NCV8881
Buck Regulator Automotive, Watchdog
1.5 A
The NCV8881 consists of a Buck switching regulator (SMPS) with
a combination SMPS output undervoltage monitor and CPU watchdog
circuit. In addition, two fixed−voltage low dropout regulator outputs
are provided, and share an LDO output voltage status output. Once
enabled, regulator operation continues until the Watchdog signal is no
longer present. The NCV8881 is intended for Automotive,
battery−connected applications that must withstand a 40 V load dump.
The switching regulator is capable of converting the typical 9 V to
19 V automotive input voltage range to outputs from 3.3 V to 8 V at a
constant switching frequency, which can be resistor programmed or
synchronized to an external clock signal. Enable input threshold and
hysteresis are programmable, with the enable input state replicated at
an open drain Ignition Buffer output. The regulators are protected by
current limiting, input overvoltage and overtemperature shutdown, as
well as SMPS short circuit shutdown.
Features
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1.5 A Switching Regulator (internal power switch)
100 mA, 5 V LDO Output
40 mA, 8.5 V LDO Output
Operating Range 5 V to 19 V
Programmable SMPS Frequency
SMPS can be Synchronized to an External Clock
Programmable SMPS Output Voltage Down to 0.8 V
$2% Reference Voltage Tolerance
Internal SMPS Soft−Start
Voltage−mode SMPS Control
SMPS Cycle−by−Cycle Current Limit and Short−Circuit Protection
Internal Bootstrap Diode
Logic level Enable Input
Enable Input Hysteresis Programmable by External Resistor Divider
Enable Input State is Replicated at an Open Drain Output
CPU Watchdog with Resistor Programmable Delays
Watchdog Reset Output also Indicates SMPS Output Out of Regulation
Battery Input Withstands Load Dump to 40 V
Low Standby Current
Thermal Shutdown (TSD)
NCV Prefix for Automotive and Other Applications Requiring Site
and Change Controls
These are Pb−Free Devices
Applications
• Audio
• Infotainment
© Semiconductor Components Industries, LLC, 2011
September, 2019 − Rev. 1
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MARKING
DIAGRAMS
16
SO−16W EP
PW SUFFIX
CASE 751AG
16
NCV8881
AWLYYWWG
1
1
A
WL
YY
WW
G
= Assembly Location
= Wafer Lot
= Year
= Work Week
= Pb−Free Package
(Note: Microdot may be in either location)
PIN CONNECTIONS
IGNBUF
WDI
RDLY
RESB
EN
SYNC
ROSC
GND
1
16
5P0
LDOMON
8P5
VIN
SW
BST
FB
COMP
(Top View)
ORDERING INFORMATION
See detailed ordering and shipping information in the package
dimensions section on page 32 of this data sheet.
• Safety – Vision Systems
• Instrumentation
1
Publication Order Number:
NCV8881/D
NCV8881
IGNITION
RIGBUF
BUFFER
FROM CPU
WATCHDOG OUT
IGNBUF
REGULATED
5.0V
5P0
WDI
LDO
MONITOR
LDOMON
8P5
RDLY
REGULATED
8.5V
BEAD
RDLY
TO CPU
RESET
CS5P0
RMON
C8P5
CS8P5
BATTERY
RRESB
RESB
VIN
CIN
ENABLE
REGULATED
SMPS OUTPUT
R1
EN
SW
L1
R2
CBST
COUT
DFW
SYNC
SYNC
CZ1
BST
RP2
ROSC
RFB1
FB
ROSC
CP1
RZ1
GND
RFB2
CP3
COMP
Figure 1. Typical Application
RIGBUF
IGNITION
BUFFER
IGNBUF
1
WATCHDOG
INPUT
BUFFERED
ENABLE
LOGIC
RMON
QIB
WDI
2
RDLY
3
TSD
WATCHDOG
TIMER
TEMP
SENSE
RRESB
8P5
DBST2
5V
REGULATOR
8.5V
REGULATOR
FAULT(H)
SYNC
6
GND
8
CBST
BST
11
HYSTERESIS
OSCILLATOR
CZ1
ERROR
AMP
NCV8881
Figure 2. NCV8881 Detailed Block Diagram
2
RFB1
FB
10
REF
CP1
RZ1
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COUT
RP2
SHORT CKT
MONITOR
PWM
COMPARATOR
L1
DFW
UNDERVOLTAGE
MONITOR
OC
RUN
ROSC
SWITCHER
OUT
SW
12
SW_UV
ROSC
7
CIN
RH
QH
SYNC
BATTERY
POWER
ENABLE
CLAMP
S+8.5
CS8P5
SWITCH
EN
5
R1
R2
C8P5
VIN
13
VIN_OV
/UVLO
RESB
4
BEAD
LDO
MONITOR
14
DBST1
QRB
ENABLE
QLM
MONITOR
CS5
LDOMON
15
NOPULSE
RDLY
CPU
RESET
S+5
5P0
16
COMP
9
CP3
RFB2
NCV8881
MAXIMUM RATINGS
Value
Unit
Min/Max Voltage on WDI
Rating
Symbol
−0.3 to 7
V
Min/Max Voltage on RDLY
−0.3 to 7
V
Min/Max Voltage on RESB
−0.3 to 7
V
Min/Max Voltage on EN
−0.3 to 10
V
10
mA
Max EN Current
Min EN Current (with zero VIN voltage)
−10
mA
Min/Max Voltage on SYNC
−0.3 to 7
V
Min/Max Voltage on ROSC
−0.3 to 7
V
Min/Max Voltage COMP
−0.3 to 7
V
Min/Max Voltage FB
−0.3 to 7
V
−0.7
−3
V
Max Voltage VIN to SW
40
V
Max Voltage VIN
40
V
Min/Max Voltage BST
−0.3 to 30
V
Min/Max Voltage BST to SW
−0.3 to 15
V
Min/Max Voltage on 8P5
−0.3 to 9.5
V
70
mA
Min/Max Voltage on LDOMON
−0.3 to 7
V
Min/Max Voltage on 5P0
−0.3 to 7
V
Min Voltage SW
– DC
− 20 ns
Max 8P5 Current
Min/Max Voltage IGNBUF
−0.3 to 7
V
−55 to +150
°C
TJ
−40 to + 150
°C
ESD withstand Voltage Human Body Model
VESD
2.0
200
>1.0
kV
V
kV
Moisture Sensitivity
MSL
Level 1
Storage Temperature range
Operating Junction Temperature Range
Machine Model
Charged Device Model
Peak Reflow Soldering Temperature
260
°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.
THERMAL CHARACTERISTICS
Board/Mounting Conditions Typical Value
Minimum Pad (Note 1)
1 sq. inch (Note 2)
Unit
Junction−to−case top (YJT, qJT)
30
16
°C/W
Junction−to−pin 1(YJL1, qJL1)
70
65
°C/W
Junction−to−board (YJB, qJB) (Note 3)
15
17
°C/W
Junction−to−ambient (RqJA, qJA)
150
55
°C/W
Parameter
Specific Notes on Thermal Characterization Conditions:
NOTE:
All boards are 0.062” thick FR4, 3” square, with varying amounts of copper heat spreader, in still air (free convection) conditions.
Numerical values are derived from an axisymmetric finite−element model where active die area, total die area, flag area, pad area,
and board area are equated to the actual corresponding areas.
1. 1 oz. copper, 17.2 mm2 spreader area (minimum exposed pad, not including traces which are assumed).
2. 1 oz. copper, 645 mm2 (1 in2) spreader area (includes exposed pad).
3. “Board” is defined as center of exposed pad soldered to board; this is the recommended number to be used for thermal calculations, as it
best represents the primary heat flow path and is least sensitive to board and ambient properties.
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3
NCV8881
PIN FUNCTION DESCRIPTIONS
Pin No.
Symbol
1
IGNBUF
2
WDI
CMOS compatible Watchdog pulse input from a CPU. To be valid, the time between falling edges of this
signal must be less than the programmed Watchdog Delay.
3
RDLY
Delay programming pin for POR, BOOT and Watchdog delays. Connect a resistor between this pin and
ground.
4
RESB
This is an open drain output for resetting a CPU. RESB goes low if the WDI signal period is longer than
the programmed Watchdog delay, if VIN is above or below operating voltage, if the SMPS output is out of
regulation, or if the part is in thermal shutdown.
5
EN
Logic compatible Enable input. Once a high is received at the EN pin, the part enters a startup
sequence. Until expiration of the Soft−Start Timer, a low at the EN pin will shut off the part. Upon
expiration of the Soft−Start Timer, a low at the EN pin will shut the part off only if the SMPS output is out
of regulation, or the signal at the WDI input is not valid.
6
SYNC
Logic compatible Synchronization input. Grounding this input allows a resistor between the ROSC pin
and ground to control the switching frequency. Connecting this pin to an external clock synchronizes
switching to the rising edge of the clock.
7
ROSC
Oscillator frequency programming pin. Connect an external resistor from this pin to GND to set the
switching frequency. Leave this pin floating to operate at the default frequency of the internal oscillator.
Switching frequency is not controlled by this resistance if a clock is present at the SYNC pin, but the
resistance remains in control of the modulator ramp amplitude.
8
GND
9
COMP
10
FB
11
BST
Bootstrap input provides drive voltage higher than VIN to the SMPS N−channel Power Switch for
minimum switch RDS(on) and highest efficiency. For a typical application connect a 0.1 mF ceramic
capacitor from this pin to the SW pin, in close proximity to both pins.
12
SW
Switching node of the Switching Regulator. Connect the SMPS output inductor and cathode of the SMPS
freewheeling diode to this pin.
13
VIN
Input voltage from battery. Place an input filter capacitor in close proximity to this pin.
14
8P5
Output of the internal 8.5 V linear regulator. This provides regulated gate drive voltage to the SMPS
Power Switch. For a typical application connect a 4.7 mF ceramic capacitor in series with 0.5 W from this
pin to ground.
15
LDOMON
16
5P0
EXPOSED
PAD
Description
This open drain output is pulled low whenever the EN signal is latched and a low level is recognized at
the EN input.
Battery return, and ground reference for output voltages.
Switching Regulator Error Amplifier output for tailoring SMPS transient response with external
compensation components.
Feedback input pin to program Switching Regulator output voltage, and detect a low or shorted SMPS
output condition.
This open drain output is pulled low if either the 5P0 or 8P5 output is out of regulation.
Output of the internal 5 V linear regulator. For a typical application connect a 4.7 mF ceramic capacitor in
series with 0.5 W from this pin to ground.
Solder this to a low thermal impedance path for cooling.
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4
NCV8881
GENERAL SPECIFICATIONS
ELECTRICAL CHARACTERISTICS (VVIN = 13.2 V, VEN = 2.0 V, CIN = 4.7 mF unless specified otherwise) Min/Max values are valid
for the temperature range −40°C vTJ v 150 °C unless noted otherwise, and are guaranteed by test, design or statistical correlation.
Parameter
Symbol
Conditions
Min
Typ
Max
Unit
VIN UVLO
START Voltage Threshold
VSTRT
5.0
5.6
6.0
V
STOP Voltage Threshold
VSTP
4.2
4.6
5.0
V
VINHYST
0.7
1.1
STOP Voltage Threshold
VOVSTP
19
20
RESTART Voltage Threshold
VOVSTT
18
19.2
VIN UVLO Hysteresis
V
VIN OVERVOLTAGE
21
V
V
QUIESCENT CURRENT
VIN Quiescent Current
IqMAX
VFB = 1 V, TJ = 25°C, VSW = 0 V
2
5
mA
VIN Shutdown Current
IqSBMAX
VEN = 0 V, TJ = 25°C, VSW = 0 V
10
15
mA
1.6
V
ENABLE (EN PIN)
EN Logic High Threshold
VENSTHH
EN Logic Low Threshold
VENSTHL
1.2
V
EN Input Current
IENSWL
VEN = 1.2 V
35
42
55
mA
EN Input Current
IENSWH
VEN = 1.6 V
0.8
1.4
3.0
mA
Response to Open Input
NCV8881 is disabled
Enable Delay
EN high to LDO turn−on
Clamp Current
VEN = 5 V
Clamp Voltage
IEN = 10 mA
38
50
ms
5
20
mA
10.5
12
V
VEN > 1.6 V
0
5
mA
VIGBLO
VEN < 1.2 V, sinking 0.5 mA
0.02
0.1
V
TTSD
(Note 4)
170
180
°C
9
IGNITION BUFFER (IGNBUF PIN)
IGNBUF Output leakage
IGNBUF Output Voltage Low
THERMAL SHUTDOWN (TSD)
Thermal Shutdown
Thermal Shutdown Hysteresis
(Note 4)
4. Guaranteed by design.
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5
160
35
°C
NCV8881
LDO REGULATORS
ELECTRICAL CHARACTERISTICS (VVIN = 13.2 V, VEN = 2.0 V, CIN = 4.7 mF unless specified otherwise) Min/Max values are valid
for the temperature range −40°C vTJ v 150°C unless noted otherwise, and are guaranteed by test, design or statistical correlation.
Parameter
Symbol
Conditions
Min
Typ
Max
Unit
5P0 OUTPUT
Output UV START Threshold
V5UVSTT
Percent of VO5P0
91
95
99
%
Output UV STOP Threshold
V5UVSTP
Percent of VO5P0
89
93
97
%
Output UV Hysteresis
V5VUVH
Percent of VO5P0
Output Voltage Range
VO5P0
Line Regulation
No load
4.8
5.0
105
Dropout Voltage
I5P0 = 70 mA, DV5P0 = 2%
CO
V
4
mV/V
160
205
mA
315
(Note 6)
400
mV
Output capacitance for stability (Note 5)
3.9
100
mF
0.2
5
W
Output Load Capacitance ESR Range
ESRCo
ESR for stability (Note 5)
Power Supply Ripple Rejection
PSRR
VVIN = 13.2 V + 0.5 Vpp 100 Hz
sine−wave, C5P0 = 10 mF (Note 5)
Startup Overshoot
%
5.2
IOUT = 1 mA, 6 V < VIN < 19 V
Current Limit
Output Load Capacitance Range
2
60
R5P0LOAD = 5 kW; C5P0 = 10 mF
(Note 5)
dB
3
%
8P5 OUTPUT
Output UV START Threshold
V8UVSTT
Percent of VO8P5
91
95
99
%
Output UV STOP Threshold
V8UVSTP
Percent of VO8P5
89
93
97
%
Output UV Hysteresis
V8VUVH
Percent of VO8P5
Output Voltage Range
VO8P5
Line Regulation
No load; 9 V < VIN < 19 V
8.26
8.5
44
Dropout Voltage
I8P5 = 20 mA, DV8P5 = 2%
CO
%
8.74
V
7
mV/V
68
85
mA
165
(Note 6)
300
mV
IOUT = 1 mA, 9.5 V < VIN < 19 V
Current Limit
Output Load Capacitance Range
2
Output capacitance for stability (Note 5)
3.9
100
mF
Output Load Capacitance ESR Range
ESRCo
ESR for stability (Note 5)
0.2
5
W
Power Supply Ripple Rejection
PSRR
VVIN = 13.2 V + 0.5 Vpp 100 Hz sine
wave, C8P5 = 10 mF (Note 5)
Startup Overshoot
Output Clamp Voltage
60
3
%
11
13
V
V5P0 > V5UVSTT and V8P5 > V8UVSTT
0.2
5
mA
V5P0 < V5UVSTP or V8P5 < V8UVSTP,
sinking 0.5 mA
0.03
0.1
V
R8P5LOAD = 10 kW; C8P5 = 10 mF (Note 5)
VCLP8P5
dB
I8P5 = 67 mA into the NCV8881
9
LDOMON OUTPUT
Output leakage
Output Voltage Low
VRBLO
5. Guaranteed by design.
6. TJ = 125°C
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6
NCV8881
SMPS REGULATOR
ELECTRICAL CHARACTERISTICS (VVIN = 13.2 V, VEN = 2.0 V, VBST = VSW + 8.2 V, CBST = 0.1 mF, CIN = 4.7 mF unless specified
otherwise) Min/Max values are valid for the temperature range −40°C vTJ v 150 °C unless noted otherwise, and are guaranteed by test,
design or statistical correlation.
Parameter
Symbol
Conditions
Min
Typ
Max
Unit
3
5
7
ms
0.792
0.784
0.8
0.8
0.808
0.816
V
SOFT−START
Soft−Start Completion Time
tSS
VOLTAGE REFERENCE (FB Pin)
FB Voltage (COMP connected to FB)
VFBR
TJ = 25°C
−40°C vTJ v 150°C
FB PIN MONITOR (SMPS Output Monitor)
FB Monitor High Threshold
VFBMONH
VFB increasing; Percent of VFBR
91
95
99
%
FB Monitor Low Threshold
VFBMONL
VFB decreasing; Percent of VFBR
89
93
97
%
FB Monitor Hysteresis
VFBMONY
10
20
FB Low to RESB Output Delay
tFBLDLY
2.5
mV
10
ms
0.1
mA
ERROR AMPLIFIER
FB Bias Current
DC Gain
IFBBIAS
VFB = VFBR
−0.1
AV
(Note 7)
70
dB
GBW
(Note 7)
8
MHz
Slew Rate COMP Rising
VFB = VFBR − 25 mV, CCOMP = 50 pF,
ICOMP = −1 mA, VCOMP within ramp
voltage levels. (Note 7)
6
V/ms
Slew Rate COMP Falling
VFB = VFBR +25 mV, CCOMP = 50 pF,
ICOMP = 1 mA, VCOMP within ramp
voltage levels. (Note 7)
6
V/ms
Gain−Bandwidth Product
COMP Source Current
ISOURCE
VCOMP = 2.2 V
VCOMP = 3.2 V
1.5
1.8
4
4
10
10
mA
mA
ISINK
VCOMP = 2.2 V
VCOMP = 1.1 V
1.3
0.6
3
1.6
10
10
mA
mA
Ramp Peak Voltage
2.8
3.1
3.2
V
Ramp Valley Voltage
1.1
1.2
1.3
V
Ramp Amplitude
1.6
1.9
2.0
V
RROSC = open
ROSC = 36 kW
154
337
170
186
429
kHz
Resistor from ROSC to GND
500
700
850
kHz
0.970
1.02
1.080
V
600
kHz
COMP Sink Current
OSCILLATOR
Frequency
Maximum ROSC Controlled Frequency
ROSC Pin Voltage
FOSC
FOSCMAX
VROSC
RROSC = open
SYNCHRONIZATION
Frequency Range
fSYNCMX
(Note 7)
160
Synchronization Delay
tSNCDLY
From rising SYNC edge
200
370
500
ns
De−Synchronization Delay
tUSNCDLY
From last rising SYNC edge;
ROSC = open
6.6
7.8
10
ms
5
10
mA
2
V
Input Current
VSYNC = 5.0 V
SYNC Logic High Threshold
VSNCTHH
SYNC Logic Low Threshold
VSNCTHL
Response to Input Held High
0.8
Reverts to internal oscillator
(Note 7)
7. Guaranteed by design.
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7
V
NCV8881
SMPS REGULATOR
ELECTRICAL CHARACTERISTICS (VVIN = 13.2 V, VEN = 2.0 V, VBST = VSW + 8.2 V, CBST = 0.1 mF, CIN = 4.7 mF unless specified
otherwise) Min/Max values are valid for the temperature range −40°C vTJ v 150 °C unless noted otherwise, and are guaranteed by test,
design or statistical correlation.
Parameter
Symbol
Conditions
Min
Typ
Max
Unit
SYNCHRONIZATION
Minimum High Pulse Width
tPWHIMIN
time VSYNC is above 2 V (Note 7)
50
ns
Minimum Low Pulse Width
tPWLIMIN
time VSYNC is below 0.8 V (Note 7)
50
ns
Minimum Off Time
tMINOFF
SW falling to SW rising
50
120
200
ns
Minimum On Time
tMINON
SW rising to SW falling
100
330
550
ns
1.75
2.2
DUTY CYCLE LIMITATIONS
CURRENT LIMIT
Current Limit
Current Limit Response Time (Note 7)
From time of power switch turn−on
3
A
200
ns
85
%
250
%
360
mW
SHORT CIRCUIT DETECTOR
FB Pin Threshold
VFBSC
% of VFBR
70
Soft−Start Timer
tSSTIMR
From start of Soft−start, % of tSS (Note 7)
100
RDSON
VBST= VSW + 6.0 V, TJ = 25°C
(Note 7)
76
POWER SWITCH
ON Resistance
SW Risetime
Inductor current = 1 A, TJ = 25°C
(Note 7)
30
ns
SW Falltime
Inductor current = 1 A, TJ = 25°C
(Note 7)
30
ns
7. Guaranteed by design.
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8
NCV8881
WATCHDOG
ELECTRICAL CHARACTERISTICS (VVIN = 13.2 V, VEN = 2 V, CIN = 4.7 mF unless specified otherwise) Min/Max values are valid for
the temperature range −40°C vTJ v 150°C unless noted otherwise, and are guaranteed by test, design or statistical correlation.
Parameter
Symbol
Conditions
Min
Typ
Max
Unit
WATCHDOG INPUT (WDI pin)
2.0
Input High Voltage
V
Input Low Voltage
Input Current
Threshold Frequency
VWDI = 5.0 V
fWDTH
5
0.8
V
10
mA
to prevent RESB low
RDLY = 10 kW
RDLY = 20 kW
RDLY = 30 kW
20.85
10.42
6.95
Hz
Output Voltage
RDLY = 10 kW
0.917
0.99
1.067
V
Output Voltage
RDLY = 30 kW
0.940
1.02
1.092
V
RDLY INPUT
RESB OUTPUT
VFB < VFBMONL, sinking 0.5 mA
0.03
0.1
V
Output leakage
VFB > VFBMONH
0.4
5
mA
POR Delay Time
VFB > VFBMONH to RESB high;
RDLY = 10 kW
RDLY = 20 kW (Note 8)
RDLY = 30 kW (Note 8)
RDLY = open; ROSC = 36 kW (Note 8)
RDLY = open; ROSC = open
4.0
8
12
5
10
15
6.0
12
18
50
110
40
80
120
50
100
150
60
120
180
500
1100
48
96
144
60
120
180
72
144
216
550
1300
Output Voltage Low
VRBLO
tPOR
Boot Delay Time
tBD
Watchdog Delay Time
tWD
RESB high to low;
RDLY = 10 kW
RDLY = 20 kW (Note 8)
RDLY = 30 kW (Note 8)
RDLY = open; ROSC = 36 kW (Note 8)
RDLY = open; ROSC = open
WDI low to RESB low;
RDLY = 10 kW
RDLY = 20 kW (Note 8)
RDLY = 30 kW (Note 8)
RDLY = open; ROSC = 36 kW (Note 8)
RDLY = open; ROSC = open
8. Guaranteed by design.
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9
ms
ms
ms
NCV8881
FAULT RESPONSES
INPUTS
RESPONSE TO A SINGLE FAULT EVENT
FULL OPERATION
RESTORED BY:
FAULT EVENT
EN
EN Latch
5P0
8P5
SMPS
RESB
VIN Undervoltage
L
UNLATCH
SHUTDOWN
SHUTDOWN
SHUTDOWN
LOW
VIN > UVLO, EN
High
VIN Undervoltage
H
UNLATCH
SHUTDOWN
SHUTDOWN
SHUTDOWN
LOW
VIN > UVLO
VIN Overvoltage
L
Stays Latched
SHUTDOWN
SHUTDOWN
SHUTDOWN
LOW
VIN < OV Threshold
VIN Overvoltage
H
Stays Latched
SHUTDOWN
SHUTDOWN
SHUTDOWN
LOW
VIN < OV Threshold
Thermal Shutdown
L
Stays Latched
SHUTDOWN
SHUTDOWN
SHUTDOWN
LOW
Decrease Temp
Thermal Shutdown
H
Stays Latched
SHUTDOWN
SHUTDOWN
SHUTDOWN
LOW
Decrease Temp
5P0 Out of Regulation
L
Stays Latched
Current limited
Stays ON
Stays ON
No Effect
Remove Overload
5P0 Out of Regulation
H
Stays Latched
Current limited
Stays ON
Stays ON
No Effect
Remove Overload
8P5 Out of Regulation
L
Stays Latched
Stays ON
Current limited
Stays ON
No Effect
Remove Overload
8P5 Out of Regulation
H
Stays Latched
Stays ON
Current limited
Stays ON
No Effect
Remove Overload
SMPS Out of Regulation
L
UNLATCH
SHUTDOWN
SHUTDOWN
SHUTDOWN
LOW
EN High
SMPS Out of Regulation
H
Stays Latched
Stays ON
Stays ON
Stays ON
LOW
Remove Overload
SMPS shorted to ground
L
UNLATCH
SHUTDOWN
SHUTDOWN
SHUTDOWN
LOW
EN High
SMPS shorted to ground
H
UNLATCH
Stays ON
Stays ON
Latched OFF
LOW
EN Low, then High
Watchdog Signal Invalid
L
UNLATCH
SHUTDOWN
SHUTDOWN
SHUTDOWN
LOW
EN High
Watchdog Signal Invalid
H
Stays Latched
Stays ON
Stays ON
Stays ON
Pulses Low
Apply Valid WDI
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NCV8881
TYPICAL PERFORMANCE CHARACTERISTICS
3.0
14.0
2.5
13.2 V SUPPLY
10.0
8.0
CURRENT (mA)
CURRENT (mA)
12.0
6.0 V SUPPLY
6.0
4.0
6.0 V SUPPLY
1.5
1.0
0.5
2.0
0.0
−40 −20
0
20
40 60 80 100 120
TEMPERATURE (°C)
0.0
−40 −20
140 160
Figure 3. Supply Current (EN Low) vs.
Temperature
0
20
40 60 80 100 120 140 160
TEMPERATURE (°C)
Figure 4. Supply Current (EN High) vs.
Temperature
12.0
50.0
45.0
11.5
40.0
VOLTAGE (V)
35.0
DELAY (ms)
13.2 V SUPPLY
2.0
30.0
25.0
20.0
15.0
10.0
11.0
10.5
10.0
9.5
5.0
0.0
−40 −20
0
20
40 60 80 100 120
TEMPERATURE (°C)
9.0
−40 −20
140 160
5.0
5.9
4.9
5.8
4.8
5.7
4.7
VOLTAGE (V)
VOLTAGE (V)
6.0
5.6
5.5
5.4
5.3
4.6
4.5
4.4
4.3
5.2
4.2
5.1
4.1
0
20
40 60 80 100 120
TEMPERATURE (°C)
20
40 60 80 100 120 140 160
TEMPERATURE (°C)
Figure 6. EN Clamp Voltage vs. Temperature
Figure 5. En Delay vs. Temperature
5.0
−40 −20
0
140 160
4.0
−40 −20
Figure 7. VIN UVLO START Voltage vs.
Temperature
0
20
40 60 80 100 120
TEMPERATURE (°C)
140 160
Figure 8. VIN UVLO STOP Voltage vs.
Temperature
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NCV8881
20.8
19.8
20.7
19.7
20.6
19.6
20.5
19.5
VOLTAGE (V)
VOLTAGE (V)
TYPICAL PERFORMANCE CHARACTERISTICS
20.4
20.3
20.2
20.1
19.4
19.3
19.2
19.1
20.0
19.0
19.9
18.9
19.8
−40 −20
0
20
40
60
80
100 120
140 160
18.8
−40 −20
0
20
40
60
80
100 120
140 160
TEMPERATURE (°C)
TEMPERATURE (°C)
Figure 9. VIN OV STOP Voltage vs.
Temperature
Figure 10. VIN OV RESTART Voltage vs.
Temperature
5.000
810
808
4.998
804
VOLTAGE (V)
VOLTAGE (mV)
806
802
800
798
4.996
4.994
796
794
4.992
792
790
−40 −20
0
20
40
60
80
100 120
140 160
4.990
5.0
10.0
15.0
TEMPERATURE (°C)
VOLTAGE (V)
Figure 11. Reference Voltage vs. Temperature
Figure 12. 5P0 Output Voltage vs. Input
Voltage
189
20.0
350
300
185
VOLTAGE (mV)
CURRENT (mA)
187
183
181
179
250
200
177
175
−40 −20
0
20
40 60 80 100 120
TEMPERATURE (°C)
140 160
150
−40 −20
Figure 13. 5P0 Output Current Limit vs.
Temperature
0
20 40 60 80 100 120 140 160
TEMPERATURE (°C)
Figure 14. 5P0 Dropout Voltage Limit vs.
Temperature
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NCV8881
TYPICAL PERFORMANCE CHARACTERISTICS
8.500
75.0
74.0
73.0
8.490
CURRENT (mA)
FREQUENCY (kHz)
8.495
8.485
8.480
72.0
71.0
70.0
69.0
68.0
67.0
8.475
66.0
8.470
9.0
12.0
15.0
65.0
−40 −20
18.0
40
60
80
100 120 140 160
Figure 15. 8P5 Output Voltage vs. Input
Voltage
Figure 16. 8P5 Output Current Limit vs.
Temperature
12.0
11.8
180
11.6
11.4
160
VOLTAGE (V)
VOLTAGE (mV)
20
TEMPERATURE (°C)
200
140
120
100
11.2
11.0
10.8
10.6
10.4
10.2
80
10.0
60
−40 −20
0
20
40
60
80
100 120
140 160
9.8
−40 −20
0
20
40
60
80
100 120 140 160
TEMPERATURE (°C)
TEMPERATURE (°C)
Figure 17. 8P5 Dropout Voltage vs.
Temperature
Figure 18. 8P5 Output Clamp vs. Temperature
0.050
0.20
0.040
0.18
CURRENT (mA)
VOLTAGE (mV)
0
VOLTAGE (V)
0.030
0.020
0.010
0.16
0.14
0.12
0.000
−40 −20
0
20
40
60
80
100 120 140 160
0.10
−40 −20
0
20
40
60
80
100 120 140 160
TEMPERATURE (°C)
TEMPERATURE (°C)
Figure 19. LDOMON Low Voltage vs.
Temperature
Figure 20. LDOMON Leakage vs. Temperature
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NCV8881
TYPICAL PERFORMANCE CHARACTERISTICS
0.00
0.05
−0.05
−0.10
CURRENT (mA)
VOLTAGE (V)
0.04
0.03
0.02
−0.15
−0.20
−0.25
−0.30
0.01
−0.35
0.00
−40 −20
0
20
40 60 80 100 120
TEMPERATURE (°C)
−0.40
140 160
−40 −20
1.050
1.010
1.045
1.005
1.040
1.000
1.035
1.030
1.025
0.990
0.985
0.980
1.015
0.975
180
178
0
20
40
60
80
100 120
0.970
−40 −20
140 160
0
20
40
60
80
100 120
140 160
TEMPERATURE (°C)
TEMPERATURE (°C)
Figure 23. ROSC Voltage vs. Temperature
Figure 24. RDLY Voltage vs. Temperature
400
ROSC Open
395
FREQUENCY (kHz)
174
172
170
168
166
385
380
375
370
365
164
360
162
355
160
−40 −20
ROSC = 36 kW
390
176
FREQUENCY (kHz)
140 160
0.995
1.020
1.010
−40 −20
20
40 60 80 100 120
TEMPERATURE (°C)
Figure 22. RESB Leakage vs. Temperature
VOLTAGE (V)
VOLTAGE (V)
Figure 21. RESB Low Voltage vs. Temperature
0
0
20
40
60
80
100 120
140 160
350
−40 −20
0
20
40
60
80
100 120
140 160
TEMPERATURE (°C)
TEMPERATURE (°C)
Figure 25. Switching Frequency vs.
Temperature
Figure 26. Switching Frequency vs.
Temperature
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NCV8881
TYPICAL PERFORMANCE CHARACTERISTICS
750
2.50
ROSC = 0
2.45
730
2.40
720
2.35
CURRENT (A)
FREQUENCY (kHz)
740
710
700
690
680
2.30
2.25
2.20
2.15
670
2.10
660
2.05
650
−40 −20
0
20
40
60
80
100 120
2.00
−40 −20
140 160
0
TEMPERATURE (°C)
Figure 27. Maximum Switching Frequency vs.
Temperature
20 40 60 80 100 120 140 160
TEMPERATURE (°C)
Figure 28. SMPS Current Limit vs.
Temperature
2.00
80.0
1.95
1.90
VOLTAGE (V)
VOLTAGE (% of Vref)
79.0
78.0
77.0
1.85
1.80
1.75
1.70
76.0
1.65
75.0
−40 −20
0
20
40 60 80 100 120
TEMPERATURE (°C)
1.60
−40 −20
140 160
Figure 29. SMPS Short−Circuit Threshold vs.
Temperature
20
40 60 80 100 120
TEMPERATURE (°C)
140 160
Figure 30. SMPS Ramp Amplitude vs.
Temperature
5.0
4.5
4.0
VCOMP = 2.2 V
4.5
3.5
VCOMP = 3.2 V
CURRENT (mA)
CURRENT (mA)
0
4.0
3.5
VCOMP = 2.2 V
3.0
2.5
2.0
VCOMP = 1.1 V
1.5
1.0
3.0
−40 −20
0
20
40 60 80 100 120
TEMPERATURE (°C)
0.5
−40 −20
140 160
Figure 31. Error Amp Source Current vs.
Temperature
0
20
40 60 80 100 120
TEMPERATURE (°C)
140 160
Figure 32. Error Amp Sink Current vs.
Temperature
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NCV8881
TYPICAL PERFORMANCE CHARACTERISTICS
0.050
5.30
0.040
5.10
VOLTAGE (V)
SOFT−START TIME (ms)
5.20
5.00
4.90
0.020
4.80
0.010
4.70
4.60
−40 −20
650
600
550
500
450
400
350
300
250
200
150
100
50
0
0
20
40
60
80
100 120
0.000
−40 −20
140 160
20
40
60
80
100 120
140 160
TEMPERATURE (°C)
TEMPERATURE (°C)
Figure 34. IGNBUF Low Voltage vs.
Temperature
24
22
20
18
16
14
12
10
8
6
10
100
ROSC RESISTANCE (kW)
4
10
1000
Figure 35. Switching Frequency vs. ROSC
Resistance
300
300
275
275
250
250
225
200
175
150
125
100
75
50
10
15
20
25
30
35
40
RDLY RESISTANCE (kW)
45
50
Figure 36. POR Delay vs. RDLY Resistance
WATCHDOG DELAY (ms)
BOOT DELAY (ms)
0
Figure 33. Soft−Start Time vs. Temperature
POR DELAY (ms)
SWITCHING FREQUENCY (kHz)
0.030
225
200
175
150
125
100
75
15
20
25
30
35
40
RDLY RESISTANCE (kW)
45
50
10
50
Figure 37. Boot Delay vs. RDLY Resistance
15
20
25
30
35
40
RDLY RESISTANCE (kW)
45
Figure 38. Watchdog Delay vs. RDLY
Resistance
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50
NCV8881
TYPICAL PERFORMANCE CHARACTERISTICS
250
TJ = 25°C
300
DROPOUT VOLTAGE (mV)
DROPOUT VOLTAGE (mV)
350
250
200
150
100
50
0
0
10
20
30 40 50 60 70
LOAD CURRENT (kW)
80
90
200
150
100
50
0
100
TJ = 25°C
0
Figure 39. 5P0 Dropout Voltage vs. Load
Current
5
10
15
20
25
30
LOAD CURRENT (kW)
35
Figure 40. 8P5 Dropout Voltage vs. Load
Current
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40
NCV8881
OPERATING DESCRIPTION
INPUT VOLTAGE
reset, and the LDOs are shut off. Upon dropping below the
VOVSTT threshold, the LDOs will powerup and the SMPS
will begin a soft−start sequence regardless of the state of the
EN signal.
VIN is the power supply input for all NCV8881 functions.
Prior to the appearance of a valid high at the Enable input
(EN pin), VIN voltage above the VSTRT threshold produces
a low level at the Reset output (RESB).
STATE DIAGRAM
INPUT UNDERVOLTAGE SHUTDOWN
Figure 41 shows the State Diagram for the NCV8881.
States within numbered ellipses have common responses
(such as to input overvoltage and high temperature
shutdown) which force an exit from all states within.
An Undervoltage Lockout (UVLO) circuit monitors the
voltage at the VIN pin. If the voltage is below the VSTP
threshold it pulls RESB low, inhibits switching, and shuts
down the LDOs.
INPUT OVERVOLTAGE SHUTDOWN
If input voltage is above the VOVSTP threshold, RESB is
pulled low, switching is inhibited, the Soft−start circuit is
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NCV8881
5
RESB LOW
LDOS ON,
SMPS OFF
VIN < 19V &
Temp Vstrt
RESB LOW
LDOS OFF,
SMPS OFF
VIN > 19V or
Temp > Shutdown
Enable = 0
RESB LOW
LDOS, SMPS OFF
LDOMON OFF
Enable = 0
VIN > 19V or
Temp > Shutdown
5P0 or 8P5
in regulation
RESB LOW
LDOS ON, SMPS OFF
LDOMON ACTIVE
INIT SS TIMER
Enable = 0
LATCH
ENABLE
UNLATCH
ENABLE
VIN < Vstp
Enable = 1
RESB LOW
LDOS, SMPS OFF
LDOMON ACTIVE
VIN < 19V &
Temp Shutdown
1
RESB LOW
LDOS ON, SMPS OFF
INIT SS TIMER
5P0 or 8P5
in regulation
SS Timer Expired
RESB LOW
LDOS, SMPS ON
SS TIMER GOING
VFB > SC
Threshold
2
VFB < SC
Threshold
RESB LOW
Enable = 0 &
SMPS in LDOS, SMPS ON
SS Timer Expired
regulation INIT DELAYS
SMPS out of
regulation
POR DELAY
LDOS, SMPS ON
RESB LOW
3
4
POWER
ON
RESET
BOOT DELAY
LDOS, SMPS ON
RESB HIGH
WDI
Invalid
RESB HIGH
LDOS, SMPS ON
Figure 41. State Diagram
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NCV8881
ENABLE (EN PIN)
After VIN rises above VSTRT, EN below VENSTHL will
maintain a standby mode which keeps the switching
regulator, Watchdog Circuit, and LDO outputs off, and
minimizes supply current. In this state the RESB output is
low. A high logic level at the EN input activates all functions.
Upon EN exceeding VENSTHH, 5P0 and 8P5 voltages are
established, followed by soft−start of the switching
0
1
2
3
4
regulator. Once either the 5P0 or 8P5 LDO reaches
regulation, EN dropping below VENSTHL has no effect until
the SS Timer expires. Thereafter, if the SMPS output voltage
is out of regulation, or WDI pulse period exceeds the
Watchdog Delay time tWD, EN below VENSTHL puts the
part in standby mode.
5
6
7
8
9
10
11
12
VIN
ENABLE
8P5 Regulation Monitor Threshold
8P5
5P0 Regulation Monitor Threshold
5P0
SMPS
OUTPUT
Figure 42. Enable High Time Insufficient to be Latched
0
1
2
3
4
5
6
7
8
VIN
ENABLE
8P5 Regulation Monitor Threshold
8P5
5P0 Regulation Monitor Threshold
5P0
SMPS
OUTPUT
Figure 43. Enable High Time Long Enough to be Latched
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9
10
11
12
NCV8881
ENABLE
SIGNAL
THRESHOLD
R1
EXTERNAL
RESISTORS
NCV8881
EN
PIN
R2
RHYST
30K
COMPARATOR
CLAMP
RPDOWN
1MEG
Figure 44. Enable Input Hysteresis Mechanism
When the EN pin is below VENSTHL, RHYST is in
parallel with RPDOWN making the internal resistance from
the EN pin to ground lower than when the EN pin is above
VENSTHH. This produces hysteresis in the Enable function
when there is resistance between the source of the Enable
signal and the EN pin. A resistive divider from the Enable
signal source to the EN pin (Figure 44) allows a wide range
of activation/deactivation voltages. Note that this divider is
also used in conjunction with an internal zener clamp to keep
the EN pin voltage below the maximum voltage rating when
battery is the enable signal. Given the lowest voltage that
must enable the part VIHMIN, and the highest voltage that
must disable the part VILMAX the divider resistor values
are:
R1 = 0.7874 * (VILMAX – 1.27)/(0.0005556 * 1/R2) [kW]
[R2 in kW]
R2 = 1800*(1.2283 * VILMAX − VIHMIN )/( VIHMIN –
86.823 * VILMAX + 108.7) [kW]
Minimum hysteresis is: 0.0415 * R1 [V] [R1 in kW]
NCV8881 Enable Input VILmax Programming Range versus VIHmin Setting
7
6
Voltage (V)
5
4
3
2
MUST BE OFF
1
0
2
2.5
3
3.5
4
4.5
5
5.5
6
VIHmin Setting (V)
Figure 45. Enable Input VILmax Programming Range versus VIHmin Setting
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6.5
NCV8881
IGNITION BUFFER
8P5 OUTPUT
The Ignition Buffer output IGNBUF reports the EN pin
voltage level (high or low) detected by the EN input circuitry
when the EN signal is latched. The NCV8881 will pull the
IGNBUF output low if the Enable signal is low, and release
the IGNBUF output if the Enable signal is high. The
IGNBUF output is an open drain device which requires an
external pullup resistor to a logic supply. IGNBUF is no
longer controlled by EN when EN transitions low if the EN
signal is not latched.
The regulated voltage provided by the 8P5 output is used
to power the internal gate drive circuitry, but can also
provide current to modest external circuit loads that can
tolerate significant spike noise at the SMPS switching
frequency.
CURRENT LIMIT
8P5 output current is limited above the specified output
current capability in order to limit inrush current at turn−on
and also minimize power dissipation in the event of an
output short circuit.
THERMAL SHUTDOWN
A thermal shutdown circuit will inhibit switching, reset
the Soft−start circuit, and power down the 5P0 and 8P5
outputs if internal die temperature exceeds a safe level.
Operation is automatically restored when die temperature
has dropped below the thermal restart threshold regardless
of the state of the EN signal.
Either the 8P5 output voltage must exceed V8UVSTT or the
5P0 output voltage must exceed V5UVSTT before the SMPS
will begin soft−start. The LDOMON output will be pulled
low if the 8P5 output voltage is below V8UVSTP.
5P0 OUTPUT
OUTPUT OVERVOLTAGE CLAMP
OUTPUT UNDERVOLTAGE MONITOR
If current is forced into the 8P5 output, a clamp will limit
the voltage in order to protect the gate driver circuit from
excessive voltage.
CURRENT LIMIT
5P0 output current is limited above the specified output
current capability in order to limit inrush current at turn−on
and also minimize power dissipation in the event of an
output short circuit.
STABILITY CONSIDERATIONS
The output capacitor helps determine three main
performance characteristics of a linear regulator: starting
delay, load transient response, and loop stability. The
optimum capacitor type and value will depend on these three
characteristics, as well as cost, availability, size and
temperature constraints. Tantalum, aluminum electrolytic,
film, and ceramic are all acceptable capacitor types for most
applications. Values of 1 mF or more work in many cases,
however attention must be paid to the Equivalent Series
Resistance (ESR). Aluminum electrolytic capacitors are the
least expensive solution but both the value and ESR of this
type of capacitor change considerably at low temperatures
(−25°C or −40°C). The capacitor manufacturer’s data sheet
must be consulted for this information. Stability under all
load and temperature conditions is guaranteed by a capacitor
value greater than or equal to 4.7 mF and ESR between 0.2 W
and 5 W.
OUTPUT UNDERVOLTAGE MONITOR
Either the 5P0 output voltage must exceed V5UVSTT or the
8P5 output voltage must exceed V8UVSTT before the SMPS
will begin soft−start. If the output is below V5UVSTP, the
LDOMON output will be pulled low.
STABILITY CONSIDERATIONS
The output capacitor helps determine three main
performance characteristics of a linear regulator: starting
delay, load transient response, and loop stability. The
optimum capacitor type and value will depend on these three
characteristics, as well as cost, availability, size and
temperature constraints. Tantalum, aluminum electrolytic,
film, and ceramic are all acceptable capacitor types for most
applications. Values of 1 mF or more work in many cases,
however attention must be paid to the Equivalent Series
Resistance (ESR). Aluminum electrolytic capacitors are the
least expensive solution but both the value and ESR of this
type of capacitor change considerably at low temperatures
(−25°C or −40°C). The capacitor manufacturer’s data sheet
must be consulted for this information. Stability under all
load and temperature conditions is guaranteed by a capacitor
value greater than or equal to 4.7 mF and ESR between 0.2
and 5 W.
Besides powering external loads, the 5P0 output can be
used to provide a regulated voltage to an ROSC pullup
resistor as a convenient way to decrease the factory−set
switching frequency.
SMPS OPERATION
LDO OUTPUT UNDERVOLTAGE MONITOR
Besides requiring the input voltage to be above VSTRT
and the EN input to be above VENSTHH, either the 5P0
output voltage must exceed V5UVSTT or the 8P5 output
voltage must exceed V8UVSTT before the SMPS will begin
soft−start.
SOFT−START
Upon being enabled and released from all fault
conditions, and after one of the LDO outputs reaches
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NCV8881
regulation, a soft−start circuit slowly raises the switching
regulator error amplifier reference to VFBR in order to avoid
overloading the input supply.
programmed switching frequency should be no higher than
the highest synchronization frequency if synchronization is
used.
VOLTAGE REFERENCE
SMPS SYNCHRONIZATION
An internal, temperature compensated Bandgap voltage
reference provides the SMPS Error Amplifier and the 5P0
and 8P5 linear regulators with a stable, precision reference
voltage.
Applying a clock signal to the SYNC pin will cause power
switch turn−on edges to coincide with rising edges of the
applied clock signal. When synchronization will be
significantly higher than the default frequency, an ROSC
resistor which sets the internal oscillator frequency at (but
no higher than) the synchronization frequency can be used
to maintain the switching frequency approximately the same
as the synchronization frequency in the absence of the
SYNC signal.
Besides controlling the switching frequency, the ROSC
resistor controls the internal ramp slope, and can be used to
adjust the gain of the pulse width modulator.
A steady low or high SYNC input will restore SMPS
operation to the factory−set default or ROSC programmed
frequency after the De−synchronization delay.
SMPS ERROR AMPLIFIER
The error amplifier is an operational amplifier. The
Voltage Mode control method employed by the NCV8881
requires Type III compensation for optimum regulator
response to load and line transients.
The output voltage of the error amplifier controls the duty
cycle of the power switch by controlling the moment at
which the power switch shuts off (power switch turn−ons
occur at a fixed rate).
SMPS OSCILLATOR
With no connections to the ROSC or SYNC pins, the
NCV8881 switching frequency will be the factory−set
default frequency fOSC of the internal oscillator.
OUTPUT VOLTAGE REGULATION MONITOR
When the FB voltage is below VFBMONL, RESB is pulled
low, and the POR, BOOT and Watchdog Delays are
initialized. When FB voltage exceeds VFBMONH the POR
Delay begins to time out. If, when the FB voltage is below
VFBMONL, the Soft−Start Timer has expired and the EN
input is low, the NCV8881 will completely shut off (see
Figures 46 through 48).
ROSC SMPS FREQUENCY CONTROL
Connection of a resistor between the ROSC pin and
ground will raise the switching frequency above the
factory−set default according to the following equation.
F SW + 6840
R ROSC
−0.97 ) 170
Connection of a resistor between the ROSC pin and 5P0 will
lower the switching frequency below the default. The
0
1
2
3
4
5
6
7
8
VIN
ENABLE
8P5
5P0
SMPS
OUTPUT
Regulation Threshold
Short−Circuit Threshold
SOFT−START TIMER
Current is Limited
Figure 46. SMPS Overload During Startup
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9
10
11
NCV8881
0
1
2
3
4
5
6
7
8
9
10
11
12
9
10
11
12
VIN
ENABLE
8P5
5P0
SOFT−START TIMER
Regulation Threshold
Short−Circuit Threshold
SMPS
OUTPUT
Current is Limited
Figure 47. SMPS Overload after Successful Startup #1
SMPS OVERLOAD AFTER SUCCESSFUL STARTUP #2
0
1
2
3
4
5
6
7
8
VIN
ENABLE
8P5
5P0
SOFT−START TIMER
SMPS
OUTPUT
Regulation Threshold
Short−Circuit Threshold
Current is Limited
Figure 48. SMPS Overload after Successful Startup #2
SMPS CURRENT LIMIT AND SHORT CIRCUIT
PROTECTION
current limit by detecting excessively low voltage at the FB
pin and latching the SMPS regulator off. Toggling the EN
input low then high, or cycling input voltage off and on is
required to restart the SMPS (see bubble 5 of Figure 41, and
Figures 49 − 51).
Every cycle, the power switch will be shut off if switch
current exceeds the internal, fixed, current limit. After the
Soft−Start Timer has expired, an extreme overload is
prevented from producing switch current in excess of the
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NCV8881
0
1
2
3
4
5
6
7
8
9
10
11
12
9
10
11
12
VIN
ENABLE
8P5
5P0
SMPS
OUTPUT
SOFT−START TIMER
Regulation Threshold
Short−Circuit Threshold
Current is Limited
SMPS LATCHED OFF
Figure 49. SMPS Short−Circuit during Startup
0
1
2
3
4
5
6
7
8
VIN
ENABLE
8P5
5P0
SOFT−START TIMER
SMPS
OUTPUT
Regulation Threshold
Short−Circuit Threshold
Current is Limited
SMPS LATCHED OFF
Figure 50. SMPS Short−Circuit after Successful Startup #1
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NCV8881
0
1
2
3
4
5
6
7
8
9
10
11
12
VIN
ENABLE
8P5
5P0
SOFT−START TIMER
SMPS
OUTPUT
Regulation Threshold
Short−Circuit Threshold
SMPS LATCHED OFF
Figure 51. SMPS Short−Circuit After Successful Startup #2
WATCHDOG
Watchdog Delay period is initiated. Otherwise the
NCV8881 enters another POR Delay period and the RESB
pin is pulled low, while the SMPS and LDO outputs continue
to regulate. If EN is low when the Watchdog Delay expires
(no falling edge has occurred at the WDI input), RESB is
pulled low and the NCV8881 shuts off all power outputs
(SMPS and LDOs) and minimizes supply current.
In order to ensure that WDI pulses keep RESB from being
pulled low, they must never occur further apart than the
minimum specified tWD. However, RESB is not guaranteed
to be pulled low unless pulses occur further apart than the
maximum specified tWD.
Removal of other conditions that cause RESB to go low
(VIN > VOVSTP, temperature > TTSD, and SMPS output
voltage low) also initiate POR and BOOT Delays prior to
resumption of WDI monitoring.
Figures 52 through 57 illustrate the action of RESB and
the POR, BOOT, and Watchdog Delays during start−up and
shutdown.
The Watchdog Delay is internally limited to a maximum
value proportional to the switching period in case the
resistance at the RDLY pin becomes excessively high, such
as would occur if the path from the RDLY pin through the
RDLY resistance becomes an open circuit.
WATCHDOG FUNCTION
The Watchdog function monitors the WDI input to check
that WDI pulses arrive more frequently than the
programmed minimum rate. Monitoring commences after
two sequential time periods (the POR and BOOT Delays)
which start when the SMPS output reaches regulation. After
these initial time periods, time between WDI falling edges
exceeding the Watchdog Delay indicates abnormal
microcontroller activity, and the NCV8881 responds by
pulling the open drain RESB output low. A single external
resistor from the RDLY pin to ground programs the POR,
BOOT and Watchdog Delays.
When enabled and upon the SMPS output reaching
regulation, the NCV8881 enters the POR Delay period
tPOR, during which the RESB pin is held low. When the
POR Delay expires, the NCV8881 enters the BOOT Delay
period tBD during which the RESB output is allowed to be
pulled up by the external resistance. When the BOOT Delay
expires, the Watchdog circuit begins monitoring the WDI
pin for a falling edge (from a microprocessor or other signal
source). If a falling edge arrives before the Watchdog Delay
period tWD expires, RESB remains high and a new
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NCV8881
0
;
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
VIN
POR
DELAY
ENABLE
POR
DELAY
POR
DELAY
BOOT DELAY
BOOT DELAY
RESB
WATCHDOG
DELAY
POR
DELAY
BOOT DELAY
WATCHDOG
DELAY
WATCHDOG
DELAY
WDI
3.3V
5V
Figure 52. Watchdog Never Appears; EN Input HIGH
WATCHDOG STUCK HIGH, THEN RECOVERS; ENABLE = HIGH
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
VIN
ENABLE
POR
DELAY
POR
DELAY
RESB
BOOT DELAY
POR
DELAY
BOOT DELAY
WATCHDOG
DELAY
WATCHDOG
DELAY
WDI
BOOT DELAY
WDI STUCK HIGH
NORMAL RESPONSE
NORMAL RESPONSE
3.3V
5V
Figure 53. Watchdog Stuck HIGH, Then Normal; EN Input HIGH
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NCV8881
WATCHDOG STUCK LOW, THEN RECOVERS; ENABLE = HIGH
0
1
2
3
4
5
6
7
9
8
10
11
VIN
ENABLE
POR
DELAY
POR
DELAY
BOOT DELAY
RESB
P
D
WATCHDOG
DELAY
BOOT DELAY
WATCHDOG
DELAY
WDI
WDI STUCK LOW
NORMAL RESPONSE
3.3V
5V
Figure 54. Watchdog Stuck LOW, Then Normal; EN Input HIGH
0
1
2
3
4
5
6
7
8
9
10
11
VIN
ENABLE
RESB
POR
DELAY
POR
DELAY
BOOT DELAY
WATCHDOG
DELAY
PO
DELA
BOOT DELAY
WATCHDOG
DELAY
WDI
WDI TOO SLOW
3.3V
5V
Figure 55. Watchdog is Too Slow; EN Input HIGH
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WDI TOO SLOW
NCV8881
WATCHDOG STUCK HIGH; ENABLE = LOW, THEN EN = HIGH RESTARTS
0
1
2
3
4
5
6
7
8
9
10
11
13
12
14
15
16
VIN
ENABLE
POR
DELAY
POR
DELAY
RESB
WATCHDOG
DELAY
BOOT DELAY
BOOT DELAY
WDI
NORMAL RESPONSE WDI STUCK HIGH
NORMAL RESPONSE
3.3V
5V
Figure 56. Watchdog Stuck HIGH, EN Input LOW; then EN Goes HIGH to Restart the Regulators
SMPS OUTPUT OUT OF REGULATION TO RESB LOW DELAY
0
1
2
3
4
5
6
7
9
8
10
11
12
13
14
VFBMONL
THRESHOLD
3.3V
tFBLDLY
RESB
Figure 57. RESB Pulled Low as the SMPS Output Voltage (pullup source for RESB) Drops Out of Regulation
APPLICATION INFORMATION
Input Capacitors
requirements. Tantalum, Aluminum or Polymer
Electrolytic, capacitors can be used. Ceramic capacitors
should have series resistance added to be within the
recommended ESR range. There are many capacitor
vendors which supply automotive rated parts that fall within
these ranges. For example, the SUNCON EP−series
Aluminum Electrolytic capacitors are well suited well for
automotive radio applications.
The primary input capacitor should be a ceramic of at least
4.7 mF placed between the VIN pin and the ground terminal
of the SMPS freewheeling diode in order to reduce input
voltage perturbations present when the NCV8881 SMPS is
heavily loaded. A secondary 0.1 mF ceramic capacitor
positioned as closely as possible between the VIN and GND
pins of the NCV8881 provides greater reduction of input
perturbations than further increasing the value of the
primary ceramic capacitor, and can be more effectively
positioned than the larger 4.7 mF capacitor without
compromising PCB thermal conductivity.
Setting the SMPS Output Voltage
To set the output voltage of the switching regulator, use
the following equation:
V SWOUT + V REF
LDO Output Capacitor Selection
The LDOs have been compensated to work with output
capacitors above 3.3 mF having an ESR from 200 mW up to
5 W over the full range of output current and temperature.
Lower capacitance and ESR can be used for lighter load
ǒ1 ) R1Ǔ
R2
(eq. 1)
where VREF is the Reference voltage, R1 is the resistor
connected from VSWOUT to the FB pin and R2 is the resistor
connected from the FB pin to ground. To reduce the effect
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NCV8881
the necessary capacitance, at the expense of higher ripple
current.
In continuous conduction mode, the peak−to−peak ripple
current is calculated using the following equation:
of input offset current error, it is customary to calculate R1
with R2 set at 1 kW.
SMPS Snubber
A resistor and ceramic capacitor must be connected in
series between the SW pin and ground. Typical values are
10 W and 1 nF.
I PP + T SW
The freewheeling diode in the SMPS provides the
inductor current path when the power switch turns off, and
is sometimes referred to as the commutation diode. The
diode peak inverse voltage must exceed the maximum
operating input voltage in order to accommodate any higher
peak voltage produced by switchnode ringing. The peak
conducting current is determined by the internal current
limit. The average diode current can be calculated from the
output current IOUT, the input voltage VIN and the output
voltage VSWOUT by:
I D(avg) + I OUT
ǒ
1*
V IN
Ǔ
(eq. 2)
DV SWOUT(ESR) + DI SWOUT
Mechanical and electrical considerations, as well as cost
influence the selection of an output inductor. From a
mechanical perspective, smaller inductor values generally
correspond to smaller physical size. Since the inductor is
often one of the largest components in SMPS system, a
minimum inductor value is particularly important in
space−constrained applications. From an electrical
perspective, smaller inductor values correspond to faster
transient response. The maximum current slew rate through
the output inductor for a buck regulator is given by:
dt
+
VL
L
V IN
(eq. 4)
The output capacitor is a basic component for the fast
response of the power supply. In fact, during load transient,
it supplies the current to the load for first few microseconds,
where after the controller recognizes the load transient and
proceeds to increase the duty cycle. Neglecting the effect of
the ESL, the output voltage has a first drop due to the ESR
of the capacitor.
Inductor Selection
dI L
Ǔ
V SWOUT
SMPS Output Capacitor Selection
The freewheeling diode should have a current rating equal
to the maximum NCV8881 current limit, such as the
MBRA340T3.
Inductor Slew Rate +
L
1*
Where TSW is the switching period. From this equation it
is clear that the ripple current increases as L decreases,
emphasizing the trade−off between dynamic response and
ripple current. For most applications, the inductor value falls
in the range between 10 mH and 22 mH. There are many
magnetic component suppliers providing energy storage
inductor product lines suitable such as the Wurth TPC series
or TOKO DSH104C series inductors, which are
recommended for the automotive radio applications.
SMPS Freewheeling Diode Selection
V SWOUT
ǒ
V SWOUT
ESR
(eq. 5)
A lower ESR produces a lower DV during load transient.
In addition, a lower ESR produces a lower output voltage
ripple. The voltage drop due to the output capacitance
discharge can be approximated using the following
equation:
DV SWOUT(CHARGE)
+
ǒDI SWOUTǓ
2
C SWOUT
ǒVIN(MIN)
(eq. 6)
2
L
D MAX * V SWOUTǓ
Where, DMAX is the maximum duty cycle value, which is
90%. Although the ESR effect is not in phase with the
discharging of the output voltage, DVSWOUT(ESR) can be
added to DVSWOUT(CHARGE) to give a rough indication of
the maximum DVSWOUT during a transient condition.
Simulation can also help determine the maximum
DVSWOUT; however, it will ultimately have to be verified
with the actual load since the ESL effect is dependent on
layout and the actual load’s di/dt.
(eq. 3)
Where IL is the inductor current, L is the output inductance,
and VL is the voltage drop across the inductor.
This equation indicates that larger inductor values limit
the regulator’s ability to slew current through the output
inductor in response to output load transients.
Consequently, output capacitors must supply sufficient
charge to maintain regulation while the inductor current
“catches up” to the load. This results in larger values of
output capacitance to maintain tight output voltage
regulation. In contrast, smaller values of inductance increase
the regulator’s maximum achievable slew rate and decrease
SMPS Input Capacitor Selection
Besides voltage rating, a primary consideration for
selecting the input capacitor is input RMS current rating.
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NCV8881
I IN(RMS) + D
ȡ
ȧ
ȧ(1 * D)
ȧ
ȧ
ȧ
Ȣ
I SWOUT )
Ǹ
ǒ
(1 * D )
(1 * D )
2
I SWOUT 2 )
T
SW
ǒVSWOUT)VFǓ
L
12
Ǔ ȣȧȧ
2
ȧ
ȧ
ȧ
Ȥ
(eq. 7)
voltage initially rises past the Undervoltage Lockout
threshold.
Where D is the Duty Cycle = tON/(tON+tOFF), and VF is the
forward voltage of the freewheeling diode.
Another consideration for the value of the input capacitor
is the ability to supply enough input charge to satisfy sudden
increases in output current (such as produced at start−up, or
upon maximum load step) without an unacceptable drop in
input voltage. This is sometimes important when the input
SMPS Compensation
The NCV8855 utilizes voltage mode control. The control
loop regulates VSWOUT by monitoring it and controlling the
power switch duty cycle. Inherent with all voltage−mode
control loops is a compensation network.
VIN
POWER
SWITCH
VOLTAGE
RAMP
LOUT
DCR
VOUT
DFW
C1
R2
COMP
R1
C2
C3
VREF
ERROR
AMP
R3
ESR
COUT
Figure 58.
The compensation network consists of the internal error
amplifier and the impedance networks ZIN (R1, R3 and C3)
and ZFB (R2, C1 and C2). The compensation network has to
provide a loop transfer function with the highest 0 dB
crossing frequency to have fast response and the highest gain
in DC conditions to minimize the load regulation. The
open-loop gain magnitude versus frequency plot of a stable
control loop crosses zero dB with close to −20 dB/decade
slope and a phase margin greater than 45°.
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NCV8881
dB
wZ 1 =
1
R2 ‧ C2
wZ 2 =
1
(R1 + R3 )‧ C3
wP1 =
1
⎛ C1 ‧ C2 ⎞
R2 ‧⎢⎢
⎟⎟
⎝ C1 + C2 ⎠
wP 2 =
1
R3 ‧ C3
w
wLC =
1
LOUT ‧ COUT
wESR =
Error Amplifier
Compensation Network
Modulator Gain
Closed Loop Gain
1
ESR‧ COUT
Figure 59.
crossover frequency cannot exceed 1/2 FSW and the phase
margin has to be greater than 0° at crossover. However, a
SMPS operating towards these absolutes will experience
severe ringing before it dampens out.
To achieve the above goals, the following guidelines
should be adopted.
− Place wZ1 at half the resonance of wLC
− Place wZ2 at or around wLC
− Place wP1 at wESR
− Place wP2 at half the switching frequency
Performing these calculations will take some amount of
iteration and bench testing is needed to verify results.
ON Semiconductor has developed a tool to speed up the
design process tremendously with great ease and accuracy.
This tool can be downloaded by following the link below:
http://www.onsemi.com/pub/Collateral/COMPCALC.ZIP
To reiterate, there are 3 primary goals to compensating.
Goal 1 is to have a high a unity gain bandwidth (UGB) that
is greater than 1/10 the switching frequency FSW, but less
than 1/2 the switching frequency. UGB is also known as the
crossover frequency. This is the point where the loop gain =
0 dB or a gain of 1. In the plot above, the UGB is the point
where the red line crosses the TBD axis. Goal 2 is to have the
loop gain cross 0 dB with a −20 dB/decade slope also known
as a −1 slope. Goal 3 is to achieve over 45° of phase margin
when the gain crosses 0 dB. These are just goals. Sometimes
the crossover frequency is reduced below 1/10 FSW in order
to meet goal 3.
Conversely, some designs will push the crossover
frequency as high as it can (as long as it is below 1/2 FSW)
with a reduced phase margin of 30° in order to get a faster
transient response. The only two absolutes are that the
ORDERING INFORMATION
Device
NCV8881PWR2G
Package
Shipping†
SOIC−16W EP
(Pb−Free)
1000 / Tape & Reel
†For information on tape and reel specifications, including part orientation and tape sizes, please refer to our Tape and Reel Packaging
Specifications Brochure, BRD8011/D.
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onsemi,
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and/or subsidiaries in the United States and/or other countries. onsemi owns the rights to a number of patents, trademarks, copyrights, trade secrets, and other intellectual property.
A listing of onsemi’s product/patent coverage may be accessed at www.onsemi.com/site/pdf/Patent−Marking.pdf. onsemi reserves the right to make changes at any time to any
products or information herein, without notice. The information herein is provided “as−is” and onsemi makes no warranty, representation or guarantee regarding the accuracy of the
information, product features, availability, functionality, or suitability of its products for any particular purpose, nor does onsemi 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. Buyer is responsible for its products
and applications using onsemi products, including compliance with all laws, regulations and safety requirements or standards, regardless of any support or applications information
provided by onsemi. “Typical” parameters which may be provided in onsemi 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. onsemi does not convey any license
under any of its intellectual property rights nor the rights of others. onsemi products are not designed, intended, or authorized for use as a critical component in life support systems
or any FDA Class 3 medical devices or medical devices with a same or similar classification in a foreign jurisdiction or any devices intended for implantation in the human body. Should
Buyer purchase or use onsemi products for any such unintended or unauthorized application, Buyer shall indemnify and hold onsemi and its officers, employees, subsidiaries, affiliates,
and distributors harmless against all claims, costs, damages, and expenses, and reasonable attorney fees arising out of, directly or indirectly, any claim of personal injury or death
associated with such unintended or unauthorized use, even if such claim alleges that onsemi was negligent regarding the design or manufacture of the part. onsemi is an Equal
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