L5987TR STMicroelectronics, L5987TR Datasheet
L5987TR
Specifications of L5987TR
Available stocks
Related parts for L5987TR
L5987TR Summary of contents
Page 1
Features ■ output current ■ 2 input voltage ■ Output voltage adjustable from 0.6 V ■ 250 kHz switching frequency, programmable MHz ■ Internal soft-start and inhibit ■ Low dropout ...
Page 2
Contents Contents 1 Pin settings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ...
Page 3
L5987 8 Order codes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ...
Page 4
Pin settings 1 Pin settings 1.1 Pin connection Figure 2. Pin connection (top view) 1.2 Pin description Table 1. Pin description N. Type 1 OUT 2 SYNCH 3 INH 4 COMP GND 8 V ...
Page 5
L5987 2 Maximum ratings Table 2. Absolute maximum ratings Symbol Vcc OUT F , COMP, SYNCH Analog pin SW INH FB P TOT stg 3 Thermal data Table 3. Thermal data Symbol R thJA 1. Package mounted ...
Page 6
Electrical characteristics 4 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 ...
Page 7
L5987 Table 4. Electrical characteristics (continued) Symbol Error amplifier V High level output voltage CH V Low level output voltage CL I Bias source current FB I Source COMP pin O SOURCE I Sink COMP pin O SINK G Open ...
Page 8
Functional description 5 Functional description The L5987 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, ...
Page 9
L5987 5.1 Oscillator and synchronization Figure 4 shows the block diagram of the oscillator circuit. The internal oscillator provides a constant frequency clock. Its frequency depends on the resistor externally connect to FSW pin. In case the FSW pin is ...
Page 10
Functional description Figure 5. Sawtooth: voltage and frequency feed forward; external synchronization Figure 6. Oscillator frequency versus FSW pin resistor 10/41 Doc ID 14972 Rev 3 L5987 ...
Page 11
L5987 5.2 Soft-start The soft-start is essential to assure correct and safe start up of the step-down converter. It avoids inrush current surge and makes the output voltage increases monothonically. The soft-start is performed by a staircase ramp on the ...
Page 12
Functional description 5.3 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 ...
Page 13
L5987 5.4 Overcurrent protection The L5987 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 ...
Page 14
Functional description Figure 8. Over-current protection strategy 5.5 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 ...
Page 15
L5987 5.7 Maximum DC output current L5987A (HSOP8) The L5987A can manage DC output currents and the rated RMS current of its internal power switch the L5987A can deliver 3 A with ...
Page 16
Functional description With the duty 73%, so the maximum DC output current results 2.926 A, higher than the desired current. Figure 9. Maximum DC output current for VQFN package vs duty ...
Page 17
L5987 6 Application information 6.1 Input capacitor selection The capacitor connected to the input has to be capable to support the maximum input operating voltage and the maximum RMS input current required by the device. The input capacitor is subject ...
Page 18
Application information 6.2 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 ...
Page 19
L5987 6.3 Output capacitor selection The current in the capacitor has a triangular waveform which generates a voltage ripple across it. This ripple is due to the capacitive component (charge or discharge of the output capacitor) and the resistive component ...
Page 20
Application information 6.4 Compensation network The compensation network has to assure stability and good dynamic performance. The loop of the L5987 is based on the voltage mode control. The error amplifier is a voltage operational amplifier with high bandwidth. So ...
Page 21
L5987 Equation 17 where: Equation 18 Equation 19 As seen in Chapter 5.3 following paragraph the guidelines to select the Type II and Type III compensation network are illustrated. 6.4.1 Type III compensation network The methodology to stabilize the loop ...
Page 22
Application information Equation 21 Figure 11. Type III compensation network In Figure 12 the Bode diagram of the PWM and LC filter transfer function (G and the open loop gain (G Figure 12. Open loop gain: module Bode diagram The ...
Page 23
L5987 Equation 22 where K is the feed forward constant and 1/K is equals Calculate C 4 Equation 23 4. Calculate C 5 Equation 24 5. Set also the first pole at four times the system bandwidth ...
Page 24
Application information Figure 13. Open loop gain Bode diagram with ceramic output capacitor 24/41 Doc ID 14972 Rev 3 L5987 ...
Page 25
L5987 6.4.2 Type II compensation network If the equivalent series resistance (ESR) of the output capacitor introduces a zero with a frequency lower than the desired bandwidth (that is: 2π∗ESR∗COUT>1/BW), this zero helps stabilize the loop. Electrolytic capacitors show not ...
Page 26
Application information Figure 15. 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 and C5 not comparable ...
Page 27
L5987 Equation 29 For example with V ESR = 35 mΩ, the type II compensation network is: In Figure 16 is shown the module and phase of the open loop gain. The bandwidth is about 32 kHz and the phase ...
Page 28
Application information Figure 16. Open loop gain Bode diagram with electrolytic/tantalum output capacitor 28/41 Doc ID 14972 Rev 3 L5987 ...
Page 29
L5987 6.5 Thermal considerations The thermal design is important to prevent the thermal shutdown of device if junction temperature goes above 150 °C. The three different sources of losses within the device are: a) conduction losses due to the not ...
Page 30
Application information of heat. The Rth JA paragraph is about 60 °C/W for the VFQFPN package and about 40 °C/W for the HSOP package. Figure 17. Switching losses 6.6 Layout considerations The PC board layout of switching DC/DC regulator is ...
Page 31
L5987 Figure 18. Layout example Doc ID 14972 Rev 3 Application information 31/41 ...
Page 32
... W 0603 330 Ω, 1%, 0.1 W 0603 2 kΩ, 1%, 0.1 W 0603 100k. STPS2L25V 5.2 μH, 30%, 5.28 A, MSS1038-522NL DCR MAX Doc ID 14972 Rev 3 L1 5.2uH MSS1038 Vout=1.8V C2 22u D1 25V STPS2L25 R1 4.99K 2.2nF 330 2.49k Description Manufacturer MURATA MURATA STMicroelectronics Coilcraft = 22 mΩ L5987 ...
Page 33
L5987 Figure 20. PCB layout: L5987 and L5987A (component side) Figure 21. PCB layout: L5987 and L5987A (bottom side) Figure 22. PCB layout: L5987 and L5987A (front side) Doc ID 14972 Rev 3 Application information 33/41 ...
Page 34
Application information Figure 23. Junction temperature vs output current V Figure 25. Junction temperature vs output current V Figure 27. Efficiency vs output current =5V =5V ...
Page 35
L5987 Figure 29. Load regulation 1.2 1 0.8 0.6 0.4 0 0.5 Figure 31. Load transient: from 0 OUT OUT 100mV/div 100mV/div AC coupled AC coupled I I 1A/div 1A/div L L ...
Page 36
Package mechanical data 7 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: ...
Page 37
L5987 Table 10. VFQFPN8 ( 1.08 mm) mechanical data Dim ddd Figure 34. Package dimensions mm Min Typ Max 0.80 0.90 1.00 0.02 0.05 0.70 0.20 ...
Page 38
Package mechanical data Table 11. HSOP8 mechanical data Dim ccc Figure 35. Package dimensions 38/41 mm Min Typ Max 1.70 0.00 0.15 1.25 0.31 0.51 0.17 0.25 4.80 ...
Page 39
... L5987 8 Order codes Table 12. Order codes Order codes L5987 L5987A L5987TR L5987ATR Package VFQFPN8 HSOP8 VFQFPN8 HSOP8 Doc ID 14972 Rev 3 Order codes Packaging Tube Tape and reel 39/41 ...
Page 40
Revision history 9 Revision history Table 13. Document revision history Date 29-Aug-2008 29-Jan-2009 19-Jun-2009 40/41 Revision 1 Initial release 2 Updated: Equation 22 3 Updated Table 4 on page 5 Doc ID 14972 Rev 3 Changes and Figure 6 on ...
Page 41
... L5987 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. ...