10A SWITCHING REGULATOR

10A SWITCHING REGULATOR
L4970A
10A SWITCHING REGULATOR
10A OUTPUT CURRENT
5.1V TO 40V OUTPUT VOLTAGE RANGE
0 TO 90% DUTY CYCLE RANGE
INTERNAL FEED-FORWARD LINE REGULATION
INTERNAL CURRENT LIMITING
PRECISE 5.1V ± 2% ON CHIP REFERENCE
RESET AND POWER FAIL FUNCTIONS
SOFT START
INPUT/OUTPUT SYNC PIN
UNDER VOLTAGE LOCK OUT WITH HYSTERETIC TURN-ON
PWM LATCH FOR SINGLE PULSE PER PERIOD
VERY HIGH EFFICIENCY
SWITCHING FREQUENCY UP TO 500KHz
THERMAL SHUTDOWN
CONTINUOUS MODE OPERATION
DESCRIPTION
The L4970A is a stepdown monolithic power
switching regulator delivering 10A at a voltage
variable from 5.1 to 40V.
MULTIPOWER BCD TECHNOLOGY
Multiwatt15V
ORDERING NUMBER: L4970A
Realized with BCD mixed technology, the device
uses a DMOS output transistor to obtain very high
efficiency and very fast switching times. Features
of the L4970A include reset and power fail for microprocessors, feed forward line regulation, soft
start, limiting current and thermal protection. The
device is mounted in a 15-lead multiwatt plastic
power package and requires few external components. Efficient operation at switching frequencies
up to 500KHz allows reduction in the size and
cost of external filter components.
BLOCK DIAGRAM
November 1991
1/21
This is advanced information on a new product now in development or undergoing evaluation. Details are subject to change without notice.
L4970A
ABSOLUTE MAXIMUM RATINGS
Symbol
Value
Unit
V9
Input Voltage
Parameter
55
V
V9
Input Operating Voltage
50
V
V7
Output DC Voltage
Output Peak Voltage at t = 0.1µs f = 200KHz
-1
-7
V
V
I7
Maximum Output Current
V6
Bootstrap Voltage
Bootstrap Operating Voltage
V3, V12
Internally Limited
65
V9 + 15
V
V
V
Input Voltage at Pins 3, 12
12
V4
Reset Output Voltage
50
V
I4
Reset Output Sink Current
50
mA
Input Voltage at Pin 5, 10, 11, 13
7
V
mA
V5, V10, V11, V13
I5
Reset Delay Sink Current
30
I10
Error Amplifier Output Sink Current
1
A
I12
Soft Start Sink Current
30
mA
Ptot
Total Power Dissipation at Tcase < 120°C
Tj, Tstg
Junction and Storage Temperature
30
W
-40 to 150
°C
PIN CONNECTION (Top view)
THERMAL DATA
Symbol
Rth j-case
R th j-amb
2/21
Parameter
Thermal Resistance Junction-case
Thermal Resistance Junction-ambient
max
max
Value
Unit
1
35
°C/W
°C/W
L4970A
PIN FUNCTIONS
o
N
Name
Function
1
OSCILLATOR
Rosc. External resistor connected to ground determines the constant charging
current of C osc.
2
OSCILLATOR
Cosc. External capacitor connected to ground determines (with R osc) the
switching frequency.
3
RESET INPUT
Input of Power Fail Circuit. The threshold is 5.1V. It may be connected via a
divider to the input for power fail function. It must be connected to the pin 14 an
external 30KΩ resistor when power fail signal not required.
4
RESET OUT
Open Collector Reset/power Fail Signal Output. This output is high when the
supply and the output voltages are safe.
5
RESET DELAY
A C d capacitor connected between this terminal and ground determines the
reset signal delay time.
6
BOOTSTR AP
A C boot capacitor connected between this terminal and the output allows to
drive properly the internal D-MOS transistor.
7
OUTPUT
Regulator Output.
8
GROUND
Common Ground Terminal
9
SUPPLY VOLTAGE
Unregulated Input Voltage.
10
FREQUENCY
COMPENSATION
A series RC network connected between this terminal and ground determines
the regulation loop gain characteristics.
11
FEEDBACK INPUT
The Feedback Terminal of the Regulation Loop. The output is connected
directly to this terminal for 5.1V operation; It is connected via a divider for higher
voltages.
12
SOFT START
Soft Start Time Constant. A capacitor is connected between thi sterminal and
ground to define the soft start time constant.
13
SYNC INPUT
Multiple L4970A are synchronized by connecting pin 13 inputs together or via
an external syncr. pulse.
14
Vref
5.1V Vref Device Reference Voltage.
15
Vstart
Internal Start-up Circuit to Drive the Power Stage.
CIRCUIT OPERATION (refer to the block diagram)
The L4970A is a 10A monolithic stepdown switching
regulator working in continuous mode realized in the
new BCD Technology. This technology allows the integration of isolated vertical DMOS power transistors
plus mixed CMOS/Bipolar transistors.
The device can deliver 10A at an output voltage
adjustable from 5.1V to 40V, and contains diagnostic and control functions that make it particularly suitable for microprocessor based systems.
BLOCK DIAGRAM
The block diagram shows the DMOS power transistor and the PWM control loop. Integrated functions include a reference voltage trimmed to 5.1V
± 2%, soft start, undervoltage lockout, oscillator
with feedforward control, pulse by pulse current
limit, thermal shutdown and finally the reset and
power fail circuit. The reset and power fail circuit
provides an output signal for a microprocessor indicating the status of the system.
Device turn on is around 11V with a typical 1V
hysteresis, this threshold provides a correct voltage for the driving stage of the DMOS gate and
the hysteresis prevents instabilities.
An external bootstrap capacitor charged to 12V
by an internal voltage reference is needed to provide correct gate drive to the power DMOS. The
driving circuit is able to source and sink peak currents of around 0.5A to the gate of the DMOS
transistor. A typical switching time of the current
in the DMOS transistor is 50ns. Due to the fast
commutation switching frequencies up to 500kHz
are possible.
The PWM control loop consists of a sawtooth oscillator, error amplifier, comparator, latch and the
output stage. An error signal is produced by comparing the output voltage with the precise 5.1V ±
2% on chip reference. This error signal is then
compared with the sawtooth oscillator, in order to
generate a fixed frequency pulse width modulated
drive for the output stage. A PWM latch is included to eliminate multiple pulsing within a period even in noisy environments. The gain and
3/21
L4970A
Figure 1: Feedforward Waveform
Figure 2: Soft Start Function
Figure 3: Limiting Current Function
4/21
L4970A
stability of the loop can be adjusted by an external RC network connected to the output of the error amplifier. A voltage feedforward control has
been added to the oscillator, this maintains superior line regulation over a wide input voltage
range. Closing the loop directly gives an output
voltage of 5.1V, higher voltages are obtained by
inserting a voltage divider.
At turn on output overcurrents are prevented by
the soft start function (fig. 2). The error amplifier is
initially clamped by an external capacitor Css and
allowed to rise linearly under the charge of an internal constant current source.
Output overload protection is provided by a current limit circuit (fig. 3). The load current is sensed
by an internal metal resistor connected to a comparator. When the load current exceeds a preset
threshold the output of the comparator sets a flip
flop which turns off the power DMOS. The next
clock pulse, from an internal 40kHz oscillator will
reset the flip flop and the power DMOS will again
conduct. This current protection method, ensures
a constant current output when the system is
overloaded or short circuited and limits the
switching frequency, in this condition, to 40kHz.
The Reset and Power fail circuitry (fig 4) generates an output signal when the supply voltage exceeds a threshold programmed by an external
voltage divider. The reset signal, is generated
with a delay time programmed by an external capacitor on the delay pin. When the supply voltage
falls below the threshold or the output voltage
goes below 5V the reset output goes low immediately. The reset output is an open collector-drain.
Fig 4A shows the case when the supply voltage is
higher than the threshold, but the output voltage
is not yet 5V.
Fig 4B shows the case when the output is 5.1V
but the supply voltage is not yet higher than the
fixed threshold.
The thermal protection disables circuit operation
when the junction temperature reaches about
150°C and has an hysterysis to prevent unstable
conditions.
Figure 4: Reset and Power Fail Functions.
A
B
5/21
L4970A
ELECTRICAL CHARACTERISTICS (Refer to the test circuit, Tj = 25°C, Vi = 35V, R4 = 16KΩ,
C9 = 2.2nF, fSW = 200KHz typ, unless otherwise specified)
DYNAMIC CHARACTERISTICS
Symbol
Parameter
Test Condition
Min.
Vi
input Voltage Range (pin 9)
Vo = Vref to 40V
Io = 10A
15
Vo
Output Votage
Vi = 15V to 50V
Io = 5A; Vo = Vref
5
∆Vo
Line Regulation
Vi = 15V to 50V
Io = 5A; Vo = Vref
∆Vo
Load Regulation
Vo = Vref
Io = 3A to 6A
Io = 2A to 10A
Typ.
Max.
Unit
Fig.
50
V
5
5.1
5.2
V
5
12
30
mV
5
10
20
30
50
mV
mV
0.55
1.1
0.8
1.6
V
V
5
15
A
5
5
Vd
Dropout Voltage Between
Pin 9 and 7
Io = 5A
Io = 10A
I7L
Max. Limiting Current
Vi = 15 to 50V
11
13
η
Efficiency
Io = 5A
Vo = Vref
Vo = 12V
80
85
92
%
%
Io = 10A
Vo = Vref
Vo = 12V
75
80
87
%
%
56
60
dB
5
180
200
220
KHz
5
6
%
5
%
5
KHz
5
Unit
Fig.
SVR
Supply Voltage Ripple
Reject.
f
∆f
∆ Vi
∆f
Tj
Switching Frequency
fmax
Vi = 2VRMS; Io = 5A
f = 100Hz; Vo = Vref
5
5
Voltage Stability of
Swiching Frequency
Vi = 15V to 45V
2
Temperature Stability of
Swiching Frequency
T j = 0 to 125°C
1
Maximum Operating
Switching Frequency
Vo = Vref; R4 = 10KΩ
Io = 10A; C9 = 1nF
500
Test Condition
Min.
Typ.
Max.
5
5.1
5.2
V
7
10
25
mV
7
40
Vref SECTION (pin 14)
Symbol
Parameter
V14
Reference Voltage
∆V14
Line Regulation
∆V14
∆ V14
∆T
I14 sho rt
Vi = 15V to 50V
Load Regulation
I14 = 0 to 1mA
20
mV
7
Average Temperature
Coefficient Reference
Voltage
T j = 0°C to 125°C
0.4
mV/°C
7
Short Circuit Current Limit
V14 = 0
70
mA
7
VSTART SECTION (pin 15)
Symbol
Parameter
Test Condition
Min.
Typ.
Max.
Unit
Fig.
11.4
12
12.6
V
7
1.4
V
7
200
mV
7
mA
7
V15
Reference Voltage
∆V15
Line Regulation
Vi = 15 to 50V
0.6
∆V15
Load Regulation
I15 = 0 to 1mA
50
Short Circuit Current Limit
V15 = 0V
80
I15 sho rt
6/21
L4970A
ELECTRICAL CHARACTERISTICS (continued)
DC CHARACTERISTICS
Symbol
Parameter
V9on
Turn-on Threshold
V9 Hyst
Turn-off Hysteresys
Test Condition
Min.
Typ.
Max.
Unit
Fig.
10
11
12
V
7A
V
7A
I9Q
Quiescent Current
V12 = 0; S1 = D
13
19
mA
7A
I9OQ
Operating Supply Current
V12 = 0; S1 = C; S2 = B
16
23
mA
7A
Out Leak Current
Vi = 55V; S3 = A; V12 = 0
2
mA
7A
Fig.
I7L
1
SOFT START
Symbol
Parameter
Test Condition
I12
Soft Start Source Current
V12 = 3V; V11 = 0V
V12
Output Saturation Voltage
I12 = 20mA; V9 = 10V
I12 = 200µA; V9 = 10V
Min.
Typ.
Max.
Unit
70
100
130
µA
7B
1
0.7
V
V
7B
7B
Max.
Unit
Fig.
V
7C
V
7C
ERROR AMPLIFIER
Symbol
Parameter
Test Condition
Min.
Typ.
V10H
High Level Out Voltage
I10 = -100µA; S1 = C
V11 = 4.7V
V10L
Low Level Out Voltage
I10 = +100µA; S1 = C
V11 = 5.3V;
I10H
Source Output Current
V10 = 1V; S1 = E
V11 = 4.7V
100
150
µA
7C
I10L
Sink Output Current
V10 = 6V; S1 = D
V11 = 5.3V
100
150
µA
7C
I11
Input Bias Current
R S = 10KΩ
GV
DC Open Loop Gain
VVCM = 4V;
R S = 10Ω
60
SVR
Supply Voltage Rejection
15 < Vi < 50V;
R S = 10Ω
60
VOS
Input Offset Voltage
R S = 50Ω
6
1.2
0.4
3
80
µA
–
dB
–
dB
–
2
10
mV
–
Min.
Typ.
Max.
Unit
Fig.
1.2
1.5
V
7A
2.5
5.5
V
V
7A
7A
RAMP GENERATOR (pin 2)
Symbol
Parameter
Test Condition
V2
Ramp Valley
S1 = C; S2 = B
V2
Ramp Peak
S1 = C;
S2 = B;
I2
Min. Ramp Current
S1 = A; I1 = 100µA
I2
Max. Ramp Current
S1 = A; I1 = 1mA
Vi = 15V
Vi = 45V
270
2.4
2.7
Min.
Typ.
300
µA
7A
mA
7A
SYNC FUNCTION (pin 13)
Symbol
Max.
Unit
Fig.
V13
Low Input Voltage
Parameter
Vi = 15V to 50V; V12 = 0;
S1 = C; S2 = B; S4 = B
Test Condition
–0.3
0.9
V
7A
V13
High Input voltage
V12 = 0;
S1 = C; S2 = B; S4 = B
3.5
5.5
V
7A
I13L
Sync Input Current with
Low Input Voltage
V13 = V2 = 0.9V; S4 = A;
S1 = C; S2 = B
0.4
mA
7A
I13H
Input Current with High
Input Voltage
V13 = 3.5V; S4 = A;
S1 = C; S2 = B
1.5
mA
7A
V13
Output Amplitude
V
–
tW
Output Pulse Width
0.8
µs
–
Vthr = 2.5V
4
5
0.3
0.5
7/21
L4970A
ELECTRICAL CHARACTERISTICS (continued)
RESET AND POWER FAIL FUNCTIONS
Symbol
Parameter
Min.
Typ.
Max.
Unit
Fig.
V11R
Rising Threshold Voltage
(pin 11)
Vi = 15 to 50V
V3 = 5.3V
Test Condition
Vref
–120
Vref
–100
Vref
–80
V
mV
7D
V11F
Falling Threshold Voltage
(pin 11)
Vi = 15 to 50V
V3 = 5.3V
4.77
Vref
–200
Vref
–160
V
mV
7D
V5H
Delay High Threshold
Voltage
Vi = 15 to 50V
V14 = V11
V3 = 5.3V
4.95
5.1
5.25
V
7D
V5L
Delay Low Threshold
Voltage
Vi = 15 to 50V
V14 = V11
V3 = 5.3V
1
1.1
1.2
V
7D
–I5SO
60
80
Delay Source Current
V3 = 5.3V; V5 = 3V
40
I5SI
Delay Sink Current
V3 = 4.7V; V5 = 3V
10
V4S
Out Saturation Voltage
I4 = 15mA; S1 = B
V3 = 4.7V
Output Leak Current
V4 = 50V; S1 = A
V3 = 5.3V
V3R
Rising Threshold Voltage
V11 = V14
V3H
Hysteresys
I4
I3
7D
7D
0.4
V
7D
100
µA
7D
4.95
5.1
5.25
V
7D
0.4
0.5
0.6
V
7D
1
3
µA
7D
Input Bias Current
Figure 5: Test and Evaluation Board Circuit
TYPICAL PERFORMANCES (using evaluation board) :
n = 83% (Vi = 35V ; Vo = VREF ; Io = 10A ; fSW = 200KHz)
Vo RIPPLE = 30mV (at 10A) with output filter capacitor ESR ≤ 60mΩ
Line regulation = 5mV (Vi = 15 to 50V)
Load regulation = 15mV (Io = 2 to 10A)
For component values, refer to test circuit part list.
8/21
µA
mA
L4970A
Figure 6a: P.C. Board (components side) and Components Layout of Figure 5 (1:1 scale).
PARTS LIST
Table A
R1 = 30KΩ
C 1, C2 = 3300µF 63VL EYF (ROE
R2 = 10KΩ
C 3, C4, C5, C6 = 2.2µF
R3 = 15KΩ
C 7 = 390pF Film
R4 = 16KΩ
C 8 = 22nF MKT 1817 (ERO)
R5 = 22Ω 0,5W
R6 = 4K7
C 9 = 2.2nF KP1830
R7 = 10Ω
C 10 = 220nF MKT
R8 = see tab. A
C 11 = 2.2nF MP1830
R9 = OPTION
**C12 , C13, C14 = 220µF 40VL EKR
R10 = 4K7
C 15 = 1µF Film
V0
R9
R7
12V
15V
18V
24V
4.7kΩ
4.7kΩ
4.7kΩ
4.7kΩ
6.2kW
9.1kΩ
12kΩ
18kΩ
Table B
SUGGESTED BOOTSTRAP CAPACITORS
Operating Frequency
Bootstrap Cap.c10
D1 = MBR 1560CT (or 16A/60V or equivalent)
f = 20KHz
≥680nF
L1 = 40µH
f = 50KHz
≥470nF
f = 100KHz
≥330nF
f = 200KHz
≥220nF
f = 500KHz
≥100nF
R11 = 10Ω
core 58071 MAGNETICS
27 TURNS Ø 1,3mm (AWG 16)
COGEMA 949178
* 2 capacitors in parallel to increase input RMS current capability
** 3 capacitors in parallel to reduce total output ESR
9/21
L4970A
Figure 6b: P.C. Board (Back side) and Components Layout of the Circuit of Fig. 5. (1:1 scale)
Figure 7: DC Test Circuits
10/21
L4970A
Figure 7A
Figure 7B
11/21
L4970A
Figure 7D
Figure 7C
12/21
L4970A
Figure 8: Quiescent Drain Current vs. Supply
Voltage (0% duty cycle - see fig. 7A).
Figure 9: Quiescent Drain Current vs. Junction
Temperature (0% duty cycle).
Figure 10: Quiescent Drain Current vs. Duty
Cycle
Figure 11: Reference Voltage (pin14) vs. Vi (see
fig. 7)
Figure 12: Reference Voltage (pin 14) vs.
Junction Temperature (see fig. 7)
Figure 13: Reference Voltage (pin15) vs. Vi (see
fig. 7)
13/21
L4970A
Figure 14: Reference Voltage (pin 15) vs.
Junction Temperature (see fig. 7)
Figure 15: Reference Voltage 5.1V (pin 14)
Supply Voltage Ripple Rejection vs.
Frequency
Figure 16: Switching Frequency vs. Input
Voltage (see fig. 5)
Figure 17: Switching Frequency vs. Junction
Temperature (see fig 5)
Figure 18: Switching Frequency vs. R4 (see fig. 5)
Figure 19: Max. Duty Cycle vs. Frequency
14/21
L4970A
Figure 20: Supply Voltage Ripple Rejection vs.
Frequency (see fig. 5)
Figure 21: Line Transient Response (see fig. 5)
Figure 22: Load Transient Response (see fig. 5)
Figure 23: Dropout Voltage Between Pin 9 and
Pin 7 vs. Current at Pin 7
Figure 24: Dropout Voltage Between Pin 9 and
Pin 7 vs. Junction Temperature
Figure 25: Power Dissipation (device only) vs.
Input Voltage
15/21
L4970A
Figure 26: Power Dissipation (device only) vs.
Output Voltage
Figure 27: Heatsink Used to Derive the Device’s
Power Dissipation
Tcase − Tamb
Rth - Heatsink =
Pd
Figure 28: Efficiency vs. Output Current
Figure 29: Efficiency vs. Output Voltage
Figure 30: Efficiency vs. Output Voltage
16/21
Figure 31: Open Loop Frequency and Phase
Response of Error Amplifier (see
fig.7C)
L4970A
Figure 32: Power Dissipation Derating Curve
Figure 33: A5.1V/12V Multiple Supply. Note the Synchronization between the L4970A and the L4974A
17/21
L4970A
Figure 34: 5.1V / 10A Low Cost Application
Figure 35: 10A Switching Regulator, Adjustable from 0V to 25V.
18/21
L4970A
Figure 36: L4970A’sSync. Example
19/21
L4970A
MULTIWATT15 PACKAGE MECHANICAL DATA
DIM.
mm
MIN.
TYP.
MAX.
MIN.
TYP.
MAX.
A
5
0.197
B
2.65
0.104
C
1.6
0.063
D
1
0.039
E
0.49
0.55
0.019
F
0.66
0.75
0.026
G
1.14
1.27
1.4
0.045
0.050
0.055
G1
17.57
17.78
17.91
0.692
0.700
0.705
H1
19.6
L
0.022
0.030
0.772
H2
20/21
inch
20.2
0.795
22.1
22.6
0.870
0.890
L1
22
22.5
0.866
0.886
L2
17.65
18.1
0.695
L3
17.25
17.5
17.75
0.679
0.689
L4
10.3
10.7
10.9
0.406
0.421
L7
2.65
2.9
0.104
0.713
0.699
0.429
0.114
M
4.2
4.3
4.6
0.165
0.169
0.181
M1
4.5
5.08
5.3
0.177
0.200
0.209
S
1.9
2.6
0.075
S1
1.9
2.6
0.075
0.102
0.102
Dia1
3.65
3.85
0.144
0.152
L4970A
Information furnished is believed to be accurate and reliable. However, SGS-THOMSON Microelectronics 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 SGS-THOMSON Microelectronics. Specifications mentioned in this publication are subject to change without notice. This publication supersedes and replaces all information previously supplied.
SGS-THOMSON Microelectronics products are not authorized for use as critical components in life support devices or systems without express written approval of SGS-THOMSON Microelectronics.
 1994 SGS-THOMSON Microelectronics - All Rights Reserved
MULTIWATT  is a Registered Trademark of SGS-THOMSON Microelectronics
SGS-THOMSON Microelectronics GROUP OF COMPANIES
Australia - Brazil - France - Germany - Hong Kong - Italy - Japan - Korea - Malaysia - Malta - Morocco - The Netherlands - Singapore Spain - Sweden - Switzerland - Taiwan - Thaliand - United Kingdom - U.S.A.
21/21
Was this manual useful for you? yes no
Thank you for your participation!

* Your assessment is very important for improving the work of artificial intelligence, which forms the content of this project

Download PDF

advertising