ON NCV887103D1R2G Automotive grade non-synchronous boost controller Datasheet

NCV8871
Automotive Grade
Non-Synchronous Boost
Controller
The NCV8871 is an adjustable output non−synchronous boost
controller which drives an external N−channel MOSFET. The device
uses peak current mode control with internal slope compensation. The
IC incorporates an internal regulator that supplies charge to the gate
driver.
Protection features include internally−set soft−start, undervoltage
lockout, cycle−by−cycle current limiting, hiccup−mode short−circuit
protection and thermal shutdown.
Additional features include low quiescent current sleep mode and
externally−synchronizable switching frequency.
Features
•
•
•
•
•
•
•
•
•
•
•
•
Peak Current Mode Control with Internal Slope Compensation
1.2 V ±2% Reference voltage
Fixed Frequency Operation
Wide Input Voltage Range of 3.2 V to 40 Vdc, 45 V Load Dump
Input Undervoltage Lockout (UVLO)
Internal Soft−Start
Low Quiescent Current in Sleep Mode
Cycle−by−Cycle Current Limit Protection
Hiccup−Mode Overcurrent Protection (OCP)
Hiccup−Mode Short−Circuit Protection (SCP)
Thermal Shutdown (TSD)
This is a Pb−Free Device
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MARKING
DIAGRAM
8
SOIC−8
D SUFFIX
CASE 751
8
1
8871xx
ALYW
G
1
8871xx = Specific Device Code
xx = 00, 01, 02, 03, 04
A
= Assembly Location
L
= Wafer Lot
Y
= Year
W
= Work Week
G
= Pb−Free Package
PIN CONNECTIONS
EN/SYNC 1
8 VFB
ISNS 2
7 VC
GND 3
6 VIN
GDRV 4
5 VDRV
(Top View)
ORDERING INFORMATION
Device
Package
Shipping†
NCV887100D1R2G
SOIC−8
(Pb−Free)
2500 / Tape &
Reel
NCV887101D1R2G
SOIC−8
(Pb−Free)
2500 / Tape &
Reel
NCV887102D1R2G
SOIC−8
(Pb−Free)
2500 / Tape &
Reel
NCV887103D1R2G
SOIC−8
(Pb−Free)
2500 / Tape &
Reel
NCV887104D1R2G
SOIC−8
(Pb−Free)
2500 / Tape &
Reel
†For information on tape and reel specifications,
including part orientation and tape sizes, please
refer to our Tape and Reel Packaging Specification
Brochure, BRD8011/D.
© Semiconductor Components Industries, LLC, 2012
September, 2012 − Rev. 3
1
Publication Order Number:
NCV8871/D
NCV8871
6
TEMP
VDRV
FAULT
LOGIC
EN/SYNC
SYNC
1
OSC
SC
VC
5
CLK
7
PWM
EN/
4
2
CL
+
RC
DRIVE
LOGIC
CSA
3
CDRV
VDRV
Cg
L
D
Vo
Q
GDRV
ISNS
GND
Co
RSNS
RF1
SCP
CC
Vg
VIN
8
Gm
SS
VFB
RF2
Vref
Figure 1. Simplified Block Diagram and Application Schematic
PACKAGE PIN DESCRIPTIONS
Pin No.
Pin
Symbol
1
EN/SYNC
2
ISNS
Current sense input. Connect this pin to the source of the external N−MOSFET, through a current−sense
resistor to ground to sense the switching current for regulation and current limiting.
3
GND
Ground reference.
4
GDRV
Gate driver output. Connect to gate of the external N−MOSFET. A series resistance can be added from
GDRV to the gate to tailor EMC performance.
5
VDRV
Driving voltage. Internally−regulated supply for driving the external N−MOSFET, sourced from VIN. Bypass
with a 1.0 mF ceramic capacitor to ground.
6
VIN
Input voltage. If bootstrapping operation is desired, connect a diode from the input supply to VIN, in addition to a diode from the output voltage to VDRV and/or VIN.
7
VC
Output of the voltage error amplifier. An external compensator network from VC to GND is used to stabilize
the converter.
8
VFB
Output voltage feedback. A resistor from the output voltage to VFB with another resistor from VFB to GND
creates a voltage divider for regulation and programming of the output voltage.
Function
Enable and synchronization input. The falling edge synchronizes the internal oscillator. The part is disabled
into sleep mode when this pin is brought low for longer than the enable time−out period.
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NCV8871
ABSOLUTE MAXIMUM RATINGS (Voltages are with respect to GND, unless otherwise indicated)
Rating
Value
Unit
−0.3 to 40
V
Peak Transient Voltage (Load Dump on VIN)
45
V
Dc Supply Voltage (VDRV, GDRV)
12
V
−0.3 to 6
V
−0.3 to 3.6
V
Dc Voltage (EN/SYNC)
−0.3 to 6
V
Dc Voltage Stress (VIN − VDRV)*
−0.7 to 45
V
Operating Junction Temperature
−40 to 150
°C
Storage Temperature Range
−65 to 150
°C
265 peak
°C
Dc Supply Voltage (VIN)
Peak Transient Voltage (VFB)
Dc Voltage (VC, VFB, ISNS)
Peak Reflow Soldering Temperature: Pb−Free, 60 to 150 seconds at 217°C
Stresses exceeding Maximum Ratings may damage the device. Maximum Ratings are stress ratings only. Functional operation above the
Recommended Operating Conditions is not implied. Extended exposure to stresses above the Recommended Operating Conditions may affect
device reliability.
*An external diode from the input to the VIN pin is required if bootstrapping VDRV and VIN off of the output voltage.
PACKAGE CAPABILITIES
Characteristic
ESD Capability (All Pins)
Human Body Model
Machine Model
Value
Unit
w2.0
w200
kV
V
Moisture Sensitivity Level
Package Thermal Resistance
Junction−to−Ambient, RqJA (Note 1)
1
−
100
°C/W
1. 1 in2, 1 oz copper area used for heatsinking.
Device Variations
The NCV8871 features several variants to better fit a
multitude of applications. The table below shows the typical
values of parameters for the parts that are currently
available.
TYPICAL VALUES
Part No.
Dmax
fs
tss
Sa
Vcl
Isrc
Isink
VDRV
SCE
NCV887100
88%
170 kHz
7.4 ms
53 mV/ms
400 mV
800 mA
600 mA
10.5 V
Y
NCV887101
86%
1000 kHz
1.25 ms
16 mV/ms
400 mV
575 mA
350 mA
6.3 V
Y
NCV887102
91%
1000 kHz
1.25 ms
53 mV/ms
400 mV
800 mA
600 mA
6.3 V
N
NCV887103
93%
340 kHz
3.7 ms
53 mV/ms
200 mV
575 mA
350 mA
8.4 V
Y
NCV887104
93%
340 kHz
3.7 ms
53 mV/ms
200 mV
800 mA
600 mA
8.4 V
N
DEFINITIONS
Symbol
Dmax
Characteristic
Symbol
Characteristic
Symbol
Characteristic
Maximum Duty Cycle
fs
Switching Frequency
tss
Soft−Start Time
Sa
Slope Compensating Ramp
Vcl
Current Limit Trip Voltage
Isrc
Gate Drive Sourcing Current
Isink
Gate Drive Sinking Current
VDRV
Drive Voltage
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SCE
Short Circuit Enable
NCV8871
ELECTRICAL CHARACTERISTICS (−40°C < TJ < 150°C, 3.2 V < VIN < 40 V, unless otherwise specified) Min/Max values are
guaranteed by test, design or statistical correlation.
Characteristic
Symbol
Conditions
Min
Typ
Max
Unit
GENERAL
Quiescent Current, Sleep Mode
Iq,sleep
VIN = 13.2 V, EN = 0, TJ = 25°C
−
2.0
−
mA
Quiescent Current, Sleep Mode
Iq,sleep
VIN = 13.2 V, EN = 0, −40°C < TJ < 125°C
−
2.0
6.0
mA
Quiescent Current, No switching
Iq,off
Into VIN pin, EN = 1, No switching
−
1.5
2.5
mA
Quiescent Current, Switching,
normal operation
Iq,on
Into VIN pin, EN = 1, Switching
−
3.0
6.0
mA
90
115
140
ns
OSCILLATOR
Minimum pulse width
ton,min
Maximum duty cycle
Dmax
NCV887100
NCV887101
NCV887102
NCV887103
NCV887104
86
84
89
91
91
88
86
91
93
93
90
88
93
95
95
%
Switching frequency
fs
NCV887100
NCV887101
NCV887102
NCV887103
NCV887104
153
900
900
306
306
170
1000
1000
340
340
187
1100
1100
374
374
kHz
Soft−start time
tss
From start of switching with VFB = 0 until
reference voltage = VREF
NCV887100
NCV887101
NCV887102
NCV887103
NCV887104
6.0
1.0
1.0
3.0
3.0
7.4
1.25
1.25
3.7
3.7
8.8
1.5
1.5
4.4
4.4
From EN → 1 until start of switching with
VFB = 0
−
240
280
NCV887100
NCV887101
NCV887102
NCV887103
NCV887104
46
13
46
46
46
53
16
53
53
53
60
19
60
60
60
mV/ms
VEN/SYNC = 5 V
−
5.0
10
mA
Soft−start delay
Slope compensating ramp
tss,dly
Sa
ms
ms
ENABLE/SYNCHRONIZATION
EN/SYNC pull−down current
IEN/SYNC
EN/SYNC input high voltage
Vs,ih
2.0
−
5.0
V
EN/SYNC input low voltage
Vs,il
0
−
800
mV
EN/SYNC time−out ratio
%ten
From SYNC falling edge, to oscillator control (EN high) or shutdown (EN low), Percent of typical switching period
−
−
350
%
Percent of fs
−
−
80
%
SYNC minimum frequency ratio
SYNC maximum frequency
%fsync,min
fsync,max
Synchronization delay
ts,dly
Synchronization duty cycle
Dsync
1.1
−
−
MHz
−
50
100
ns
25
−
75
%
Input−to−output gain at dc, ISNS v 1 V
0.9
1.0
1.1
V/V
2.5
−
−
MHz
−
30
50
mA
From SYNC falling edge to GDRV falling
edge
CURRENT SENSE AMPLIFIER
Low−frequency gain
Acsa
Bandwidth
BWcsa
Gain of Acsa − 3 dB
ISNS input bias current
Isns,bias
Out of ISNS pin
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NCV8871
ELECTRICAL CHARACTERISTICS (−40°C < TJ < 150°C, 3.2 V < VIN < 40 V, unless otherwise specified) Min/Max values are
guaranteed by test, design or statistical correlation.
Characteristic
Symbol
Conditions
Min
Typ
Max
Unit
360
360
360
180
180
400
400
400
200
200
440
440
440
220
220
−
80
125
ns
125
150
175
%
−
−
125
ns
0.8
1.2
1.5
mS
2.0
−
−
MW
−
0.5
2.0
mA
Vref
1.176
1.200
1.224
V
VEA maximum output voltage
Vc,max
2.5
−
−
V
VEA minimum output voltage
Vc,min
−
−
0.3
V
CURRENT SENSE AMPLIFIER
Current limit threshold voltage
Vcl
Voltage on ISNS pin
NCV887100
NCV887101
NCV887102
NCV887103
NCV887104
Current limit,
Response time
tcl
CL tripped until GDRV falling edge,
VISNS = Vcl + 40 mV
Overcurrent protection,
Threshold voltage
%Vocp
Overcurrent protection,
Response Time
tocp
Percent of Vcl
From overcurrent event, Until switching
stops, VISNS = VOCP + 40 mV
mV
VOLTAGE ERROR OPERATIONAL TRANSCONDUCTANCE AMPLIFIER
Transconductance
gm,vea
VEA output resistance
Ro,vea
VFB input bias current
Ivfb,bias
Reference voltage
VFB – Vref = ± 20 mV
Current out of VFB pin
VEA sourcing current
Isrc,vea
VEA output current, Vc = 2.0 V
80
100
−
mA
VEA sinking current
Isnk,vea
VEA output current, Vc = 0.7 V
80
100
−
mA
GATE DRIVER
Sourcing current
Isrc
VDRV ≥ 6 V, VDRV − VGDRV = 2 V
NCV887100
NCV887101
NCV887102
NCV887103
NCV887104
600
400
600
400
600
800
575
800
575
800
−
−
−
−
−
Sinking current
Isink
VGDRV ≥ 2 V
NCV887100
NCV887101
NCV887102
NCV887103
NCV887104
500
250
500
250
500
600
350
600
350
600
−
−
−
−
−
VIN − VDRV, IvDRV = 25 mA
−
0.3
0.6
V
VIN − VDRV = 1 V
35
45
−
mA
−
−
0.7
V
Driving voltage dropout
Vdrv,do
mA
mA
Driving voltage source current
Idrv
Backdrive diode voltage drop
Vd,bd
VDRV − VIN, Id,bd = 5 mA
Driving voltage
VDRV
IVDRV = 0.1 − 25 mA
NCV887100
NCV887101
NCV887102
NCV887103
NCV887104
10
6.0
6.0
8.0
8.0
10.5
6.3
6.3
8.4
8.4
11
6.6
6.6
8.8
8.8
Undervoltage lock−out,
Threshold voltage
Vuvlo
VIN falling
3.0
3.1
3.2
V
Undervoltage lock−out,
Hysteresis
Vuvlo,hys
VIN rising
50
125
200
mV
V
UVLO
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NCV8871
ELECTRICAL CHARACTERISTICS (−40°C < TJ < 150°C, 3.2 V < VIN < 40 V, unless otherwise specified) Min/Max values are
guaranteed by test, design or statistical correlation.
Characteristic
Symbol
Conditions
Min
Typ
Max
Unit
SHORT CIRCUIT PROTECTION
Startup blanking period
%tscp,dly
From start of soft−start, Percent of tss
100
120
150
%
Hiccup−mode period
%thcp,dly
From shutdown to start of soft−start,
Percent of tss
70
85
100
%
VFB as percent of Vref
60
67
75
%
tscp
From VFB < Vscp to stop switching
−
35
100
ns
Thermal shutdown threshold
Tsd
TJ rising
160
170
180
°C
Thermal shutdown hysteresis
Tsd,hys
TJ falling
10
15
20
°C
Thermal shutdown delay
tsd,dly
From TJ > Tsd to stop switching
−
−
100
ns
Short circuit threshold voltage
Short circuit delay
%Vscp
THERMAL SHUTDOWN
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NCV8871
TYPICAL PERFORMANCE CHARACTERISTICS
5.5
TJ = 25°C
Iq,on, QUIESCENTCURRENT (mA)
Iq,sleep, SLEEP CURRENT (mA)
7
6
5
4
3
2
1
0
0
10
20
30
VIN, INPUT VOLTAGE (V)
5.0
4.5
4.0
3.5
40
TJ = 25°C,
VIN = 13.2 V
0
Figure 2. Sleep Current vs. Input Voltage
3.30
Iq,on, QUIESCENTCURRENT (mA)
Iq,sleep, SLEEP CURRENT (mA)
VIN = 13.2 V
5
4
3
2
1
0
50
100
150
VIN = 13.2 V
3.25 fs = 170 kHz
3.20
3.15
3.10
3.05
3.00
−40
200
TJ, JUNCTION TEMPERATURE (°C)
NORMALIZED CURRENT LIMIT (25°C)
ton,min MINIMUM ON TIME (ns)
125
123
121
119
117
10
60
110
TJ, JUNCTION TEMPERATURE (°C)
10
60
110
TJ, JUNCTION TEMPERATURE (°C)
160
Figure 5. Quiescent Current vs. Temperature
Figure 4. Sleep Current vs. Temperature
115
−40
1000
Figure 3. Quiescent Current vs. Switching
Frequency
6
0
−50
200
400
600
800
fs, SWITCHING FREQUENCY (kHz)
160
1.010
1.005
1.000
0.995
0.990
−40
Figure 6. Minimum On Time vs. Temperature
10
60
110
TJ, JUNCTION TEMPERATURE (°C)
Figure 7. Normalized Current Limit vs.
Temperature
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160
NCV8871
TYPICAL PERFORMANCE CHARACTERISTICS
7
Vref, REFERENCE VOLTAGE (V)
Ienable, PULLDOWN CURRENT (mA)
1.205
1.203
1.201
1.199
1.197
TJ = 25°C
5
4
3
2
1
0
0
TJ, JUNCTION TEMPERATURE (°C)
2
3
4
Venable, VOLTAGE (V)
Figure 8. Reference Voltage vs. Temperature
Figure 9. Enable Pulldown Current vs. Voltage
10
60
110
160
1
8.0
Ienable, PULLDOWN CURRENT (mA)
1.195
−40
6
7.5
7.0
6.5
6.0
5.5
5.0
−40
10
60
110
TJ, JUNCTION TEMPERATURE (°C)
Figure 10. Enable Pulldown Current vs.
Temperature
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160
5
6
NCV8871
THEORY OF OPERATION
VIN
Oscillator
PWM Comparator
−
GDRV
S
Q
VOUT
Gate
Drive
R
+
+
L
ISNS
+
CO
RL
−
CSA
Slope
Compensation
Voltage Error
VFB
−
+
VEA
NCV8871
Compensation
Figure 11. Current Mode Control Schematic
Current Mode Control
If the voltage across the current sense resistor exceeds the
over current threshold voltage the device enters over current
hiccup mode. The device will remain off for the hiccup time
and then go through the soft−start procedure.
The NCV8871 incorporates a current mode control
scheme, in which the PWM ramp signal is derived from the
power switch current. This ramp signal is compared to the
output of the error amplifier to control the on−time of the
power switch. The oscillator is used as a fixed−frequency
clock to ensure a constant operational frequency. The
resulting control scheme features several advantages over
conventional voltage mode control. First, derived directly
from the inductor, the ramp signal responds immediately to
line voltage changes. This eliminates the delay caused by the
output filter and the error amplifier, which is commonly
found in voltage mode controllers. The second benefit
comes from inherent pulse−by−pulse current limiting by
merely clamping the peak switching current. Finally, since
current mode commands an output current rather than
voltage, the filter offers only a single pole to the feedback
loop. This allows for a simpler compensation.
The NCV8871 also includes a slope compensation
scheme in which a fixed ramp generated by the oscillator is
added to the current ramp. A proper slope rate is provided to
improve circuit stability without sacrificing the advantages
of current mode control.
Short Circuit Protection
If the short circuit enable bit is set (SCE = Y) the device
will attempt to protect the power MOSFET from damage.
When the output voltage falls below the short circuit trip
voltage, after the initial short circuit blanking time, the
device enters short circuit latch off. The device will remain
off for the hiccup time and then go through the soft−start.
EN/SYNC
The Enable/Synchronization pin has three modes. When
a dc logic high (CMOS/TTL compatible) voltage is applied
to this pin the NCV8871 operates at the programmed
frequency. When a dc logic low voltage is applied to this pin
the NCV8871 enters a low quiescent current sleep mode.
When a square wave of at least %fsync,min of the free running
switching frequency is applied to this pin, the switcher
operates at the same frequency as the square wave. If the
signal is slower than this, it will be interpreted as enabling
and disabling the part. The falling edge of the square wave
corresponds to the start of the switching cycle. If device is
disabled, it must be disabled for 7 clock cycles before being
re−enabled.
Current Limit
The NCV8871 features two current limit protections,
peak current mode and over current latch off. When the
current sense amplifier detects a voltage above the peak
current limit between ISNS and GND after the current limit
leading edge blanking time, the peak current limit causes the
power switch to turn off for the remainder of the cycle. Set
the current limit with a resistor from ISNS to GND, with R
= VCL / Ilimit.
UVLO
Input Undervoltage Lockout (UVLO) is provided to
ensure that unexpected behavior does not occur when VIN
is too low to support the internal rails and power the
controller. The IC will start up when enabled and VIN
surpasses the UVLO threshold plus the UVLO hysteresis
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NCV8871
voltage is higher than the output voltage, the minimum duty
cycle will be negative. This is because a boost converter
cannot have an output lower than the input. In situations
where the input is higher than the output, the output will
follow the input, minus the diode drop of the output diode
and the converter will not attempt to switch.
If the calculated Dmax is higher the Dmax of the NCV8871,
the conversion will not be possible. It is important for a boost
converter to have a restricted Dmax, because while the ideal
conversion ration of a boost converter goes up to infinity as
D approaches 1, a real converter’s conversion ratio starts to
decrease as losses overtake the increased power transfer. If
the converter is in this range it will not be able to regulate
properly.
If the following equation is not satisfied, the device will
skip pulses at high VIN:
and will shut down when VIN drops below the UVLO
threshold or the part is disabled.
Internal Soft−Start
To insure moderate inrush current and reduce output
overshoot, the NCV8871 features a soft start which charges a
capacitor with a fixed current to ramp up the reference voltage.
This fixed current is based on the switching frequency, so
that if the NCV8871 is synchronized to twice the default
switching frequency the soft start will last half as long.
VDRV
An internal regulator provides the drive voltage for the
gate driver. Bypass with a ceramic capacitor to ground to
ensure fast turn on times. The capacitor should be between
0.1 mF and 1 mF, depending on switching speed and charge
requirements of the external MOSFET.
D min
w t on(min)
fs
APPLICATION INFORMATION
Where: fs: switching frequency [Hz]
ton(min): minimum on time [s]
Design Methodology
This section details an overview of the component selection
process for the NCV8871 in continuous conduction mode
boost. It is intended to assist with the design process but does
not remove all engineering design work. Many of the
equations make heavy use of the small ripple approximation.
This process entails the following steps:
1. Define Operational Parameters
2. Select Current Sense Resistor
3. Select Output Inductor
4. Select Output Capacitors
5. Select Input Capacitors
6. Select Feedback Resistors
7. Select Compensator Components
8. Select MOSFET(s)
9. Select Diode
2. Select Current Sense Resistor
Current sensing for peak current mode control and current
limit relies on the MOSFET current signal, which is
measured with a ground referenced amplifier. The easiest
method of generating this signal is to use a current sense
resistor from the source of the MOSFET to device ground.
The sense resistor should be selected as follows:
RS +
Where: RS: sense resistor [W]
VCL: current limit threshold voltage [V]
ICL: desire current limit [A]
3. Select Output Inductor
1. Define Operational Parameters
The output inductor controls the current ripple that occurs
over a switching period. A high current ripple will result in
excessive power loss and ripple current requirements. A low
current ripple will result in a poor control signal and a slow
current slew rate in case of load steps. A good starting point
for peak to peak ripple is around 10% of the inductor current
at the maximum load at the worst case VIN, but operation
should be verified empirically. The worst case VIN is half of
VOUT, or whatever VIN is closest to half of VIN. After
choosing a peak current ripple value, calculate the inductor
value as follows:
Before beginning the design, define the operating
parameters of the application. These include:
VIN(min): minimum input voltage [V]
VIN(max): maximum input voltage [V]
VOUT: output voltage [V]
IOUT(max): maximum output current [A]
ICL: desired typical cycle-by-cycle current limit [A]
From this the ideal minimum and maximum duty cycles
can be calculated as follows:
D min + 1 *
D max + 1 *
V CL
I CL
V IN(max)
V OUT
L+
V IN(min)
V IN(WC) 2 D WC
DI L,max f sV OUT
Where: VIN(WC): VIN value as close as possible to
half of VOUT [V]
DWC: duty cycle at VIN(WC)
DIL,max: maximum peak to peak ripple [A]
V OUT
Both duty cycles will actually be higher due to power loss
in the conversion. The exact duty cycles will depend on
conduction and switching losses. If the maximum input
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NCV8871
7. Select Compensator Components
The maximum average inductor current can be calculated
as follows:
I L,avg +
Current Mode control method employed by the NCV8871
allows the use of a simple, Type II compensation to optimize
the dynamic response according to system requirements.
V OUTI OUT(max)
V IN(min)
8. Select MOSFET(s)
The Peak Inductor current can be calculated as follows:
I L,peak + I L,avg )
In order to ensure the gate drive voltage does not drop out
the MOSFET(s) chosen must not violate the following
inequality:
V IN(min) 2 D max
Lf sV OUT
Where: IL,peak: Peak inductor current value [A]
Q g(total) v
4. Select Output Capacitors
The output capacitors smooth the output voltage and
reduce the overshoot and undershoot associated with line
transients. The steady state output ripple associated with the
output capacitors can be calculated as follows:
Where: Qg(total): Total Gate Charge of MOSFET(s) [C]
Idrv: Drive voltage current [A]
fs: Switching Frequency [Hz]
The maximum RMS Current can be calculated as follows:
V OUT(ripple) +
I OUT(max)ǒV OUT * V IN(min)Ǔ
ǒC OUTfǓ
2
)
I D(max) + I out
I OUT(max)V OUTR ESR
V IN(min)
Ǹ
V Q(max) + V OUT(max)
V OUT * V IN(min)
V IN(min)
9. Select Diode
The output diode rectifies the output current. The average
current through diode will be equal to the output current:
The use of parallel ceramic bypass capacitors is strongly
encouraged to help with the transient response.
I D(avg) + I OUT(max)
5. Select Input Capacitors
Additionally, the diode must block voltage equal to the
higher of the output voltage and the maximum input voltage:
The input capacitor reduces voltage ripple on the input to
the module associated with the ac component of the input
current.
I Cin(RMS) +
V D(max) + V OUT(max)
The maximum power dissipation in the diode can be
calculated as follows:
V IN(WC) 2 D WC
Lf sV OUT2 Ǹ3
P D + V f (max) I OUT(max)
Where: Pd: Power dissipation in the diode [W]
Vf(max): Maximum forward voltage of the diode [V]
6. Select Feedback Resistors
The feedback resistors form a resistor divider from the
output of the converter to ground, with a tap to the feedback
pin. During regulation, the divided voltage will equal Vref.
The lower feedback resistor can be chosen, and the upper
feedback resistor value is calculated as follows:
R upper + R lower
ǸD
DȀ
The maximum voltage across the MOSFET will be the
maximum output voltage, which is the higher of the
maximum input voltage and the regulated output voltaged:
The capacitors need to survive an RMS ripple current as
follows:
I Cout(RMS) + I OUT
I drv
fs
Low Voltage Operation
If the input voltage drops below the UVLO or MOSFET
threshold voltage, another voltage may be used to power the
device. Simply connect the voltage you would like to boost
to the inductor and connect the stable voltage to the VIN pin
of the device. In boost configuration, the output of the
converter can be used to power the device. In some cases it
may be desirable to connect 2 sources to VIN pin, which can
be accomplished simply by connecting each of the sources
through a diode to the VIN pin.
ǒV out * V refǓ
V ref
The total feedback resistance (Rupper + Rlower) should be in
the range of 1 kW – 100 kW.
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11
NCV8871
PACKAGE DIMENSIONS
SOIC−8 NB
CASE 751−07
ISSUE AK
−X−
NOTES:
1. DIMENSIONING AND TOLERANCING PER
ANSI Y14.5M, 1982.
2. CONTROLLING DIMENSION: MILLIMETER.
3. DIMENSION A AND B DO NOT INCLUDE
MOLD PROTRUSION.
4. MAXIMUM MOLD PROTRUSION 0.15 (0.006)
PER SIDE.
5. DIMENSION D DOES NOT INCLUDE DAMBAR
PROTRUSION. ALLOWABLE DAMBAR
PROTRUSION SHALL BE 0.127 (0.005) TOTAL
IN EXCESS OF THE D DIMENSION AT
MAXIMUM MATERIAL CONDITION.
6. 751−01 THRU 751−06 ARE OBSOLETE. NEW
STANDARD IS 751−07.
A
8
5
S
B
0.25 (0.010)
M
Y
M
1
4
−Y−
K
G
C
N
DIM
A
B
C
D
G
H
J
K
M
N
S
X 45 _
SEATING
PLANE
−Z−
0.10 (0.004)
H
D
0.25 (0.010)
M
Z Y
S
X
M
J
S
MILLIMETERS
MIN
MAX
4.80
5.00
3.80
4.00
1.35
1.75
0.33
0.51
1.27 BSC
0.10
0.25
0.19
0.25
0.40
1.27
0_
8_
0.25
0.50
5.80
6.20
INCHES
MIN
MAX
0.189
0.197
0.150
0.157
0.053
0.069
0.013
0.020
0.050 BSC
0.004
0.010
0.007
0.010
0.016
0.050
0 _
8 _
0.010
0.020
0.228
0.244
SOLDERING FOOTPRINT*
1.52
0.060
7.0
0.275
4.0
0.155
0.6
0.024
1.270
0.050
SCALE 6:1
mm Ǔ
ǒinches
*For additional information on our Pb−Free strategy and soldering
details, please download the ON Semiconductor Soldering and
Mounting Techniques Reference Manual, SOLDERRM/D.
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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NCV8871/D