Fairchild FAN5235 System electronics regulator for mobile pc Datasheet

www.fairchildsemi.com
FAN5235
System Electronics Regulator for Mobile PCs
Features
Description
•
•
•
•
•
•
•
•
•
•
•
•
•
•
The FAN5235 is a high efficiency and high precision
DC/DC controller for notebook converters. Utilization of
both input and output voltage feedback in a current-mode
control allows for fast and stable loop response over a wide
range of input and output voltage variations. The two main
regulators switch out of phase to minimize input ripple
current.
Synchronous rectification
±1% precision internal reference
>90% efficiency
Input and output voltage feedback
5.4V to 24V input voltage range
Internally set 300kHz ±15% oscillator
5V and 3.3V Main outputs switch out of phase
5V-ALWAYS and 3.3V-ALWAYS outputs
Adjustable boost converter for 12V
Boost converter slaved to 5V Main
Input UVLO
Outputs OVP of Buck Converters
Precision current limit option for 5V, 3.3V Main
Power Good Voltage Monitor
Current sense based on MOSFET Rdson gives maximum
efficiency, while also permitting use of a sense resistor for
high accuracy. An externally adjustable boost converter can
be set to generate 12V.
The FAN5235 is available in a 24-pin QSOP package, and in
a 24-pin TSSOP package.
Applications
• Notebook PCs and PDAs
• Hand-held portable instruments
Typical Application
Vin = 5.4-24V
FAN5235
1 VIN
3.3V-ALWAYS@50mA
2 3.3 ALW
5V-ALWAYS
3 CPUMP3.3
5V-ALWAYS
CPUMP5 24
HSD5 23
5V @ 5A
+
SW5 22
4 HSD3.3
ISEN5 21
5 SW3.3
LSD5 20
6 5V-ALW
GND5 19
7 LSD3.3
VFB5 18
8 GND3.3
SDN5 17
9 ISEN3.3
SW12 16
10 VFB3.3
VFB12 15
3.3V @ 5A
+
5V-ALWAYS@ 50mA
SDN3.3
11 SDN3.3
SGND 14
PGOOD
12 PGOOD
SDWN 13
SDN5
12V @ 120mA
+
VFB12
SDWN
REV. 1.3.3 1/3/02
FAN5235
Pin Assignments
Top View
VIN
3.3V-ALWAYS
CPUMP3.3
HSD3.3
SW3.3
5V-ALWAYS
LSD3.3
GND3.3
ISEN3.3
VFB3.3
SDN3.3
PGOOD
1
2
3
4
5
6
7
8
9
10
11
12
24
23
22
21
20
19
18
17
16
15
14
13
CPUMP5
HSD5
SW5
ISEN5
LSD5
GND5
VFB5
SDN5
SW12
VFB12
SGND
SDWN
Pin Description
Pin Name
2
Pin Number Pin Function Description
VIN
1
Input power.
3.3V-ALWAYS
2
3.3V Always on linear regulator. Load current on pins 2 and 6 must not exceed
50mA total.
CPUMP3.3
3
Charge Pump 3.3V. High side Gate drive voltage for 3.3V. This pin is to be
connected to SW3.3 through a 100nF cap. and to 5V-ALWAYS through a diode
HSD3.3
4
High-side gate driver for 3.3V. Connect this pin directly to the gate of an
N-channel MOSFET. The trace from this pin to the MOSFET gate should be < 1".
SW3.3
5
High side FET Source and Low Side FET Drain Switching Node. Switching
node for 3.3V.
5V-ALWAYS
6
5V Always on linear regulator output. The sum of the load currents on pins 2
and 6 must not exceed 50mA total.
LSD3.3
7
Low-side gate driver for 3.3V. Connect this pin directly to the gate of an
N-channel MOSFET. The trace from this pin to the MOSFET gate should be < 1".
GND3.3
8
Ground for 3.3V MOSFET.
ISEN3.3
9
Current sense for 3.3V. This pin should be connected to the Drain of the bottom
Mosfet with an appropriate resistor and an RC filter. See Application Section.
VFB3.3
10
Voltage feedback for 3.3V.
SDN3.3
11
Soft Start and ON/OFF for 3.3V. OFF=GND. ON=open with SDWN=High. Use
open collector device for control.
PGOOD
12
Power Good Flag. An open collector output that will be logic low if any output
voltage is not above 89% of the nominal output voltage.
SDWN
13
Master Shutdown. Shutdown for all power. Off when low. When high
5V/3.3V-ALWAYS are ON while 5V/3.3V-Main are ready to turn on if SDN5,
SDN3.3 go open.
SGND
14
Signal ground.
VFB12
15
Voltage feedback for 12V.
SW12
16
FET driver for 12V Boost.
SDN5
17
Enable/Soft Start for 5V and 12V. Soft start and ON/OFF for 5V & 12V.
OFF=Grounded. ON=open with SDWN=High.
VFB5
18
Voltage feedback for 5V.
GND5
19
Ground for 5V MOSFET.
LSD5
20
Low side FET driver for 5V. Connect this pin directly to the gate of an N-channel
MOSFET. The trace from this pin to the MOSFET gate should be < 1".
REV. 1.3.3 1/3/02
FAN5235
Pin Description (Continued)
Pin Name
Pin Number Pin Function Description
ISEN5
21
Current Sense for 5V. This pin should be connected to the drain of the bottom
Mosfet using appropriate resistor and RC filter. See Application Section.
SW5
22
High Side Driver Source and Low Side Driver Drain Switching Node.
Switching node for 5V.
HSD5
23
High side FET driver for 5V. Connect this pin directly to the gate of an N-channel
MOSFET. The trace from this pin to the MOSFET gate should be < 1".
CPUMP5
24
Charge Pump 5V. High side Gate drive voltage for 5V. High side Gate drive
voltage for 5V. This pin is to be connected to SW5 through a 100nF cap. and to
5V-ALWAYS through a diode.
Absolute Maximum Ratings1
Max.
Units
VIN
Parameter
Conditions
Min.
-0.3
Typ.
27
V
SW, ISEN Pins,SDWN Pin
-0.3
27
V
CPUMP, HSD Pins
-0.3
33
V
SDN, VFB, V_always pins
-0.3
6.5
V
CPUMP to SW pins, and all other pins
-0.3
6.5
V
The sum of the load currents on pins 2 and 6 must not exceed 60mA total
Note:
1. Stresses beyond "Absolute Maximum Ratings" may cause permanent device damage. Continuous exposure to absolute
maximum rating conditions may affect device reliability. Functional operation of the device at these or any other conditions
beyond those indicated in the operational sections of the specification is not implied.
Recommended Operating Conditions
Input Voltage, VIN
+5.4V to 24V
Ambient Temperature, TA
-20°C to 85°C
Thermal Information
Thermal Resistance, θJA
Thermal Resistance, θJC
88°C/W
QSOP
28.5°C/W
TSSOP
16°C/W
Maximum Junction Temperature
Storage Temperature Range
Maximum Lead Temperature, Soldering 10 Sec
REV. 1.3.3 1/3/02
150°C
-65°C to 150°C
300°C
3
FAN5235
ELECTRICAL SPECIFICATIONS
Operating Conditions
Recommended Operating Conditions Unless Noted Refers to Block Diagrams
Parameter
Conditions
Min.
VIN Input Supply Voltage
(DC loading only) Note 1
5.4
Input Quiescent Current
H/LSD Open
Typ.
Max.
Units
24
V
1.4
3
mA
Stand-by
300
400
µA
Shut-down
<1
5
µA
4.7
5.1
Supply
Input UVLO Threshold
Rising Vbat
4.3
hysteresis
500
V
mV
5V and 3.3V Main Regulators
Output Voltage Precision
0.1 to 5.5A, 5.4 to 24V
+2
%
300
345
kHz
HSD On-Resistance, pull up
7
12
Ω
HSD On Resistance pull down
4
10
Ω
LSD On-Resistance, pull up
6
9
Ω
LSD On Resistance pull down
5
8
Ω
Oscillator Frequency, fosc
-2
255
HSD On Output, VCPUMP-VGS
I = 10µA
100
mV
HSD Off Output, VGS
I = 10µA
100
mV
LSD On Output, V5V-Always-VGS
I = 10µA
100
mV
LSD Off Output, VGS
I = 10µA
100
mV
Ramp Amplitude, pk-pk
VIN = 16V
2
V
Ramp Offset
0.5
V
Ramp Gain from VIN
125
mV/V
Error Amplifier GBW
3
MHz
Current Limit Threshold
R2, R8 = 1KΩ
90
135
180
µA
Over Voltage Threshold
2µs delay
110
115
120
%VO
Under Voltage Threshold
2µs delay
70
75
80
%VO
(End of Soft Start)
4.2
800
mV
SDN/SS Full On Voltage Min.
V
SDN/SS Full Off Voltage Max.
Max Duty Cycle
94
%
Min PWM Time
200
nsec
VFB3.3 Input Leakage Current
40
55
70
µA
+2
%
12V Regulator
Output Voltage Precision
V_5 =4.9 to 5.1V
and Io=0 to 150mA
-2
2.472
VFB12
VFB12 Input Current
Note 2
Oscillator Frequency (fosc/3)
Gate Drive On-Resistance
4
85
High or Low
V
100
200
nA
100
115
kHz
6
12
Ω
REV. 1.3.3 1/3/02
FAN5235
Operating Conditions (Continued)
Recommended Operating Conditions Unless Noted Refers to Block Diagrams
Parameter
Conditions
Min.
Typ.
Max.
Units
12V Regulator (Continued)
On Output, V5V-Always-VGS
I = 10µA
100
mV
Off Output, VGS
I = 10µA
100
mV
Ramp Amplitude, pk-pk
2
V
Error Amplifier GBW
1
MHz
Under Voltage Shut Down
2µs delay
Over Voltage Shut Down
Measured at VFB12
Min Duty Cycle
Max Duty Cycle
70
76
80
115
%VO
0
(By design)
32
%VO
%
33
34
%
1.3
1.5
Ω
5V and 3.3V Always
Bypass Switch rdson
Linear Regulator Accuracy
5.6 to 24V, 0 to 50mA,
5V Main On or Off
-3.3
2
%
I3.3 + I5
0
50
mA
Over-current Limit
2µs delay
100
180
Under-voltage Threshold
2µs delay
70
75
0-70°C
-1
Rated Output Current
mA
80
%
1
%
800
mV
Reference
Internal Reference Accuracy
Control Functions
SDWN Off Voltage Max.
SDWN On Voltage Min.
3
V
Over-temperature Shutdown, tj
150
°C
Over-temperature Hysteresis
25
°C
PGOOD Threshold
PWM Buck Converters
PGOOD Sink Current
-14
-11
-8.5
-4
%VO1
mA
PGOOD leakage
1
µA
+5V Analog Softstart
Css=100nF
65
msec
+3.3V Analog Softstart
Css=100nF
65
msec
5
µA
10
µs
Soft Start Current
PGOOD Min Pulse Width
Note 2
5
Notes
1. The minimum input voltage does not include voltage drop in the source supply due to source resistance. It is operating voltage
for static load conditions. To get acceptable load transient performance, the input voltage required will be much higher, in the
7.5 to 8.5 volt range or even higher depending on the severity of dynamic load, source impedance and input and output
capacitance and inductor values. The user should thoroughly test the performance at minimum input voltage using intended
component values and transient loading.
2. Min/Max specifications are guaranteed by design.
REV. 1.3.3 1/3/02
5
FAN5235
5V
VIN
CPUMP
HSD
HI
CLK
VFB
PHASE
L1
GATE
LOGIC
ADAPTIVE GATE
CONTROL
VOUT
ISEN
CL
VCC
PWM
LSD
LO
PGND
+
–
+
OC DETECT
REF
–
VCC
Q
SET
D
CLK
Q CLR L
PWM LATCH
VFB
–
+
+
–
VREF
SUM
DUTY
CYCLE
CLAMP
ERROR AMP
–
+
LSD
PWM
RAMP
ISEN
LSD
–
+
CURRENT SENSE
AMP
FAN5235
5V/3.3V Switcher
Figure 1. FAN5235 5V/3.3V Internal Block Diagram of PWM Loop
FAN5235
12V Converter
CK:3
CK :3
Ve
Ramp
PWM
+5
VREF=2.5V
R
CLK:3
(30%DC, 100kHz)
Ramp
SW12
V out
16R
Vout
+
–
–
+
VFB12
S
Q
R
Q
PWM
Ve
CLK:3
DISABLE
Figure 2. FAN5235 12V Internal Block Diagram
6
REV. 1.3.3 1/3/02
FAN5235
VIN
FAN5235
5V/3.3V-ALWAYS
LDO
LDO
3.3V ALWAYS
5V ALWAYS
VFB5
Figure 3. FAN5235 5V/3.3V—ALWAYS Internal Block Diagram
Functional Description
3.3V and 5V PWM Loop Compensation
The FAN5235 is a high efficiency and high precision DC/DC
controller for notebook and other portable applications. It
provides all of the voltages necessary for system electronics:
5V, 3.3V, 12V, and both 3.3V-ALWAYS and 5V-ALWAYS.
Utilization of both input and output voltage feedback in a
current-mode control allows for fast loop response over a
wide range of input and output variations. Current sense
based on MOSFET RDS,on gives maximum efficiency, while
also permitting the use of a sense resistor for high accuracy.
The 3.3V and 5V control loops of the FAN5235 function as
voltage mode with current feedback for stability. They each
have an independent voltage feedback pin, as shown in
Figure 1. They use voltage feed-forward to guarantee loop
rejection of input voltage variation: that is to say that the
PWM (pulse width modulation) ramp amplitude is varied as
a function of the input voltage. Compensation of the control
loops is done entirely internally using current-mode feedback compensation. This scheme allows the bandwidth and
phase margin to be almost independent of output capacitance
and ESR.
3.3V and 5V Architecture
The 3.3V and 5V switching regulator outputs of the
FAN5235 are generated from the unregulated input voltage
using synchronous buck converters. Both high side and lowside MOSFETs are N-channel.
The 3.3V and 5V switchers have pins for current sensing and
for setting of output over-current threshold using MOSFET
RDS,on. Each converter has a pin for voltage-sense feedback,
a pin that shuts down the converter, and a pin for generating
the boost voltage to drive the high-side MOSFET.
The following discussion of the FAN5235 design will be
done with reference to Figures 1 through 4, showing the
internal block diagram of the IC.
3.3V and 5V PWM Current Sensing
Peak current sensing is done on the low side driver because
of the very low duty-cycle on the high side MOSFET. The
current is sampled 50ns after turn on and the value is held for
current feedback and over-current limit.
REV. 1.3.3 1/3/02
3.3V and 5V PWM Current Limit
The 3.3V and 5V converters each sense the voltage across
their own low-side MOSFET to determine whether to enter
current limit. If an output current in excess of the current
limit threshold is measured then the converter enters a pulse
skipping mode where Iout is equal to the over-current (OC)
set limit. After 8 clock cycles then the regulator is latched off
(HSD and LSD off). This is the likely scenario in the 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 2µs delay.
Selection of a current-limit set resistor must include the
tolerance of the current-limit trip point, the MOSFET on
resistance and temperature coefficient, and the ripple current,
in addition to the maximum output current.
Example: Maximum DC output current on the 5V is 5A,
the MOSFET RDS,on is 17mΩ, and the inductor is 5µH at a
current of 5A. 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
20mΩ.
7
FAN5235
Peak current is DC output current plus peak ripple current:
Ipk ≈ Idc +
TV0
2L
= 5A +
4µsec • 5V
= 7A
2 • 5µH
where T is the maximum period, VO is output voltage, and L
is the inductance. This current generates a voltage on the
low-side MOSFET of 7A • 20mΩ = 140mV. The current
limit threshold is typically 150mV (worst-case 135mV) with
R2 = 1KΩ, and so this value is suitable. R2 could be
increased a further 10% if additional noise margin is deemed
necessary.
The 3.3V (5V) main converter is turned ON if SDWN and
SDN3.3 (SDN5) are both high and is turned off if either SDWN
or SDN3.3 (SDN5) is low.
Stand-by mode is defined as the condition by which V-Mains
are OFF and V-ALWAYS are ON (SDWN=1 and
SDN3.3=SDN5=0).
ALWAYS mode of Operation
If it is desired that 5V-ALWAYS and 3.3V-ALWAYS are always
ON then the SDWN pin must be connected to Vin permanently.
This way the two ALWAYS regulators come up as soon as there
is power while the state of the Main regulators can be controlled
via the SDN5 and SDN3.3 pins.
Precision Current Limit
Precision current limiting can be achieved by placing a
discrete sense resistor between the source of the low-side
MOSFET and ground.
Sequencing Table
SDN5
X
In this case, current limit accuracy is set by the tolerance of
the IC, +10%.
HSD
3V&5V
SDN3.3 SDWN ALWAYS
X
0
0
5V
MAIN
3.3V
MAIN
0
0
0
0
1
1
0
0
1
0
1
1
1
0
0
1
1
1
0
1
1
1
1
1
1
1
SW
3.3V Voltage Adjustment
LSD
ISEN
GND
Figure 4. Using a Precision Current Sense Resistor
Shutdown (SDWN)
The SDWN pin turns off all 5 converters (+5V, +3.3V, and
+12V, 5V/3.3V-ALWAYS) and puts the FAN5235 into a lowpower mode (Shutdown mode).
This mode of operation implies the use of a push button
switch between SDWN and Vin. Pushing the button allows
(for the duration of the contact) to power the 3.3V-ALWAYS
and 5V-ALWAYS long enough for the uC to power up and in
turn latch the SDWN pin high.
Once the SDWN is high then the ALWAYS voltages are
enabled to go high if the respective SDN3.3 and SDN5 go
high.
MAIN 3.3V and 5V Softstart, Sequencing and
Stand-by
Softstart of the 3.3V and 5V converters is accomplished by
means of an external capacitor between pins SDN3.3 (SDN5)
and ground.
REV. 1.3.3 1/3/02
The output voltage of the 3.3V converter can be increased by
as much as 10% by inserting a resistor divider in the feedback
line. The feedback pin impedance is about 66KΩ. Thus, for
example, to increase the output of the 3.3V converter by 10%,
use a 2.21KΩ/33.2KΩ divider.
Note that the output of the 5V regulator cannot be adjusted.
The feedback line of the 5V regulator is used internally as a
5V supply and, therefore, cannot tolerate any impedance in
series with it.
3.3V and 5V Main Overvoltage Protection
(Soft Crowbar)
When the output voltage of the 3.3V (or the 5V) converter
exceeds approximately 115% of nominal, the converter enters
the over-voltage (OV) protection mode, with the goal of protecting the load from damage. During operation, severe load
dump or a short of an upper MOSFET could cause the output
voltage to increase significantly over normal operation range
without circuit protection. When the output exceeds the overvoltage threshold, 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, OVP comparator is disengaged.
The OVP scheme also provides a soft crowbar function
(bang-bang control followed by blow of the fuse) which
helps to tackle severe load transients but does not invert output voltage when activated—a common problem for OVP
schemes with a latch. The prevention of output inversion
eliminates the need for a Schottky diode across the load.
8
FAN5235
3.3V and 5V Under-voltage Protection
5V/3.3V-ALWAYS Operation
When the output voltage of either the 3.3V or 5V falls below
75% of the nominal value, both converters, go into undervoltage (UV) protection, after a 2usec delay. In undervoltage protection, the high and low side MOSFETs are
turned off. Once under-voltage protection is triggered, it
remains on until power is recycled or the SDWN pin is reset.
The 5V-ALWAYS supply is generated from either the onchip linear regulator or through an internal switch from the
VFB pin of the 5V switching supply.
12V Architecture
The 12V converter is a traditional non-isolated fly-back (also
known as a "boost" converter). The converter’s input voltage
is the +5V switcher output, so that +12V can only be present
if +5V is present. Also, if the external MOSFET is off, the
output of the +12V converter is +5V, not zero. This in turn
will provide non-zero output for the 12V regulator.
For complete turn-off of the 12V regulator an external
P-channel MOSFET or an LDO regulator with on/off control
may be used. If an LDO is used for 12V then the boost
converter should be set to 13.2V using the external resistor
divider network.
12V Loop Compensation
The 12V converter should be run in discontinuous conduction mode. In this mode, the converter will be stable if a
capacitor with suitable ESR value is selected. A 68uF
tantalum with 500mA ripple current rating and 95mΩ is
recommended here.
12V Protection
The 12V converter is protected against overvoltage. If the
12V feedback is more than 10–15% above the nominal set
voltage, a comparator forces the MOSFET off until the voltage falls below the comparator threshold.
The 12V converter is also protected against over-current. If a
short circuit pulls the output below 9V, all of the switching
converters go into UV protection, after a 2µs delay. In UV
protection, all MOSFETs are turned off. Once UV protection
is triggered, it remains on until the input power is recycled or
the SDWN is reset.
When the 5V switching supply is off, or if its output voltage
is not within tolerance, the 5V-ALWAYS switch is open, and
the linear regulator is on. When the 5V switching supply is
running and has an output voltage within specification, the
linear regulator is off, and the switch is on. The switch has
sufficiently low resistance that at maximum current draw on
the 5V-ALWAYS supply, the output voltage is regulated
within specifications.
The 3.3V-ALWAYS is generated from a linear regulator
attached internally to the 5V-ALWAYS.
The purpose of the two ALWAYS supplies (combined current is specified to never exceed 50mA) is to provide power
to the system micro-controller (8051 class) as well as other
IC’s needing a stand-by power. The micro-controller as well
as the other IC’s could be operated from either 5V or 3.3V
ALWAYS, so the FAN5235 provides both.
5V/3.3V-ALWAYS Protections
The two internal linear regulators are current limited and
under-voltage protected. Once protection is triggered all
outputs are turned off until power is cycled or the SDWN is
reset.
Power good
Power good is asserted when both PWM Buck converters are
above specified threshold. No other regulators are monitored
by Power good. When PGOOD goes low it will stay low for
at least 10µsec (Tw). See fig. 5.
Vmain
Vth
t
12V Softstart and Sequencing
The 12V output is started at the same time as the 5V output.
The softly rising 5V output automatically generates a softly
rising 12V output. The duty cycle of the 12V PWM is limited to prevent excessive current draw.
The 12V supply must build up a voltage higher than the
UVLO limit (9V) by the time the 5V is above its UVLO
(3.75V) in order to avoid triggering of UV protection during
soft start.
PGOOD
t
Tw
Figure 5. PGOOD Timing Diagram
REV. 1.3.3 1/3/02
9
FAN5235
Error Amplifier output voltage clamp
Input UVLO
During a load transient the error amplifier voltage is allowed
full swing. After two clock cycles, if the amplifier is still out
of range the voltage and consequently the duty cycle (DC) is
clamped. The DC clamp automatically limits the build up of
over-currents during abnormal conditions, including short
circuits:
If the input voltage falls below the UVLO threshold, the
FAN5235 turns itself off and stays off as long as Input
voltage is below threshold.
VFB=0.5V+Vo/8
VRAMP =0.5V+Vin/8
VREF
–
+
Vclamp=0.5V+
+Vo/8 +/-0.2V
0.4V
2 Cycles
Counter
LSD
Buck
LDO
OFF-LATCH OFF-LATCH
OC/UV
(LDO)
–
EA
+
HSD
Buck
OC/UV
(Bucks)
+
–
IC Protections Table
LSD
Boost
ON
OFF-LATCH
"
"
OFF-LATCH
"
OV (Buck)*
OFF
SOFT
CROWBAR
ON
ON
OV (Boost)
ON
ON
ON
OFF
SDWN=0
OFF
OFF
OFF
OFF
OT
OFF
OFF
OFF
OFF
ON
OFF-LATCH
ON
33% DC
UV (Boost)
OFF-LATCH OFF-LATCH
OC (Boost)
ON
ON
* Only the converter in Over-Voltage goes in SOFT CROWBAR mode.
Figure 6. Duty-Cycle Clamp
Thermal shutdown
If the die temperature of the FAN5235 exceeds safe limits,
the IC shuts itself off. When the over-temperature (OT)
event ends, the IC comes back to normal operation. There is
a 25°C thermal hysteresis between shutdown and start up.
Generic Mobile System Block Diagram
Vin=5.6 to 24V
5V
SDN5
3.3V
Vcpu
SDN3.3
FAN5235
µC
8051
5V-Always
PGOOD
RC5231
1.5V
CPU
2.5V
µC
µP
Clock
PGOOD
3.3V-Always
CPU
PGOOD
EN
SDWN
SDWN
µP CODE EXECUTION
RESET
LOGIC
Figure 7. System Block Diagram
10
REV. 1.3.3 1/3/02
FAN5235
Notebook Application Circuit
5.4-24V
C1
Pin 6
C2
3.3V@50mA
C10
5V@50mA
C11
3.3V@5A
D5
L1 C5
Q1
+
C12, C13
D1
Q2
R2
SDN3.3
C3
+5V
D4
1
2
3
4
5
6
7
8
9
10
11
12
U1
FAN5235
24
23
22
21
20
19
18
17
16
15
14
13
L2
C6
Q3
C7 C8
+
D2
5V@5A
R3
L3
Q4
SDN5
D3
12V@120mA
R6
Q5
SDWN
R4
C9
R5
C4
R1
PGOOD
Figure 8. FAN5235 Notebook Application Circuit
Table 1. FAN5235 Application Bill of Materials
Reference
Manufacturer, Part #
C1
SANYO
25SP33M
Quantity
1
Description
Comments
33µF, 25V
OSCON,
Irms = 3A,
19V adapter.
C2-6
Any
5
100nF, 50V
Ceramic
C7-8
C12-13
KEMET
T510X337(1)010AS
2
2
330µF, 10V
Tantalum,
ESR=35mΩ
C10-11
AVX*020R1800TPSA475
2
4.7µF, 20V
Tantalum, ESR=1.8Ω
C9
AVX
TPSV68*025R0095
1
68µF, 25V,
ESR=95mΩ
Tantalum,
Irms = 0.5A
R1
Any
1
10KΩ, 1%
R2, R3
Any
2
1KΩ, 1%
R4, R5
Any
1
380KΩ, 100KΩ
R6
Any
1
10Ω
D1-3
Fairchild SS22
3
2A, 40V Schottky
D4-5
Fairchild MBR0520L
2
500mA, 20V Schottky
L1-2
Any
2
6.4µH, 5A
L3
Any
1
5.6µH, 2A
1%
R < 25mΩ
Q1-4
Fairchild FDS6690A
4
30V N-channel MOSFET
R = 17mΩ
Q5
Fairchild NDC631N
1
20V N-channel MOSFET
R = 60mΩ
U1
Fairchild FAN5235
1
SER Controller
11
REV. 1.3.3 1/3/02
FAN5235
MOSFET Selection
3.3V and 5V Schottky Selection
The notebook application circuit shown in Figure 1 is designed
to run with an input voltage operating range of 5.4-24V.
This wide input range helps determine the selection of the
MOSFETs for the 3.3V and 5V converters, since the high-side
MOSFET is on (Vout / Vin) of the time, and the low-side
MOSFET 1 – (Vout / Vin) of the time. The maxima and minima
are tabulated in Table 2:
The maximum current at which the converters operate in PFM
mode determines selection of a Schottky. In the application
shown in Figure 8, since the transition can occur at a current as
high as 28mV * (17.5KΩ / 10KΩ) / 35mΩ = 1.4A, the diode
(with 24V input) will be conducting 86% of the period (from
Table 2). It thus has an average current of 1.4A * 0.86 = 1.2A,
which requires a Schottky current rating >1A.
Table 2. MOSFET Duty Cycles
3.3V and 5V Inductor Selection
See Table 1.
High-side FET
3.3V and 5V Output Cap Selection
Vin
Vout
5.4V
24V
3.3V
.61
.14
5V
.43
.21
Low-side FET
Vin
Vout
5.4V
24V
3.3V
.39
.86
5V
.07
.79
All four MOSFETs have maximum duty cycles greater than
50%. Thus, it is necessary to size all four approximately the
same.
12
See Table 1.
12V Component Selection
Calculation of the inductor, diode and output capacitor for the
+12V output fly-back is complex, depending on output power
and efficiency. See Applications Bulletin AB-19 for an Excel
spreadsheet calculation tool. See Table 1 also.
Input Capacitor Selection
Input capacitor selection is determined by ripple current rating.
With two converters operating in parallel at differing duty
cycles, calculation of input ripple current is complex; see
Applications Bulletin AB-19 for an Excel spreadsheet
calculation tool.
REV. 1.3.3 1/3/02
FAN5235
Mechanical Dimensions
QSOP 24-Lead
Inches
Symbol
Min.
A
A1
A2
b
c
D
E
e
H
L
N
α
ccc
Millimeters
Max.
Min.
1.35
1.75
0.1
0.25
1.37
1.57
0.20
0.30
0.19
0.25
8.55
8.74
3.81
3.99
0.635 BSC
0.228
0.016
5.79
0.40
24
1. Dimensioning and tolerancing per ANSI Y14.5M-1982.
Max.
0.0532 0.0668
0.0040 0.0098
0.054
0.062
0.008
0.012
0.0075 0.0098
0.337
0.344
0.150
0.157
0.025 BSC
0.244
0.050
Notes:
Notes
2. "D" and "E" do not include mold flash. Mold flash or
protrusions shall not exceed .006 inch (0.15mm).
3. "L" is the length of terminal for soldering to a substrate.
4. Terminal numbers are shown for reference only.
5
5
24
0°
8°
0°
8°
.004
—
0.10
6. Symbol "N" is the maximum number of terminals.
2, 4
2
6.20
1.27
—
5. "b" and "c" dimensions include solder finish thickness.
3
6
D
E
A
H
C
A1
A2
B
e
SEATING
PLANE
–C–
α
L
LEAD COPLANARITY
ccc C
REV. 1.3.3 1/3/02
13
FAN5235
Mechanical Dimensions
TSSOP 24-Lead
Inches
Symbol
Millimeters
Min.
Max.
Min.
Max.
A
A1
B
C
D
—
.002
.007
.004
.303
.047
.006
—
0.05
0.19
0.09
7.70
1.20
0.15
E
e
H
.169
.177
.026 BSC
.252 BSC
.018
.030
4.30
4.50
0.65 BSC
6.40 BSC
0.45
0.75
24
24
L
N
α
ccc
.012
.008
.316
0.30
0.20
7.90
0°
8°
0°
8°
—
.004
—
0.10
Notes:
Notes
1. Dimensioning and tolerancing per ANSI Y14.5M-1982.
2. "D" and "E" do not include mold flash. Mold flash or
protrusions shall not exceed .006 inch (0.15mm).
3. "L" is the length of terminal for soldering to a substrate.
4. Terminal numbers are shown for reference only.
5. Symbol "N" is the maximum number of terminals.
2
2
3
5
D
E
H
C
A1
A
B
e
SEATING
PLANE
–C–
α
L
LEAD COPLANARITY
ccc C
14
REV. 1.3.3 1/3/02
FAN5235
Ordering Information
Product Number
Package
FAN5235QSC
24 Lead QSOP
FAN5235MTC
24 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
1/3/02 0.0m 002
Stock#DS30005235
 2001 Fairchild Semiconductor Corporation