STMicroelectronics L4978 2a step down switching regulator Datasheet

L4978
2A STEP DOWN SWITCHING REGULATOR
1
■
■
■
■
■
■
■
■
■
■
■
■
2
Features
Figure 1. Packages
UP TO 2A STEP DOWN CONVERTER
OPERATING INPUT VOLTAGE FROM 8V TO
55V
PRECISE 3.3V (±1%) INTERNAL
REFERENCE VOLTAGE
OUTPUT VOLTAGE ADJUSTABLE FROM
3.3V TO 50V
SWITCHING FREQUENCY ADJUSTABLE UP
TO 300KHz
VOLTAGE FEEDFORWARD
ZERO LOAD CURRENT OPERATION
INTERNAL CURRENT LIMITING (PULSEBYPULSE AND HICCUP MODE)
INHIBIT FOR ZERO CURRENT
CONSUMPTION
PROTECTION AGAINST FEEDBACK
DISCONNECTION
THERMAL SHUTDOWN
SOFT START FUNCTION
DIP-8
SO16W
Table 1. Order Codes
Part Number
Package
L4978
DIP-8
L4978D
SO16
L4978D013TR
SO16 in Tape & Reel
efficency and high switching speed.
A switching frequency up to 300KHz is achievable
(the maximum power dissipation of the packages
must be observed). A wide input voltage range between 8V to 55V and output voltages regulated
from 3.3V to 50V cover the majority of today’s applications. Features of this new generations of DCDC converter include pulse-by-pulse current limit,
hiccup mode for short circuit protection, voltage
feedforward regulation, soft-start, protection
against feedback loop disconnection, inhibit for
zero current consumption and thermal shutdown.
DESCRIPTION
The L4978 is a step down monolithic power
switching regulator delivering 2A at a voltage between 3.3V and 50V (selected by a simple external
divider). Realized in BCD mixed technology, the
device uses an internal power D-MOS transistor
(with a typical Rdson of 0.25Ω) to obtain very high
The device is available in plastic dual in line, DIP8 for standard assembly, and SO16W for SMD assembly.
Figure 2. Typical Application Circuit
Vi=8V to 55V
5
8
R1
20K
L4978
3
C1
220µF
63V
C7
220nF
C2
2.7nF
C5
100nF
2
4
1
7
R2
9.1K
C4
22nF
L1
126µH
(77120)
6
C6
100nF
D1
ST
PS3L60U
VO=3.3V/2A
C8
330µF
D98IN837A
May 2005
Rev. 9
1/13
L4978
Table 2. Block Diagram
VCC
5
THERMAL
SHUTDOWN
VOLTAGES
MONITOR
CBOOT
CHARGE
2
SS_INH
INHIBIT
SOFTSTART
3.3V
INTERNAL
REFERENCE
INTERNAL
SUPPLY
5.1V
7
COMP
6
E/A
8
FB
PWM
R
3.3V
Q
S
CBOOT
CHARGE
AT LIGHT
LOADS
DRIVE
OSCILLATOR
1
3
OSC
BOOT
4
GND
D97IN594
OUT
Figure 3. Pins Connection (Top view)
N.C.
1
16
N.C.
GND
2
15
N.C.
SS_INH
3
14
FB
GND
1
8
FB
SS_INH
2
7
COMP
OSC
4
13
COMP
OSC
3
6
BOOT
OUT
5
12
BOOT
OUT
4
5
VCC
OUT
6
11
VCC
N.C.
7
10
N.C.
N.C.
8
9
N.C.
D97IN595
D97IN596
DIP-8
SO16W
Table 3. Pin Description
N°
Pin
Name
1
2
GND
2
3
SS_INH
A logic signal (active low) disables the device (sleep mode operation).
A capacitor connected between this pin and ground determines the soft start time.
When this pin is grounded disables the device (driven by open collector/drain).
3
4
OSC
An external resistor connected between the unregulated input voltage and this pin
and a capacitor connected from this pin to ground fix the switching frequency. (Line
feed forward is automatically obtained)
2/13
Function
Ground
L4978
Table 3. Pin Description (continued)
N°
Pin
Name
Function
4
5, 6
OUT
Stepdown regulator output
5
11
VCC
Unregulated DC input voltage
6
12
BOOT
A capacitor connected between this pin and OUT allows to drive the internal DMOS
Transistors
7
13
COMP
E/A output to be used for frequency compensation
8
14
FB
Stepdown feedback input. Connecting directly to this pin results in an output voltage
of 3.3V. An external resistive divider is required for higher output voltages.
(*) Pins 1, 7, 8, 9, 10, 15 and 16 are not internally, electrically connected to the die.
Table 4. Thermal Data
Symbol
Rth(j-amb)
Parameter
Thermal Resistance Junction to ambient
Minidip
SO16
Unit
90 (*)
110 (*)
°C/W
Max.
(*) Package mounted on board.
Table 5. Absolute Maximum Ratings
Symbol
Parameter
Minidip
S016
V5
V11
V4
V5,V6
I4
I5,I6
V6-V5
V12-V11
V6
V12
V7
Value
Unit
Input voltage
58
V
Output DC voltage
Output peak voltage at t = 0.1ms f=200KHz
-1
-5
V
V
Maximum output current
int. limit.
14
V
Bootstrap voltage
70
V
V13
Analogs input voltage (VCC= 24V)
12
V
V2
V3
Analogs input voltage (VCC= 24V)
13
V
V8
V14
(VCC= 20V)
6
-0.3
V
V
1
0.8
W
W
-40 to 150
°C
Ptot
Power dissipation a Tamb ≤ 60°C
Tj,Tstg
Junction and storage temperature
DIP-8
SO16
3/13
L4978
Table 6. Electrical Characteristcs
(Tj = 25°C, Cosc = 2.7nF, Rosc = 20kΩ, VCC = 24V, unless otherwise specified). “● " Specification Referred
to Tj from 0 to 125°C
Symbol
Parameter
Test Condition
Min.
Typ.
Max.
Unit
55
V
DYNAMIC CHARACTERISTIC
VI
Operating input voltage range
Vo = 3.3 to 50V; Io = 2A
Vo
Output voltage
Io = 0.5A
●
Io = 0.2 to 2A
Vcc = 8 to 55V
Vd
Dropout voltage
Vcc = 10V; Io = 2A
Maximum limiting current
Vcc = 8 to 55V
Efficiency
Vo = 3.3V; Io= 2A
●
8
3.33
3.36
3.39
V
3.292
3.36
3.427
V
3.22
3.36
3.5
V
0.58
0.733
V
●
Il
fs
SVRR
●
3
1.173
V
3.5
A
87
●
Switching frequency
2.5
90
100
%
110
60
KHz
dB
Supply voltage ripple rejection
Vi = Vcc+2VRMS; Vo= Vref;
Io = 2.5A; f ripple= 100Hz
Switching Frequency Stability
vs. Vcc
Vcc = 8 to 55V
3
Temp. stability of switching
frequency
Tj = 0 to 125°C
4
6
%
%
SOFT START
Soft start charge current
30
40
50
µA
Soft start discharge current
6
10
14
µA
INHIBIT
VLL
Low level voltage
●
IsLL
Isource Low level
●
0.9
V
5
15
µA
4
6
mA
DC CHARACTERISTICS
Iqop
Iq
Iqst-by
Total operating quiescent
current
Quiescent current
Duty Cycle = 0; VFB= 3.8V
2.5
3.5
mA
Total stand-by quiescent
current
Vinh < 0.9V
100
200
µA
Vcc = 55V; Vinh<0.9V
150
300
µA
3.36
3.39
V
5
10
mV
ERROR AMPLIFIER
VFB
Voltage Feedback Input
RL
Line regulation
3.33
Vcc = 8 to 55V
●
Ref. voltage stability vs
temperature
0.4
VoH
High level output voltage
VFB = 2.5V
VoL
Low level output voltage
VFB = 3.8V
Source output current
Vcomp= 6V; VFB= 2.5V
180
220
Io sink
Sink output current
Vcomp = 6V; VFB= 3.8V
200
300
Ib
Source bias current
Io source
SVRR E/A
gm
4/13
mV/°C
10.3
V
0.65
2
V
µA
µA
3
µA
Supply voltage ripple rejection
Vcomp = VFB; Vcc = 8 to 55V
60
80
dB
DC open loop gain
RL = ∞
50
57
dB
Transconductance
Icomp = -0.1 to 0.1mA
Vcomp = 6V
2.5
mS
L4978
Table 6. Electrical Characteristcs
(Tj = 25°C, Cosc = 2.7nF, Rosc = 20kΩ, VCC = 24V, unless otherwise specified). “● " Specification Referred
to Tj from 0 to 125°C
Symbol
Parameter
Test Condition
Min.
Typ.
Max.
Unit
0.78
0.85
0.92
V
Vcc = 8V
2
2.15
2.3
V
Vcc = 55V
9
9.6
10.2
V
95
97
300
kHz
OSCILLATOR SECTION
Ramp Valley
Ramp peak
Maximum duty cycle
Maximum Frequency
Duty Cycle = 0%
Rosc = 13kΩ, Cosc = 820pF
%
Figure 4. Test and evaluation board circuit.
Vi=8V to 55V
5
8
R1
20K
L4978
3
C1
220µF
63V
C7
220nF
C2
2.7nF
1
7
2
C5
100nF
VO=3.3V/2A
4
R2
9.1K
L1
126µH
(77120)
6
C6
100nF
D1
STPS3L60U
R3
C8
330µF
C4
22nF
R4
D98IN834B
C1=220µF/63V EKE
C2=2.7nF
C5=100nF
C6=100nF
C7=220nF/63V
C8=330µF/35V CG Sanyo
L1=126µH KoolMu 77120 - 55 Turns - 0.5mm
R1=20K
R2=9.1K
D1=STPS3L60U
L4978
VO(V)
R3(KΩ)
3.3
0
R4(KΩ)
5.1
2.7
4.7
12
12
4.7
15
16
4.7
18
20
4.7
24
30
4.7
Figure 5. PCB and component layout of the figure 4.
5/13
L4978
Figure 6. Quiescent drain current vs. input
voltage.
Iq
(mA)
D97IN724
200KHz
R1=22K
C2=1.2nF
5
Figure 9. Line Regulation
.
VO
(V)
D97IN733
3.377
Tj=125˚C
3.376
100KHz
R1=20K
C2=2.7nF
4
3.375
Tj=25˚C
3.374
3
0Hz
3.373
3.372
2
3.371
Tamb=25˚C
0% DC
3.370
1
0
5 10 15 20 25 30 35 40 45 50
Figure 7. Quiescent current vs. junction
temperature
D97IN731
Iq
(mA)
200KHz
R1=22K
C2=1.2nF
5
4
0
Vcc(V)
5 10 15 20 25 30 35 40 45 50 VCC(V)
Figure 10. Load regulation
.
VO
(V)
3.378
D98IN835
VCC=35V
3.376
3.374
3.372
100KHz
R1=20K
C2=2.7nF
Tj=25˚C
3.370
3
Tj=125˚C
3.368
0Hz
3.366
VCC=35V
0% DC
2
3.364
3.362
1
3.360
-50 -30 -10 10 30 50 70 90 110
Tj(˚C)
Figure 8. Stand by drain current vs. input
voltage.
Ibias
(µA)
D97IN732
Vss=GND
150
0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 IO(A)
Figure 11. Switching frquency vs. R1 and C2
.
fsw
(KHz)
D97IN784
500
Tamb=25˚C
Tj=25˚C
140
0.8
130
200
120
100
2nF
1.2
nF
2.2
nF
110
Tj=125˚C
100
90
50
3.3n
F
4.7n
F
20
5.6n
80
F
10
70
60
6/13
0
5 10 15 20 25 30 35 40 45 50 VCC(V)
5
0
20
40
60
80
R1(KΩ)
L4978
Figure 12. Switching Frequency vs. input
voltage..
fsw
(KHz)
D97IN735
Figure 15. Efficiency vs output voltage.
.
[%]
98
fsw=100kHz
96
107.5
94
105.0
fsw=200kHz
92
102.5
Tj=25˚C
90
100.0
88
97.5
86
95.0
84
92.5
82
80
90.0
0
5 10 15 20 25 30 35 40 45 50 VCC(V)
Figure 13. Switching frequency vs. junction
temperature.
fsw
(KHz)
D97IN785
Vcc=35V
Io=2A
0
5
10
15
Vo [V]
20
25
30
Figure 16. Efficiency vs. output current.
.
[%]
95
Vcc=8V
Vcc=12V
90
105
85
Vcc=24V
80
100
75
Vcc=48V
70
95
fsw=100kHz
Vo=5.1V
65
60
90
-50
0
50
100
Figure 14. Dropout voltage between pin 5 and
4.
∆V
(V)
0.7
0
Tj(˚C)
D98IN836
0.2 0.4 0.6 0.8
1 1.2 1.4 1.6 1.8
Io [A]
2
2.2
Figure 17. Efficiency vs. output current.
.
[%]
95
Vcc=8V
90
Tj=125˚C
0.6
85
Vcc=12V
˚C
0.5
5
=2
Tj
80
0.4
75
0.3
Vcc=24V
Tj=-25˚C
70
0.2
65
0.1
Vcc=48V
Vo=3.36V
fsw=100kHz
60
0.0
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 IO(A)
0
0.2 0.4 0.6 0.8
1 1.2 1.4 1.6 1.8
Io [A]
2
2.2
7/13
L4978
Figure 18. Efficiency vs. output current.
.
Figure 21. Power dissipation vs. Vcc.
.
Pdiss [mW]
D97IN740
η
(%)
1000
VCC=8V
90
Vo=5.1V
fsw=100kHz
VCC=12V
800
Io=2A
VCC=24V
85
600
80
Io=1A
VCC=48V
Io=1.5A
75
400
70
fsw=200KHz
VO=5.1V
Io=0.5A
200
65
0
60
0
0
0.2 0.4 0.6 0.8 1.0 1.2 1.4 IO(A)
Figure 19. Efficiency vs. output current.
.
η
(%)
40
50
60
Pdiss [mW]
Vcc=35V
fsw=100kHz
1200
VCC=12V
80
30
Vcc [V]
1400
VCC=8V
85
20
Figure 22. Device Power dissipation vs. Vo
.
D97IN741
90
10
Io=2A
1000
Io=1.5A
VCC=24V
800
75
600
70
VCC=48V
Io=1A
400
65
fsw=200KHz
VO=3.36V
Io=0.5A
200
60
0
55
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 IO(A)
0
10
20
Vo [V]
30
Figure 23. Pulse by pulse limiting current vs.
junction temperature..
Figure 20. Efficiency vs. Vcc.
.
n [%]
Ilim
(A)
90
Vo=5.1V fsw=100kHz
D97IN747
fsw=100KHz
VCC=35V
2.9
85
2.8
Vo=5.1V fsw=200kHz
Vo=3.36V fsw=100kHz
2.7
80
2.6
Vo=3.36V fsw=200kHz
2.5
75
Io=2A
2.4
70
0
8/13
10
20
30
Vcc [V]
40
50
60
2.3
-50 -25
0
25
50
75 100 125 Tj(˚C)
L4978
Figure 27. Soft start capacitor selection Vs
inductor and Vccmax.
Figure 24. Load transient.
.
L
(µH)
D97IN746
56nF
fsw=200KHz
300
47nF
200
33nF
22nF
100
0
15 20 25 30 35 40 45 50 VCCmax(V)
Figure 25. Line transient.
.
Figure 28. Open loop frequency and phase of
error amplifier .
VCC
(V)
GAIN
(dB)
D97IN786
30
D97IN787
Phase
50
GAIN
20
0
0
-50
45
10
VO
(mV)
1
IO = 1A
fsw = 100KHz
100
2
90
-100
0
Phase
135
-150
-100
1ms/DIV
-200
10
102 103 104 105 106 107 108 f(Hz)
Figure 26. Soft start capacitor selection Vs
inductor and Vccmax.
D97IN745
L
(µH)
680nF
470nF
fsw=100KHz
400
330nF
300
200
100
220nF
100nF
0
15 20 25 30 35 40 45 50 VCCmax(V)
9/13
L4978
3
Package Informations
Figure 29. DIP-8 Mechanical Data & Package Dimensions
mm
inch
DIM.
MIN.
A
TYP.
MIN.
3.32
TYP.
MAX.
0.51
B
1.15
1.65
0.045
0.065
b
0.356
0.55
0.014
0.022
b1
0.204
0.304
0.008
0.012
E
0.020
10.92
7.95
9.75
0.430
0.313
0.384
e
2.54
0.100
e3
7.62
0.300
e4
7.62
0.300
F
6.6
0.260
I
5.08
0.200
L
Z
3.18
OUTLINE AND
MECHANICAL DATA
0.131
a1
D
10/13
MAX.
3.81
1.52
0.125
0.150
0.060
DIP-8
L4978
Figure 30. SO16 Wide Mechanical Data & Package Dimensions
mm
inch
DIM.
MIN.
TYP.
MAX.
MIN.
TYP.
MAX.
A
2.35
2.65
0.093
0.104
A1
0.10
0.30
0.004
0.012
B
0.33
0.51
0.013
0.200
C
0.23
0.32
0.009
0.013
D (1)
10.10
10.50
0.398
0.413
E
7.40
7.60
0.291
0.299
e
1.27
0.050
H
10.0
10.65
0.394
0.419
h
0.25
0.75
0.010
0.030
L
0.40
1.27
0.016
0.050
k
ddd
OUTLINE AND
MECHANICAL DATA
0˚ (min.), 8˚ (max.)
0.10
0.004
(1) “D” dimension does not include mold flash, protusions or gate
burrs. Mold flash, protusions or gate burrs shall not exceed
0.15mm per side.
SO16 (Wide)
0016021 C
11/13
L4978
Table 7. Revision History
Date
Revision
October 2001
8
First Issue
May 2005
9
Modified D1 on the Fig. 4.
12/13
Description of Changes
L4978
Information furnished is believed to be accurate and reliable. However, STMicroelectronics assumes no responsibility for the consequences
of use of such information nor for any infringement of patents or other rights of third parties which may result from its use. No license is granted
by implication or otherwise under any patent or patent rights of STMicroelectronics. Specifications mentioned in this publication are subject
to change without notice. This publication supersedes and replaces all information previously supplied. STMicroelectronics products are not
authorized for use as critical components in life support devices or systems without express written approval of STMicroelectronics.
The ST logo is a registered trademark of STMicroelectronics.
All other names are the property of their respective owners
© 2005 STMicroelectronics - All rights reserved
STMicroelectronics group of companies
Australia - Belgium - Brazil - Canada - China - Czech Republic - Finland - France - Germany - Hong Kong - India - Israel - Italy - Japan Malaysia - Malta - Morocco - Singapore - Spain - Sweden - Switzerland - United Kingdom - United States of America
www.st.com
13/13
Similar pages