ≤ ILOAD ≤ 50mA
Rated Output Current
I3.3 + I5
Overcurrent Limit
2µs delay
100
Undervoltage Threshold
2µs delay
70
REV. 1.1.1 10/7/02
75
3
FAN5232
PRODUCT SPECIFICATION
Electrical Specifications (Continued)
(VBATT = 16V, TA = -20 to 85°C, circuit of Figure 1, unless otherwise specified.)
Parameter
Conditions
Min.
Typ.
Max.
Units
600
mV
Control and Signal Functions
Control Logic Low
Control Logic High
2
Softstart Current
3
V
5
7
µA
Over-temperature Shutdown
150
°C
Over-temperature Hysteresis
25
°C
PWRGD Threshold
-14
-12
-9
%VO
PWRGD Saturation Voltage
Isink = 4mA
400
mV
PWRGD Leakage Current
VCC = 5.5V
1
µA
PWRGD Pulse Width for Trip
Low → High, High → Low
10
µsec
5
Application Circuit
Vin = 16–22V
+
C1
1
14
2
13
C2
3.3V-Always
D1
R2
Q1
C5
R3
3
5V-Always
C3
4
5
SDWN
12
U1
FAN5232
12V @ 8A
L1
+
C6
11
10
Q2
R4
SDNADJ
6
9
7
8
R5
C4
PWRGD
R6
R1
5V
Figure 1. Application Circuit for LCD PC Main Power
4
REV. 1.1.1 10/7/02
PRODUCT SPECIFICATION
FAN5232
Table 1. RC5232 Application Bill of Materials
Reference
Manufacturer, Part #
C1
SANYO
25SV47M
Quantity Description
1
47µF, 25V
Comments
OSCON, Irms = 3.5A
C2-5
Any
4
100nF, 50V
Ceramic
C6
AVX
TPSE227M016#0100
1
220µF, 16V
Tantalum, ESR=100mΩ
R1
Any
1
10KΩ, 1%
R2, R4
Any
2
4.7Ω, 1%
R3, R5
Any
2
1KΩ, 1%
R6
Any
1
715Ω, 1%
D1
Fairchild
MBR0540L
1
500mA, 40V Schottky
L1
Coiltronics
UP2B-1R5
1
1.5µH, 8.3A
R < 8mΩ
Q1
Fairchild
FDS6690A
1
30V N-channel MOSFET
R = 20mΩ @ VGS = 4.5V
Q2
Fairchild
FDS6680S
1
30V N-channel MOSFET
with Integrated Schottky
R = 17mΩ @ VGS = 4.5V
U1
Fairchild FAN5232
1
Controller
Application Information
Overview
Shutdown
The FAN5232 is a high efficiency and high precision DC/DC
controller for LCD PCs and portable applications. It provides
a switcher controller capable of generating a voltage between
5V to 80% of Vin, and a 5V and a 3.3V linear regulator for
standby applications. The controller has a power good output
and an enable/soft start to permit proper system sequencing.
There are two separate shutdown pins to provide output
power control – SDWN, and SDNADJ. Taking the SDNADJ
pin low will disable the switcher output and reset the output’s
internal latches for short circuit, under-voltage and over-voltage. Taking the SDWN pin low puts the entire chip in shutdown. Each of the SDN pins has an internal
pull-up.
Initialization
The FAN5232 automatically initializes upon receipt of input
power. The Power-on Reset (POR) function continually
monitors the input supply voltage on the VCC pin and
initiates soft start operation after the input supply voltage
exceeds 4.5V. Should this voltage drop below 4.0V, POR
disables the chip.
Soft Start
When soft start is initiated by POR, and if the SDWN pin is
not held low, the voltage on the SDNADJ pin begins ramping
up, with the rate of rise set by the external capacitor on the
pin. Below 700mV, the output is off. Between 700mV and
1.6V, the output is allowed to linearly ramp up. Above 1.6V,
the output is fully enabled, and regulates.
REV. 1.1.1 10/7/02
Switcher Architecture
Overview
The switcher output of the FAN5232 is generated from the
unregulated input (battery) voltage using a synchronous buck
converter. Both high-side and low-side MOSFETs are
N-channel.
The converter has pins for current sensing using the low-side
MOSFET RDS,on; a pin for voltage-sense feedback; a pin
that enables the converter and permits soft-start; a power
good pin; and a pin for generating the boost voltage to drive
the high-side MOSFET.
5
FAN5232
PRODUCT SPECIFICATION
Loop Compensation
Precision Current Limit
The switcher regulator control loop of the FAN5232 is
current-mode with voltage feed-forward. It uses voltage
feed-forward to guarantee loop rejection of input voltage
variation: the ramp amplitude is varied as a function of the
input voltage. Compensation of the control loop is done
entirely internally using current-mode compensation. This
scheme allows the bandwidth and phase margin to be almost
independent of output capacitance and capacitors’ ESR. Use
of a current sense resistor other than the recommended 1KΩ
may affect the converter’s stability.
Precision current limiting can be achieved by placing a discrete sense resistor between the source of the low-side
MOSFET and ground. Sensing is then accomplished with
the 1KΩ resistor between the sense resistor and the IFBSW
pin, as shown in Figure 2. In this case, current limit accuracy
is set by the tolerance of the IC, ±10%.
LSD
ISNS
Current Sensing
Current sensing is done by measuring the voltage across the
low side MOSFET 50nsec after it is turned on. This value is
then held for current feedback and over-current limit. The
gain is set by an external resistor from the drain to the ISNS
pin, which is normally set to be 1KΩ.
PGND
Figure 2. Precision Current Sensing
Current Limit
Softstart
The converter senses the voltage across its low-side
MOSFET to determine when to enter current limit. If output
current in excess of the current limit threshold is measured,
the converter enters pulse skip mode with Iout equal to the
over-current (OC) limit. If this situation persists for 8 clock
cycles then the regulator is latched off (HSD and LSD off).
This is the likely scenario in case of a “soft” short. If the
short is “hard”, it will instantly trigger the under-voltage
protection, which again will latch the regulator off (HSD and
LSD off) after a 2µsec delay.
Softstart of the switcher is accomplished by means of an
external capacitor between pins SDNADJ and ground.
Selection of a current-limit set resistor must include the tolerance of the current-limit trip point, the MOSFET resistance and temperature coefficient, and the ripple current, in
addition to the maximum output current.
Example: Maximum DC output current on the 12V is 8A,
the MOSFET RDS,on is 17mΩ, and the inductor is 4.7µH
at a current of 8A. Because of the low RDS,on, the low-side
MOSFET will have a maximum temperature (ambient +
self-heating) of only 75° C, at which its RDS,on increases to
24mΩ.
Overvoltage Protection (Soft Crowbar)
When the output voltage of the switcher exceeds approximately 115% of nominal, it enters into over-voltage (OV)
protection, with the goal of protecting the load from damage.
During operation, severe load dump or a short of an upper
MOSFET can cause the output voltage to increase significantly over normal operation range. When the output
exceeds the over-voltage threshold of 115%, the over-voltage
comparator forces the lower gate driver high and turns the
lower MOSFET on. This will pull down the output voltage
and eventually may blow the battery fuse. As soon as output
voltage drops below the threshold, the OVP comparator is
disengaged.
This OVP scheme provides a soft crowbar function (bangbang control followed by blow of the fuse), which helps to
tackle severe load transients and does not invert the output
voltage when activated – common problem for OVP schemes
with a latch. The prevention of the output inversion saves the
use of a Schottky diode across the load.
Peak current is DC output current plus peak ripple current:
TV O • ( V in – V o )
I pk ≈ I DC + ------------------------------------------2 • L • V in
4µs • 12V • ( 19V – 12V )
= 8A + ---------------------------------------------------------------- = 11A
2 • 4.7µH • 12V
where T is the maximum period, VO is output voltage, Vin is
input voltage, and L is the inductance. This current generates
a voltage on the low-side MOSFET of 11A • 24mΩ =
254mV. The current limit threshold is typically 150mV
(worst-case 135mV) with R2 = 1KΩ, and so this value must
be decreased to (135/254) • 1KΩ = 531Ω.
6
Undervoltage Protection
When the output voltage of the switcher falls below 75% of
nominal value, after a 2usec delay it goes into under-voltage
protection. In under-voltage protection, the high and low side
MOSFETs are turned off. Once under-voltage protection is
triggered, it remains on until power is recycled.
5V/3.3V-ALWAYS Operation
The 5V-ALWAYS supply is generated from the on-chip
linear regulator off the input supply voltage. The
3.3V-ALWAYS is generated from a linear regulator attached
internally to the 5V-ALWAYS.
REV. 1.1.1 10/7/02
PRODUCT SPECIFICATION
FAN5232
The purpose of these two supplies -whose combined current
is specified to never exceed 50mA- is to provide power to the
system micro-controller (8051 class) as well as a few other
ICs needing a stand-by power. The micro-controller as well
as the other IC’s discussed here are migrating from 5V to
3.3V power at different times and we expect that some
“legacy” devices will continue to need 5V indefinitely.
where Iout is the output current of the converter, and DC is
the duty cycle, DC = Vin / Vout. Capacitor ripple current
rating is a function of temperature and switching frequency,
and so the manufacturer should be contacted to find out the
ripple current rating at the expected operational temperature
and frequency.
Soft Start Capacitor selection
5V/3.3V-ALWAYS Protections
The two internal linear regulators are current limit and
undervoltage protected. Once protection is triggered all outputs go off until power is recycled.
The recommended value of the soft start capacitor is 100nF.
This will result in roughly 20msec turn on time. The general
formula is:
( I SS • T SS )
C SS = --------------------------1.125V
ALWAYS mode of Operation
If it is desired that the ALWAYS voltages are always ON
then the SDWN pin must be connected to VCC permanently.
This way the ALWAYS regulator comes up as soon as there
is power while the state of the switcher can be controlled via
the SDNADJ pin.
Where ISS is the soft start current (5µA), TSS is the soft start
delay (i.e. 20msec).
Control and Signal Circuitry
Component Selection
Power Good
Switcher MOSFET Selection
The application circuit shown in Figure 1 is designed to run
with an input voltage operating range of 16–22V. This input
range helps determine the selection of the MOSFETs for the
switcher, since the high-side MOSFET can be on as much as
(Vout / Vin) = 12V / 16V = 75% of the time, and the low-side
MOSFET as much as 1 – (Vout / Vin) = 1 – (12V / 22V) =
45% of the time.
The MOSFETs have maximum duty cycles greater than
45%. Thus, it is necessary to size both approximately the
same.
Switcher Schottky Selection
In the application shown in Figure 1, the use of a SynchFET
eliminates the need of a Schottky diode for the synchronous
buck. If SynchFETs are not used, selection of a schottky is
determined by the maximum current at which the converter
operates. Select a diode whose instantaneous Vf is less than
0.75V at the maximum output current. The schottky dissipates no power, because it is on for only a very small portion
of the switching cycle.
Power Good is an open-collector signal, and is asserted when
the outputs are greater than 88% of nominal for more than
2µsec. When PWRGD goes low it will stay low for at least
2µsec.
Fault Handling
The FAN5232 has a full suite of protection against faults.
Consult Table 2 for an overview, and the individual sections
for details.
Table 2. Fault Handling
Fault
Condition
Switcher
3V- and
5V-Always
OC Switcher
Latch off
No Change
OC Always
No Change
Ramp Down
till UV
UV Switcher
Latch off after
2µsec
No Change
UV Always
No Change
Latch off after
2µsec
UV VCC
Off
Off
Input Capacitor Selection
Input capacitor selection is determined by ripple current
rating by the formula:
I rms = I out DC – DC
REV. 1.1.1 10/7/02
2
7
FAN5232
PRODUCT SPECIFICATION
Mechanical Dimensions
14-Lead TSSOP
Inches
Symbol
Notes:
Millimeters
Min.
Max.
Min.
Max.
A
A1
A2
—
.002
.031
.047
.006
.041
—
0.05
0.80
1.20
0.15
1.05
B
C
D
H
E
.007
.011
.004
.008
.252
.260
.252 BSC
.169
.177
0.17
0.27
0.09
0.20
6.40
6.60
6.40 BSC
4.30
4.50
e
L
N
α
ccc
.026 BSC
.018
.030
0.65 BSC
0.45
0.75
14
14
0°
8°
0°
8°
—
.004
—
0.10
Notes
1. Dimensioning and tolerancing per ANSI Y14.5M-1982.
2. "D" and "E1" do not include mold flash. Mold flash or
protrusions shall not exceed .010 inch (0.25mm).
3. "L" is the length of terminal for soldering to a substrate.
4. Terminal numbers are shown for reference only.
5
5
2, 4
5. "B" & "C" dimensions include solder finish thickness.
6. Symbol "N" is the maximum number of terminals.
3
6
D
E
H
A2
C
A1
A
SEATING
PLANE
e
B
–C–
α
L
LEAD COPLANARITY
ccc C
8
REV. 1.1.1 10/7/02
FAN5232
Ordering Information
Product Number
FAN5232MTC
Package
14 Lead TSSOP
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.
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 THE PRESIDENT 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.
www.fairchildsemi.com
10/7/02 0.0m 003
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