L5981 STMicroelectronics, L5981 Datasheet

IC REG SW STEP DOWN 1A 8-VFQFPN

L5981

Manufacturer Part Number
L5981
Description
IC REG SW STEP DOWN 1A 8-VFQFPN
Manufacturer
STMicroelectronics
Type
Step-Down (Buck)r
Datasheet

Specifications of L5981

Internal Switch(s)
Yes
Synchronous Rectifier
No
Number Of Outputs
1
Voltage - Output
0.6 ~ 18 V
Current - Output
1A
Frequency - Switching
250kHz ~ 1MHz
Voltage - Input
2.9 ~ 18 V
Operating Temperature
-40°C ~ 125°C
Mounting Type
Surface Mount
Package / Case
8-VFQFN, 8-VFQFPN
Power - Output
1.5W
Output Voltage
3 V
Output Current
1 A
Input Voltage
2.9 V to 18 V
Switching Frequency
220 KHz to 275 KHz
Operating Temperature Range
- 40 C to + 150 C
Mounting Style
SMD/SMT
Duty Cycle (max)
100 %
Low Dropout Operation
100 % duty cycle
For Use With
497-6385 - BOARD EVAL FOR L5981
Lead Free Status / RoHS Status
Lead free / RoHS Compliant

Available stocks

Company
Part Number
Manufacturer
Quantity
Price
Part Number:
L5981
Manufacturer:
STMicroelectronics
Quantity:
10 000
Part Number:
L5981TR
Manufacturer:
STMicroelectronics
Quantity:
10 000
Part Number:
L5981TR
Manufacturer:
STM
Quantity:
2
Features
Applications
June 2009
Figure 1.
1 A DC output current
2.9 V to 18 V input voltage
Output voltage adjustable from 0.6 V
250 kHz switching frequency, programmable
up to 1 MHz
Internal soft-start and inhibit
Low dropout operation: 100 % duty cycle
Voltage feed-forward
Zero load current operation
Overcurrent and thermal protection
VFQFPN8 3 mm x 3 mm package
Consumer: STB, DVD, DVD recorder, car
audio, LCD TV and monitors
Industrial: chargers, PLD, PLA, FPGA
Networking: XDSL, modems, DC-DC modules
Computer: optical storage, hard disk drive,
printers, audio/graphic cards
LED driving
Application circuit
Doc ID 13004 Rev 6
1 A step-down switching regulator
Description
The L5981 is step-down switching regulator with
1.5 A (min.) current limited embedded power
MOSFET, so it is able to deliver in excess of 1 A
DC current to the load depending on the
application condition.
The input voltage can range from 2.9 V to 18 V,
while the output voltage can be set starting from
0.6 V to V
2.9 V, the device is suitable also for 3.3 V bus.
Requiring a minimum set of external components,
the device includes an internal 250 kHz switching
frequency oscillator that can be externally
adjusted up to 1 MHz.
The VFQFPN8 package with exposed pad allows
reducing the R
60 °C/W.
IN
. Having a minimum input voltage of
VFQFPN8 3 mm x 3 mm
thJA
down to approximately
L5981
www.st.com
1/37
37

Related parts for L5981

L5981 Summary of contents

Page 1

... Figure 1. Application circuit June 2009 1 A step-down switching regulator VFQFPN8 Description The L5981 is step-down switching regulator with 1.5 A (min.) current limited embedded power MOSFET able to deliver in excess current to the load depending on the application condition. The input voltage can range from 2 while the output voltage can be set starting from ...

Page 2

... Inductor selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 5.3 Output capacitor selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 5.4 Compensation network . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 5.4.1 5.4.2 5.5 Thermal considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 5.6 Layout considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 5.7 Application circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 6 Package mechanical data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35 7 Order codes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38 8 Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39 2/37 Type III compensation network . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 Type II compensation network . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 Doc ID 13004 Rev 6 L5981 ...

Page 3

... L5981 1 Pin settings 1.1 Pin connection Figure 2. Pin connection (top view) 1.2 Pin description Table 1. Pin description Pin n° Type 1 OUT 2 SYNCH 3 INH 4 COMP GND 8 V OUT OUT SYNCH SYNCH INH INH COMP COMP Regulator output Master/slave synchronization. When it is left floating, a signal with a phase shift of half a period respect to the power turn on is present at the pin ...

Page 4

... Inhibit pin Feedback voltage Power dissipation at T < 60 °C A Junction temperature range Storage temperature range Parameter Maximum thermal resistance (1) junction-ambient Doc ID 13004 Rev 6 Value -0.3 to 1.5 1.5. -40 to 150 -55 to 150 Value VFQFPN 60 L5981 Unit V W °C °C Unit °C/W ...

Page 5

... L5981 3 Electrical characteristics ° unless otherwise specified Table 4. Electrical characteristics Symbol Operating input voltage V CC range V Turn on V CCON V V UVLO hysteresis CCHYS CC R MOSFET on resistance DS(on) I Maximum limiting current LIM Oscillator F Switching frequency SW V FSW pin voltage FSW D Duty cycle ...

Page 6

... V SYNCH I = 4.5 mA SOURCE SYNCH floating from -40 to +125 °C. Specification in the -40 to +125 °C temperature range are J Doc ID 13004 Rev 6 Values Min Typ Max 3 0 COMP = COMP 100 2 3.3 1 0.7 0.9 2.0 110 70 1 150 30 L5981 Unit V μ μA °C ...

Page 7

... L5981 4 Functional description The L5981 is based on a “voltage mode”, constant frequency control. The output voltage V is sensed by the feedback pin (FB) compared to an internal reference (0.6 V) providing OUT an error signal that, compared to a fixed frequency sawtooth, controls the on and off time of the power switch ...

Page 8

... Figure Clock Clock Synchronization Synchronization Generator Generator Doc ID 13004 Rev 6 5.a). (Figure 5.b) in order to Section 5.4 for PWM gain Clock Clock Clock SYNCH SYNCH Ramp Ramp Sawtooth Sawtooth Generator Generator L5981 ...

Page 9

... L5981 Figure 5. Sawtooth: voltage and frequency feed forward; external synchronization Figure 6. Oscillator frequency versus FSW pin resistor Doc ID 13004 Rev 6 Functional description 9/37 ...

Page 10

... Soft-start time results: Equation 2 For example with a switching frequency of 250 kHz the SS 10/37 ⎛ ⎞ R1 ⋅ ------- - ⎝ ⎠ OUT VREF R2 Figure 7). The soft-start stair case consists of 64 steps of ⋅ ----------------- TIME Fsw TIME Doc ID 13004 Rev 6 L5981 ) of the error REF is 8 ms. ...

Page 11

... L5981 4.3 Error amplifier and compensation The error amplifier (E/A) provides the error signal to be compared with the sawtooth to perform the pulse width modulation. Its non-inverting input is internally connected to a 0.6 V voltage reference, while its inverting input (FB) and output (COMP) are externally available for feedback and frequency compensation ...

Page 12

... Functional description 4.4 Overcurrent protection The L5981 implements the over current protection sensing current flowing through the power MOSFET. Due to the noise created by the switching activity of the power MOSFET, the current sensing is disabled during the initial phase of the conduction time. This avoids an erroneous detection of a fault condition. This interval is generally known as “ ...

Page 13

... L5981 Figure 8. Overcurrent protection strategy 4.5 Inhibit function The inhibit feature allows to put in stand-by mode the device.With INH pin higher than 1.9 V the device is disabled and the power consumption is reduced to less than 30 μA. With INH pin lower than 0.6 V, the device is enabled. If the INH pin is left floating, an internal pull up ensures that the voltage at the pin reaches the inhibit threshold and the device is disabled ...

Page 14

... D ⋅ – -------------- - RMS O η OUT ------------------------------------ - MAX V – V INMIN OUT ------------------------------------- - MIN V V – INMAX SW Table 6 some multi layer ceramic capacitors suitable for this device Series Cap value (μF) GRM31 GRM55 C3225 Doc ID 13004 Rev ------ - η2 is voltage drop across SW Rated voltage ( L5981 ...

Page 15

... L5981 5.2 Inductor selection The inductance value fixes the current ripple flowing through the output capacitor. So the minimum inductance value in order to have the expected current ripple has to be selected. The rule to fix the current ripple value is to have a ripple the output current. ...

Page 16

... OUT OUT Series Cap value (μF) GRM32 22 to 100 GRM31 ECJ EEFCD TPA/B/C 100 to 470 C3225 22 to 100 Doc ID 13004 Rev 6 ΔI MAX + ------------------------------------ - ⋅ ⋅ OUT SW Rated voltage (V) ESR (mΩ 6.3 6 6.3 L5981 < 5 < 5 < 5 < 5 ...

Page 17

... Compensation network The compensation network has to assure stability and good dynamic performance. The loop of the L5981 is based on the voltage mode control. The error amplifier is a voltage operational amplifier with high bandwidth. So selecting the compensation network the E/A will be considered as ideal, that is, its bandwidth is much larger than the system one. ...

Page 18

... In the two , They expression are ----------------------------------------------- - ⋅ ⋅ 2π Doc ID 13004 Rev 6 s ------------------------- - ⋅ 2π f zESR ⎛ ⎞ ------------------ - + ⎝ ⎠ ⋅ 2π ------------------------------------------- - ⋅ ⋅ zESR 2π ESR C OUT ) ESR V OUT , R = -------------- OUT I OUT ----------------------------- - ⋅ ⋅ Z2 2π L5981 ...

Page 19

... L5981 Equation 17 Figure 10. Type III compensation network In Figure 11 the Bode diagram of the PWM and LC filter transfer function (G and the open loop gain (G Figure 11. Open loop gain: module Bode diagram The guidelines for positioning the poles and the zeroes and for calculating the component values can be summarized as follow: 1 ...

Page 20

... -------------------------- - ⋅ ----------------- 1 – =33 μ 3 OUT 1.1kΩ 110Ω 5.6kΩ Doc ID 13004 Rev 6 ⋅ ⋅ ⋅ ⋅ – ---------------------------------------- - ⋅ ⋅ ⋅ 3 2π set higher than 500 kHz μF, ESR < 1 mΩ, OUT , , , C = 4.7nF C = 10nF 3 4 L5981 ): 100pF 5 ...

Page 21

... L5981 Figure 12. Open loop gain Bode diagram with ceramic output capacitor Doc ID 13004 Rev 6 Application information 21/37 ...

Page 22

... The singularity of the network are: In Figure 14 the Bode diagram of the PWM and LC filter transfer function (G and the open loop gain (G 22/ ----------------------------- - = ⋅ ⋅ 2π ( · G (f) · G LOOP PW0 LC Doc ID 13004 Rev ------------------------------------------- - ⋅ ⋅ ⋅ ------------------- - 2π · G PW0 (f)) are drawn. TYPEII L5981 (f)) LC ...

Page 23

... L5981 Figure 14. Open loop gain: module Bode diagram The guidelines for positioning the poles and the zeroes and for calculating the component values can be summarized as follow: 1. Choose a value for R C5 not comparable with parasitic capacitance of the board. 2. Choose a gain (R Equation 22 Where f ...

Page 24

... The bandwidth is about 33 kHz and the phase margin is 46°. 24/ ------------------------------------------------------------- - ⋅ ⋅ 5 2π μ 3 OUT 1.1kΩ 249Ω Doc ID 13004 Rev ⋅ ⋅ – 220 μF, OUT , , 10kΩ 10nF C = 100pF 4 5 L5981 ...

Page 25

... L5981 Figure 15. Open loop gain Bode diagram with electrolytic/tantalum output capacitor Doc ID 13004 Rev 6 Application information 25/37 ...

Page 26

... T + Rth the sum of the power losses just seen. TOT Doc ID 13004 Rev 6 of the power switch; these are DS(on ⋅ OUT is 220 mΩ. Note that DSON but actually it is quite OUT IN ⋅ ⋅ ⋅ OUT ⋅ P TOT L5981 ) DS Figure 16. ...

Page 27

... L5981 of heat. The R thJA paragraph is about 60 °/W. Figure 16. Switching losses 5.6 Layout considerations The PC board layout of switching DC/DC regulator is very important to minimize the noise injected in high impedance nodes and interferences generated by the high switching current loops step-down converter the input loop (including the input capacitor, the power MOSFET and the free wheeling diode) is the most critical one ...

Page 28

... Application information Figure 17. Layout example 28/37 Doc ID 13004 Rev 6 L5981 ...

Page 29

... D1 L1 VCC VCC VCC VCC OUT OUT OUT OUT SYNCH SYNCH SYNCH SYNCH INH INH INH INH L5985 L5981 L5985 L5981 GND GND GND GND 10nF C4 10nF C4 10nF C4 10nF COMP COMP COMP COMP COMP COMP COMP COMP FSW FSW FSW FSW R4 3 ...

Page 30

... Application information Figure 19. PCB layout (component side) Figure 20. PCB layout (bottom side) Figure 21. PCB layout (front side) 30/37 Doc ID 13004 Rev 6 L5981 ...

Page 31

... L5981 Figure 22. Junction temperature vs output current Figure 24. Junction temperature vs output current Figure 26. Efficiency vs output current VCC= =250KHz SW 76 0.1 0.2 0.3 0.4 0.5 0.6 Io [A] Figure 23. Junction temperature vs output Figure 25. Efficiency vs output current 0.1 Figure 27. Efficiency vs output current 95 90 Vo=3.3V 85 Vo=2.5V ...

Page 32

... Figure 31. Soft-start C C =47μF =47μF OUT OUT L=15μH L=15μ =520KHz =520KHz SW SW Time base 5ms/div Time base 5ms/div Doc ID 13004 Rev VCC [ 500mA/div 500mA/div Time base 1ms/div Time base 1ms/div L5981 Io= OUT OUT 500mV/div 500mV/div 200mV/div 200mV/div ...

Page 33

... L5981 6 Package mechanical data In order to meet environmental requirements, ST offers these devices in different grades of ECOPACK® packages, depending on their level of environmental compliance. ECOPACK® specifications, grade definitions and product status are available at: ECOPACK® trademark. Doc ID 13004 Rev 6 Package mechanical data www.st.com. ...

Page 34

... Doc ID 13004 Rev 6 L5981 inch Min Typ Max 0.0315 0.0354 0.0394 0.0008 0.0020 0.0276 0.0079 0.0071 0.0091 0.0118 0.1161 0.1181 0.1200 0.0878 0.0937 ...

Page 35

... L5981 7 Order codes Table 11. Order codes Order codes L5981 L5981TR Package VFQFPN8 ( 1.08 mm) Doc ID 13004 Rev 6 Order codes Packaging Tube Tube and reel 35/37 ...

Page 36

... Table 8 on page 16, Table 10 on page 34 Added: Table 3 on page 4 4 Updated: Table 4 on page 5 5 Updated: Equation 18 6 Updated Table 4 on page 5 Doc ID 13004 Rev 6 Changes Figure 2 on page 3, Figure 8 on page 28, Figure 18 on page and Figure 6 on page 9 L5981 13, 29, ...

Page 37

... L5981 Information in this document is provided solely in connection with ST products. STMicroelectronics NV and its subsidiaries (“ST”) reserve the right to make changes, corrections, modifications or improvements, to this document, and the products and services described herein at any time, without notice. All ST products are sold pursuant to ST’s terms and conditions of sale. ...

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