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NX9511B
9A SYNCHRONOUS BUCK SWITCHING REGULATORWITH 1MHz OPERATION FREQUENCY
PRELIMINARY DATA SHEET Pb Free Product
DESCRIPTION
The NX9511B is synchronous buck switching converter in multi chip module designed for step down DC to DC converter applications. They are optimized to convert bus voltages from 2V to 25V to as low as 0.8V output voltage. The output current can be up to 9A. The NX9511B offer an Enable pin that can be used to program the converter's start up. NX9511B operates at fixed internal frequency of 1MHz and employ loss-less current limiting protection by sensing the Rdson of synchronous MOSFET followed by latch out feature. Feedback under voltage triggers Hiccup. Other features are: Internal digital soft start; Vcc undervoltage lock out and shutdown capability via the enable pin or comp pin. NX9511B is available in 5x5 MCM package. n n n n n n n
FEATURES
Switching Controller and MOSFETs in one package Bus voltage operation from 2V to 25V Fixed 1MHz Internal Digital Soft Start Function Output current up to 9A Enable pin to program BUS UVLO Programmable current limit triggers latch out by sensing Rdson of Synchronous MOSFET n No negative spike at Vout during startup and shutdown n Pb-free and RoHS compliant
APPLICATIONS
n n n n Low Profile On board DC to DC Application Graphic Card on board converters Memory Vddq Supply ADSL Modem
TYPICAL APPLICATION
Vin1 +12V Vin2 +5V
D1
2*22uF
VCC
1uF
BAT54A
EN COMP
820p 15p 20k
NX9511B
BST S1 D2 SW OCP HG HDRV S2
0.1uF 1uH
Vout +1.2V,9A
6x (22uF,X5R)
5k 200
FB LG AGND
40k
390p
16k
Figure 1 - Typical application of 9511B
ORDERING INFORMATION
Device NX9511BCMTR Temperature 0 to 70oC Package 5X5 MCM-32L Frequency 1MHz Pb-Free Yes
Rev.1.5 01/16/08
1
NX9511B
ABSOLUTE MAXIMUM RATINGS
VCC to GND & BST to SW voltage .................... -0.3V to 6.5V D1 to GND ........................................................ 25V BST to GND Voltage ........................................ -0.3V to 35V D2,S1 to GND .................................................. -2V to 35V All other pins .................................................... -0.3V to VCC+0.3V or 6.5V Storage Temperature Range ............................... -65oC to 150oC Operating Junction Temperature Range ............... -40oC to 125oC ESD Susceptibility ........................................... 2kV Power Dissipation ............................................. TBD Output Current ...................................................TBD CAUTION: Stresses above those listed in "ABSOLUTE MAXIMUM RATINGS", may cause permanent damage to the device. This is a stress only rating and operation of the device at these or any other conditions above those indicated in the operational sections of this specification is not implied.
PACKAGE INFORMATION
32-LEAD PLASTIC MCM 5 x 5
AGND
HDRV
BST
D1
32 31 30 29 28 27 26 25 S1 S1 S1 D1 D2 1 2 3 4 5 D2 (PAD3) D1 (PAD2) AGND (PAD1) 24 OCP 23 COMP 22 FB 21 AGND 20 EN 19 D2 18 VCC 17 NC 9 10 11 12 13 14 15 16 S2 S2 NC LG S2 S2 S2 S2
D2 6 D2 7 D2 8
D1
SW
HG
D1
Rev.1.5 01/16/08
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NX9511B
ELECTRICAL SPECIFICATIONS
Unless otherwise specified, these specifications apply over Vcc = 5V, VIN = 12V and TA= 0 to 70oC. Typical values refer to TA = 25oC. Low duty cycle pulse testing is used which keeps junction and case temperatures equal to the ambient temperature.
PARAMETER Reference Voltage Ref Voltage Ref Voltage line regulation Supply Voltage(Vcc) VCC Voltage Range VCC Supply Current (Static) Supply Voltage(VBST) VBST Supply Current (Static) VCC, VBST Supply Current (Dynamic) Under Voltage Lockout VCC-Threshold VCC-Hysteresis Oscillator Frequency Ramp-Amplitude Voltage Max Duty Cycle Min Duty Cycle Error Amplifiers Transconductance Input Bias Current EN & SS Soft Start time Enable HI Threshold Enable Hysterises Ouput Stage High Side MOSFET RDSON Low Side MOSFET RDSON Output Current OCP Adjust OCP current FB Under Voltage Protection FB Under Voltage Threshold
SYM VREF
Test Condition
Min
TYP 0.8 0.2
MAX
Units V %
VCC ICC (Static) Outputs not switching IBST (Static) Outputs not switching I(Dynamic)
4.5
5 3 0.2 15
5.5
V mA mA mA
VCC_UVLO VCC Rising VCC_Hyst FS VRAMP VCC Falling
4 0.2 1 1.5 75 0 2000 10 2 1.25 150 17 17 9 40 0.48
V V MHz V % % umho nA mS V mV ohm ohm A uA V
Ib Tss
Rev.1.5 01/16/08
3
NX9511B
PIN DESCRIPTIONS
PIN # 1-3 5-8,19 9-14 15,17 16 18 PIN SYMBOL PIN DESCRIPTION S1 Bus input which is connected to high side MOSFET's drain. D2 S2 NC LG VCC Low side gate driver output for monitoring. Power supply voltage. A high freq 1uF ceramic capacitor is placed as close as possible to and connected to this pin and ground pin. The maximum rating of this pin is 5V. External enable signal input for the controller. This pin is the error amplifier inverting input. It is connected via resistor divider to the output of the switching regulator to set the output DC voltage. When FB pin voltage is lower than 0.6V, hiccup circuit starts to recycle the soft start circuit after 2048 switching cycles. This pin is the output of error amplifier and is used to compensate the voltage control feedback loop. This pin can also be used to perform a shutdown if pulled lower than 0.3V. This pin is connected to the drain of the external low side MOSFET via resistor and is the input of the over current protection(OCP) comparator. An internal current source 40uA is flown to the external resistor which sets the OCP voltage across the Rdson of the low side MOSFET. Current limit point is this voltage divided by the Rds-on. Once this threshold is reached the Hdrv and Ldrv pins are latched out. Ground pin. SW is the controller pin out which needs to be connected to S1and D2 and provides return path for the high side driver. High side gate driver output which needs to be connected high side MOSFET gate HG. This pin supplies voltage to high side FET driver. A high freq 0.1uF ceramic capacitor is placed as close as possible to and connected to these pins and respected SW pins. Analog ground. High side MOSFET gate which needs to be connected to high side gate driver output HDRV. Drain of High side MOSFET. Drain of low side MOSFET. Source of low side MOSFET and need to be connected to power ground.
20 22
EN FB
23
COMP
24
OCP
25
SW
26
HDRV
27
BST
21,28 29
AGND HG
30-32,4
D1
Rev.1.5 01/16/08
4
NX9511B
BLOCK DIAGRAM
BST HDRV HG D1
VCC
FB 0.6V Bias Generator 1.25V 0.8V UVLO POR START Hiccup Logic
OC
EN 1.25 /1.15 OC START 0.8V OSC Digital start Up ramp S R FB S2 COMP START AGND 0.6V CLAMP 1.3V CLAMP Latch Out OCP comparator 40uA LG OCP Q OC PWM Control Logic VCC SW D2 S1
Figure 2 - Simplified block diagram of the NX9511B
Rev.1.5 01/16/08
5
NX9511B
Vin1 +12V
Vin2 +5V
Cin 2*22uF
D1
VCC
C1 1uF
D1 BAT54A
EN
C4 820p R5 20k
NX9511B
BST S1 D2 SW OCP HG HDRV S2
C2 0.1uF L1 1uH Cout 6x (22uF,X5R)
COMP
C5 15p
Vout +1.2V,9A
R1 5k R2 200 C3 390p R3 40k
FB LG AGND
R4 16k
Figure 3- Demo board schematic
Rev.1.5 01/16/08
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NX9511B
Bill of Materials
Item 1 2 3 4 5 6 7 8 9 10 11 12 13 14 Quantity 1 1 1 8 1 1 1 1 1 1 1 1 1 1 Reference C1 C2 C5 Cin,Cout C4 C3 D1 L2 R5 R3 R2 R4 U1 U2 Value 1u 0.1u 15p 22u 820p 390p BAT54A DO3316P-102HC 20k 40k 200 16k NX9511B/MLPQ32 L78L05AB/sot89 Manufacture
Coilcraft
NEXSEM INC.
Rev.1.5 01/16/08
7
NX9511B
Demoboard waveforms
Figure 4 - Output ripple (VIN=12V,VOUT=1.2V)
Figure 5 - Output voltage transient response (VIN=12V, VOUT=1.2V, IOUT=4A)
Figure 6 - Over current protection
Figure 7 - Startup
85.00% 80.00% EFFICIENCY 75.00% 70.00% 65.00% 60.00% 0 2 4 6 8 10 OUTPUT CURRENT(A)
Figure 8 - Output Efficiency @VOUT=1.2V,VIN=12V
Rev.1.5 01/16/08
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NX9511B
Efficiency v.s. Output Voltage Vin=12V Iout=4A 95.00% 90.00% Efficiency(%) 85.00% 80.00% 75.00% 70.00% 1 2 3 Vout(V) 4 5
Figure 9 - Output Efficiency
Ef f icienc y v .s. Output Voltage V in=12V Iout=6A 95.00% 90.00% Efficiency(%) 85.00% 80.00% 75.00% 70.00% 1 2 3 Vout(V ) 4 5
Figure 10 - Output Efficiency
Rev.1.5 01/16/08
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NX9511B
Efficiency v.s. Output Voltage Vin=12V Iout=8A 95.00% 90.00% Efficiency(%) 85.00% 80.00% 75.00% 70.00% 1 2 3 Vout(V) 4 5
Figure 11 - Output Efficiency
Ef f iciency v.s. Output Voltage V in=12V Iout=9A 95.00% 90.00% Efficiency(%) 85.00% 80.00% 75.00% 70.00% 65.00% 1 2 3 Vout(V ) 4 5
Figure 12 - Output Efficiency
Rev.1.5 01/16/08
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NX9511B
Typical application
Vin
30 30
+5V to 7.5V
D1
2*22uF
VCC
1uF TL431
35k 25k
BAT54A
EN COMP
560p 15p 25k
NX9511B
BST
0.1uF
S1 D2 SW
3k
0.33uH
Vout +1.2V,7A
6x (22uF,X5R)
FB LG AGND
OCP HG HDRV S2
200
40k
330p
16k
Figure 13 - Typical application of 9511B
88.00% 86.00% 84.00% 82.00% 80.00% 78.00% 76.00% 74.00% 72.00% 0 2 4 OUTPUT CURRENT(A) 6 8
Figure 14 - Output voltage transient response (VIN=5V, VOUT=1.2V, IOUT=1.5A)
Figure 15 - Output Efficiency @VOUT=1.2V,VIN=5V
Rev.1.5 01/16/08
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NX9511B
APPLICATION INFORMATION
Symbol Used In Application Information:
VIN VOUT IOUT FS - Input voltage - Output voltage - Output current
IRIPPLE = =
VIN -VOUT VOUT 1 x x LOUT VIN FS
...(2) 12V-1.8V 1.8V 1 x x = 2.25A 0.68uH 12V 1000kHz
DVRIPPLE - Output voltage ripple - Working frequency DIRIPPLE - Inductor current ripple
Output Capacitor Selection
Output capacitor is basically decided by the amount of the output voltage ripple allowed during steady state(DC) load condition as well as specification for the load transient. The optimum design may require a couple of iterations to satisfy both condition. The amount of voltage ripple during the DC load condition is determined by equation(3).
Design Example
The following is typical application for NX9511B: VIN = 12V VOUT=1.8V FS=1000kHz IOUT=9A DVRIPPLE <=20mV DVDROOP<=100mV @ 9A step
VRIPPLE = ESR x IRIPPLE +
IRIPPLE 8 x FS x COUT ...(3)
Where ESR is the output capacitors' equivalent series resistance,COUT is the value of output capacitors. Typically ceramic capacitors are selected as output capacitors in NX9811B applications. DC ripple spec is easy to be met, usually mutiple ceramic capacitors are required at the output to meet transient requirement. In this example, two 47uF,X5R are used.
Output Inductor Selection
The selection of inductor value is based on inductor ripple current, power rating, working frequency and efficiency. Larger inductor value normally means smaller ripple current. However if the inductance is chosen too large, it brings slow response and lower efficiency. Usually the ripple current ranges from 20% to 40% of the output current. This is a design freedom which can be decided by design engineer according to various application requirements. The inductor value can be calculated by using the following equations:
Compensator Design
Due to the double pole generated by LC filter of the power stage, the power system has 180o phase shift , and therefore, is unstable by itself. In order to achieve accurate output voltage and fast transient response,compensator is employed to provide highest possible bandwidth and enough phase margin.Ideally,the Bode plot of the closed loop system has crossover frequency between1/10 and 1/5 of the switching frequency, phase margin greater than 50o and the gain crossing 0dB with -20dB/decade. Power stage output capacitors usually decide the compensator type. If electrolytic capacitors are chosen as output capacitors, type II compensator can be used to compensate the system, because the zero caused by output capacitor ESR is lower than crossover frequency. Otherwise type III compensator should be chosen.
L OUT =
VIN -VOUT VOUT 1 x x IRIPPLE VIN FS
IRIPPLE =k x IOUTPUT
where k is between 0.2 to 0.4. Select k=0.3, then
12V-1.8V 1.8V 1 x x 0.4 x 9A 12V 1000kHz L OUT =0.42uH L OUT =
...(1)
Choose inductor from COILCRAFT DO3316H681MLD with L=0.68uH is a good choice. Current Ripple is recalculated as
Rev.1.5 01/16/08
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NX9511B
A. Type III compensator design
For low ESR output capacitors, typically such as Sanyo oscap and poscap, the frequency of ESR zero caused by output capacitors is higher than the crossover frequency. In this case, it is necessary to compensate the system with type III compensator. The following figures and equations show how to realize the type III compensator by transconductance amplifier.
Zin R3
Vout
Zf C1 C2 Fb gm Ve R4
R2 C3 R1
FZ1 = FZ2 = FP1 = FP2 =
1 2 x x R 4 x C2 1 2 x x (R 2 + R 3 ) x C 3 1 2 x x R 3 x C3 1 C x C2 2 x x R4 x 1 C1 + C 2
...(4) ...(5) ...(6) ...(7)
Vref
Figure 16 - Type III compensator using transconductance amplifier
power stage
where FZ1,FZ2,FP1 and FP2 are poles and zeros in the compensator. Their locations are shown in figure 4. The transfer function of type III compensator for transconductance amplifier is given by:
Ve 1 - gm x Z f = VOUT 1 + gm x Zin + Z in / R1
Gain(db)
FLC
40dB/decade
loop gain 20dB/decade
For the voltage amplifier, the transfer function of compensator is
FESR FO
compensator
Ve -Z f = VOUT Zin
To achieve the same effect as voltage amplifier, the compensator of transconductance amplifier must satisfy this condition: R 4>>2/gm. And it would be desirable if R 1||R2||R3>>1/gm can be met at the same time.
FZ1 FZ2
FP2 FP1 F S
Figure 17 - Bode plot of Type III compensator
Rev.1.5 01/16/08
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NX9511B
Design example for type III compensator are in order. The crossover frequency has to be selected as FLCC2 = = 1 2 x x FZ1 x R 4
1 2 x x 0.5 x 2 0 k H z x 30k = 533pF
FLC = =
1 2 x x L OUT x COUT 1
Choose C2=520pF. 6. Calculate C 1 by equation (14) with pole F p2 at half the switching frequency.
2 x x 0.68uH x 94uF = 20kHz
C1 = =
1 2 x x R 4 x FP2
FESR = =
1 2 x x ESR x C OUT
1 2 x x 0.5m x 94uF = 3.4MHz
1 2 x x 30k x 500kHz = 10pF
Choose C1=12pF 7. Calculate R 3 by equation (13).
R3 = = 1 2 x x FP1 x C3
2. Set R2 equal to 20k.
R1=
R 2 x VREF 60k x 0.8V = = 48k VOUT -VREF 1.8V-0.8V
Choose R1=48k. 3. Set zero FZ2 = 0.75FLC and Fp1 =FESR . 4. Calculate R4 and C3 with the crossover frequency at 1/10~ 1/5 of the switching frequency. Set FO=100kHz.
C3 = = 1 11 x( ) 2 x x R2 Fz2 Fp1
1 2 x x 3.4MHz x 180pF = 261
Choose R3=300.
Output Voltage Calculation
Output voltage is set by reference voltage and external voltage divider. The reference voltage is fixed at 0.8V. The divider consists of two ratioed resistors so that the output voltage applied at the Fb pin is 0.8V when the output voltage is at the desired value. The following equation and picture show the relationship between
1 1 1 x( ) 2 x x 60k 15kHz 3.4MHz =180pF
V 2 x x FO x L R4 = OSC x x Cout Vin C3 1.5V 2 x x 100kHz x 0.68uH = x x 94uF 12V 180pF =28k
VOUT , VREF and voltage divider. .
R 1= R 2 x VR E F V O U T -V R E F
...(8)
where R2 is part of the compensator, and the value of R1 value can be set by voltage divider. See compensator design for R1 and R2 selection.
Choose C3=180pF, R 4=30k. 5. Calculate C2 with zero Fz1 at 50% of the LC double pole by equation (11).
Rev.1.5 01/16/08
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NX9511B
The NX9511B can be turned off by pulling down the
Vout R2 Fb R1 Vref
Enable pin by extra signal MOSFET as shown in the above Figure. When Enable pin is below 1.25V, the digital soft start is reset to zero. In addition, all the high side and low side driver is off and no negative spike will be generated during the turn off.
Over Current Protection
Voltage divider
Figure 18 - Voltage divider Over current protection is achieved by sensing current through the low side MOSFET. An internal current source of 40uA flows through an external resistor connected from OCP pin to SW node sets the over current protection threshold. When synchronous FET is on, the voltage at node SW is given as
Soft Start and Enable
NX9511B has digital soft start for switching controller and has one enable pin for this start up. When the Power Ready (POR) signal is high and the voltage at enable pin is above 1.25V the internal digital counter starts to operate and the voltage at positive input of Error amplifier starts to increase, the feedback network will force the output voltage follows the reference and starts the output slowly. After 2048 cycles, the soft start is complete and the output voltage is regulated to the desired voltage decided by the feedback resistor divider.
VSW =-IL x RDSON
The voltage at pin OCP is given as
IOCP x ROCP +VSW
When the voltage is below zero, the over current occurs.
vbus I OCP 40uA OCP R OCP OCP comparator SW
Vbus
+
Figure 20 - Over current protection
POR OFF ON R2 10k R1 EN 1.25V/ 1.15V Digital start up
The over current limit can be set by the following equation
ISET =
Figure 19 - Enable and Shut down the NX9511B with Enable pin. The start up of NX9511B can be programmed through resistor divider at Enable pin. For example, if the input bus voltage is12V and we want NX9511B starts when Vbus is above 9V. We can select using the following equation.
IOCP x ROCP K x RDSON
The internal MOSFET RDSON=17m, the worst case thermal consideration K=1.3 and the current limit is set at 10A, then
R OCP = ISET x K x R DSON 10A x 1.3 x 17m = = 5.5k IOCP 40uA
Choose ROCP=5.5k
R1 =
(9V - 1.25V) x R2 1.25V
Rev.1.5 01/16/08
15
NX9511B
MLPQ 32 PIN 5 x 5 PACKAGE OUTLINE DIMENSIONS
NOTE: ALL DIMENSIONS ARE DISPLAYED IN MILLIMETERS.
Rev.1.5 01/16/08
16

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