Datasheet

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This is information on a product in full production.

June 2012 Doc ID 023203 Rev 1 1/35

PM6644

350 mA adjustable step-down regulator

Datasheet − production data

Features

■ 4.5 V to 25 V input voltage range

■ Output voltage V

OUT

: fixed 3.47 V or adjustable

0.9 V to 8 V

■ 350 mA valley current limit

■ Constant-on-time control

■ Programmable switching frequency

■ Pulse skipping mode (skip mode) at light loads

■ Independent EN signals

■ Latched OVP and UVP

Applications

■ Networking power supply

■ Portable applications

■ Microcontroller supply

■ Industrial supply

Description

The PM6644 is a 350 mA valley current limit step-

down regulator capable of delivering an

adjustable output voltage in the range between

0.9 V and 8 V. A fixed value of output voltage is

also available (3.47 V), saving the external

resistor divider. It is housed in a small DFN10 3x3

package. The switching regulator is based on

COT (constant-on-time) architecture, that assures

fast load transient response; the embedded

voltage feed-forward provides nearly constant

switching frequency operation. The pulse skipping

technique increases efficiency at very light load.

The switching frequency can be adjusted from

200 kHz to 600 kHz through a simple resistor. The

switching regulator can be programmed to

regulate a fixed value of 3.47 V or it can deliver an

adjustable voltage, depending on the FB pin set-

up.

DFN10

Table 1. Device summary

Part number Package Packing

PM6644 DFN10 Tube

PM6644TR DFN10 Tape and reel

www.st.com

Summary of content (35 pages)

PAGE 1
PM6644 350 mA adjustable step-down regulator Datasheet − production data Features ■ 4.5 V to 25 V input voltage range ■ Output voltage VOUT: fixed 3.47 V or adjustable 0.9 V to 8 V ■ 350 mA valley current limit ■ Constant-on-time control ■ Programmable switching frequency ■ Pulse skipping mode (skip mode) at light loads ■ Independent EN signals ■ Latched OVP and UVP DFN10 switching regulator can be programmed to regulate a fixed value of 3.
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Contents PM6644 Contents 1 2 Simplified application schematic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 1.1 Pin description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 1.2 Absolute maximum ratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 1.3 Thermal data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 1.4 Recommended operating conditions . . .
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PM6644 Contents 4.2 Characterization report . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 4.3 Efficiency vs. load (VIN = 12 V, VOUT = 8 V) . . . . . . . . . . . . . . . . . . . . . . . 27 5 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 6 Package mechanical data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31 7 Revision history . . . . . . . . . . . . . . . . . . . . . . .
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List of tables PM6644 List of tables Table 1. Table 2. Table 3. Table 4. Table 5. Table 6. Table 7. Table 8. Table 9. Table 10. Table 11. Table 12. Table 13. Table 14. 4/35 Device summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1 Pin description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7 Absolute maximum ratings . . . . . . . . . . . . . . . . . . . . .
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PM6644 List of figures List of figures Figure 1. Figure 2. Figure 3. Figure 4. Figure 5. Figure 6. Figure 7. Figure 8. Figure 9. Figure 10. Figure 11. Figure 12. Figure 13. Figure 14. Figure 15. Figure 16. Figure 17. Figure 18. Figure 19. Figure 20. Figure 21. Figure 22. Figure 23. Figure 24. Figure 25. Figure 26. Figure 27. Figure 28. Figure 29. Figure 30. Figure 31. Figure 32. Figure 33. Figure 34. Figure 35. VOUT = 3.47 V fixed configuration. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
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Simplified application schematic 1 PM6644 Simplified application schematic Figure 1. VOUT = 3.47 V fixed configuration 6). 6). 6## 34 0- 2%& &" 4/. %. '.$ 2%& "90 6## 6). 37 6 TO 6 , 6/54 6/54 6). %0 %0 6## 6 #/54 #). 6). !- V Figure 2. Adjustable VOUT configuration #ONTROLLER SUPPLY 6 TO 6 6). 6 TO 6 , 6/54 6). #).
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PM6644 Simplified application schematic Figure 3. Pinout 1.1 Pin description Table 2. Pin description Pin Name 1 REF Description 1.216 V internal reference voltage. Do not connect this pin to any external component. 2 FB Feedback input for the switching section: If this pin is connected to VCC, OUT operates at 3.47 V (Fixed mode). If this pin is connected to a resistive divider from OUT to GND, OUT can be adjusted from 0.9 V to 8 V. 3 TON Switching frequency setting.
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Simplified application schematic PM6644 1.2 Absolute maximum ratings Table 3. Absolute maximum ratings Parameter Value Unit -0.3 to 35 V -0.3 to VIN +0.3 V -0.3 to 6 V REF, FB to GND -0.3 to VCC +0.3 V REF3 to GND -0.3 to BYP +0.3 V 2.25 W ±1000 V VIN to GND EN, SW, TON to GND VCC, BYP Power dissipation at Tamb = 25 °C Maximum withstanding voltage range test condition: CDF-AECQ100002- “human body model” acceptance criteria: “normal performance”. 1.3 Thermal data Table 4.
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PM6644 1.5 Simplified application schematic Electrical characteristics VIN=12 V, no load on REF3, EN=VIN, FB=VCC, R=1 MΩ between TON and VIN, Tj=25 °C unless otherwise specified. Table 6. Electrical characteristics Symbol Parameter Test condition Min. Typ. Max. Unit 3.40 3.47 3.54 V 0.92 V Switching controller output accuracy BYP FB Fixed output voltage valley regulation FB=VCC, no load No load, BYP=3.47 V; Adjustable output voltage valley regulation (FB=ADJ) Tj=0 °C - 70 °C(1) 0.
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Simplified application schematic Table 6. PM6644 Electrical characteristics (continued) Symbol Parameter Test condition Min. Typ. Max. Unit FB Overvoltage trip threshold Referred to FB nominal regulation point, BYP= 3.47 V +14 +20 % FB Undervoltage threshold Referred to FB nominal regulation point, BYP= 3.47 V 62 73 % Inputs and outputs FB FB logic level EN EN level FB logic level to be in fixed mode VCC-0.8 V All circuitry OFF 1.3 All circuitry ON V 2.4 V 1.
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PM6644 Simplified application schematic Figure 6. VOUT vs. load Figure 7. VREF3 vs. output load 62%& ;6= 6OUT ;6= 6OUT ,OAD REGULATION 6). 6 62%& 63 6OUT LOAD 6). 6 62%& 63 6OUT LOAD 6). 6 62%& 63 6OUT LOAD 6). 6 62%& 63 6OUT LOAD 6). 6 6OUT ,OAD REGULATION 6). 6 6OUT ,OAD REGULATION 6). 6 6OUT ,OAD REGULATION 6). 6 Figure 8. ,/!$;!= !- V Shutdown VIN current vs.
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Simplified application schematic PM6644 Figure 12. Soft-end, no load Figure 13. Soft-end, 69 Ω load Figure 14. Load transient 0-200 mA Figure 15. VREF3 load regulation 2%& ,OAD 2EGULATION 62%& ;6= ,OAD ;!= !- V Figure 16. VREF3 line regulation Figure 17.
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PM6644 Simplified application schematic Figure 18. Simplified block diagram BYP VCC 3.8 V generator VIN + - 800mV EN_ok HS command 1.216V reference VCC REF generator EN + VCC_OK 2.1V (falling thr.) Bias reference generator EN BIAS + EN BIAS_OK FB_REF=0.9V Ith_bias REF_OK + REF_OK GND - LS gate driver 3.2V (rising thr.) Boot_fuses_OK 900mV SW BYP_ON REF - Anticross conduction HS gate driver LS mos Not (BYP_ON) BYP_ON HS mos REF3 3.
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Device description 2 PM6644 Device description The PM6644 combines a 350 mA valley current limit step-down regulator with a high accuracy 3.3 V voltage reference in a small DFN10 3x3 package. The switching regulator is based on constant-on-time (COT) architecture. This type of control offers a very fast load transient response with a minimum external component count. The switching regulator can regulate 3.47 V in Fixed mode (the FB pin tied at VCC) or it can deliver an adjustable voltage between 0.
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PM6644 Device description The COT architecture bases its algorithm on the output ripple derived across the output capacitor’s ESR. The controller has an internal on-time (TON) generator triggered on the output voltage valley: when VOUT reaches the regulation value a new TON starts. The TON duration is given by the following equation: Equation 2 0.9V ⋅ R TON ⋅ C T ON = --------------------------------------------V IN where TON is the on-time duration, C is an integrated capacitance (9.3 pF typ.
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Device description PM6644 Equation 5 V OUT V OUT D - = ---------------------------------------------------------------- = ---------------------------------------------------------------fsw = ---------V IN TON 0.9V ⋅ R TON ⋅ ( C + C 1 ) ---------------------------------------------------------------0.
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PM6644 Device description Figure 20. Constant-on-time controller architecture ToffMIN VIN Vout sense PHASE - GND + 320mV - S Q R Q PHASE Α*Rdson*ILS + R1 Vout sense ILS - PWM COMPARATOR FB Α*Rdson*ILS R2 + 0.725 VREF GND 0.
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Device description PM6644 Figure 21. Inductor current in skip mode IL Load> ∆IL/2 Load< ∆IL/2 IL ∆IL ∆IL t t TSWDCM TSWCCM AM11781v1 2.1.5 Current sensing and current limit The PM6644 implements a positive valley current limit to protect the application from an overcurrent fault. The inductor current is sensed during the OFF-time TOFF by measuring the voltage drop across the integrated low-side MOSFET using the MOSFET RDS(on) as a lossless sensing element.
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PM6644 2.1.6 Device description Soft-start and soft-end The switching section has an EN pin. A non-programmable soft-start procedure takes place when the EN pin rises above 2.1 V. To prevent high input inrush currents, the current limit is increased from 25% to 100% of the current limit threshold with steps of 25%. The procedure is not programmable and ends typically in 2.8 ms. The overvoltage protection is always active while the undervoltage protection is enabled at the end of the 2.8 ms.
PAGE 20
Device description 2.1.11 PM6644 VCC and BYP power management VCC supplies both the controller and the drivers of the integrated high-side and low-side MOSFETs. An integrated 3.8 V generator from the VIN pin provides the voltage to the VCC pin. The PM6644 provides a switch-over function that allows the turning-off of the 3.8 V generator when a voltage is applied at the BYP pin. If the voltage at the BYP pin is higher than 3.
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PM6644 Application information 3 Application information 3.1 External component selection 3.1.1 Inductor selection Once the switching frequency is defined, inductor selection depends on the desired inductor ripple current and load transient performance. Low inductance means greater ripple current and may generate greater output noise. On the other hand, low inductor values involve fast load transient response.
PAGE 22
Application information . Table 10. PM6644 Inductor part number Part number Inductance (µH) DCR (Ω) RMS current (A)(1) Saturation current (A)(2) Coilcraft EPL3015-333ML 33 0.989 0.59 0.32 Coilcraft LPS3314-333ML 33 0.92 0.58 0.38 Coilcraft MSS5121-333ML 33 0.48 0.76 0.64 Manufacturer 3.1.2 1. 40 °C temperature rise. 2. 20% inductance drop.
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PM6644 Application information K is a constant (< 0.1) that defines the ratio between the controller bandwidth and the switching frequency. The output capacitor must store the inductor energy generating an output ripple within the output voltage ripple requirements. If an output tantalum capacitor is used, in CCM the voltage ripple VRIPPLEout is given by: Equation 14 V RIPPLEout = R out ⋅ ∆I L A low ESR capacitor is required to reduce the output voltage ripple.
PAGE 24
Application information PM6644 Equation 17 2 I RMS, LS = I LRMS = ( 1 – D ) ⋅ 2 ( ∆I L ) ( ILOAD ) + --------------- = 300mA 12 where ILOAD is the RMS output current.
PAGE 25
PM6644 4 Typical application configuration VOUT = 8 V Typical application configuration VOUT = 8 V This section is intended as a guideline for all the measurements involving the PM6644 device with VIN = 12 V ±5%, VOUT = 8 V. 4.1 Test set configuration The device-under-test (D.U.T.) has been mounted on the designed evaluation kit with the following schematic and bill of materials. Figure 23. Schematic and bill of materials #/-0/.%.4 &//402).
PAGE 26
Typical application configuration VOUT = 8 V PM6644 Figure 26. Load = 100 mA. Switching frequency = Figure 27. Load = 300 mA. Switching frequency = 370 kHz 410 kHz Figure 28.
PAGE 27
PM6644 Efficiency vs. load (VIN = 12 V, VOUT = 8 V) The output voltage varies from 8.096 V at light load to 7.916 V at heavy load. Load regulation = 180 mV. Figure 29. Efficiency %FFICIENCY ; = ,/!$;!= !- V Figure 30. Load regulation 6OUT ;6= 4.
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Typical application configuration VOUT = 8 V PM6644 Bias current 28/35 VIN =12.158 V VIN = 12.158 V Vout = 8.150 V (externally forced) Vout = 8.
PAGE 29
PM6644 5 Conclusion Conclusion The device regulates VOUT = 8 V properly with the designed schematic and bill of material. The 12 V input voltage range should have an accuracy of ± 5%. PCB design guidelines The layout is very important in terms of efficiency, stability and system noise. It is possible to refer to the PM6644 evaluation kit board for a complete layout example.
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Conclusion PM6644 Figure 33.
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PM6644 6 Package mechanical data 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: www.st.com. ECOPACK® is an ST trademark. Table 13. DFN10 (3x3 mm) mechanical data mm Dim. A Min. Typ. Max. 0.80 0.90 1.00 0.02 0.05 0.65 0.80 A1 A2 0.55 A3 0.20 b 0.18 0.25 0.30 D 2.
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Package mechanical data PM6644 Figure 34.
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PM6644 Package mechanical data Figure 35.
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Revision history 7 PM6644 Revision history Table 14. 34/35 Document revision history Date Revision 19-Jun-2012 1 Changes Initial release.
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PM6644 Please Read Carefully: 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.