ON NCP1550SN27T1G 600 khz pwm/pfm step−down dc−dc controller Datasheet

NCP1550
600 kHz PWM/PFM
Step−Down DC−DC
Controller
The NCP1550 is a monolithic micropower high frequency voltage
mode step−down controller IC, specially designed for battery operated
hand−held electronic products. With appropriate external P−type
MOSFET, the device can provide up to 2.0 A loading current with high
conversion efficiency. The device operates in Constant−Frequency
PWM mode at normal operation, that ensures low output ripple noise,
and which will automatically switch to PFM mode at low output loads
for higher efficiency. Additionally, value−added features of Chip
Enable to reduce IC Off−State current and integrated feedback resistor
network, make it the best choice for portable applications. The device is
designed to operate for voltage regulation with minimum external
components and board space. This device is available in a TSOP−5
package with six standard output voltage options.
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TSOP−5
SN SUFFIX
CASE 483
Features
• High Efficiency 92%, Typical
• Low Quiescent Bias Current of 50 mA
•
•
•
•
•
•
•
•
•
•
•
•
•
MARKING DIAGRAM
(Typical at PFM Mode with No Load)
Output Voltage Options from 1.8 V to 3.3 V
with High Accuracy $2.0%
Low Output Voltage Ripple, 50 mV, Typical
PWM Switching Frequency at 600 kHz
Automatic PWM/PFM Switchover at Light Load Condition
Very Low Dropout Operation, 100% Max. Duty Cycle
Chip Enable Pin with On−Chip 150 nA Pullup Current Source
Low Shutdown Current, 0.3 mA, Typical
Input Voltage Range from 2.45 V to 5.5 V
Built−in Soft−Start
Internal Undervoltage Lockout (UVLO) Protection
Low Profile and Minimum External Components
Micro Miniature TSOP−5 Package
Pb−Free Packages are Available
Typical Applications
•
•
•
•
•
•
Personal Digital Assistant (PDA)
Camcorders and Digital Still Camera
Hand−Held Instrument
Distributed Power System
Computer Peripheral
Conversion from Four NiMH or NiCd or One Lithium−ion Cells to
3.3 V/1.8 V
5
xxx AYW G
G
1
xxx = Specific Device Code
A
= Assembly Location
Y
= Year
W = Work Week
G
= Pb−Free Package
(Note: Microdot may be in either location)
PIN CONNECTIONS
CE
1
GND
2
VOUT
3
5
VIN
4
EXT
(Top View)
ORDERING INFORMATION
See detailed ordering and shipping information in the package
dimensions section on page 16 of this data sheet.
© Semiconductor Components Industries, LLC, 2006
July, 2006 − Rev. 8
1
Publication Order Number:
NCP1550/D
NCP1550
+
CP1
2.2 V
PWM
Controller
VOUT
5
VIN
4
EXT
1
CE
+
−
600 kHz
Oscillator
TON t
TON(PFM)
3
UVLO
−
A1
−
+
Driver
Voltage Reference
and Soft−Start
GND
2
M1
Figure 1. Simplified Block Diagram
PIN FUNCTION DESCRIPTIONS
Pin
Symbol
Description
1
CE
2
GND
Ground Connection
3
VOUT
Output voltage monitoring input. This pin must be connected to the regulated output node as a feedback to on−chip
control circuitry. VOUT is internally connected to the on−chip voltage divider that determines the output voltage level.
4
EXT
Gate drive for external P−MOSFET
5
VIN
Power supply input
Chip Enable pin, active high (internal pullup current source). By connecting this pin to GND, the switching operation
of the controller will be stopped.
MAXIMUM RATINGS (TA = 25°C unless otherwise noted)
Rating
Symbol
Value
Unit
VIN
−0.3 to 6.0
V
VCE
VOUT
VEXT
−0.3 to 6.0
−0.3 to 6.0
−0.3 to 6.0
RqJA
250
°C/W
Operating Junction Temperature Range
TJ
−40 to +150
°C
Operating Ambient Temperature Range
TA
−40 to +85
°C
Storage Temperature Range
Tstg
−55 to +150
°C
Device Power Supply, VIN (Pin 5)
Input/Output Pins
CE (Pin 1)
VOUT (Pin 3)
EXT (Pin 4)
V
Thermal Characteristics
TSOP−5 Plastic Package, Case 483−01
Thermal Resistance, Junction−to−Air
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.
NOTE: ESD data available upon request.
1. This device series contains ESD protection and exceeds the following tests:
Human Body Model (HBM) $2.0 kV per JEDEC standard: JESD22−A114.
Machine Model (MM) $200V per JEDEC standard: JESD22−A115.
2. Latchup Current Maximum Rating: 150 mA per JEDEC standard: JESD78.
3. Moisture Sensitivity Level (MSL): 1 per IPC/JEDEC standard: J−STD−020A.
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NCP1550
ELECTRICAL CHARACTERISTICS (VIN = 5.0 V, TA = 25°C for typical value, −40°C v TA v 85°C for min/max values unless
otherwise noted.)
Characteristic
Symbol
Min
Typ
Max
Unit
VIN
2.45
−
5.50
V
1.764
1.862
2.450
2.646
2.940
3.234
1.8
1.9
2.5
2.7
3.0
3.3
1.836
1.938
2.550
2.754
3.060
3.366
−
−
−
−
−
−
2.5
2.5
2.5
2.5
2.5
2.5
4.0
4.0
4.0
4.0
4.0
4.0
−
100
−
−
−
−
−
−
−
50
50
50
50
50
50
80
80
80
80
80
80
−
−
−
−
−
−
0.3
0.3
0.3
0.3
0.3
0.3
0.5
0.5
0.5
0.5
0.5
0.5
TOTAL DEVICE
Input Voltage
Output Voltage (ILOAD = 0 mA, TA = 25°C)
NCP1550SN18T1
NCP1550SN19T1
NCP1550SN25T1
NCP1550SN27T1
NCP1550SN30T1
NCP1550SN33T1
VOUT
Input Current into VOUT Pin
NCP1550SN18T1
NCP1550SN19T1
NCP1550SN25T1
NCP1550SN27T1
NCP1550SN30T1
NCP1550SN33T1
IVOUT
DVOUT/DVT
Temperature Coefficient
Operating Current (VIN = 5.0 V, VCE = 5.0 V, No External Components)
NCP1550SN18T1
NCP1550SN19T1
NCP1550SN25T1
NCP1550SN27T1
NCP1550SN30T1
NCP1550SN33T1
IDD
Off−State Current (VIN = 5.0 V, VCE = 0 V, TA = 25°C)
NCP1550SN18T1
NCP1550SN19T1
NCP1550SN25T1
NCP1550SN27T1
NCP1550SN30T1
NCP1550SN33T1
IOFF
V
mA
ppm/°C
mA
mA
OSCILLATOR
FOSC
510
600
690
kHz
DFOSC/DTA
−
0.11
−
%/°C
DMAX
100
−
−
%
TON(PFM)
167
320
500
ns
Tss
−
8.0
−
ms
Tprot
−
8.0
−
ms
EXT “H” Output Current (VEXT = VIN – 0.4 V)
IEXTH
−
−60
−
mA
EXT “L” Output Current (VEXT = 0.4 V)
IEXTL
−
100
−
mA
EXT “L−H” Rise Time (CLOAD = 1000 pF) (VIN = 5.0 V)
Tr
−
65
−
ns
EXT “H−L” Fall Time (CLOAD = 1000 pF) (VIN = 5.0 V)
Tf
−
40
−
ns
EXT “L−H” Rise Time (CLOAD = 5.0 nF) (VIN = 5.0 V)
Tr
−
140
−
ns
EXT “H−L” Fall Time (CLOAD = 5.0 nF) (VIN = 5.0 V)
Tf
−
90
−
ns
Frequency
Frequency Temperature Coefficient (TA = −40°C to 85°C)
Maximum Duty Cycle
PWM/PFM Switchover ON Time Threshold (Note 4)
Soft−Start Delay Time (Note 4)
Protection Delay Time (Auto Restart)
OUTPUT DRIVE (PIN 4)
4. PWM/PFM Switchover ON Time Threshold min/max guaranteed by design only.
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NCP1550
ELECTRICAL CHARACTERISTICS (continued) (VIN = 5.0 V, TA = 25°C for typical value, −40°C v TA v 85°C for min/max values
unless otherwise noted.)
Symbol
Min
Typ
Max
Unit
CE “H” Input Voltage
VCEH
1.3
−
−
V
CE “L” Input Voltage
VCEL
−
−
0.3
V
CE “H” Input Current (VIN = VCE = 5.0 V)
ICEH
−0.5
0
0.5
mA
CE “L” Input Current (VIN = 5.0, VCE = 0 V)
ICEL
−0.5
0.15
0.5
mA
Undervoltage Lockout Threshold
VUVLO
1.60
2.20
2.40
V
Undervoltage Lockout Hysteresis
VUVLO_HYS
−
50
−
mV
Characteristic
CE (PIN 1)
Undervoltage Lockout
L
M
VIN
VOUT
4
EXT
3
CE
2
VIN
5
CIN
1
SD
VOUT
COUT
CE
GND
GND
GND
Figure 2. Typical Application Diagram
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NCP1550
TYPICAL OPERATING CHARACTERISTICS
100
100
VIN = 3.0 V
VIN = 4.0 V
EFFICIENCY (%)
80
5.0 V
60
NCP1550SN33T1
L = 3.3 mH
CIN = 33 mF
COUT = 33 mF
M = NTGS3441T1
SD = MBRM120LT3
40
20
4.0 V
5.0 V
60
NCP1550SN25T1
L = 5.6 mH
CIN = 33 mF
COUT = 33 mF
M = NTGS3441T1
SD = MBRM120LT3
40
20
0
0
1
10
100
1000
1
10
ILOAD, OUTPUT LOADING CURRENT (mA)
Figure 4. Efficiency versus Load Current
100
4.0 V
VIN = 3.0 V
80
5.0 V
60
NCP1550SN18T1
L = 6.8 mH
CIN = 33 mF
COUT = 33 mF
M = NTGS3441T1
SD = MBRM120LT3
40
20
0
1
100
ILOAD, OUTPUT LOADING CURRENT (mA)
Figure 3. Efficiency versus Load Current
EFFICIENCY (%)
EFFICIENCY (%)
80
10
100
ILOAD, OUTPUT LOADING CURRENT (mA)
Figure 5. Efficiency versus Load Current
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1000
1000
NCP1550
100
VIN = 5.0 V
CIN = 33 mF
COUT = 33 mF
M = NTGS3441T1
SD = MBRM120LT3
0.6
0.3
1.9 V
1.8 V
2.5 V
0
−0.3
2.7 V
3.0 V
3.3 V
−0.6
NCP1550
CIN = 33 mF
COUT = 33 mF
IOUT = 500 mA
SD = MBRM120LT3
80
3.3 V
3.0 V
60
2.7 V
40
20
2.5 V
1.8 V 1.9 V
0
−0.9
10
100
1000
2.5
3
3.5
4
4.5
5
ILOAD, OUTPUT LOADING CURRENT (mA)
VIN, BATTERY INPUT VOLTAGE (V)
Figure 7. Output Ripple Voltage versus
Input Voltage
100
80
1.9 V
2.5 V
1.8 V
60
40
3.3 V
3.0 V 2.7 V
NCP1550
CIN = 33 mF
COUT = 33 mF
CE = VIN
SD = MBRM120LT3
20
0
2
2
Figure 6. Output Voltage Change versus
Load Current
2.5
3
3.5
4
4.5
5
5.5
0.6
1.8 V
0.3
NCP1550
VIN = 5.0 V
CIN = 33 mF
COUT = 33 mF
IOUT = 500 mA
SD = MBRM120LT3
−0.3
−0.6
2
3.3 V
2.5
3
3.5
4
4.5
5
VIN, INPUT VOLTAGE (V)
Figure 9. Output Voltage Change versus
Input Voltage
3.3 V
NCP1550
VIN = 5.0 V
CIN = 33 mF
COUT = 33 mF
IOUT = 500 mA
SD = MBRM120LT3
3.0 V
2.7 V
45
30
1.9 V
15
1.8 V
2.5 V
0
1
3.0 V
2.7 V
−0.9
90
60
1.9 V 2.5 V
0
Figure 8. No Load Operating Current versus
Input Voltage
75
10
100
ILOAD, OUTPUT CURRENT (mA)
Figure 10. Output Ripple Voltage versus
Output Current
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5.5
0.9
VIN, INPUT VOLTAGE (V)
VRIPPLE, RIPPLE VOLTAGE (mVp−p)
IBATT, NO LOAD OPERATING CURRENT (mA)
VRIPPLE, RIPPLE VOLTAGE (mVp−p)
0.9
DVOUT, OUTPUT VOLTAGE CHANGE (mV)
DVOUT, OUTPUT VOLTAGE CHANGE (%)
TYPICAL OPERATING CHARACTERISTICS
1000
5.5
NCP1550
(VIN = 5.0 V, ILOAD = 500 mA, L = 3.3 mH, COUT = 100 mF)
(VIN = 5.0 V, ILOAD = 100 mA, L = 3.3 mH, COUT = 100 mF)
Upper Trace: Output Voltage Ripple, 50 mV/Division
Middle Trace: Inductor Current, IL, 500 mA/Division
Lower Trace: Voltage at Cathode of Schottky Diode, 2.0 V/Division
Upper Trace: Output Voltage Ripple, 50 mV/Division
Middle Trace: Inductor Current, IL, 500 mA/Division
Lower Trace: Voltage at Cathode of Schottky Diode, 2.0 V/Division
Figure 11. Continuous Conduction Mode PWM
Switching Waveform for VOUT = 3.3 V
Figure 12. Discontinuous Conduction Mode PWM
Switching Waveform for VOUT = 3.3 V
(VIN = 5.0 V, ILOAD = 10 mA, L = 3.3 mH, COUT = 100 mF)
(VIN = 5.0 V, ILOAD = 500 mA, L = 5.6 mH, COUT = 33 mF)
Upper Trace: Output Voltage Ripple, 50 mV/Division
Middle Trace: Inductor Current, IL, 500 mA/Division
Lower Trace: Voltage at Cathode of Schottky Diode, 2.0 V/Division
Upper Trace: Output Voltage Ripple, 50 mV/Division
Middle Trace: Inductor Current, IL, 500 mA/Division
Lower Trace: Voltage at Cathode of Schottky Diode, 2.0 V/Division
Figure 14. Continuous Conduction Mode PWM
Switching Waveform for VOUT = 2.5 V
Figure 13. Discontinuous Conduction Mode PFM
Switching Waveform for VOUT = 3.3 V
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NCP1550
(VIN = 5.0 V, ILOAD = 100 mA, L = 5.6 mH, COUT = 33 mF)
(VIN = 5.0 V, ILOAD = 30 mA, L = 5.6 mH, COUT = 33 mF)
Upper Trace: Output Voltage Ripple, 50 mV/Division
Middle Trace: Inductor Current, IL, 500 mA/Division
Lower Trace: Voltage at Cathode of Schottky Diode, 2.0 V/Division
Upper Trace: Output Voltage Ripple, 50 mV/Division
Middle Trace: Inductor Current, IL, 500 mA/Division
Lower Trace: Voltage at Cathode of Schottky Diode, 2.0 V/Division
Figure 15. Discontinuous Conduction Mode PWM
Switching Waveform for VOUT = 2.5 V
Figure 16. Discontinuous Conduction Mode PFM
Switching Waveform for VOUT = 2.5 V
(VIN = 5.0 V, ILOAD = 500 mA, L = 6.8 mH, COUT = 33 mF)
(VIN = 5.0 V, ILOAD = 60 mA, L = 6.8 mH, COUT = 33 mF)
Upper Trace: Output Voltage Ripple, 50 mV/Division
Middle Trace: Inductor Current, IL, 500 mA/Division
Lower Trace: Voltage at Cathode of Schottky Diode, 2.0 V/Division
Upper Trace: Output Voltage Ripple, 50 mV/Division
Middle Trace: Inductor Current, IL, 500 mA/Division
Lower Trace: Voltage at Cathode of Schottky Diode, 2.0 V/Division
Figure 17. Continuous Conduction Mode
PWM Switching Waveform for VOUT = 1.8 V
Figure 18. Discontinuous Conduction Mode
PWM Switching Waveform for VOUT = 1.8 V
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NCP1550
(VIN = 5.0 V, ILOAD = 30 mA, L = 6.8 mH, COUT = 33 mF)
Upper Trace: Output Voltage Ripple, 50 mV/Division
Middle Trace: Inductor Current, IL, 500 mA/Division
Lower Trace: Voltage at Cathode of Schottky Diode, 2.0 V/Division
Upper Trace: Input Voltage, 2.0 V/Division
Lower Trace: Output Voltage, 2.0 V/Division
Figure 19. Discontinuous Conduction Mode
PFM Switching Waveform for VOUT = 1.8 V
Figure 20. Startup Transient Response for
VOUT = 3.3 V
Upper Trace: Input Voltage, 2.0 V/Division
Lower Trace: Output Voltage, 1.0 V/Division
Upper Trace: Output Voltage Waveform, 2.0 V/Division
Lower Trace: Chip Enable/Disable Pin Waveform, 0.5 V/Division
Figure 21. Startup Transient Response for
VOUT = 1.8 V
Figure 22. Chip Enable/Disable Output Voltage
Waveform
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NCP1550
(VIN = 4.0 to 5.0 V, L = 3.3 mH, COUT = 33 mF, ILOAD = 1.0 A)
Upper Trace: Output Voltage Ripple, 100 mV/Division
Lower Trace: Input Voltage, 2.0 V/Division
(VIN = 3.0 to 5.0 V, L = 5.6 mH, COUT = 33 mF, ILOAD = 1.0 A)
Upper Trace: Output Voltage Ripple, 100 mV/Division
Lower Trace: Input Voltage, 2.0 V/Division
Figure 23. Line Transient Response for
VOUT = 3.3 V
Figure 24. Line Transient Response for
VOUT = 2.5 V
(VIN = 3.0 to 5.0 V, L = 6.8 mH, COUT = 33 mF, ILOAD = 1.0 A)
(VIN = 5.0 V, ILOAD = 100 mA to 1.0 A, L = 3.3 mH,
COUT = 33 mF)
Upper Trace: Output Voltage Ripple, 200 mV/Division
Lower Trace: Load Current, ILOAD, 500 mA/Division
Upper Trace: Output Voltage Ripple, 100 mV/Division
Lower Trace: Input Voltage, VIN, 2.0 V/Division
Figure 25. Line Transient Response for
VOUT = 1.8 V
Figure 26. Load Transient Response for
VOUT = 3.3 V
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NCP1550
(VIN = 5.0 V, ILOAD = 100 mA to 1.0 A, L = 5.6 mH,
COUT = 33 mF)
(VIN = 5.0 V, ILOAD = 100 mA to 1.0 A, L = 6.8 mH,
COUT = 33 mF)
Upper Trace: Output Voltage Ripple, 100 mV/Division
Lower Trace: Load Current, ILOAD, 500 mA/Division
Upper Trace: Output Voltage Ripple, 100 mV/Division
Lower Trace: Load Current, ILOAD, 500 mA/Division
Figure 27. Load Transient Response for
VOUT = 2.5 V
Figure 28. Load Transient Response for
VOUT = 1.8 V
1.6
3.3 V
1.2
2.5 V
0.8
1.8 V
0.4
0
−50
FOSC, OSCILLATOR FREQUENCY (kHz)
IDD, OPERATING CURRENT (mA)
70
−25
0
25
50
75
60
50
2.5 V
3.3 V
1.8 V
40
VIN = 5.0 V
VCE = 5.0 V
30
20
−50
100
−25
0
25
50
75
100
TA, AMBIENT TEMPERATURE (°C)
TA, AMBIENT TEMPERATURE (°C)
Figure 29. Off−Stage Current versus Ambient
Temperature
Figure 30. Operating Current versus Ambient
Temperature
700
450
2.5 V
650
1.8 V
600
3.3 V
550
500
VIN = 5.0 V
450
−50
−25
0
25
50
75
TA, AMBIENT TEMPERATURE (°C)
TON(PFM), PWM/PFM SWITCH ON
TIME THRESHOLD (ns)
IOFF, OFF−STATE CURRENT (mA)
2.0
400
350
2.5 V
300
1.8 V
250
VIN = 5.0 V
200
−50
100
Figure 31. Oscillator Frequency versus Ambient
Temperature
3.3 V
−25
0
25
50
75
TA, AMBIENT TEMPERATURE (°C)
100
Figure 32. PWM/PFM Switch ON Time Threshold
versus Ambient Temperature
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NCP1550
2.55
VOUT, OUTPUT VOLTAGE (V)
VOUT, OUTPUT VOLTAGE (V)
3.35
3.33
3.31
3.29
VIN = 5.0 V
3.27
3.25
−50
−25
0
25
50
75
2.53
2.51
2.49
VIN = 5.0 V
2.47
2.45
−50
100
TA, AMBIENT TEMPERATURE (°C)
IEXTH, EXT “H” OUTPUT CURRENT (mA)
VOUT, OUTPUT VOLTAGE (V)
1.83
1.81
1.79
VIN = 5.0 V
1.77
0
25
50
75
100
3.3 V
−60
2.5 V
−70
−80
VEXT = VIN − 0.4 V
VIN = 5.0 V
−90
−100
−50
2.5 V
3.3 V
1.8 V
VEXT = 0.4 V
VIN = 5.0 V
−25
0
25
50
−25
0
25
50
75
100
75
Figure 36. NCP1550 EXT “H” Output Current
versus Ambient Temperature
IVOUT, INPUT CURRENT INTO VOUT PIN (mA)
IEXTH, EXT “L” OUTPUT CURRENT (mA)
170
50
−50
100
TA, AMBIENT TEMPERATURE (°C)
200
80
75
1.8 V
−50
TA, AMBIENT TEMPERATURE (°C)
110
50
−40
Figure 35. NCP1550SN18T1 Output Voltage versus
Ambient Temperature
140
25
Figure 34. NCP1550SN25T1 Output Voltage
versus Ambient Temperature
1.85
−25
0
TA, AMBIENT TEMPERATURE (°C)
Figure 33. NCP1550SN33T1 Output Voltage versus
Ambient Temperature
1.75
−50
−25
100
3.5
VIN = 5.0 V
3.0
2.5 V
2.5
1.8 V
2.0
3.3 V
1.5
−50
−25
0
25
50
75
TA, AMBIENT TEMPERATURE (°C)
TA, AMBIENT TEMPERATURE (°C)
Figure 37. NCP1550 EXT “L” Output Current
versus Ambient Temperature
Figure 38. NCP1550 Input Current into
VOUT Pin versus Ambient Temperature
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100
NCP1550
DETAILED OPERATING DESCRIPTION
Detailed Operating Description
voltage at its output. This error voltage is compared with the
ramp function to generate the control pulse to drive the
external power switch. On a cycle−by−cycle basis, the
greater the error voltage, the longer the switch is held on.
Hence, corresponding corrective action will be made to keep
the output voltage within regulation. Constant−Frequency
PWM reduces output voltage ripple and noise, which is one
of the important characteristics for noise sensitive
communication applications. The high switching frequency
allows small size surface mount components to improve
layout compactness and reduce PC board area, and eliminate
audio and emission interference.
The NCP1550 series are step−down (Buck) DC−DC
controllers designed primarily for use in portable
applications powered by battery cells. With an appropriate
external P−channel MOSFET connected, the device can
provide up to 2 A loading current with high conversion
efficiency. The NCP1550 series using an unique control
scheme combines the advantages of Pulse−Frequency−
Modulation (PFM) that can provide excellent efficiency
even at light loading conditions and Constant−Frequency
Pulse−Width−Modulation that can achieve high efficiency
and low output voltage ripple at heavy loads. The NCP1550
working at high switching frequency makes it possible to use
small size surface mount inductor and capacitors to reduce
PCB area and provide better interference handling for noise
sensitive applications. The simplified functional blocks of
the device are shown in Figure 1 and descriptions for each
of the functions are given below.
Power−Saving Pulse−Frequency−Modulation (PFM)
Control Scheme
While the loading is decreasing, the converter enters the
Discontinuous Conduction Mode (DCM) operation, which
means the inductor current will decrease to zero before the
next switching cycle starts. In DCM operation, the ON time
for each switching cycle will decrease significantly when
the output current decreases. In order to maintain a high
conversion efficiency even at light load conditions, the ON
time for each switching cycle is closely monitored and for
any ON time smaller than the preset value, 320 nsec, the
switching pulse will be skipped. As a result, when the
loading current is small, the converter will be operating in a
“Constant ON time (320 nsec nominal), variable OFF time”
Pulse−Frequency Modulation (PFM) mode. This innovative
control scheme improves the conversion efficiency for the
system at light load and standby operating conditions hence
extend the operating life of the battery.
The Internal Oscillator
An oscillator that governs the switching of a PWM control
cycles is required. NCP1550 have an internal Fixed−
Frequency oscillator. The oscillator frequency is trimmed to
600 kHz with an accuracy of ±15%. All other timing signals
needed for operation are derived from this oscillator signal.
Voltage Reference and Soft−Start
An internal high accuracy voltage reference is included in
NCP1550. This reference voltage is connected to the
inverting input terminal of the error amplifier, A1, which
compared with portion of the output voltage, VOUT derived
from an integrated voltage divider with precise trimming to
give the required output voltage at ±2% accuracy. NCP1550
also comes with a built−in soft−start circuit that controls the
ramping up of the internal reference voltage during the
power−up of the converter. This function effectively enables
the output voltage to rise gradually over the specified
soft−start time, 8 msec typical. This prevents the output
voltage from overshooting during startup of the converter.
Low Power Shutdown Mode
NCP1550 can be disabled whenever the CE pin (Pin 1) is
tied to GND. In shutdown, the internal reference, oscillator,
control circuitry, driver and internal feedback voltage
divider are turned off and the output voltage falls to 0 V.
During the shutdown mode, as most of the internal functions
are stopped and current paths are cut−off, the device
consume extremely small current in this condition.
Voltage Mode Pulse−Width−Modulation (PWM)
Control Scheme
Under−Voltage Lockout (UVLO)
For normal operation, NCP1550 is working in
Constant−Frequency Pulse−Width−Modulation (PWM)
Voltage Mode Control. The controller operates with the
internal oscillator, which generates the required ramp
function to compare with the output of the error amplifier, A1.
The error amplifier compares the internally divided−down
output voltage with the voltage reference to produce an error
To prevent operation of the P−Channel MOSFET below
safe input voltage levels, an Undervoltage Lockout is
incorporated into the NCP1550. When the input supply
voltage drops below approximately 2.2 V, the comparator,
CP1 will turn−off the control circuitry and shut the converter
down.
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NCP1550
APPLICATIONS INFORMATION
Inductor Value Calculation
P−Channel switch duty cycle. At high input voltages, the
diode conducts most of the time. In case of VIN approaches
VOUT, the diode conducts only a small fraction of the cycle.
While the output terminals are shorted, the diode will subject
to its highest stress. Under this condition, the diode must be
able to safely handle the peak current circulating in the loop.
So, it is important to select a flywheel diode that can meet the
diode peak current and average power dissipation
requirements. Under normal conditions, the average current
conducted by the flywheel diode is given by:
Selecting the proper inductance is a trade−off between
inductor’s physical size, transient respond and power
conversion requirements. Lower value inductor saves cost,
PC board space and providing faster transient response, but
result in higher ripple current and core losses. Considering an
application with loading current, IOUT = 0.5 A and the
inductor ripple current, IL−RIPPLE(P−P) is designed to be less
than 40% of the load current, i.e. 0.5 A x 40% = 0.2 A.
The relationship between the inductor value and inductor
ripple current is given by,
T
* (VIN * RDS(ON) IOUT * VOUT)
L + ON
IL*RIPPLE(P*P)
ID + VIN * VOUT
VIN ) VF
(eq. 1)
Input and Output Capacitor Selection (CIN and COUT)
12
In continuous mode operation, the source current of the
P−Channel MOSFET is a square wave of duty cycle (VOUT +
VF)/VIN. To prevent large input voltage transients, a low ESR
input capacitor that can support the maximum RMS input
current must be selected. The maximum RMS input current,
IRMS(MAX) can be estimated by the equation in below:
RDS(ON) = 0.1 W
10
L, INDUCTANCE (mH)
(eq. 2)
Where ID is the average diode current and VF is the forward
diode voltage drop.
A fast switching diode must also be used to optimize
efficiency. Schottky diodes are a good choice for low forward
drop and fast switching times.
Where RDS(ON) is the ON resistance of the external
P−channel MOSFET. Figure 39 is a plot for recommended
inductance against nominal input voltage for different output
options.
2.5 V
8
6
IOUT
1.9 V
1.8 V
1
4
IRMS(MAX) [ IOUT
3.3 V
2.7 V
0
2.2
2.7
3.2
3.7
4.2
4.7
(eq. 3)
VIN
Above estimation has a maximum value at VIN = 2VOUT,
where IRMS(MAX) = IOUT/2. As a general practice, this simple
worst−case condition is used for design.
Selection of the output capacitor, COUT is primarily
governed by the required effective series resistance (ESR) of
the capacitor. Typically, once the ESR requirement is met, the
capacitance will be adequate for filtering. The output voltage
ripple, VRIPPLE is approximated by:
3.0 V
2
VOUT(VIN * VOUT) 2
5.2
VIN, INPUT VOLTAGE OF NCP1550 (V)
Figure 39. Inductor Selection Chart
P−Channel Power MOSFET Selection
VRIPPLE [ IL * RIPPLE(P*P)
An external P−Channel power MOSFET must be used with
the NCP1550. The key selection criteria for the power
MOSFET are the gate threshold, VGS, the “ON” resistance,
RDS(ON) and its total gate charge, QT. For low input voltage
operation, we need to select a low gate threshold device that
can work down to the minimum input voltage level. RDS(ON)
determines the conduction losses for each switching cycle,
the lower the ON resistance, the higher the efficiency can be
achieved. A power MOSFET with lower gate charge can give
lower switching losses but the fast transient can cause
unwanted EMI to the system. Compromise in between is
required during the design stage. For 1.0 A and 2.0 A load
current, NTGS3441T1 and NTGS3443T1 are tested to be
appropriate for most applications.
(ESR )
(eq. 4)
1
)
4 FOSCCOUT
Where FOSC is the switching frequency and ESR is the
effective series resistance of the output capacitor.
From equation (4), it can be noted that the output voltage
ripple contributed by two parts. For most of the case, the
major contributor is the capacitor ESR. Ordinary
aluminum−electrolytic capacitors have high ESR and should
be avoided. Higher quality Low ESR aluminum−electrolytic
capacitors are acceptable and relatively inexpensive. For even
better performance, Low ESR tantalum capacitors should be
used. Surface−mount tantalum capacitors are better and
provide neat and compact solution for space sensitive
applications.
Flywheel Diode Selection
The flywheel diode is turned on and carries load current
during the off time. The average diode current depends on the
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14
NCP1550
PCB Layout Recommendations
Good PCB layout plays an important role in switching
mode power conversion. Careful PCB layout can help to
minimize ground bounce, EMI noise and unwanted
feedbacks that can affect the performance of the converter.
Suggested hints below can be used as a guideline in most
situations.
Components Placement
Grounding
Feedback Path
Star−ground connection should be used to connect the
output power return ground, the input power return ground
and the device power ground together at one point. All high
current running paths must be thick enough for current
flowing through and producing insignificant voltage drop
along the path. Feedback signal path must be separated from
the main current path and sensing directly at the anode of the
output capacitor.
Feedback of the output voltage must be a separate trace
separated from the power path. The output voltage sensing
trace to the feedback (VOUT, pin 3) pin should be connected
to the output voltage directly at the anode of the output
capacitor.
Power components, i.e. input capacitor, inductor and
output capacitor, must be placed as close together as possible.
All connecting traces must be short, direct and thick. High
current flowing and switching paths must be kept away from
the feedback (VOUT, pin 3) terminal to avoid unwanted
injection of noise into the feedback path.
External Component Reference Data
Inductor
(L)
External MOSFET
(M)
Diode
(SD)
Output and Input
Capacitor
COUT/CIN
Device
VOUT
Inductor Model
NCP1550SN18T1
1.8 V
CDD5D23 6R8 (1A)
CDRH6D38 6R8 (2A)
Sumida
6.8 mH
NTGS3441T1 (1A)
NTGS3443T1 (2A)
ON Semiconductor
MBRM120LT3
ON Semiconductor
33 mF/33 mF (1A)
68 mF/33 mF (2A)
KEMET
(T494 series)
NCP1550SN19T1
1.9 V
CDC5D23 6R8 (1A)
CDRH6D38 6R8 (2A)
Sumida
6.8 mH
NTGS3441T1 (1A)
NTGS3443T1 (2A)
ON Semiconductor
MBRM120LT3
ON Semiconductor
33 mF/33 mF (1A)
68 mF/33 mF (2A)
KEMET
(T494 series)
NCP1550SN25T1
2.5 V
CDC5D23 5R6 (1A)
CDRH6D38 5R0 (2A)
Sumida
5.6 mH
5.0 mH
NTGS3441T1 (1A)
NTGS3443T1 (2A)
ON Semiconductor
MBRM120LT3
ON Semiconductor
33 mF/33 mF (1A)
68 mF/33 mF (2A)
KEMET
(T494 series)
NCP1550SN27T1
2.7 V
CDC5D23 5R6 (1A)
CDRH6D38 5R0 (2A)
Sumida
5.6 mH
5.0 mH
NTGS3441T1 (1A)
NTGS3443T1 (2A)
ON Semiconductor
MBRM120LT3
Semiconductor
33 mF/33 mF (1A)
68 mF/33 mF (2A)
KEMET
(T494 series)
NCP1550SN30T1
3.0 V
CDC5D23 4R7 (1A)
CDRH6D28 5R0 (2A)
Sumida
5.6 mH
5.0 mH
NTGS3441T1 (1A)
NTGS3443T1 (2A)
ON Semiconductor
MBRM120LT3
ON Semiconductor
33 mF/33 mF (1A)
68 mF/33 mF (2A)
KEMET
(T494 series)
NCP1550SN33T1
3.3 V
CD43
3R3 (1A)
CDRH6D38 3R3 (2A)
Sumida
3.3 mH
NTGS3441T1 (1A)
NTGS3443T1 (2A)
ON Semiconductor
MBRM120LT3
ON Semiconductor
68 mF/33 mF (1A)
100 mF/68 mF (2A)
KEMET
(T494 series)
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15
NCP1550
ORDERING INFORMATION
Part Number
Output Voltage
(VOUT)
Switching
Frequency
Device Marking
Package
NCP1550SN33T1
3.3 V
DCD
TSOP−5
NCP1550SN33T1G
3.3 V
DCD
TSOP−5
(Pb−Free)
NCP1550SN30T1
3.0 V
DBF
TSOP−5
NCP1550SN30T1G
3.0 V
DBF
TSOP−5
(Pb−Free)
NCP1550SN27T1
2.7 V
DCB
TSOP−5
NCP1550SN27T1G
2.7 V
DCB
TSOP−5
(Pb−Free)
NCP1550SN25T1
2.5 V
DCA
TSOP−5
NCP1550SN25T1G
2.5 V
DCA
TSOP−5
(Pb−Free)
NCP1550SN19T1
1.9 V
DBE
TSOP−5
NCP1550SN19T1G
1.9 V
DBE
TSOP−5
(Pb−Free)
NCP1550SN18T1
1.8 V
DBZ
TSOP−5
NCP1550SN18T1G
1.8 V
DBZ
TSOP−5
(Pb−Free)
600 kHz
Shipping†
3000 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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16
NCP1550
PACKAGE DIMENSIONS
THIN SOT23−5/TSOP−5/SC59−5
SN SUFFIX
CASE 483−02
ISSUE F
NOTE 5
2X
0.10 T
2X
0.20 T
NOTES:
1. DIMENSIONING AND TOLERANCING PER
ASME Y14.5M, 1994.
2. CONTROLLING DIMENSION: MILLIMETERS.
3. MAXIMUM LEAD THICKNESS INCLUDES
LEAD FINISH THICKNESS. MINIMUM LEAD
THICKNESS IS THE MINIMUM THICKNESS
OF BASE MATERIAL.
4. DIMENSIONS A AND B DO NOT INCLUDE
MOLD FLASH, PROTRUSIONS, OR GATE
BURRS.
5. OPTIONAL CONSTRUCTION: AN
ADDITIONAL TRIMMED LEAD IS ALLOWED
IN THIS LOCATION. TRIMMED LEAD NOT TO
EXTEND MORE THAN 0.2 FROM BODY.
D 5X
0.20 C A B
5
1
4
2
3
M
B
S
K
L
DETAIL Z
G
A
DIM
A
B
C
D
G
H
J
K
L
M
S
DETAIL Z
J
C
0.05
SEATING
PLANE
H
T
MILLIMETERS
MIN
MAX
3.00 BSC
1.50 BSC
0.90
1.10
0.25
0.50
0.95 BSC
0.01
0.10
0.10
0.26
0.20
0.60
1.25
1.55
0_
10 _
2.50
3.00
SOLDERING FOOTPRINT*
0.95
0.037
1.9
0.074
2.4
0.094
1.0
0.039
0.7
0.028
SCALE 10:1
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
nor the rights of others. SCILLC products are not designed, intended, or authorized for use as components in systems intended for surgical implant into the body, or other applications
intended to support or sustain life, or for any other application in which the failure of the SCILLC product could create a situation where personal injury or death may occur. Should
Buyer purchase or use SCILLC products for any such unintended or unauthorized application, Buyer shall indemnify and hold SCILLC and its officers, employees, subsidiaries, affiliates,
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 SCILLC was negligent regarding the design or manufacture of the part. SCILLC is an Equal
Opportunity/Affirmative Action Employer. This literature is subject to all applicable copyright laws and is not for resale in any manner.
PUBLICATION ORDERING INFORMATION
LITERATURE FULFILLMENT:
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Phone: 303−675−2175 or 800−344−3860 Toll Free USA/Canada
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Phone: 81−3−5773−3850
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ON Semiconductor Website: www.onsemi.com
Order Literature: http://www.onsemi.com/orderlit
For additional information, please contact your local
Sales Representative
NCP1550/D