ON CS5165GDWR16 5−bit synchronous cpu buck controller Datasheet

CS5165
5−Bit Synchronous CPU
Buck Controller
The CS5165 synchronous 5−bit NFET buck controller is optimized to
manage the power of the next generation Pentium II processors. It’s
V2™ control architecture delivers the fastest transient response (100 ns),
and best overall voltage regulation in the industry today. It’s feature rich
design gives end users the maximum flexibility to implement the best
price/performance solutions for their end products.
The CS5165 has been carefully crafted to maximize performance and
protect the processor during operation. It has a 5−bit DAC on board that
holds a ±1.0% tolerance over temperature. Its on board programmable
Soft Start insures a control start up, and the FET nonoverlap circuitry
ensures that both FETs do not conduct simultaneously.
The on board oscillator can be programmed up to 1.0 MHz to give
the designer maximum flexibility in choosing external components
and setting systems costs.
The CS5165 protects the processor during potentially catastrophic
events like overvoltage (OVP) and short circuit. The OVP feature is
part of the V2 architecture and does not require any additional
components. During short circuit, the controller pulses the MOSFETs
in a “hiccup” mode (3.0% duty cycle) until the fault is removed. With
this method, the MOSFETs do not overheat or self destruct.
The CS5165 is designed for use in both single processor desktop and
multiprocessor workstation and server applications. The CS5165’s
current sharing capability allows the designer to build multiple
parallel and redundant power solutions for multiprocessor systems.
The CS5165 contains other control and protection features such as
Power Good, ENABLE, and adaptive voltage positioning. It is
available in a 16 lead SOIC wide body package.
Features
• V2 Control Topology
• Dual N−Channel Design
• 100 ns Controller Transient Response
• Excess of 1.0 MHz Operation
• 5−Bit DAC with 1.0% Tolerance
• Power Good Output With Internal Delay
• Enable Input Provides Micropower Shutdown Mode
• 5.0 V & 12 V Operation
• Adaptive Voltage Positioning
• Remote Sense Capability
• Current Sharing Capability
• VCC Monitor
• Hiccup Mode Short Circuit Protection
• Overvoltage Protection (OVP)
• Programmable Soft Start
• 150 ns PWM Blanking
• 65 ns FET Nonoverlap Time
• 40 ns Gate Rise and Fall Times (3.3 nF Load)
© Semiconductor Components Industries, LLC, 2001
July, 2006 − Rev. 4
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MARKING
DIAGRAM
16
16
1
CS5165
SO−16L
DW SUFFIX
CASE 751G
AWLYYWW
1
A
WL, L
YY, Y
WW, W
= Assembly Location
= Wafer Lot
= Year
= Work Week
PIN CONNECTIONS
VID0
VID1
VID2
VID3
SS
VID4
COFF
ENABLE
1
16
VFB
COMP
LGND
PWRGD
GATE(L)
PGND
GATE(H)
VCC
ORDERING INFORMATION
Device
1
Package
Shipping
CS5165GDW16
SO−16L
46 Units/Rail
CS5165GDWR16
SO−16L
1000 Tape & Reel
Publication Order Number:
CS5165/D
CS5165
5.0 V
12 V
1200 μF/10 V × 3
1.0 μF
IRL3103
0.1 μF
0.1 μF
330 pF
VCC
SS
COMP
COFF
VID4
PCB trace
6.0 mΩ
VCC
GATE(H)
1200 μF/10 V × 5
GATE(L)
VSS
IRL3103
PGND
VID3
VID2
1.2 μH
PWRGD
ENABLE
LGND
CS5165
VID1
VID0
VID0
3.3 k
VFB
VID1
1000 pF
Pentium II
System
VID2
PWRGD
VID3
ENABLE
VID4
Figure 1. Application Diagram, 5.0 V to 2.8 V @ 14.2 A for 300 MHz Pentium II
ABSOLUTE MAXIMUM RATINGS*
Rating
Operating Junction Temperature, TJ
Lead Temperature Soldering:
Reflow: (SMD styles only) (Note 1)
Storage Temperature Range, TS
ESD Susceptibility (Human Body Model)
1. 60 second maximum above 183°C.
*The maximum package power dissipation must be observed.
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2
Value
Unit
0 to 150
°C
230 peak
°C
−65 to +150
°C
2.0
kV
CS5165
ABSOLUTE MAXIMUM RATINGS
Pin Name
Pin Symbol
VMAX
VMIN
ISOURCE
ISINK
IC Power Input
VCC
16 V
−0.3 V
N/A
1.5 A peak, 200 mA DC
Soft Start Capacitor
SS
6.0 V
−0.3 V
200 μA
10 μA
Compensation Capacitor
COMP
6.0 V
−0.3 V
10 mA
1.0 mA
Voltage Feedback Input
VFB
6.0 V
−0.3 V
10 μA
10 μA
Off−Time Capacitor
COFF
6.0 V
−0.3 V
1.0 mA
50 mA
Voltage ID DAC Inputs
VID0−VID4
6.0 V
−0.3 V
1.0 mA
10 μA
High−Side FET Driver
GATE(H)
16 V
−0.3 V
1.5 A peak, 200 mA DC
1.5 A peak, 200 mA DC
Low−Side FET Driver
GATE(L)
16 V
−0.3 V
1.5 A peak, 200 mA DC
1.5 A peak, 200 mA DC
Enable Input
ENABLE
6.0 V
−0.3 V
100 μA
1.0 mA
Power Good Output
PWRGD
6.0 V
−0.3 V
10 μA
30 mA
Power Ground
PGND
0V
0V
1.5 A peak, 200 mA DC
N/A
Logic Ground
LGND
0V
0V
100 mA
N/A
ELECTRICAL CHARACTERISTICS (0°C < TA < +70°C; 0°C < TJ < +125°C; 8.0 V < VCC < 14 V; 2.8 DAC Code:
(VID4 = VID2 = VID1 = VID0 = 1; VID3 = 0); CGATE(H) and CGATE(L) = 3.3 nF; COFF = 330 pF; CSS = 0.1 μF, unless otherwise specified.)
Characteristic
Test Conditions
Min
Typ
Max
Unit
VCC Supply Current
Operating
1.0 V < VFB < VDAC (max on−time)
No Loads on GATE(H) and GATE(L)
−
12
20
mA
Sleep Mode
ENABLE = 0 V
−
300
600
μA
VCC Monitor
Start Threshold
GATE(H) switching
3.75
3.95
4.15
V
Stop Threshold
GATE(H) not switching
3.65
3.87
4.05
V
Hysteresis
Start−Stop
−
80
−
mV
VFB Bias Current
VFB = 0 V
−
0.1
1.0
μA
COMP Source Current
COMP = 1.2 V to 3.6 V; VFB = 2.7 V
15
30
60
μA
COMP CLAMP Voltage
VFB = 2.7 V, Adjust COMP voltage for Comp
current = 50 μA
0.85
1.0
1.15
V
COMP Clamp Current
COMP = 0 V
0.4
1.0
1.6
mA
COMP Sink Current
VCOMP = 1.2 V; VFB = 3.0 V; VSS > 2.5 V
180
400
800
μA
Open Loop Gain
Note 2
50
60
−
dB
Unity Gain Bandwidth
Note 2
0.5
2.0
−
MHz
PSRR @ 1.0 kHz
Note 2
60
85
−
dB
High Voltage at 100 mA
Measure VCC − GATE
−
1.2
2.0
V
Low Voltage at 100 mA
Measure GATE
−
1.0
1.5
V
Rise Time
1.6 V < GATE < (VCC − 2.5 V)
−
40
80
ns
Fall Time
(VCC − 2.5 V) > GATE > 1.6 V
−
40
80
ns
GATE(H) to GATE(L) Delay
GATE(H) < 2.0 V; GATE(L) > 2.0 V
30
65
100
ns
GATE(L) to GATE(H) Delay
GATE(L) < 2.0 V; GATE(H) > 2.0 V
30
65
100
ns
GATE pull−down
Resistor to PGND, Note 2
20
50
115
kΩ
Error Amplifier
GATE(H) and GATE(L)
2. Guaranteed by design, not 100% tested in production.
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CS5165
ELECTRICAL CHARACTERISTICS (continued) (0°C < TA < +70°C; 0°C < TJ < +125°C; 8.0 V < VCC < 14 V; 2.8 DAC Code:
(VID4 = VID2 = VID1 = VID0 = 1; VID3 = 0); CGATE(H) and CGATE(L) = 3.3 nF; COFF = 330 pF; CSS = 0.1 μF, unless otherwise specified.)
Characteristic
Test Conditions
Min
Typ
Max
Unit
Fault Protection
SS Charge Time
VFB = 0 V
1.6
3.3
5.0
ms
SS Pulse Period
VFB = 0 V
25
100
200
ms
SS Duty Cycle
(Charge Time/Period) × 100
1.0
3.3
6.0
%
SS COMP Clamp Voltage
VFB = 2.7 V; VSS = 0 V
0.50
0.95
1.10
V
VFB Low Comparator
Increase VFB till no SS pulsing and normal Off−time
0.9
1.0
1.1
V
Transient Response
VFB = 1.2 to 5.0 V. 500 ns after GATE(H)
(after Blanking time) to GATE(H) = (VCC −1.0 V)
to 1.0 V
−
100
150
ns
Minimum Pulse Width
(Blanking Time)
Drive VFB. 1.2 to 5.0 V upon GATE(H) rising edge
(> VCC − 1.0 V), measure GATE(H) pulse width
50
150
250
ns
Normal Off−Time
VFB = 2.7 V
1.0
1.6
2.3
μs
Extended Off−Time
VSS = VFB = 0 V
5.0
8.0
12.0
μs
Time−Out Time
VFB = 2.7 V, Measure GATE(H) Pulse Width
10
30
50
μs
Fault Duty Cycle
VFB = 0V
30
50
70
%
ENABLE Threshold
GATE(H) Switching
0.8
1.15
1.30
V
Shutdown delay (Note 3)
ENABLE−to−GATE(H) < 2.0 V
−
3.0
−
μs
Pull−up Current
ENABLE = 0 V
3.0
7.0
15
μA
Pull−up Voltage
No load on ENABLE pin
1.30
1.8
3.0
V
Input Resistance
ENABLE = 5.0 V, R = (5.0 V − VPULLUP)/IENABLE
10
20
50
kΩ
Low to High Delay
VFB = (0.8 × VDAC) to VDAC
30
65
110
μs
High to Low Delay
VFB = VDAC to (0.8 × VDAC)
30
75
120
μs
Output Low Voltage
VFB = 2.4 V, IPWRGD = 500 μA
−
0.2
0.3
V
Sink Current Limit
VFB = 2.4 V, PWRGD = 1.0 V
0.5
4.0
15.0
mA
PWM Comparator
COFF
Time−Out Timer
Enable Input
Power Good Output
3. Guaranteed by design, not 100% tested in production.
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CS5165
ELECTRICAL CHARACTERISTICS (continued) (0°C < TA < +70°C; 0°C < TJ < +125°C; 8.0 V < VCC < 14 V; 2.8 DAC Code:
(VID4 = VID2 = VID1 = VID0 = 1; VID3 = 0); CGATE(H) and CGATE(L) = 3.3 nF; COFF = 330 pF; CSS = 0.1 μF, unless otherwise specified.)
Characteristic
Test Conditions
Min
Typ
Max
Unit
−1.0
−
+1.0
%
Voltage Identification DAC
Accuracy (all codes except 11111)
Measure VFB = COMP (COFF = 0 V)
25°C ≤ TJ ≤ 125°C; VCC = 12 V
VID4
VID3
VID2
VID1
VID0
1
0
0
0
0
−
3.505
3.540
3.575
V
1
0
0
0
1
−
3.406
3.440
3.474
V
1
0
0
1
0
−
3.307
3.340
3.373
V
1
0
0
1
1
−
3.208
3.240
3.272
V
1
0
1
0
0
−
3.109
3.140
3.171
V
1
0
1
0
1
−
3.010
3.040
3.070
V
1
0
1
1
0
−
2.911
2.940
2.969
V
1
0
1
1
1
−
2.812
2.840
2.868
V
1
1
0
0
0
−
2.713
2.740
2.767
V
1
1
0
0
1
−
2.614
2.640
2.666
V
1
1
0
1
0
−
2.515
2.540
2.565
V
1
1
0
1
1
−
2.416
2.440
2.464
V
1
1
1
0
0
−
2.317
2.340
2.363
V
1
1
1
0
1
−
2.218
2.240
2.262
V
1
1
1
1
0
−
2.119
2.140
2.161
V
0
0
0
0
0
−
2.069
2.090
2.111
V
0
0
0
0
1
−
2.020
2.040
2.060
V
0
0
0
1
0
−
1.970
1.990
2.010
V
0
0
0
1
1
−
1.921
1.940
1.959
V
0
0
1
0
0
−
1.871
1.890
1.909
V
0
0
1
0
1
−
1.822
1.840
1.858
V
0
0
1
1
0
−
1.772
1.790
1.808
V
0
0
1
1
1
−
1.723
1.740
1.757
V
0
1
0
0
0
−
1.673
1.690
1.707
V
0
1
0
0
1
−
1.624
1.640
1.656
V
0
1
0
1
0
−
1.574
1.590
1.606
V
0
1
0
1
1
−
1.525
1.540
1.555
V
0
1
1
0
0
−
1.475
1.490
1.505
V
0
1
1
0
1
−
1.426
1.440
1.455
V
0
1
1
1
0
−
1.376
1.390
1.405
V
0
1
1
1
1
−
1.327
1.340
1.353
V
1
1
1
1
1
−
1.223
1.247
1.273
V
Input Threshold
VID4, VID3, VID2, VID1, VID0
1.000
1.250
2.400
V
Input Pull−up Resistance
VID4, VID3, VID2, VID1, VID0
25
50
100
kΩ
4.85
5.00
5.15
V
Input Pull−up Voltage
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CS5165
ELECTRICAL CHARACTERISTICS (continued) (0°C < TA < +70°C; 0°C < TJ < +125°C; 8.0 V < VCC < 14 V; 2.8 DAC Code:
(VID4 = VID2 = VID1 = VID0 = 1; VID3 = 0); CGATE(H) and CGATE(L) = 3.3 nF; COFF = 330 pF; CSS = 0.1 μF, unless otherwise specified.)
Lower Threshold
Threshold Accuracy
Min
Typ
−12
−8.5
Upper Threshold
Max
Min
Typ
Max
Unit
−5.0
5.0
8.5
12
%
DAC CODE
% of Nominal DAC Output
VID4
VID3
VID2
VID1
VID0
1
0
0
0
0
3.115
3.239
3.363
3.717
3.841
3.965
V
1
0
0
0
1
3.027
3.148
3.268
3.612
3.732
3.853
V
1
0
0
1
0
2.939
3.056
3.173
3.507
3.624
3.741
V
1
0
0
1
1
2.851
2.965
3.078
3.402
3.515
3.629
V
1
0
1
0
0
2.763
2.873
2.983
3.297
3.407
3.517
V
1
0
1
0
1
2.675
2.782
2.888
3.192
3.298
3.405
V
1
0
1
1
0
2.587
2.690
2.793
3.087
3.190
3.293
V
1
0
1
1
1
2.499
2.599
2.698
2.982
3.081
3.181
V
1
1
0
0
0
2.411
2.507
2.603
2.877
2.973
3.069
V
1
1
0
0
1
2.323
2.416
2.508
2.772
2.864
2.957
V
1
1
0
1
0
2.235
2.324
2.413
2.667
2.756
2.845
V
1
1
0
1
1
2.147
2.233
2.318
2.562
2.647
2.733
V
1
1
1
0
0
2.059
2.141
2.223
2.457
2.539
2.621
V
1
1
1
0
1
1.971
2.050
2.128
2.352
2.430
2.509
V
1
1
1
1
0
1.883
1.958
2.033
2.250
2.322
2.397
V
0
0
0
0
0
1.839
1.912
1.986
2.195
2.268
2.341
V
0
0
0
0
1
1.795
1.867
1.938
2.142
2.213
2.285
V
0
0
0
1
0
1.751
1.821
1.810
2.090
2.159
2.229
V
0
0
0
1
1
1.707
1.775
1.843
2.037
2.105
2.173
V
0
0
1
0
0
1.663
1.729
1.796
1.985
2.051
2.117
V
0
0
1
0
1
1.619
1.684
1.748
1.932
1.996
2.061
V
0
0
1
1
0
1.575
1.638
1.701
1.880
1.942
2.005
V
0
0
1
1
1
1.531
1.592
1.653
1.827
1.888
1.949
V
0
1
0
0
0
1.487
1.546
1.606
1.775
1.834
1.893
V
0
1
0
0
1
1.443
1.501
1.558
1.722
1.779
1.837
V
0
1
0
1
0
1.399
1.455
1.511
1.670
1.725
1.781
V
0
1
0
1
1
1.355
1.409
1.463
1.617
1.671
1.724
V
0
1
1
0
0
1.311
1.363
1.416
1.565
1.617
1.669
V
0
1
1
0
1
1.267
1.318
1.368
1.512
1.562
1.613
V
0
1
1
1
0
1.223
1.272
1.321
1.460
1.508
1.557
V
0
1
1
1
1
1.179
1.226
1.273
1.407
1.454
1.501
V
1
1
1
1
1
1.097
1.141
1.185
1.309
1.353
1.397
V
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CS5165
PACKAGE PIN DESCRIPTION
PACKAGE PIN #
SO−16L
PIN SYMBOL
FUNCTION
1, 2, 3, 4, 6
VID0−VID4
Voltage ID DAC input pins. These pins are internally pulled up to 5.0 V if left open. VID4
selects the DAC range. When VID4 is high (logic one), the Error Amp reference range is
2.14 V to 3.45 V with 100 mV increments. When VID4 is low (logic zero), the Error Amp
reference voltage 1.34 V to 2.09 V with 50 mV increments.
5
SS
Soft Start Pin. A capacitor from this pin to LGND sets the Soft Start and fault timing.
7
COFF
Off−Time Capacitor Pin. A capacitor from this pin to LGND sets both the normal and
extended off time.
8
ENABLE
9
VCC
10
GATE(H)
11
PGND
12
GATE(L)
Low Side Synchronous FET driver pin.
13
PWRGD
Power Good Output. Open collector output drives low when VFB is out of regulation. Active when ENABLE input is low.
14
LGND
Reference ground. All control circuits are referenced to this pin.
15
COMP
Error Amp output. PWM Comparator reference input. A capacitor to LGND provides Error
Amp compensation.
16
VFB
Output Enable Input. This pin is internally pulled up to 1.8 V. A logic Low (< 0.8) on this
pin disables operation and places the CS5165 into a low current sleep mode.
Input Power Supply Pin.
High Side Switch FET driver pin.
High current ground for the GATE(H) and GATE(L) pins.
Error Amp, PWM Comparator, and Low VFB Comparator feedback input.
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CS5165
VCC
7.0 μA
20 k
ENABLE
−
VCC Monitor
−
VCC
+
3.95 V
3.87V
Circuit Bias
+
1.25 V
VGATE(H)
Enable
Comparator
5.0 V
−
SS Low
Comparator
+
60 μA
0.7 V
SS
+
2.0 μA
S
Q
FAULT
FAULT
PGND
FAULT
Latch
SS High
Comparator
VCC
−
VCC1
Error Amplifier
VID1
VGATE(L)
−
VID3
VID4
−8.5%
−
−
PWM COMP
+
Blanking
PWM
Comparator
+8.5%
+
PGND
+
5 BIT
DAC
VID2
−
Maximum
On−Time
Timeout
R
Q
S
Q
Normal
Off−Time
Timeout
+
Extended
Off−Time
Timeout
PWM
Latch
Off−Time
Timeout
GATE(H) = ON
GATE(H) = OFF
COFF
One Shot
R
S
65 μs
Delay
VFB
Time−Out
Timer
(30 μs)
−
+
LGND
Q
2.5 V
COMP
VID0
PWRGD
R
1.0 V
VFB Low
Comparator
Figure 2. Block Diagram
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Edge Triggered
COFF
Q
CS5165
TYPICAL PERFORMANCE CHARACTERISTICS
180
160
160
140
140
Risetime (ns)
200
180
120
120
100
100
80
60
60
VCC = 12 V
40
0
2000 4000
TA = 25°C
20
0
6000 8000 10000 12000 14000 16000
0
2000 4000
Load Capacitance (pF)
Figure 3. GATE(L) Risetime vs. Load Capacitance
Figure 4. GATE(H) Risetime vs. Load Capacitance
0.04
200
DAC Output Voltage Deviation (%)
180
160
120
100
80
60
40
VCC = 12 V
20
TA = 25°C
−0.02
−0.04
−0.06
−0.08
−0.1
6000 8000 10000 12000 14000 16000
0
20
Load Capacitance (pF)
0.04
0.05
0.02
0
DAC Output Voltage Setting (V)
DAC Output Voltage Setting (V)
Figure 7. Percent Output Error vs. DAC Voltage
Setting, VCC = 12 V, TA = 255C, VID4 = 0
Figure 8. Percent Output Error vs. DAC Output
Voltage Setting VCC = 12 V, TA = 255C, VID4 = 1
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3.54
3.44
3.34
3.24
2.14
2.09
2.04
1.99
1.89
1.94
1.84
1.79
1.69
1.74
−0.25
1.64
−0.10
1.59
−0.20
1.54
−0.08
1.49
120
−0.15
3.14
−0.06
1.44
100
−0.10
3.04
−0.04
1.39
80
−0.05
2.44
−0.02
2.34
Output Error (%)
0
1.34
60
Figure 6. DAC Output Voltage vs. Temperature,
DAC Code = 10111, VCC = 12 V
2.24
Figure 5. GATE(H) & GATE(L) Falltime vs. Load
Capacitance
Output Error (%)
40
Junction Temperature (°C)
2.94
2000 4000
0
2.84
0
0.02
2.54
Falltime (ns)
140
0
6000 8000 10000 12000 14000 16000
Load Capacitance (pF)
2.74
0
VCC = 12 V
40
TA = 25°C
20
80
2.64
Risetime (ns)
200
CS5165
APPLICATIONS INFORMATION
THEORY OF OPERATION
The error signal loop can have a low crossover frequency,
since transient response is handled by the ramp signal loop.
The main purpose of this ‘slow’ feedback loop is to provide
DC accuracy. Noise immunity is significantly improved,
since the error amplifier bandwidth can be rolled off at a low
frequency. Enhanced noise immunity improves remote
sensing of the output voltage, since the noise associated with
long feedback traces can be effectively filtered.
Line and load regulation are drastically improved because
there are two independent voltage loops. A voltage mode
controller relies on a change in the error signal to
compensate for a deviation in either line or load voltage.
This change in the error signal causes the output voltage to
change corresponding to the gain of the error amplifier,
which is normally specified as line and load regulation. A
current mode controller maintains fixed error signal under
deviation in the line voltage, since the slope of the ramp
signal changes, but still relies on a change in the error signal
for a deviation in load. The V2 method of control maintains
a fixed error signal for both line and load variation, since the
ramp signal is affected by both line and load.
V2 Control Method
The V2 method of control uses a ramp signal that is
generated by the ESR of the output capacitors. This ramp is
proportional to the AC current through the main inductor
and is offset by the value of the DC output voltage. This
control scheme inherently compensates for variation in
either line or load conditions, since the ramp signal is
generated from the output voltage itself. This control
scheme differs from traditional techniques such as voltage
mode, which generates an artificial ramp, and current mode,
which generates a ramp from inductor current.
PWM
Comparator
GATE(H)
C
GATE(L)
−
+
Ramp
Signal
Output
Voltage
Feedback
Error
Amplifier
COMP
Error
Signal
V2
Constant Off Time
To maximize transient response, the CS5165 uses a
constant off time method to control the rate of output pulses.
During normal operation, the off time of the high side switch
is terminated after a fixed period, set by the COFF capacitor.
To maintain regulation, the V2 control loop varies switch on
time. The PWM comparator monitors the output voltage
ramp, and terminates the switch on time.
Constant off time provides a number of advantages.
Switch duty cycle can be adjusted from 0 to 100% on a pulse
by pulse basis when responding to transient conditions. Both
0% and 100% duty cycle operation can be maintained for
extended periods of time in response to load or line
transients. PWM slope compensation to avoid
sub−harmonic oscillations at high duty cycles is avoided.
Switch on time is limited by an internal 30 μs (typical)
timer, minimizing stress to the power components.
−
E
+
Reference
Voltage
Figure 9. V2 Control Diagram
The
control method is illustrated in Figure 9. The
output voltage is used to generate both the error signal and
the ramp signal. Since the ramp signal is simply the output
voltage, it is affected by any change in the output regardless
of the origin of that change. The ramp signal also contains
the DC portion of the output voltage, which allows the
control circuit to drive the main switch to 0% or 100% duty
cycle as required.
A change in line voltage changes the current ramp in the
inductor, affecting the ramp signal, which causes the V2
control scheme to compensate the duty cycle. Since the
change in inductor current modifies the ramp signal, as in
current mode control, the V2 control scheme has the same
advantages in line transient response.
A change in load current will have an affect on the output
voltage, altering the ramp signal. A load step immediately
changes the state of the comparator output, which controls
the main switch. Load transient response is determined only
by the comparator response time and the transition speed of
the main switch. The reaction time to an output load step has
no relation to the crossover frequency of the error signal
loop, as in traditional control methods.
Programmable Output
The CS5165 is designed to provide two methods for
programming the output voltage of the power supply. A five
bit on board digital to analog converter (DAC) is used to
program the output voltage within two different ranges. The
first range is 2.14 V to 3.54 V in 100 mV steps, the second
is 1.34 V to 2.09 V in 50 mV steps, depending on the digital
input code. If all five bits are left open, the CS5165 enters
adjust mode. In adjust mode, the designer can choose any
output voltage by using resistor divider feedback to the VFB
pin, as in traditional controllers. The CS5165 is specifically
designed to meet or exceed Intel’s Pentium II specifications.
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CS5165
Start Up
Until the voltage on the VCC supply pin exceeds the 3.95 V
monitor threshold, the Soft Start and GATE pins are held
low. The FAULT latch is reset (no Fault condition). The
output of the error amplifier (COMP) is pulled up to 1.0 V by
the comparator clamp. When the VCC pin exceeds the
monitor threshold, the GATE(H) output is activated, and the
Soft Start capacitor begins charging. The GATE(H) output
will remain on, enabling the NFET switch, until terminated
by either the PWM comparator, or the maximum on time
timer.
If the maximum on time is exceeded before the regulator
output voltage achieves the 1.0 V level, the pulse is
terminated. The GATE(H) pin drives low, and the GATE(L)
pin drives high for the duration of the extended off time. This
time is set by the time out timer and is approximately equal
to the maximum on time, resulting in a 50% duty cycle. The
GATE(L) pin will then drive low, the GATE(H) pin will
drive high, and the cycle repeats.
When regulator output voltage achieves the 1.0 V level
present at the COMP pin, regulation has been achieved and
normal off time will ensue. The PWM comparator
terminates the switch on time, with off time set by the COFF
capacitor. The V2 control loop will adjust switch duty cycle
as required to ensure the regulator output voltage tracks the
output of the error amplifier.
The Soft Start and COMP capacitors will charge to their
final levels, providing a controlled turn on of the regulator
output. Regulator turn on time is determined by the COMP
capacitor charging to its final value. Its voltage is limited by
the Soft Start COMP clamp and the voltage on the Soft Start
pin.
M 250 μs
Trace 1− Regulator Output Voltage (1.0 V/div.)
Trace 2− Inductor Switching Node (2.0 V/div.)
Trace 3− 12 V Input (VCC) (5.0 V/div.)
Trace 4− 5.0 V Input (1.0 V/div.)
Figure 10. Demonstration Board Startup in Response
to Increasing 12 V and 5.0 V Input Voltages. Extended
Off Time is Followed by Normal Off Time Operation
when Output Voltage Achieves Regulation to the Error
Amplifier Output.
Power Supply Sequencing
Trace 1− Soft Start Pin (2.0 V/div.)
The CS5165 offers inherent protection from undefined
start up conditions, regardless of the 12 V and 5.0 V supply
power up sequencing. The turn on slew rates of the 12 V and
5.0 V power supplies can be varied over wide ranges without
affecting the output voltage or causing detrimental effects to
the buck regulator.
Trace 2− COMP PIn (error amplifier output) (1.0 V/div.)
Trace 4− Regulator Output Voltage (1.0 V/div.)
Figure 11. Demonstration Board Startup Waveforms
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CS5165
M 10.0 μs
Trace 1− GATE(H) (10 V/div.)
Trace 2− Inductor Switching Node (5.0 V/div.)
Trace 3− Output Inductor Ripple Current (2.0 A/div.)
Trace 4− VOUT ripple (20 mV/div.)
Trace 1− Regulator Output Voltage (1.0 V/div.)
Trace 2− Inductor Switching Node (5.0 V/div.)
Figure 12. Demonstration Board Enable Startup
Waveforms
Figure 14. Normal Operation Showing Output
Inductor Ripple Current and Output Voltage
Ripple, ILOAD = 14 A, VOUT = +2.84 V (DAC = 10111)
Normal Operation
During normal operation, switch off time is constant and
set by the COFF capacitor. Switch on time is adjusted by the
V2 control loop to maintain regulation. This results in
changes in regulator switching frequency, duty cycle, and
output ripple in response to changes in load and line. Output
voltage ripple will be determined by inductor ripple current
working and the ESR of the output capacitors (see Figures
13 and 14).
Transient Response
The CS5165 V2 control loop’s 100 ns reaction time
provides unprecedented transient response to changes in
input voltage or output current. Pulse by pulse adjustment of
duty cycle is provided to quickly ramp the inductor current
to the required level. Since the inductor current cannot be
changed instantaneously, regulation is maintained by the
output capacitor(s) during the time required to slew the
inductor current.
Overall load transient response is further improved
through a feature called “Adaptive Voltage Positioning”.
This technique pre−positions the output capacitors voltage
to reduce total output voltage excursions during changes in
load.
Holding tolerance to 1.0% allows the error amplifiers
reference voltage to be targeted +40 mV high without
compromising DC accuracy. A “Droop Resistor”,
implemented through a PC board trace, connects the Error
Amps feedback pin (VFB) to the output capacitors and load
and carries the output current. With no load, there is no DC
drop across this resistor, producing an output voltage
tracking the Error amps, including the +40 mV offset. When
the full load current is delivered, an 80 mV drop is developed
across this resistor. This results in output voltage being
offset −40 mV low.
The result of Adaptive Voltage Positioning is that
additional margin is provided for a load transient before
reaching the output voltage specification limits. When load
Trace 1− GATE(H) (10 V/div.)
Trace 2− Inductor Switching Node (5.0 V/div.)
Trace 3− Output Inductor Ripple Current (2.0 A/div.)
Trace 4− VOUT ripple (20 mV/div.)
Figure 13. Normal Operation Showing Output
Inductor Ripple Current and Output Voltage
Ripple, 0.5 A Load, VOUT = +2.84 V (DAC = 10111)
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CS5165
current suddenly increases from its minimum level, the
output capacitor is pre−positioned +40 mV. Conversely,
when load current suddenly decreases from its maximum
level, the output capacitor is pre−positioned −40 mV (see
Figures 15, 16, and 17). For best Transient Response, a
combination of a number of high frequency and bulk output
capacitors are usually used.
If the Maximum On−Time is exceeded while responding
to a sudden increase in Load current, a normal off−time
occurs to prevent saturation of the output inductor.
Trace 1− GATE(H) (10 V/div.)
Trace 2− Inductor Switching Node (5.0 V/div.)
Trace 3− Load Current (5.0 A/div)
Trace 4− VOUT (100 mV/div.)
Figure 17. Output Voltage Transient Response to a 14
A Load Turn−Off, VOUT = +2.84 V (DAC = 10111)
PROTECTION AND MONITORING FEATURES
Short Circuit Protection
A lossless hiccup mode short circuit protection feature is
provided, requiring only the Soft Start capacitor to
implement. If a short circuit condition occurs the VFB low
comparator sets the FAULT latch. This causes the top FET
to shut off, disconnecting the regulator from it’s input
voltage. The Soft Start capacitor is then slowly discharged
by a 2.0 μA current source until it reaches it’s lower 0.7 V
threshold. The regulator will then attempt to restart
normally, operating in it’s extended off time mode with a
50% duty cycle, while the Soft Start capacitor is charged
with a 60 μA charge current.
If the short circuit condition persists, the regulator output
will not achieve the 1.0 V low VFB comparator threshold
before the Soft Start capacitor is charged to it’s upper 2.5 V
threshold. If this happens the cycle will repeat itself until the
short is removed. The Soft Start charge/discharge current
ratio sets the duty cycle for the pulses (2.0 μA/60 μA =
3.3%), while actual duty cycle is half that due to the
extended off time mode (1.65%).
This protection feature results in less stress to the
regulator components, input power supply, and PC board
traces than occurs with constant current limit protection (see
Figures 18 and 19).
If the short circuit condition is removed, output voltage
will rise above the 1.0 V level, preventing the FAULT latch
from being set, allowing normal operation to resume.
Trace 3− Load Current (5.0 A/10 mV/div.)
Trace 4− VOUT (100 mV/div.)
Figure 15. Output Voltage Transient Response to
a 14 A Load Pulse, VOUT = +2.84 V (DAC = 10111)
Trace 1− GATE(H) (10 V/div.)
Trace 2− Inductor Switching Node (5.0 V/div.)
Trace 3− Load Current (5.0 A/div)
Trace 4− VOUT (100 mV/div.)
Figure 16. Output Voltage Transient Response to a
14 A Load Step, VOUT = +2.84 V (DAC = 10111)
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CS5165
implement the OVP function. If a dedicated OVP output is
required, it can be implemented using the circuit in Figure
22. In this figure the OVP signal will go high (overvoltage
condition), if the output voltage (VCORE) exceeds 20% of
the voltage set by the particular DAC code and provided that
PWRGD is low. It is also required that the overvoltage
condition be present for at least the PWRGD delay time for
the OVP signal to be activated. The resistor values shown in
Figure 22 are for VDAC = +2.8 V (DAC = 10111). The VOVP
(overvoltage trip−point) can be set using the following
equation:
ǒ
VOVP + VBEQ3 1 ) R2
R1
M 25.0 ms
Trace 4− 5.0 V Supply Voltage (2.0 V/div.)
Ǔ
Trace 3− Soft Start Timing Capacitor (1.0 V/div.)
Trace 2− Inductor Switching Node (2.0 V/div.)
Figure 18. Demonstration Board Hiccup Mode Short
Circuit Protection. Gate Pulses are Delivered While
the Soft Start Capacitor Charges, and Cease During
Discharge
M 10.0 μs
Trace 4− 5.0 V from PC Power Supply (5.0 V/div.)
Trace 1− Regulator Output Voltage (1.0 V/div.)
Trace 2− Inductor Switching Node 5.0 V/div.)
Figure 20. OVP Response to an Input−to−Output
Short Circuit by Immediately Providing 0% Duty
Cycle, Crow−Barring the Input Voltage to Ground
M 50.0 μs
Trace 4− 5.0 V from PC Power Supply (2.0 V/div.)
Trace 2− Inductor Switching Node (2.0 V/div.)
Figure 19. Demonstration Board Startup with
Regulator Output Shorted To Ground
Overvoltage Protection
Overvoltage protection (OVP) is provided as result of the
normal operation of the V2 control topology and requires no
additional external components. The control loop responds
to an overvoltage condition within 100 ns, causing the top
MOSFET to shut off, disconnecting the regulator from it’s
input voltage. The bottom MOSFET is then activated,
resulting in a “crowbar” action to clamp the output voltage
and prevent damage to the load (see Figures 20 and 21 ). The
regulator will remain in this state until the overvoltage
condition ceases or the input voltage is pulled low. The
bottom FET and board trace must be properly designed to
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CS5165
nominal output voltage. Maximum output voltage deviation
before Power Good is pulled low is ± 12%.
M 5.00 ms
Trace 4− 5.0 V from PC Power Supply (2.0 V/div.)
Trace 1− Regulator Output Voltage (1.0 V/div.)
Figure 21. OVP Response to an Input−to−Output Short
Circuit by Pulling the Input Voltage to Ground
Trace 2− PWRGD (2.0 V/div.)
Trace 4− VOUT (1.0 V/div.)
Figure 23. PWRGD Signal Becomes Logic High as
VOUT Enters −8.5% of Lower PWRGD Threshold,
VOUT = +2.84 V (DAC = 10111)
VCORE
15 k
+5.0 V
56 k
R1
R2
Q3
2N3906
5.0 k
OVP
20 k
+5.0 V
CS5165
10 k
PWRGD
10 k
Q2
2N3904
10 K
Q1
2N3906
Figure 22. Circuit To Implement A Dedicated OVP
Output Using The CS5165
Output Enable Circuit
The Enable pin (pin 8) is used to enable or disable the
regulator output voltage, and is consistent with TTL DC
specifications. It is internally pulled−up. If pulled low
(below 0.8 V), the output voltage is disabled. At the same
time the Power Good and Soft Start pins are pulled low, so
that when normal operation resumes power−up of the
CS5165 goes through the Soft Start sequence. Upon pulling
the Enable pin low, the internal IC bias is completely shut
off, resulting in total shutdown of the Controller IC.
Trace 2− PWRGD (2.0 V/div.)
Trace 4− VFB (1.0 V/div.)
Figure 24. Power Good Response to an Out of
Regulation Condition
Figure 24 shows the relationship between the regulated
output voltage VFB and the Power Good signal. To prevent
Power Good from interrupting the CPU unnecessarily, the
CS5165 has a built−in delay to prevent noise at the VFB pin
from toggling Power Good. The internal time delay is
designed to take about 75 μs for Power Good to go low and
65 μs for it to recover. This allows the Power Good signal to
be completely insensitive to out of regulation conditions that
are present for a duration less than the built in delay (see
Figure 25).
Power Good Circuit
The Power Good pin (pin 13) is an open−collector signal
consistent with TTL DC specifications. It is externally
pulled−up, and is pulled low (below 0.3 V) when the
regulator output voltage typically exceeds ± 8.5% of the
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CS5165
It is therefore required that the output voltage attains an
out of regulation or in regulation level for at least the built−in
delay time duration before the Power Good signal can
change state.
Trace 3− GATE(H) (10 V/div.)
Trace 1− GATE(H) − 5.0 VIN
Trace 4− GATE(L) (10 V/div.)
Trace 2− Inductor Switching Node (5.0 V/div.)
Figure 26. Gate Drive Waveforms Depicting
Rail to Rail Swing
Trace 2− PWRGD (2.0 V/div.)
Trace 4− VFB (1.0 V/div.)
Figure 25. Power Good is Insensitive to Out of
Regulation Conditions that are Present for a
Duration Less Than the Built In Delay
@ 2.2 V
Selecting External Components
The CS5165 buck regulator can be used with a wide range
of external power components to optimize the cost and
performance of a particular design. The following
information can be used as general guidelines to assist in
their selection.
NFET Power Transistors
Both logic level and standard FETs can be used. The
reference designs derive gate drive from the 12 V supply
which is generally available in most computer systems and
utilize logic level FETs. A charge pump may be easily
implemented to support 5.0 V only systems. Multiple FET’s
may be paralleled to reduce losses and improve efficiency
and thermal management.
Voltage applied to the FET gates depends on the
application circuit used. Both upper and lower gate driver
outputs are specified to drive to within 1.5 V of ground when
in the low state and to within 2.0 V of their respective bias
supplies when in the high state. In practice, the FET gates
will be driven rail to rail due to overshoot caused by the
capacitive load they present to the controller IC. For the
typical application where VCC = 12 V and 5.0 V is used as
the source for the regulator output current, the following
gate drive is provided:
Trace 1 = GATE(H) (5.0 V/div.)
Trace 2 = GATE(L) (5.0 V/div.)
Figure 27. Normal Operation Showing the Guaranteed
Non−Overlap Time Between the High and Low−Side
MOSFET Gate Drives, ILOAD = 14 A
The CS5165 provides adaptive control of the external
NFET conduction times by guaranteeing a typical 65 ns
non−overlap between the upper and lower MOSFET gate
drive pulses. This feature eliminates the potentially
catastrophic effect of “shoot−through current”, a condition
during which both FETs conduct causing them to overheat,
self−destruct, and possibly inflict irreversible damage to the
processor.
The most important aspect of FET performance is
RDSON, which effects regulator efficiency and FET thermal
management requirements.
The power dissipated by the MOSFETs may be estimated
as follows:
Switching MOSFET:
VGS(TOP) + 12 V * 5.0 V + 7.0 V
VGS(BOTTOM) + 12 V
(see Figure 26)
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CS5165
Power + ILOAD2
RDSON
1. Sheet Resistivity for one ounce copper, the thickness
variation typically 1.15 mil to 1.35 mil. Therefore the
error due to sheet resistivity is:
duty cycle
Synchronous MOSFET:
Power + ILOAD2
(1 * duty cycle)
RDSON
1.35 * 1.15 + 16%
1.25
Duty Cycle =
VOUT ) (ILOAD
ƪ
2. Mismatch due to L/W. The variation in L/W is
governed by variations due to the PCB manufacturing
process that affect the geometry and the power
dissipation capability of the droop resistor. The error
due to L/W mismatch is typically 1.0%.
3. Thermal Considerations. Due to I2 × R power losses
the surface temperature of the droop resistor will
increase causing the resistance to increase. Also, the
ambient temperature variation will contribute to the
increase of the resistance, according to the formula:
RDSON OF SYNCH FET)
VIN)(ILOAD RDSON OF SYNCH FET)
* (ILOAD RDSON OF SWITCH FET)
ƫ
Off Time Capacitor (COFF)
The COFF timing capacitor sets the regulator off time:
TOFF + COFF
4848.5
The preceding equations for duty cycle can also be used
to calculate the regulator switching frequency and select the
COFF timing capacitor:
COFF +
Perioid
R + R20[1 ) a20(T * 20)]
where:
R20 = resistance at 20°C
(1 * duty cycle)
4848.5
where:
Period +
a + 0.00393
°C
1
switching frequency
T = operating temperature
R = desired droop resistor value
For temperature T = 50°C, the % R change = 12%
Schottky Diode for Synchronous FET
For synchronous operation, a Schottky diode may be
placed in parallel with the synchronous FET to conduct the
inductor current upon turn off of the switching FET to
improve efficiency. The CS5165 reference circuit does not
use this device due to it’s excellent design. Instead, the
body diode of the synchronous FET is utilized to reduce
cost and conducts the inductor current. For a design
operating at 200 kHz or so, the low non−overlap time
combined with Schottky forward recovery time may make
the benefits of this device not worth the additional expense.
The power dissipation in the synchronous MOSFET due to
body diode conduction can be estimated by the following
equation:
Power + VBD
ILOAD
conduction time
Droop Resistor Tolerance
Tolerance due to sheet resistivity variation
Tolerance due to L/W error
Tolerance due to temperature variation
Total tolerance for droop resistor
In order to determine the droop resistor value the nominal
voltage drop across it at full load has to be calculated. This
voltage drop has to be such that the output voltage full load
is above the minimum DC tolerance spec.
[VDAC(MIN) * VDC(MIN)]
VDROOP(TYP) +
1 ) RDROOP(TOLERANCE)
Example: for a 300 MHz Pentium II, the DC accuracy spec
is 2.74 < VCC(CORE) < 2.9 V, and the AC accuracy spec is
2.67 V < VCC(CORE) < 2.9 3V. The CS5165 DAC output
voltage is +2.812 V < VDAC < +2.868 V. In order not to
exceed the DC accuracy spec, the voltage drop developed
across the resistor must be calculated as follows:
switching frequency
Where VBD = the forward drop of the MOSFET body
diode. For the CS5165 demonstration board:
Power + 1.6 V
14.2 A
100 ns
16%
1.0%
12%
29%
200 kHz + 0.45 W
This is only 1.1% of the 40 W being delivered to the load.
“Droop” Resistor for Adaptive Voltage Positioning
VDROOP(TYP) +
Adaptive voltage positioning is used to help keep the
output voltage within specification during load transients.
To implement adaptive voltage positioning a “Droop
Resistor” must be connected between the output inductor
and output capacitors and load. This resistor carries the full
load current and should be chosen so that both DC and AC
tolerance limits are met. An embedded PC trace resistor has
the distinct advantage of near zero cost implementation.
However, this droop resistor can vary due to three reasons:
1) the sheet resistivity variation causes the thickness of the
PCB layer to vary. 2) the mismatch of L/W, and 3)
temperature variation.
[VDAC(MIN) * VDC PENTIUMII(MIN)]
1 ) RDROOP(TOLERANCE)
+ 2.812 V * 2.74 V + 56 mV
1.3
With the CS5165 DAC accuracy being 1.0%, the internal
error amplifier’s reference voltage is trimmed so that the
output voltage will be 40 mV high at no load. With no load,
there is no DC drop across the resistor, producing an output
voltage tracking the error amplifier output voltage,
including the offset. When the full load current is delivered,
a drop of −56 mV is developed across the resistor. Therefore,
the regulator output is pre−positioned at 40 mV above the
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CS5165
nominal output voltage before a load turn−on. The total
voltage drop due to a load step is ΔV−40 mV and the
deviation from the nominal output voltage is 40 mV smaller
than it would be if there was no droop resistor. Similarly at
full load the regulator output is pre−positioned at 16 mV
below the nominal voltage before a load turn−off. The total
voltage increase due to a load turn−off is ΔV−16 mV and the
deviation from the nominal output voltage is 16 mV smaller
than it would be if there was no droop resistor. This is
because the output capacitors are pre−charged to value that
is either 40 mV above the nominal output voltage before a
load turn−on or, 16 mV below the nominal output voltage
before a load turn−off (see Figure 15).
Obviously, the larger the voltage drop across the droop
resistor ( the larger the resistance), the worse the DC and
load regulation, but the better the AC transient response.
L+
+ 0.0039
(W
L
284
717.86
t
1.37 + 2113 mil + 5.36 cm
The inductor should be selected based on its inductance,
current capability, and DC resistance. Increasing the
inductor value will decrease output voltage ripple, but
degrade transient response.
Inductor Ripple Current
Ripple Current +
[(VIN * VOUT) VOUT]
(Switching Frequency L VIN)
Example: VIN = +5.0 V, VOUT = +2.8 V, ILOAD = 14.2 A,
L = 1.2 μH, Freq = 200 kHz
Ripple Current +
The basic equation for laying an embedded resistor is:
L or R + ò
A
W
Output Inductor
Design Rules for Using a Droop Resistor
RAR + ò
RDROOP
ò
[(5.0 V * 2.8 V) 2.8 V]
+ 5.1 A
[200 kHz 1.2 mH 5.0 V]
Output Ripple Voltage
t)
VRIPPLE + Inductor Ripple Current
where:
A = W × t = cross−sectional area
ρ = the copper resistivity (μΩ − mil)
L = length (mils)
W = width (mils)
t = thickness (mils)
Output Capacitor ESR
Example:
VIN = +5.0 V, VOUT = +2.8 V, ILOAD = 14.2 A, L = 1.2 μH,
Switching Frequency = 200 kHz
Output Ripple Voltage = 5.1 A × Output Capacitor ESR
(from manufacturer’s specs)
ESR of Output Capacitors to limit Output Voltage Spikes
For most PCBs the copper thickness, t, is 35 μm (1.37
mils) for one ounce copper. ρ = 717.86 μΩ−mil
For a Pentium II load of 14.2 A the resistance needed to
create a 56 mV drop at full load is:
ESR +
DVOUT
DIOUT
This applies for current spikes that are faster than
regulator response time. Printed Circuit Board resistance
will add to the ESR of the output capacitors.
In order to limit spikes to 100 mV for a 14.2 A Load Step,
ESR = 0.1/14.2 = 0.007 Ω
Response Droop + 56 mV + 56 mV + 3.9 mW
14.2 A
IOUT
The resistivity of the copper will drift with the
temperature according to the following guidelines:
Inductor Peak Current
DR + 12% @ TA + ) 50°C
Peak Current + Maximum Load Current )
DR + 34% @ TA + ) 100°C
ǒRipple 2CurrentǓ
Example: VIN = +5.0 V, VOUT = +2.8 V, ILOAD = 14.2 A,
L = 1.2 μH, Freq = 200 kHz
Droop Resistor Width Calculations
The droop resistor must have the ability to handle the load
current and therefore requires a minimum width which is
calculated as follows (assume one ounce copper thickness):
Peak Current + 14.2 A ) (5.1ń2) + 16.75 A
A key consideration is that the inductor must be able to
deliver the Peak Current at the switching frequency without
saturating.
I
W + LOAD
0.05
where:
W = minimum width (in mils) required for proper power
dissipation, and ILOAD Load Current Amps.
The Pentium®II maximum load current is 14.2 A.
Therefore:
Response Time to Load Increase
(limited by Inductor value unless Maximum On−Time is
exceeded)
Response Time +
W + 14.2 A + 284 mils + 0.7213 cm
0.05
L DIOUT
(VIN * VOUT)
Example: VIN = +5.0 V, VOUT = +2.8 V, L = 1.2 μH, 14.2 A
change in Load Current
Droop Resistor Length Calculation
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18
CS5165
Response Time +
board will tend to reduce regulator di/dt effects on the circuit
board and input power supply. Placement of the power
component to minimize routing distance will also help to
reduce emissions.
1.2 mH 14.2 A
+ 7.7 ms
(5.0 V * 2.8 V)
Response Time to Load Decrease
(limited by Inductor value)
Response Time +
L
Layout Guidelines
Change in IOUT
VOUT
When laying out the CPU buck regulator on a printed
circuit board, the following checklist should be used to
ensure proper operation of the CS5165.
1. Rapid changes in voltage across parasitic capacitors
and abrupt changes in current in parasitic inductors
are major concerns for a good layout.
2. Keep high currents out of logic grounds.
3. Avoid ground loops as they pick up noise. Use star or
single point grounding. The source of the lower
(synchronous FET) is an ideal point where the input
and output GND planes can be connected.
4. For double−sided PCBs a single large ground plane is
not recommended, since there is little control of
where currents flow and the large surface area can act
as an antenna.
5. Even though double sided PCBs are usually sufficient
for a good layout, four−layer PCBs are the optimum
approach to reducing susceptibility to noise. Use the
two internal layers as the +5.0 V and GND planes, and
the top and bottom layers for the vias.
6. Keep the inductor switching node small by placing
the output inductor, switching and synchronous FETs
close together.
7. The FET gate traces to the IC must be as short,
straight, and wide as possible. Ideally, the IC has to be
placed right next to the FETs.
8. Use fewer, but larger output capacitors, keep the
capacitors clustered, and use multiple layer traces
with heavy copper to keep the parasitic resistance
low.
9. Place the switching FET as close to the +5.0 V input
capacitors as possible.
10. Place the output capacitors as close to the load as
possible.
11. Place the VFB filter resistor in series with theVFB pin
(pin 16) right at the pin.
12. Place the VFB filter capacitor right at the VFB pin (pin
16).
13. The “Droop” Resistor (embedded PCB trace) has to
be wide enough to carry the full load current.
14. Place the VCC bypass capacitor as close as possible to
the VCC pin.
Example: VOUT = +2.8 V, 14.2 A change in Load Current,
L = 1.2 μH
Response Time +
1.2 mH 14.2 A
+ 6.1 ms
2.8 V
Input and Output Capacitors
These components must be selected and placed carefully
to yield optimal results. Capacitors should be chosen to
provide acceptable ripple on the input supply lines and
regulator output voltage. Key specifications for input
capacitors are their ripple rating, while ESR is important for
output capacitors. For best transient response, a combination
of low value/high frequency and bulk capacitors placed
close to the load will be required.
THERMAL MANAGEMENT
Thermal Considerations for Power
MOSFETs and Diodes
In order to maintain good reliability, the junction
temperature of the semiconductor components should be
kept to a maximum of 150°C or lower. The thermal
impedance (junction to ambient) required to meet this
requirement can be calculated as follows:
Thermal Impedance +
TJUNCTION(MAX) * TAMBIENT
Power
A heatsink may be added to TO−220 components to
reduce their thermal impedance. A number of PC board
layout techniques such as thermal vias and additional copper
foil area can be used to improve the power handling
capability of surface mount components.
EMI Management
As a consequence of large currents being turned on and off
at high frequency, switching regulators generate noise as a
consequence of their normal operation. When designing for
compliance with EMI/EMC regulations, additional
components may be added to reduce noise emissions. These
components are not required for regulator operation and
experimental results may allow them to be eliminated. The
input filter inductor may not be required because bulk filter
and bypass capacitors, as well as other loads located on the
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19
CS5165
5.0 V
MBRS120
MBRS120
1.0 μF
1200 μF/10 V × 3
MBRS120
1.0 μF
VCC
VID0
VID1
VGATE(H)
CS5165
VID2
VGATE(L)
VID3
VID4
330 pF
Droop Resistor
(Embedded PCB trace)
6.0 mΩ
1.2 μH
+
1200 μF/10 V × 5
Si9410DY
COFF
SS
ENABLE
PWRGD
VFB
LGND
0.1 μF
VCC
VSS
PGND
COMP
0.1 μF
Si4410DY
3.3 k
1000 pF
ENABLE
PWRGD
PENTIUM II
SYSTEM
VID4
VID3
VID2
VID1
VID0
Figure 28. Additional Application Diagram, +5.0 V to +2.8 V @ 14.2 A for 300 MHz Pentium II
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CS5165
PACKAGE DIMENSIONS
SO−16L
DW SUFFIX
CASE 751G−03
ISSUE B
A
D
9
1
8
NOTES:
1. DIMENSIONS ARE IN MILLIMETERS.
2. INTERPRET DIMENSIONS AND TOLERANCES
PER ASME Y14.5M, 1994.
3. DIMENSIONS D AND E DO NOT INLCUDE MOLD
PROTRUSION.
4. MAXIMUM MOLD PROTRUSION 0.15 PER SIDE.
5. DIMENSION B DOES NOT INCLUDE DAMBAR
PROTRUSION. ALLOWABLE DAMBAR
PROTRUSION SHALL BE 0.13 TOTAL IN EXCESS
OF THE B DIMENSION AT MAXIMUM MATERIAL
CONDITION.
h X 45 _
H
E
0.25
8X
M
B
M
16
q
16X
T A
M
B
B
S
B
S
e
SEATING
PLANE
A1
14X
L
A
0.25
DIM
A
A1
B
C
D
E
e
H
h
L
q
MILLIMETERS
MIN
MAX
2.35
2.65
0.10
0.25
0.35
0.49
0.23
0.32
10.15
10.45
7.40
7.60
1.27 BSC
10.05
10.55
0.25
0.75
0.50
0.90
0_
7_
C
T
PACKAGE THERMAL DATA
Parameter
SO−16L
Unit
RΘJC
Typical
23
°C/W
RΘJA
Typical
105
°C/W
ON Semiconductor and
are registered trademarks of Semiconductor Components Industries, LLC (SCILLC). SCILLC reserves the right to make changes without further notice
to any products herein. SCILLC makes no warranty, representation or guarantee regarding the suitability of its products for any particular purpose, nor does SCILLC assume any liability
arising out of the application or use of any product or circuit, and specifically disclaims any and all liability, including without limitation special, consequential or incidental damages.
“Typical” parameters which may be provided in SCILLC data sheets and/or specifications can and do vary in different applications and actual performance may vary over time. All
operating parameters, including “Typicals” must be validated for each customer application by customer’s technical experts. SCILLC does not convey any license under its patent rights
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intended to support or sustain life, or for any other application in which the failure of the SCILLC product could create a situation where personal injury or death may occur. Should
Buyer purchase or use SCILLC products for any such unintended or unauthorized application, Buyer shall indemnify and hold SCILLC and its officers, employees, subsidiaries, affiliates,
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CS5165/D