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NX9415
5A SYNCHRONOUS BUCK SWITCHING REGULATOR
PRODUCTION DATA SHEET Pb Free Product
DESCRIPTION
The NX9415 is synchronous buck switching converter in multi chip module designed for step down DC to DC converter applications. It is optimized to convert bus voltages from 8V to 22V to as low as 0.8V output voltage. The output current can be up to 5A. An internal regulator converts bus voltage to 5V, which provides voltage supply to internal logic and driver circuit. The NX9415 operates from 200kHz to 2.2MHz and employs loss-less current limiting by sensing the Rdson of synchronous MOSFET followed by hiccup feature.Feedback under voltage protection triggers hiccup. Other features of the device are: internal schottky diode, thermal shutdown, 5V gate drive, adaptive deadband control, internal digital soft start, 5VREG undervoltage lock out and shutdown capability via the comp pin. NX9415 is available in 4x4 MCM package. n n n n n n n n
FEATURES
Single supply voltage from 8V to 22V Internal 5V regulator Programmable frequency up to 2.2MHz Internal Digital Soft Start Function Internal boost schottky diode Prebias Startup Less than 50 nS adaptive deadband Current limit triggers hiccup by sensing Rdson of Synchronous MOSFET n Pb-free and RoHS compliant
APPLICATIONS
n n n n Low Profile On board DC to DC Application LCD TV Hard Disk Drive ADSL Modem
TYPICAL APPLICATION
0.1uF
Vin +12V
2*(10uF/16V/X5R)
D1
VIN
BST S1 D2 SW
0.1uF 0.56uH
5VREG
4.7uF
Vout1 +5V,5A
22uF/6.3V/X5R
NX9415
10
5k
OCP
768 15.8k 220p
VCC
1uF
FB
330p 10p
15k 4.22k
3.01k
RT
COMP
GND
S2
Figure 1 - Typical application of 9415
ORDERING INFORMATION
Device NX9415CMTR Temperature 0 to 70oC Package 4X4 MCM-24L Frequency 200kHz to 2.2MHz Pb-Free Yes
Rev.1.2 12/28/09
1
NX9415
ABSOLUTE MAXIMUM RATINGS
5VREG,VCC to GND & BST to SW voltage ........ -0.3V to 6.5V VIN to GND Voltage ......................................... 25V S1 to GND ...................................................... -2V to 30V D1 to S1,D2 to S2 ............................................ 30V 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 ............................................. Internally Limited by OTP
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
24-LEAD PLASTIC MCM 4 x 4
D2
D1
D1
S2
S2
24 23 22 21 20 19 S2 D2 1 2 PAD2 PAD1 18 S1 17 S1 16 D1 15 NC PAD3 14 13 7 VIN 8 RT 9 10 11 12 GND NC FB COMP OCP BST
D2 3 NC 4 5VREG 5 VCC 6
S1
Rev.1.2 12/28/09
2
NX9415
ELECTRICAL SPECIFICATIONS
Unless otherwise specified, these specifications apply over Vin = 12V, and T A = 0 to 70oC. Followings are bypass capacitors:CVIN=1uF, C5VREG=4.7uF, all X5R ceramic capacitors. Typical values refer to T A = 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 5VREG 5VREG Voltage range 5VREG Line Regulation 5VREG Max Current Supply Voltage(Vin) Vin Voltage Range Input Voltage Current(Static) Input Voltage Current (Dynamic) Vin UVLO Vin-Threshold Vin-Hysteresis Under Voltage Lockout VCC-Threshold VCC-Hysteresis SS Soft Start time Oscillator (Rt) Frequency Ramp-Amplitude Voltage Max Duty Cycle Min Controlable On Time Error Amplifiers Transconductance Input Bias Current Comp SD Threshold FBUVLO Feedback UVLO threshold Over temperature Threshold Hysteresis OCP OCP current Internal Schottky Diode Forward voltage drop Ouput Stage High Side MOSFET RDSON Low Side MOSFET RDSON Output Current SYM VREF Vin=9V to 22V 4.75 VIN=9V to 22V Test Condition Min TYP 0.8 0.4 5 10 50 Vin No switching Rt=4.22k 9 4.8 10 6.5 0.6 3.9 0.2 400 2250 1.5 FS=2.2MHz 71 150 2000 10 0.3 0.6 150 20 37 forward current=20mA 350 31 31 5 22 5.25 MAX Units V % V mV mA V mA mA
Vin_UVLO Vin_Hyst
Vin Rising Vin Falling
V V V V uS kHz V % nS umho nA V V
o o
VCC _UVLO VCC Rising VCC _Hyst Tss FS VRAMP VCC Falling FS=2.2MHz Rt=4.22k
Ib
C C
uA mV mohm mohm A
Rev.1.2 12/28/09
3
NX9415
PIN DESCRIPTIONS
PIN # 17-19 2-3,22,PAD2 23-24,1 21-20,16,PAD1 5 PIN SYMBOL S1 D2 S2 D1 5VREG PIN DESCRIPTION Source of high side MOSFET and provides return path for the high side driver. Drain of low side MOSFET. Source of low side MOSFET and needs to be connected to power ground. Drain of high side MOSFET. An internal 5V regulator. A high frequency 4.7uF/X5R ceramic capacitor must be connected from this pin to the GND pin as close as possible. Voltage supply for internal analog circuit and driver Voltage supply for the internal 5V regulator. Oscillator's frequency can be set by using an external resistor from this pin to GND. Ground. This pin is the output of the error amplifier and is used to compensate the voltage control feedback loop. This pin is also used as a shut down pin. When this pin is pulled below 0.3V, both drivers are turned off and internal soft start is reset. This pin is the error amplifier inverting input. This pin is connected via resistor divider to the output of the switching regulator to set the output DC voltage. This pin supplies voltage to the high side driver. A high frequency ceramic capacitor of 0.1 to 1uF must be connected from this pin to SW pin. This pin is connected to the D2 of the low side MOSFET and is the input of the over current protection(OCP) comparator. An fixed internal current flows 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. Not used pin. Connecting these pins to ground is recommended.
6 7 8
VCC VIN RT
9 10
GND COMP
11
FB
13
BST
14
OCP
4,12,15, PAD3
NC
Rev.1.2 12/28/09
4
NX9415
BLOCK DIAGRAM
5VREG
BST
D1
VIN
5V Regulator
VCC
Bias Generator
1.25V 0.8V UVLO POR START
COMP 0.3V RT OC START 0.8V OSC Digital start Up ramp S R FB 0.6V CLAMP COMP START GND VCC Q Thermal Shutdown S2 Hiccup Logic SS_done 70%*Vp 1.3V CLAMP FB PWM Control Logic PVCC SW D2 S1
OCP
START
Figure 2 - Simplified block diagram of the NX9415
Rev.1.2 12/28/09
5
NX9415
TYPICAL APPLICATION
Input Voltage=12V Output Voltage=5V@5A Working Frequency=2.2MHz
C2 0.1uF
U1
Vin +12V
CIN 2*(10uF/16V/X5R)
D1 VIN
BST S1 D2 SW
C3 0.1uF L1 0.56uH
C4 4.7uF
5VREG
NX9415
R1 10 C1 1uF
R7 5k
COUT 22uF/6.3V/X5R R4 768 C5 220p R5 15.8k
Vout1 +5V,5A
OCP
VCC
FB
C6 330p 10p R3 15k R6 3.01k
R2 4.22k
RT
COMP S2
GND
Figure 3- Demo board schematic
Rev.1.2 12/28/09
6
NX9415
Bill of Materials
Item 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 Quantity 1 2 1 1 1 2 1 1 1 1 1 1 1 1 1 1 Reference C1 C2,C3 C4 C5 C6 CIN COUT L1 R1 R2 R3 R4 R5 R6 R7 U1 Value 1u 0.1u 4.7u/6.3V/X5R 220p 330p 10u/16V/X5R 22u/6.3V/X5R DO1813P-561HC 10 4.22k 15k 768 15.8k 3.01k 5k NX9415CMTR Manufacturer
Coilcraft
NEXSEM INC.
Rev.1.2 12/28/09
7
NX9415
Demoboard waveforms
Figure 4 - Output ripple (CH1 SW 10V/DIV, CH2 VOUT AC 50mV/DIV, CH4 OUTPUT CURRENT 5A/DIV)
Figure 5 - Output voltage transient response ( CH2 VOUT AC 50mV/DIV, CH4 OUTPUT CURRENT 5A/DIV)
Figure 6 - Over current protection(CH4 OUTPUT CURRENT 5A/DIV)
Figure 7 - Startup(CH2 VOUT 2V/DIV, CH4 OUTPUT CURRENT 2A/DIV)
Figure 8 - Output Efficiency @VOUT=5V,VIN=12V
Rev.1.2 12/28/09
8
NX9415
APPLICATION INFORMATION
Symbol Used In Application Information:
VIN VOUT IOUT FS - Input voltage - Output voltage - Output current - Working frequency
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.
DVRIPPLE - Output voltage ripple DIRIPPLE - Inductor current ripple
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:
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 cross-
V -V V 1 L OUT = IN OUT x OUT x VIN FS IRIPPLE IRIPPLE =k x IOUTPUT
where k is between 0.2 to 0.4.
...(1)
over 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.
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(2).
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 2 x x R4 x C1 x C 2 C1 + C 2
...(3) ...(4) ...(5) ...(6)
VRIPPLE = ESR x IRIPPLE
IRIPPLE + 8 x FS x COUT ...(2)
Where ESR is the output capacitors' equivalent series resistance,COUT is the value of output capacitors. Typically when ceramic capacitors are selected as output capacitors, DC ripple spec is easy to be met, but mutiple ceramic capacitors are required at the output to meet transient requirement.
where FZ1,FZ2,FP1 and FP2 are poles and zeros in the compensator. Their locations are shown in figure 10. 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
Rev.1.2 12/28/09
9
NX9415
For the voltage amplifier, the transfer function of compensator is
B. Type II compensator design
Type II compensator can be realized by simple RC circuit without feedback as shown in figure 12. R3 and C1 introduce a zero to cancel the double pole effect. C2 introduces a pole to suppress the switching noise. The following equations show the compensator pole zero location and constant gain.
Ve -Z f = VOUT Zin
To achieve the same effect as voltage amplifier, the compensator of transconductance amplifier must
satsf t scondion:R4>>2/gm. And it would be desiri y hi t i
able if R 1||R2||R3>>1/gm can be met at the same time.
Gain=gm x Fz =
R1 x R3 R1 +R 2
... (7) ... (8) ... (9)
Zin R3
Vout
Zf C1 C2 Fb gm Ve R4
1 2 x x R 3 x C1 1 2 x x R3 x C2
Fp
R2 C3 R1
For this type of compensator, FO has to satisfy FLCVref
Gain(db)
power stage 40dB/decade loop gain 20dB/decade
Figure 9 - Type III compensator using transconductance amplifier
power stage G in(db) a
FLC
40dB/decade
compensator Gain
loop gain 20dB/decade
FZ FLC FESR
FESR
FO FP
FO
compensator
Figure 11 - Bode plot of Type II compensator
FZ1 FZ2
FP2 FP1 F S
Figure 10 - Bode plot of Type III compensator
Rev.1.2 12/28/09
10
NX9415
Over Current Protection
Vout R2 Fb gm R1 Vref Ve R3 C2 C1
Over current protection is achieved by sensing current through the low side MOSFET. A typical internal current source of 37uA flowing 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
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 Figure 12 - Type II compensator with transconductance amplifier
I OCP
occurs.
vbus
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
OCP comparator
OCP R OCP
SW
Figure 14 - Over current protection The over current limit can be set by the following equation
VOUT , VREF and voltage divider. .
R 1= R 2 x VR E F V O U T -V R E F
...(10)
ISET =
IOCP x ROCP K x RDSON
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.
Frequency Selection
The frequency can be set by external Rt resistor. The relationship between frequency and RT pin is shown as follows.
NX9415 Frequency vs Rt
Vout R2 Fb
2500 Frequency(kHz)
R1 Vref Voltage divider
Figure 13 - Voltage divider
2000 1500 1000 500 0 3 13 23 Rt(kohm) 33
Figure 15 - Frequency versus Rt resistor
Rev.1.2 12/28/09
11
NX9415
MCM 24 PIN 4 x 4 PACKAGE OUTLINE DIMENSIONS
NOTE: ALL DIMENSIONS ARE DISPLAYED IN MILLIMETERS.
Rev.1.2 12/28/09
12

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