FAN5236MTCX [ONSEMI]

PWM/PFM 控制器,宽输入电压,双输出/DDR;
FAN5236MTCX
型号: FAN5236MTCX
厂家: ONSEMI    ONSEMI
描述:

PWM/PFM 控制器,宽输入电压,双输出/DDR

双倍数据速率 控制器 开关 光电二极管
文件: 总20页 (文件大小:682K)
中文:  中文翻译
下载:  下载PDF数据表文档文件
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Is Now  
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FAN5236  
Dual Mobile-Friendly DDR / Dual-Output PWM Controller  
Features  
Description  
The FAN5236 PWM controller provides high efficiency and  
regulation for tw o output voltages adjustable in the range  
of 0.9V to 5.5V required to pow er I/O, chip-sets, and  
memory banks in high-performance notebook computers,  
PDA s , and Internet appliances. Synchronous rectification  
and hysteretic operation at light loads contribute to high  
efficiency over a w ide range of loads. The Hysteretic  
Mode can be disabled separately on each PWM converter  
if PWM Mode is desired for all load levels. Efficiency is  
enhanced by using MOSFET RDS(ON) as a current-sense  
.
Highly Flexible, Dual Synchronous Sw itching PWM  
Controller that Includes Modes for:  
-
-
-
DDR Mode w ith In-phase Operation for Reduced  
Channel Interference  
90° Phase-shifted, Tw o-stage DDR Mode for  
Reduced Input Ripple  
Dual Independent Regulators, 180° Phase Shifted  
.
.
Complete DDR Memory Pow er Solution  
component.  
-
-
VTT Tracks VDDQ/2  
VDDQ/2 Buffered Reference Output  
Feedforw ard ramp modulation, average-current-mode  
control scheme, and internal feedback compensation  
provide fast response to load transients. Out-of-phase  
operation w ith 180-degree phase shift reduces input  
current ripple. The controller can be transformed into a  
complete DDR memory pow er supply solution by  
activating a designated pin. In DDR mode, one of the  
channels tracks the output voltage of another channel and  
provides output current sink and source capability —  
essential for proper pow ering of DDR chips. The buffered  
reference voltage required by this type of memory is also  
provided. The FAN5236 monitors these outputs and  
generates separate PGx (pow er good) signals w hen the  
soft-start is completed and the output is w ithin ±10% of  
the set point. Built-in over-voltage protection prevents the  
output voltage from going above 120% of the set point.  
Normal operation is automatically restored w hen the over-  
voltage conditions cease. Under-voltage protection  
latches the chip off w hen output drops below 75% of the  
set value after the soft-start sequence for this output is  
completed. An adjustable over-current function monitors  
the output current by sensing the voltage drop across the  
low er MOSFET. If precision current-sensing is required,  
an external current-sense resistor may be used.  
Lossless Current Sensing on Low -side MOSFET or  
Precision Over-Current Using Sense Resistor  
.
.
VCC Under-Voltage Lockout  
Converters can Operate from +5V or 3.3V or Battery  
Pow er Input (5V to 24V)  
.
Excellent Dynamic Response w ith Voltage  
Feedforw ard and Average-Current-Mode Control  
.
.
.
.
Pow er-Good Signal  
Supports DDR-II and HSTL  
Light-Load Hysteretic Mode Maximizes Efficiency  
TSSOP28 Package  
Applications  
.
.
.
.
DDR VDDQ and VTT Voltage Generation  
Mobile PC Dual Regulator  
Server DDR Pow er i  
Hand-held PC Pow er  
Related Resources  
.
http://w w w .onsemi.com/pub/Collateral/AN-  
6002.pdf.pdf  
.
http://w w w .onsemi.com/pub/Collateral/AN-  
1029.pdf.pdf  
© 2002 Semiconductor Components Industries, LLC.  
Nov ember-2017, Rev. 2  
Publication Order Number:  
FAN5236/D  
Ordering Information  
B Operating  
Temperature  
Range  
Packing  
Method  
Part Number  
Package  
FAN5236MTCX  
-10 to +85°C  
28-Lead Thin-Shrink Small-Outline Package (TSSOP)  
Tape and Reel  
Block Diagrams  
V
(BATTERY)  
IN  
= 5 to 24V  
VCC  
+5  
FAN5236  
Q1  
V
ILIM1  
OUT1  
L
OUT1  
= 2.5V  
PWM 1  
COUT1  
Q2  
DDR  
Q3  
V
ILIM2/  
REF2  
OUT 2  
L
OUT2  
= 1.8V  
PWM 2  
COUT2  
Q4  
Figure 1. Dual-Output Regulator  
V
(BATTERY)  
= 5 to 24V  
IN  
VCC  
+5  
FAN5236  
Q1  
ILIM1  
V
DDQ  
= 2.5V  
L OUT1  
PWM 1  
COUT1  
Q2  
R
R
DDR  
+5  
Q3  
V
=
TT  
L OUT2  
V
PG2/REF  
1.25V  
DDQ /2  
COUT2  
Q4  
PWM 2  
ILIM2/REF2  
Figure 2. Complete DDR Memory Power Supply  
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2
Pin Configuration  
AGND  
LDRV1  
PGND1  
SW1  
VCC  
1
2
3
4
5
6
28  
27  
26  
25  
24  
23  
LDRV2  
PGND2  
SW2  
HDRV1  
BOOT1  
ISNS1  
EN1  
HDRV2  
BOOT2  
ISNS2  
7
22  
21  
20  
19  
18  
17  
16  
15  
FAN5236  
EN2  
8
FPWM1  
VSEN1  
ILIM1  
FPWM2  
VSEN2  
ILIM2/REF2  
SS2  
9
10  
11  
12  
13  
14  
SS1  
DDR  
PG2/REF2OUT  
PG1  
VIN  
Figure 3. Pin Configuration  
Pin Definitions  
Pin #  
Name  
Description  
Analog Ground. This is the signal ground reference for the IC. All voltage levels are measured  
w ith respect to this pin.  
1
AGND  
2
27  
3
LDRV1  
LDRV2  
PGND1  
PGND2  
SW1  
Low-Side Drive. The low -side (low er) MOSFET driver output. Connect to gate of low -side  
MOSFET.  
Power Ground. The return for the low -side MOSFET driver. Connect to source of low -side  
MOSFET.  
26  
4
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.  
25  
5
SW2  
HDRV1  
HDRV2  
BOOT1  
BOOT2  
ISNS1  
ISNS2  
EN1  
High-Side Drive. High-side (upper) MOSFET driver output. Connect to gate of high-side  
MOSFET.  
24  
6
BOOT. Positive supply for the upper MOSFET driver. Connect as show n in Figure 4.  
23  
7
Current-Sense Input. Monitors the voltage drop across the low er MOSFET or external sense  
resistor for current feedback.  
22  
8
Enable. Enables operation w hen pulled to logic HIGH. Toggling EN resets the regulator after a  
latched fault condition. These are CMOS inputs w hose state is indeterminate if left open.  
21  
9
EN2  
FPWM1  
Forced PWM Mode. When logic LOW, inhibits the regulator from entering Hysteretic Mode;  
otherw ise tie to VOUT . The regulator uses VOUT on this pin to ensure a smooth transition from  
20  
FPWM2  
Hysteretic Mode to PWM Mode. When VOUT is expected to exceed VCC, tie to VCC  
.
10  
19  
11  
12  
17  
V SEN1  
V SEN2  
ILIM1  
SS1  
Output Voltage Sense. The feedback from the outputs. Used for regulation as w ell as PG,  
under-voltage, and over-voltage protection and monitoring.  
Current Limit 1. A resistor from this pin to GND sets the current limit.  
Soft Start. A capacitor from this pin to GND programs the slew rate of the converter during  
initialization. During initialization, this pin is charged w ith a 5mA current source.  
SS2  
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3
Pin Descriptions (Continued)  
Pin #  
Name  
Description  
DDR Mode Control. HIGH = DDR Mode. LOW = tw o separate regulators operating 180° out of  
phase.  
13  
DDR  
Input Voltage. Normally connected to battery, providing voltage feedforw ard to set the  
amplitude of the internal oscillator ramp. When using the IC for tw o-step conversion from 5V  
input, connect through 100Kresistor to ground, w hich sets the appropriate ramp gain and  
synchronizes the channels 90° out of phase.  
14  
15  
VIN  
Power Good Flag. An open-drain output that pulls LOW w hen VSEN is outside a ±10% range  
of the 0.9V reference.  
PG1  
Power Good 2. When not in DDR Mode, open-drain output that pulls LOW w hen the VOUT is out  
of regulation or in a fault condition.  
PG2 /  
REF2OUT  
16  
Reference Out 2. When in DDR Mode, provides a buffered output of REF2. Typically used as  
the VDDQ/2 reference.  
Current Limit 2. When not in DDR Mode, a resistor from this pin to GND sets the current limit.  
18  
28  
ILIM2 / REF2  
VCC  
Reference for reg #2 w hen in DDR Mode. Typically set to VOUT 1 / 2  
.
VCC. This pin pow ers the chip as w ell as the LDRV buffers. The IC starts to operate w hen  
voltage on this pin exceeds 4.6V (UVLO rising) and shuts dow n w hen it drops below 4.3V  
(UVLO falling).  
www.onsemi.com  
4
Absolute Maximum Ratings  
Stresses exceeding the absolute maximum ratings may damage the device. The device may not function or be operable  
above the recommended operating conditions and stressing the parts to these levels is not recommended. In addition,  
extended exposure to stresses above the recommended operating conditions may affect device reliability. The absolute  
maximum ratings are stress ratings only.  
Symbol  
VCC  
Parameter  
Min.  
Max.  
6.5  
Unit  
V
VCC Supply Voltage  
VIN  
VIN Supply Voltage  
27  
V
BOOT, SW, ISNS, HDRV  
BOOTx to SWx  
33  
V
6.5  
V
All Other Pins  
-0.3  
-40  
-65  
VCC+0.3  
+150  
+150  
+300  
V
TJ  
TSTG  
TL  
Junction Temperature  
Storage Temperature  
Lead Temperature (Soldering,10 Seconds)  
ºC  
ºC  
ºC  
Recommended Operating Conditions  
The Recommended Operating Conditions table defines the conditions for actual device operation. Recommended  
operating conditions are specified to ensure optimal performance to the datasheet specifications. ON Semiconductor  
does not recommend exceeding them or designing to Absolute Maximum Ratings.  
Symbol  
VCC  
Parameter  
Min.  
Typ.  
Max.  
5.25  
24  
Unit  
V
VCC Supply Voltage  
4.75  
5.00  
VIN  
VIN Supply Voltage  
V
TA  
Ambient Temperature  
-10  
+85  
90  
°C  
ΘJA  
Thermal Resistance, Junction to Ambient  
°C/W  
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5
Electrical Characteristics  
Recommended operating conditions, unless otherw ise noted.  
Symbol  
Parameter  
Conditions  
Min. Typ. Max. Units  
Power Supplies  
LDRV, HDRV Open, VSEN Forced Above  
Regulation Point  
2.2  
-15  
3.0  
µA  
IVCC  
VCC Current  
Shutdow n (EN-0)  
VIN = 24V  
30  
30  
µA  
µA  
µA  
µA  
V
ISINK  
ISOURCE  
ISD  
VIN Current, Sinking  
VIN Current, Sourcing  
VIN Current, Shutdow n  
10  
VIN = 0V  
-30  
1
Rising VCC  
Falling  
4.30  
4.10  
4.55  
4.25  
300  
4.75  
4.45  
VUVLO  
UVLO Threshold  
UVLO Hysteresis  
V
VUVLOH  
Oscillator  
fosc  
mV  
Frequency  
255  
300  
2
345  
KHz  
V
VIN = 16V  
VIN = 5V  
VPP  
VRAMP  
G
Ramp Amplitude  
Ramp Offset  
Ramp / VIN Gain  
1.25  
0.5  
125  
250  
V
V
VIN 3V  
mV/V  
mV/V  
1V < VIN < 3V  
Reference and Soft Start  
VREF Internal Reference Voltage  
ISS  
0.891 0.900 0.909  
5
V
Soft-Start Current  
At Startup  
µA  
Soft-Start Complete  
Threshold  
VSS  
1.5  
V
PWM Converters  
Load Regulators  
IOUT X f rom 0 to 5A, VIN from 5 to 24V  
-2  
50  
+2  
120  
65  
%
nA  
KΩ  
%
ISEN  
VSEN Bias Current  
80  
55  
VOUT Pin Input Impedance  
45  
UVLOTSD Under-Voltage Shutdow n  
% of Set Point, 2µs Noise Filter  
% of Set Point, 2µs Noise Filter  
70  
75  
80  
UVLO  
ISNS  
Over-Voltage Threshold  
Over-Current Threshold  
115  
112  
120  
140  
125  
168  
%
RILIM= 68.5KΩ, Figure 12  
µA  
Output Drivers  
Sourcing  
Sinking  
12.0  
2.4  
15.0  
4.0  
HDRV Output Resistance  
Sourcing  
Sinking  
12.0  
1.2  
15.0  
2.0  
LDRV Output Resistance  
Continued on following page…  
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6
Electrical Characteristics (Continued)  
Symbol Parameter  
Conditions  
Min. Typ. Max. Units  
Power-Good Output and Control Pins  
Low er Threshold  
% of Set Point, 2µs Noise Filter  
% of Set Point, 2µs Noise Filter  
IPG = 4mA  
-86  
-94  
116  
0.5  
1
%
%
V
Upper Threshold  
108  
PG Output Low  
Leakage Current  
VPULLUP = 5V  
µA  
PG2/REF2OUT Voltage  
DDR, EN Inputs  
DDR = 1, 0mA < IREF2OUT 10mA  
99.00  
2
1.01 % VREF2  
VINH  
VINL  
Input High  
Input Low  
V
0.8  
0.1  
V
FPWM Inputs  
FPWM Low  
V
V
FPWM High  
FPWM Connected to Output  
0.9  
Block Diagram  
Figure 4. IC Block Diagram  
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7
 
Typical Application  
V
(BATTERY)  
IN  
= 5 to 24V  
VIN  
C1  
C9  
14  
D1  
VCC  
BOOT1  
Q1A  
28  
6
+5  
+5  
C4  
C5  
HDRV1  
VDDQ  
= 2.5V  
5
4
R3  
L1  
ILIM1  
EN1  
SS1  
11  
8
SW1  
C6A C6B  
Q1B  
PW M 1  
R5  
LDRV1  
2
12  
C2  
R7  
PGND2  
ISNS1  
+5  
3
7
R4  
FPWM1(VOUT1)  
VSEN1  
9
PG1  
15  
R1  
10  
DDR  
EN2  
SS2  
+5  
13  
21  
17  
BOOT2  
Q2A  
23  
R6  
D2  
+5  
HDRV2  
SW2  
C7  
C3  
24  
25  
VTT  
VDDQ/2  
=
L2  
R2  
1.25V at 10mA  
PG2/REF  
Q2B  
C8A  
16  
1
PW M 2  
LDRV2  
27  
AGND  
PGND2  
26  
22  
R8  
ISNS2  
C8B  
FPWM2  
VSEN2  
20  
19  
18  
ILIM2/REF2  
Figure 5. DDR Regulator Application  
Table 1. DDR Regulator BOM  
Description  
Qty.  
Ref.  
Vendor  
Part Number  
Capacitor 68µf, Tantalum, 25V, ESR 150mΩ  
Capacitor 10nf, Ceramic  
1
2
1
2
2
1
2
3
1
2
2
1
2
2
1
1
1
1
C1  
AVX  
Any  
AVX  
Any  
TPSV686*025#0150  
C2, C3  
C4  
Capacitor 68µf, Tantalum, 6V, ESR 1.8Ω  
Capacitor 150nF, Ceramic  
Capacitor 180µf, Specialty Polymer 4V, ESR 15mΩ  
Capacitor 1000µf, Specialty Polymer 4V, ESR 10mΩ  
Capacitor 0.1µF, Ceramic  
TAJB686*006  
C5, C7  
C6A, C6B Panasonic  
EEFUE0G181R  
C8  
Kemet  
Any  
Any  
Any  
Any  
Any  
Any  
Any  
T510E108(1)004AS4115  
C9  
18.2K, 1% Resistor  
R1, R2  
R6  
1.82K, 1% Resistor  
56.2K, 1% Resistor  
R3  
10K, 5% Resistor  
R4  
3.24K, 1% Resistor  
R5  
1.5K, 1% Resistor  
R7, R8  
D1, D2  
L1  
Schottky Diode 30V  
ON Semiconductor BAT54  
Inductor 6.4µH, 6A, 8.64mΩ  
Inductor 0.8µH, 6A, 2.24mΩ  
Dual MOSFET w ith Schottky  
DDR Controller  
Panasonic  
Panasonic  
ON Semiconductor FDS6986AS(1)  
ETQ-P6F6R4HFA  
ETQ-P6F0R8LFA  
L2  
Q1, Q2  
U1  
ON Semiconductor FAN5236  
Note:  
1. Suitable for typical notebook computer application of 4A continuous, 6A peak for VDDQ. If continuous operation above  
6A is required, use single SO-8 packages. For more information, refer to the Power MOSFET Selection Section and  
use AN-6002 for design calculations.  
www.onsemi.com  
8
 
 
Typical Applications (Continued)  
V
(BATTERY)  
= 5 to 24V  
IN  
VIN  
C9  
C1  
14  
D1  
L1  
VCC  
BOOT1  
Q1A  
28  
11  
6
+5  
+5  
C4  
C5  
HDRV1  
5
4
R2  
ILIM1  
2.5V at 6A  
C6  
SW1  
EN1  
SS1  
Q1B  
LDRV1  
8
PW M 1  
2
12  
R6  
C2  
PGND2  
ISNS1  
+5  
3
7
R4  
R3  
FPWM1(VOUT1)  
VSEN1  
9
PG1  
DDR  
15  
13  
10  
V
IN  
BOOT2  
23  
R5  
D2  
Q2A  
+5  
EN2  
HDRV2  
21  
C7  
24  
25  
SW2  
PG2  
SS2  
L2  
16  
17  
1.8V at 6A  
Q2B  
C8  
PW M 2  
LDRV2  
C3  
27  
R7  
AGND  
PGND2  
ISNS2  
R8  
1
26  
22  
R9  
R1  
FPWM2  
VSEN2  
ILIM2  
20  
19  
18  
Figure 6. Dual Regulator Application  
Table 2. DDR Regulator BOM  
Item  
1
Description  
Capacitor 68µf, Tantalum, 25V, ESR 95mΩ  
Capacitor 10nf, Ceramic  
Qty.  
Ref.  
C1  
Vendor  
Part Number  
1
2
1
2
2
2
2
2
1
AVX  
Any  
TPSV686*025#095  
TAJB686*006  
4TPB330ML  
2
C2, C3  
C4  
3
Capacitor 68µf, Tantalum, 6V, ESR 1.8Ω  
Capacitor 150nF, Ceramic  
AVX  
Any  
4
C5, C7  
C6, C8  
C9  
5
Capacitor 330µf, Poscap, 4V, ESR 40mΩ  
Capacitor 0.1µF, Ceramic  
Sanyo  
Any  
5
11  
12  
13  
56.2K, 1% Resistor  
R1, R2  
R3  
Any  
10K, 5% Resistor  
Any  
3.24K, 1% Resistor  
R4  
Any  
R5, R8,  
R9  
14  
1.82K, 1% Resistor  
3
Any  
15  
27  
1.5K, 1% Resistor  
2
2
1
1
1
R6, R7  
D1, D2  
L1, L2  
Q1  
Any  
Schottky Diode 30V  
ON Semiconductor  
Panasonic  
BAT54  
28  
Inductor 6.4µH, 6A, 8.64mΩ  
Dual MOSFET w ith Schottky  
DDR Controller  
ETQ-P6F6R4HFA  
FDS6986AS(2)  
FAN5236  
29  
ON Semiconductor  
ON Semiconductor  
30  
U1  
Note:  
2. If currents above 4A continuous are required, use single SO-8 packages. For more information, refer to the Power  
MOSFET Selection Section and AN-6002 for design calculations.  
www.onsemi.com  
9
 
 
Circuit Description  
Overview  
When VIN is from the battery, it’s typically higher than  
7.5V. As show n in Figure 7, 180° operation is undesirable  
because the turn-on of the VDDQ converter occurs very  
near the decision point of the VTT converter.  
CL K  
The FAN5236 is  
a multi-mode, dual-channel PWM  
controller intended for graphic chipset, SDRAM, DDR  
DRAM, or other low -voltage pow er applications in modern  
notebook, desktop, and sub-notebook PCs. The IC  
integrates control circuitry for tw o synchronous buck  
converters. The output voltage of each controller can be  
set in the range of 0.9V to 5.5V by an external resistor  
divider.  
VDDQ  
VTT  
The tw o synchronous buck converters can operate from  
either an unregulated DC source (such as a notebook  
battery), w ith voltage ranging from 5.0V to 24V, or from a  
regulated system rail of 3.3V to 5.0V. In either mode, the  
IC is biased from a +5V source. The PWM modulators use  
an average-current-mode control w ith input voltage  
feedforw ard for simplified feedback loop compensation  
and improved line regulation. Both PWM controllers have  
integrated feedback loop compensation that reduces the  
external components needed.  
Figure 7. Noise -Susceptible 180° Phasing for DDR1  
In-phase operation is optimal to reduce inter-converter  
interference w hen VIN is higher than 5V (w hen VIN is  
from a battery), as show n in Figure 8. Because the duty  
cycle of PWM1 (generating VDDQ) is short, the sw itching  
point occurs far aw ay from the decision point for the VTT  
regulator, w hose duty cycle is nominally 50%.  
Figure 8. Optimal In-Phase Operation for DDR1  
Depending on the load level, the converters can operate in  
fixed-frequency PWM Mode or in a Hysteretic Mode.  
Sw itch-over from PWM to Hysteretic Mode improves the  
converters’ efficiency at light loads and prolongs battery  
run time. In Hysteretic Mode, comparators are  
synchronized to the main clock, w hich allow s seamless  
transition betw een the modes and reduces channel-to-  
channel interaction. The Hysteretic Mode can be inhibited  
independently for each channel if variable frequency  
operation is not desired.  
CLK  
When  
VDDQ  
VIN  
V
TT  
5V, 180° phase-shifted operation can be rejected for the  
reasons demonstrated in Figure 7.  
In-phase operation w ith VIN 5V is even w orse, since the  
sw itch point of either converter occurs near the sw itch  
point of the other converter, as seen in Figure 9. In this  
case, as VIN is a little higher than 5V, it tends to cause  
early termination of the VTT pulse w idth. Conversely, the  
VTT sw itch point can cause early termination of the VDDQ  
pulse w idth w hen VIN is slightly low er than 5V.  
CLK  
The FAN5236 can be configured to operate as a complete  
DDR solution. When the DDR pin is set HIGH, the second  
channel provides the capability to track the output voltage  
of the first channel. The PWM2 converter is prevented  
from going into Hysteretic Mode if the DDR pin is set HIGH.  
In DDR Mode, a buffered reference voltage (buffered  
voltage of the REF2 pin), required by DDR memory chips,  
is provided by the PG2 pin.  
Converter Modes and Synchronization  
Table 3. Converter Modes and Synchronization  
VDDQ  
DDR PWM 2 w.r.t.  
V
Mode  
VIN VIN Pin  
TT  
Pin  
HIGH  
HIGH  
LOW  
PWM1  
IN PHASE  
+90°  
DDR1 Battery  
VIN  
R to GND  
VIN  
Figure 9. Noise-Susceptible In-Phase Operation  
for DDR2  
DDR2  
DUAL  
+5V  
These problems are solved by delaying the second  
converter’s clock by 90°, as show n in Figure 10. In this  
w ay, all sw itching transitions in one converter take place  
far aw ay from the decision points of the other converter.  
ANY  
+180°  
When used as a dual converter, as show n in Figure 6,  
out-of-phase operation w ith 180-degree phase shift  
reduces input current ripple.  
CLK  
For “tw o-step” conversion (w here the VTT is converted  
f rom V DDQ as in Figure 5) used in DDR Mode, the duty  
cycle of the second converter is nominally 50% and the  
optimal phasing depends on VIN. The objective is to keep  
noise generated from the sw itching transition in one  
converter from influencing the "decision" to sw itch in the  
other converter.  
VDDQ  
V
TT  
Figure 10. Optimal 90° Phasing for DDR  
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10  
 
 
 
 
converters operate in fixed-frequency PWM Mode, as  
show n in Figure 11. This mode achieves high efficiency at  
nominal load. When the load current decreases to the  
point w here the inductor current flow s through the low er  
MOSFET in the ‘reverse’ direction, the SW node becomes  
positive and the mode is changed to hysteretic, w hich  
achieves higher efficiency at low currents by decreasing  
the effective sw itching frequency.  
Initialization and Soft Start  
Assuming EN is HIGH, FAN5236 is initialized w hen VCC  
exceeds the rising UVLO threshold. Should VCC drop  
below the UVLO threshold, an internal pow er-on reset  
function disables the chip.  
The voltage at the positive input of the error amplifier is  
limited by the voltage at the SS pin, w hich is charged w ith  
a 5µA current source. Once CSS has charged to VREF  
(0.9V) the output voltage is in regulation. The time it takes  
SS to reach 0.9V is:  
To prevent accidental mode change or "mode chatter," the  
transition from PWM to Hysteretic Mode occurs w hen the  
SW node is positive for eight consecutive clock cycles, as  
show n in Figure 11. The polarity of the SW node is  
sampled at the end of the low er MOSFET conduction time.  
At the transition betw een PWM and Hysteretic Mode, the  
upper and low er MOSFETs are turned off. The phase  
node “rings” based on the output inductor and the  
parasitic capacitance on the phase node and settles out  
at the value of the output voltage.  
0.9xCSS  
t0.9  
=
(1)  
5
w here t0.9 is in seconds if CSS is in µF.  
When SS reaches 1.5V, the pow er-good outputs are  
enabled and Hysteretic Mode is allow ed. The converter is  
forced into PWM Mode during soft-start.  
The boundary value of inductor current, w here current  
becomes discontinuous, can be estimated by the  
follow ing expression:  
Operation Mode Control  
The mode-control circuit changes the converter mode  
f rom PWM to hysteretic and vice versa, based on the  
voltage polarity of the SW node w hen the low er MOSFET  
is conducting and just before the upper MOSFET turns on.  
For continuous inductor current, the SW node is negative  
w hen the low er MOSFET is conducting and the  
(V V  
)V  
OUT  
IN  
OUT  
I
=
(2)  
LOAD( DIS )  
2F  
L
V
OUT IN  
SW  
VCORE  
PWMMode  
HystereticMode  
I L  
0
1
2
3
4
5
6
7
8
VCORE  
HystereticMode  
3
PWMMode  
I L  
0
1
2
4
5
6
7
8
Figure 11. Transitioning Between PWM and Hysteretic Mode  
Hysteretic Mode  
Conversely, the transition from Hysteretic Mode to PWM  
Mode occurs w hen the SW node is negative for eight  
consecutive cycles.  
monitored and sw itched off w hen VDS(ON) goes positive  
(current flow ing back from the load), allow ing the diode to  
block reverse conduction.  
A sudden increase in the output current causes a change  
f rom Hysteretic to PWM Mode. This load increase causes  
an instantaneous decrease in the output voltage due to  
the voltage drop on the output capacitor ESR. If the load  
causes the output voltage (as presented at VSNS) to drop  
below the hysteretic regulation level (20mV below VREF),  
the mode is changed to PWM on the next clock cycle.  
The hysteretic comparator initiates a PFM signal to turn on  
HDRV at the rising edge of the next oscillator clock, w hen  
the output voltage (at VSNS) falls below the low er  
threshold (10mV below VREF) and terminates the PFM  
signal or w hen VSNS rises over the higher threshold (5mV  
above VREF). The sw itching frequency is primarily a  
function of:  
In Hysteretic Mode, the PWM comparator and the error  
amplifier that provide control in PWM Mode are inhibited  
and the hysteretic comparator is activated. In Hysteretic  
.
.
.
Spread betw een the tw o hysteretic thresholds  
ILOAD  
Mode, the low -side MOSFET is operated as  
a
Output inductor and capacitor ESR.  
synchronous rectifier, w here the voltage across VDS(ON) is  
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11  
 
A transition back to PWM continuous conduction mode  
(CCM) mode occurs w hen the inductor current rises  
sufficiently to stay positive for eight consecutive cycles.  
This occurs w hen:  
w here VHYSTERESIS = 15mV and ESR is the equivalent  
series resistance of COUT  
.
Because of the different control mechanisms, the value of  
the load current w here transition into CCM operation takes  
place is typically higher compared to the load level at  
w hich transition into Hysteretic Mode occurs. Hysteretic  
Mode can be disabled by setting the FPWM pin LOW.  
VHYSTERESIS  
I
=
(3)  
LOAD(CCM )  
2 ESR  
Figure 12. Current Limit / Summing Circuits  
Current Processing Section  
The current through the RSENSE resistor (ISNS) is sampled  
(typically 400ns) after Q2 is turned on, as show n in  
Figure 12. That current is held and summed w ith the  
output of the error amplifier. This effectively creates a  
current-mode control loop. The resistor connected to  
ISNSx pin (RSENSE) sets the gain in the current feedback  
accurate if the voltage drop on the sw itching-node side of  
RSENSE is an accurate representation of the load current.  
When using the MOSFET as the sensing element, the  
variation of RDS(ON) causes proportional variation in the  
ISNS. This value varies from device to device and has a  
typical junction temperature coefficient of about 0.4%/°C  
(consult the MOSFET datasheet for actual values), so the  
actual current limit set point decreases proportional to  
increasing MOSFET die temperature. A factor of 1.6 in the  
current limit set point should compensate for MOSFET  
RDS(ON) variations, assuming the MOSFET heat sinking  
keeps its operating die temperature below 125°C.  
loop.  
The follow ing expression estimates  
the  
recommended value of RSENSE as a function of the  
maximum load current (ILOAD(MAX)) and the value of the  
MOSFET RDS(ON)  
:
I
RDS(ON )  
LOAD(MAX )  
RSENSE  
=
100  
(4)  
75µA  
RSENSE must, how ever, be kept higher than 700even if  
the number calculated comes out to be less than 700.  
Q2  
LDRV  
RSENSE  
ISNS  
Setting the Current Limit  
A ratio of ISNS is compared to the current established  
w hen a 0.9V internal reference drives the ILIM pin:  
PGND  
(100 + R  
)
11  
SENSE  
RLIM  
=
x
(5)  
ILOAD  
RDS(ON )  
Figure 13. Improving Current-Sensing Accuracy  
Since the tolerance on the current limit is largely  
dependent on the ratio of the external resistors, it is fairly  
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12  
 
 
Frequency Loop Compensation  
More accurate sensing can be achieved by using a  
resistor (R1) instead of the RDS(ON) of the FET, as show n  
in Figure 13. This approach causes higher losses, but  
yields greater accuracy in both VDROOP and ILIMIT. R1 is a  
low value resistor (e.g. 10m).  
Due to the implemented current-mode control, the  
modulator has a single-pole response w ith -1 slope at  
frequency determined by load:  
1
f
=
(8)  
PO  
Current limit (ILIMIT) should be set high enough to allow  
inductor current to rise in response to an output load  
transient. Typically, a factor of 1.2 is sufficient. In addition,  
since ILIMIT is a peak current cut-off value, multiply  
ILOAD(MAX) by the inductor ripple current (e.g. 25%). For  
2πROCO  
w here RO is load resistance; CO is load capacitance.  
For this type of modulator, a Type-2 compensation circuit  
is usually sufficient. To reduce the number of external  
components and simplify the design, the PWM controller  
has an internally compensated error amplifier. Figure 14  
example, in Figure 6, the target for ILIMIT  
:
ILIMIT > 1.2 x 1.25 x 1.6 x 6A  
14.5A  
(6)  
show s  
responses of  
a
Type-2 amplifier, its response, and the  
current-mode modulator and the  
a
Duty Cycle Clamp  
converter. The Type-2 amplifier, in addition to the pole at  
the origin, has a zero-pole pair that causes a flat gain  
region at frequencies betw een the zero and the pole.  
During severe load increase, the error amplifier output can  
go to its upper limit, pushing a duty cycle to almost 100%  
for significant amount of time. This could cause a large  
increase of the inductor current and lead to a long  
recovery from a transient, over-current condition, or even  
to a failure at especially high input voltages. To prevent  
this, the output of the error amplifier is clamped to a fixed  
value after tw o clock cycles if severe output voltage  
excursion is detected, limiting the maximum duty cycle to:  
1
f
f
=
=
= 6kHz  
(9)  
Z
2πR2C1  
1
= 600kHz  
(10)  
P
2ππ2C2  
This region is also associated w ith phase “bump” or  
reduced phase shift. The amount of phase-shift reduction  
depends on the w idth of the region of flat gain and has a  
maximum value of 90°. To further simplify the converter  
compensation, the modulator gain is kept independent of  
the input voltage variation by providing feedforw ard of VIN  
to the oscillator ramp. The zero frequency, the amplifier  
high-frequency gain, and the modulator gain are chosen  
to satisfy most typical applications. The crossover  
frequency appears at the point w here the modulator  
attenuation equals the amplifier high-frequency gain. The  
system designer must specify the output filter capacitors  
to position the load main pole somew here w ithin a decade  
low er than the amplifier zero frequency. With this type of  
compensation, plenty of phase margin is achieved due to  
zero-pole pair phase “boost.”  
V
2.4  
VIN  
OUT  
DC  
=
+
(7)  
MAX  
V
IN  
This is designed to not interfere w ith normal PWM  
operation. When FPWM is grounded, the duty cycle clamp  
is disabled and the maximum duty cycle is 87%.  
Gate Driver Section  
The adaptive gate control logic translates the internal PWM  
control signal into the MOSFET gate drive signals,  
providing necessary amplification, level shifting, and  
shoot-through protection. It also has functions that  
optimize the IC performance over a w ide range of  
operating conditions. Since MOSFET sw itching time can  
vary dramatically from type to type and w ith the input  
voltage, the gate control logic provides adaptive dead time  
by monitoring the gate-to-source voltages of both upper  
and low er MOSFETs. The low er MOSFET drive is not  
turned on until the gate-to-source voltage of the upper  
MOSFET has decreased to less than approximately 1V.  
Similarly, the upper MOSFET is not turned on until the gate-  
to-source voltage of the low er MOSFET has decreased to  
less than approximately 1V. This allow s a w ide variety of  
upper and low er MOSFETs to be used w ithout a concern  
for simultaneous conduction or shoot-through.  
C2  
C1  
R2  
R1  
VIN  
EA Out  
REF  
C
o
n
v
e
r
e
r
o
r
r
t
a
e
m
r
p
modul ator  
18  
14  
There must be a low -resistance, low -inductance path  
betw een the driver pin and the MOSFET gate for the  
adaptive dead-time circuit to function properly. Any delay  
along that path subtracts f rom the delay generated by the  
adaptive dead-time circuit and shoot-through may occur.  
0
f
f
f
P
P0  
Z
Figure 14. Compensation  
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13  
 
Conditional stability may occur only w hen the main load  
pole is positioned too much to the left side on the  
frequency axis due to excessive output filter capacitance.  
In this case, the ESR zero placed w ithin the 10kHz to  
50kHz range gives some additional phase boost. There is  
an opposite trend in mobile applications to keep the output  
capacitor as small as possible.  
clock cycle, the ILIM det is again reached, the over-  
current protection latch is set, disabling the regulator. If  
ILIM det does not occur betw een cycles nine and sixteen,  
normal operation is restored and the over-current circuit  
resets itself.  
If a larger inductor value or low -ESR values are required  
by the application, additional phase margin can be  
achieved by putting  
a zero at the LC crossover  
frequency. This can be achieved w ith a capacitor across  
the feedback resistor (e.g. R5 from Figure 6), as show n in  
Figure 15.  
L(OUT)  
VOUT  
R5 C(Z)  
R6  
C(OUT)  
VSEN  
Figure 15. Improving Phase Margin  
Figure 16. Over-Current Protection Waveforms  
The optimal value of C(Z) is:  
Over-Voltage / Under-Voltage Protection  
Should the VSNS voltage exceed 120% of VREF (0.9V) due  
to an upper MOSFET failure or for other reasons, the  
over-voltage protection comparator forces LDRV HIGH.  
This action actively pulls dow n the output voltage and, in  
the event of the upper MOSFET failure, eventually blow s  
the battery fuse. As soon as the output voltage drops  
below the threshold, the OVPcomparator is disengaged.  
L(OUT)×C(OUT)  
(11)  
C(Z) =  
R
Protections  
The converter output is monitored and protected against  
extreme overload, short-circuit, over-voltage, and under-  
voltage conditions.  
This OVP scheme provides a ”soft” crow bar function,  
w hich accommodates severe load transients and does  
not invert the output voltage w hen activated — a common  
problem for latched OVPschemes.  
A sustained overload on an output sets the PGx pin LOW  
and latches off the regulator on w hich the fault occurs.  
Operation can be restored by cycling the VCC voltage or  
by toggling the EN pin.  
Similarly, if an output short-circuit or severe load transient  
causes the output to drop to less than 75% of the  
regulation set point, the regulator shuts dow n.  
If VOUT drops below the under-voltage threshold, the  
regulator shuts dow n immediately.  
Over-Temperature Protection  
Over-Current Sensing  
The chip incorporates an over-temperature protection  
circuit that shuts the chip dow n if a die temperature of  
about 150°C is reached. Normal operation is restored at  
die temperature below 125°C w ith internal pow er-on reset  
asserted, resulting in a full soft-start cycle.  
If the circuit’s current limit signal (“ILIM det” in Figure 12) is  
HIGH at the beginning of a clock cycle, a pulse-skipping  
circuit is activated and HDRV is inhibited. The circuit  
continues to pulse skip in this manner for the next eight  
clock cycles. If at any time from the ninth to the sixteenth  
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14  
 
Design and Component Selection Guidelines  
As an initial step, define operating input voltage range,  
output voltage, and minimum and maximum load currents  
for the controller.  
Output Capacitor Selection  
The output capacitor serves tw o major functions in a  
sw itching pow er supply. Along w ith the inductor, it filters  
the sequence of pulses produced by the sw itcher and it  
supplies the load transient currents. The output capacitor  
requirements are usually dictated by ESR, inductor ripple  
current (I), and the allow able ripple voltage (V):  
Setting the Output Voltage  
The internal reference voltage is 0.9V. The output is  
divided dow n by a voltage divider to the VSEN pin (for  
example, R5 and R6 in Figure 5). The output voltage  
therefore is:  
V  
I  
(18)  
ESR <  
V
0.9V  
0.9V  
R6  
OUT  
(12)  
=
In addition, the capacitor’s ESR must be low enough to  
allow the converter to stay in regulation during a load  
step. The ripple voltage due to ESR for the converter in  
Figure 6 is 120mVPP. Some additional ripple appears due  
to the capacitance value itself:  
R5  
To minimize noise pickup on this node, keep the resistor to  
GND (R6) below 2K; for example, R6 at 1.82K. Then  
choose R5:  
(
1.82KΩ  
)
(
V
0.9  
)
I  
OUT  
R5 =  
= 3.24K  
(13)  
V =  
(19)  
0.9  
C
× 8× f  
SW  
OUT  
For DDR applications converting from 3.3V to 2.5V or  
other applications requiring high duty cycles, the duty  
cycle clamp must be disabled by tying the converter’s  
FPWM to GND. When converter’s FPWM is at GND, the  
converter’s maximum duty cycle is greater than 90%.  
When using as a DDR converter w ith 3.3V input, set up  
the converter for in-phase synchronization by tying the  
VIN pin to +5V.  
w hich is only about 1.5mV , for the converter in Figure 6,  
and can be ignored.  
The capacitor must also be rated to w ithstand the RMS  
current, w hich is approximately 0.3 X (I), or about  
400mA for the converter in Figure 6. High-frequency  
decoupling capacitors should be placed as close to the  
loads as physically possible.  
Input Capacitor Selection  
Output Inductor Selection  
The input capacitor should be selected by its ripple  
current rating.  
The minimum practical output inductor value keeps  
inductor current just on the boundary of continuous  
conduction at some minimum load. The industry standard  
practice is to choose the minimum current somew here  
from 15% to 35% of the nominal current. At light load, the  
controller can automatically sw itch to Hysteretic Mode of  
operation to sustain high efficiency. The follow ing  
equations help to choose the proper value of the output  
filter inductor:  
Two-Stage Converter Case  
In DDR Mode (show n in Figure 5), the VTT pow er input is  
pow ered by the VDDQ output; therefore, all of the input  
capacitor ripple current is produced by the VDDQ  
converter. A conservative estimate of the output current  
required for the 2.5V regulator is:  
V  
I
OUT  
VTT  
(14)  
(20)  
I = 2×1  
=
I
= I  
+
VDDQ  
MIN  
REGI  
ESR  
2
w here I is the inductor ripple current and VOUT is the  
maximum ripple allow ed:  
As an example, if the average IVDDQ is 3A and average  
IVTT is 1A, IVDDQ current is about 3.5A. If average input  
voltage is 16V, RMS input ripple current is:  
V
V  
V
OUT  
IN  
OUT  
L =  
×
(15)  
I
= I  
OUT(MAX)  
D D2  
f
× ∆I  
V
IN  
(21)  
SW  
RMS  
for this example, use:  
= 20,V = 2.5  
w here D is the duty cycle of the PWM1 converter:  
V
V
2.5  
OUT  
IN  
OUT  
D <  
=
(22)  
(23)  
(16)  
(17)  
I = 20%6A = 1.2A  
= 300KHz  
V
16  
IN  
f
SW  
therefore:  
therefore:  
2
2.5  
16  
2.5  
16  
L 6µH  
I
= 3.5  
= 1.49A  
RMS  
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15  
PUPPER is the upper MOSFET’s total losses and PSW and  
PCOND are the sw itching and conduction losses for a given  
MOSFET. RDS(ON) is at the maximum junction temperature  
(TJ). tS is the sw itching period (rise or fall time), show n as  
t2+t3 in Figure 17.  
Dual Converter 180° Phased  
In dual mode (show n in Figure 6), both converters  
contribute to the capacitor input ripple current. With each  
converter operating 180° out of phase, the RMS currents  
add in the follow ing fashion:  
C
CGD  
CISS  
ISS  
2
2
VDS  
I
= I  
+ I  
or  
(24)  
RMS  
RMS(1)  
RMS(2)  
2
2 D1 D1  
)
+
(
I2  
)
(
2 D2 D2  
)
2
(25)  
IRMS  
=
(
I1  
)
(
w hich, for the dual 3A converters show n in Figure 6,  
calculates to:  
ID  
IRMS = 1.4A  
(26)  
QGS  
QGD  
Power MOSFET Selection  
4.5V  
Losses in a MOSFET are the sum of its sw itching (P )  
SW  
VSP  
and conduction (PCOND) losses.  
VTH  
QG(SW)  
In typical applications, the FAN5236 converter’s output  
voltage is low w ith respect to its input voltage. Therefore,  
the low er MOSFET (Q2) is conducting the full load current  
for most of the cycle. Q2 should therefore be selected to  
minimize conduction losses, thereby selecting a MOSFET  
VGS  
t1  
t2  
t3  
t4  
t5  
Figure 17. Switching Losses and QG  
w ith low RDS(ON)  
.
VI N  
5V  
In contrast, the high-side MOSFET (Q1) has a shorter duty  
cycle and it’s conduction loss has less impact. Q1,  
how ever, sees most of the sw itching losses, so Q1’s  
primary selection criteria should be gate charge.  
CGD  
RD  
RGATE  
HDRV  
SW  
G
CGS  
High-Side Losses  
Figure 17 show s a MOSFET’s sw itching interval, w ith the  
upper graph being the voltage and current on the drain-to-  
source and the low er graph detailing VGS vs. time w ith a  
constant current charging the gate. The X-axis, therefore,  
Figure 18. Drive Equivalent Circuit  
is also representative of gate charge (QG). C = CGD  
+
ISS  
The driver’s impedance and C determine t2, w hile t3’s  
ISS  
CGS and it controls t1, t2, and t4 timing. CGD receives the  
current from the gate driver during t3 (as VDS is falling).  
The gate charge (QG) parameters on the low er graph are  
either specified or can be derived from MOSFET  
datasheets.  
period is controlled by the driver’s impedance and QGD  
.
Since most of tS occurs w hen VGS = VSP, use a constant  
current assumption for the driver to simplify the  
calculation of tS:  
Q
I
Q
G(SW)  
G(SW)  
Assuming sw itching losses are about the same for both  
the rising edge and falling edge, Q1’s sw itching losses  
occur during the shaded time w hen the MOSFET has  
voltage across it and current through it.  
t
=
=
s
V
V  
(30)  
DRIVER  
CC  
SP  
R
+ R  
GATE  
DRIVER  
Most MOSFET vendors specify QGD and QGS. QG(SW) can  
be determined as:  
These losses are given by:  
QG(SW ) = QGD + QGS QTH  
PUPPER = PSW + PCOND  
(27)  
(28)  
(31)  
w here QTH is the gate charge required to get the MOSFET  
to its threshold (VTH).  
V
×I  
DS  
L
P
=
× 2× t  
f
s
SW  
SW  
2
V
2
OUT  
(29)  
P
=
×I  
×R  
DS(ON)  
COND  
OUT  
V
IN  
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16  
 
For the high-side MOSFET, VDS = VIN, w hich can be as  
high as 20V in a typical portable application. Care should  
be taken to include the delivery of the MOSFET’s gate  
pow er (PGATE) in calculating the pow er dissipation  
required for the FAN5236:  
Layout Considerations  
Sw itching converters, even during normal operation,  
produce short pulses of current that could cause  
substantial ringing and be a source of EMI if layout  
constraints are not observed.  
P
= Q ×V × f  
G CC SW  
(32)  
G
ATE  
There are tw o sets of critical components in a DC-DC  
converter. The sw itching pow er components process  
large amounts of energy at high rates and are noise  
generators. The low -pow er components responsible for  
bias and feedback functions are sensitive to noise.  
w here QG is the total gate charge to reach VCC  
.
Low-Side Losses  
Q2, how ever, sw itches on or off w ith its parallel Schottky  
diode conducting; therefore VDS 0.5V. Since PSW is  
proportional to VDS, Q2’s sw itching losses are negligible  
and Q2 is selected based on RDS(ON) only.  
A
multi-layer printed circuit board is recommended.  
Dedicate one solid layer for a ground plane. Dedicate  
another solid layer as a pow er plane and break this plane  
into smaller islands of common voltage levels.  
Conduction losses for Q2 are given by:  
Notice all the nodes that are subjected to high-dV/dt  
voltage sw ing; such as SW, HDRV, and LDRV. All  
surrounding circuitry tends to couple the signals from  
these nodes through stray capacitance. Do not oversize  
copper traces connected to these nodes. Do not place  
traces connected to the feedback components adjacent to  
these traces. It is not recommended to use high-density  
interconnect systems, or micro-vias, on these signals.  
The use of blind or buried vias should be limited to the  
low -current signals only. The use of normal thermal vias  
is at the discretion of the designer.  
P
=
(
1 D  
)
×I  
2 ×R  
OUT DS(ON )  
(33)  
COND  
w here RDS(ON) is the RDS(ON) of the MOSFET at the highest  
operating junction temperature, and:  
V
OUT  
D =  
(34)  
V
IN  
is the minimum duty cycle for the converter.  
Since DMIN < 20% for portable computers, (1-D) 1  
produces a conservative result, further simplifying the  
calculation.  
Keep the w iring traces from the IC to the MOSFET gate  
and source as short as possible and capable of handling  
peak currents of 2A. Minimize the area w ithin the gate-  
source path to reduce stray inductance and eliminate  
parasitic ringing at the gate.  
The maximum pow er dissipation (PD(MAX)) is a function of  
the maximum allow able die temperature of the low -side  
MOSFET, the Θ , and the maximum allow able ambient  
JA  
temperature rise:  
Locate small critical components, like the soft-start  
capacitor and current sense resistors, as close as  
possible to the respective pins of the IC.  
T
T  
A(MAX)  
J(MAX)  
(35)  
P
=
D(MAX)  
ΘJA  
The FAN5236 utilizes advanced packaging technology  
w ith lead pitch of 0.6mm. High-performance analog  
semiconductors utilizing narrow lead spacing may require  
special considerations in design and manufacturing. It is  
critical to maintain proper cleanliness of the area  
surrounding these devices.  
Θ
JA  
depends primarily on the amount of PCB area that can  
be devoted to heat sinking (see ON Semiconductor  
Application Note AN-1029 Maximum Power  
Enhancement Techniques for SO-8 Power MOSFETs).  
www.onsemi.com  
17  
Physical Dimensions  
Figure 19. 28-Lead, Thin Shrink Outline Package  
Package drawings are provided as a service to customers considering ON Semiconductor components. Drawings may change  
in any manner without notice. Please note the revision and/or date on the drawing and contact an ON Semiconductor  
representative to verify or obtain the most recent revision. Package specifications do not expand the terms of ON  
Semiconductor’s worldwide terms and conditions, specifically the warranty therein, which covers ON Semiconductor  
products.  
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18  
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