Datasheet

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This is information on a product in full production.

January 2013 Doc ID 024147 Rev 1 1/33

PM8903A

3 A step-down monolithic switching regulator

Datasheet − production data

Features

■ Integrated 35 mΩ MOSFETs for high efficiency

■ 3 A continuous output current

■ 2.8 V to 6 V input voltage (V

)

■ 2.9 V to 5.5 V supply voltage (V

)

■ Adjustable output voltage down to 0.6 V

■ 1% output voltage accuracy

■ 1.1 MHz switching frequency operation

■ PSKIP mode to optimize light load efficiency

■ Embedded bootstrap diode

■ Thermally compensated loss-less current

sense across HS and LS MOSFETs

■ OV/UV/OC and overtemperature protection

■ Internal soft-start and soft-stop

■ Interleaving synchronization (up to 2 ICs)

■ Power Good output

■ Shutdown function (< 15 µA quiescent current)

■ VFQFPN16 3 x 3 mm compact package

Applications

■ Subsystem power supply

■ CPU, DSP and FPGA power supplies

■ Distributed power supply

■ General DC-DC converters

Description

The PM8903A is a high efficiency monolithic step-

down switching regulator designed to deliver up to

3 A continuous current. The IC operates from 2.8

V to 6 V input voltage (V

The PM8903A features low-resistance integrated

nMOS and proprietary pulse-skipping mode for

optimum efficiency over all the loading range.

The voltage mode control loop allows the widest

range of output filters. Current sense is internally

thermally compensated for optimum precision.

The integrated 0.6 V reference allows the

regulation of output voltages with ±1% accuracy

over temperature variations. Switching frequency

is typically set to 1.1 MHz and can be

programmed to 0.8 MHz or 1.0 MHz. Out of phase

synchronization allows the reduction of input RMS

current.

The PM8903A provides precise dual-threshold

overcurrent protection as well as

over/undervoltage and overtemperature

protection. PGOOD output easily provides real-

time information on the output voltage.

The PM8903A is available in VFQFPN16 3 x 3

mm.

VFQFPN16 (3 x 3 mm)

Table 1. Device summary

Order codes Package Packaging

PM8903A VFQFPN16 (3 x 3 mm) Tube

PM8903ATR VFQFPN16 (3 x 3 mm) Tape and reel

www.st.com

Summary of content (33 pages)

PAGE 1
PM8903A 3 A step-down monolithic switching regulator Datasheet − production data Features ■ Integrated 35 mΩ MOSFETs for high efficiency ■ 3 A continuous output current ■ 2.8 V to 6 V input voltage (VIN) ■ 2.9 V to 5.5 V supply voltage (VCC) ■ Adjustable output voltage down to 0.6 V ■ 1% output voltage accuracy ■ 1.
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Contents PM8903A Contents 1 2 Typical application circuit and block diagram . . . . . . . . . . . . . . . . . . . . 3 1.1 Application circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 1.2 Block diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 Pin description and connection diagrams . . . . . . . . . . . . . . . . . . . . . . . 4 2.1 Pin description . . . . . . . . . . . . . . . . . . . . . . . . .
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PM8903A 7 Contents 6.2 Output voltage setting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 6.3 Inductor design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 6.4 Output capacitors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 6.5 Input capacitors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 PM8903A demonstration board . . . . .
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Typical application circuit and block diagram 1 Typical application circuit and block diagram 1.1 Application circuit Figure 1. 1.2 Block diagram Figure 2.
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PM8903A 2 Pin description and connection diagrams Pin description and connection diagrams Pin connection (top view) PGND PGND VIN VIN Figure 3. 16 15 14 13 1 12 2 11 3 10 4 9 5 6 7 8 VCC GND FB COMP PHASE PHASE PHASE PSKIP / MS EN SYNCH PGOOD BOOT 2.1 Pin description Table 2. Pin description Pin # Name Function 1 EN Enable. Internally pulled up by 5 µA to VCC. Force low to disable the device, set free or pull up above turn-on threshold to enable the converter operations.
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Pin description and connection diagrams Table 2. 6/33 PM8903A Pin description (continued) Pin # Name Function 9 COMP 10 FB 11 GND All the internal references are referred to this pin. Connect to the PCB Signal Ground. 12 VCC Device power supply. Operative voltage is 2.9 V - 5.5 V. Filter with at least 1 µF MLCC vs. GND. 13, 14 VIN Power input voltage, connected to embedded high-side drain. Supply range is from 2.8 V to 6 V.
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PM8903A 3 Thermal data Thermal data Table 3.
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Electrical specifications PM8903A 4 Electrical specifications 4.1 Absolute maximum ratings Table 4. Absolute maximum ratings Symbol Parameter to PGND, GND -0.3 to 6 V VIN to PGND, GND -0.3 to 7 V VBOOT to PGND, GND to PHASE -0.3 to 13 -0.3 to 6 V VPHASE to PGND, GND to PGND, GND, VIN=6 V, t<100 nsec. -0.3 to 7 -1.7 to 7.5 V VPGOOD to PGND, GND -0.3 to 7 V VSYNCH, VEN to PGND, GND -0.3 to 6 V -0.3 to 3.6 V Recommended operating conditions Table 5.
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PM8903A 4.3 Electrical specifications Electrical characteristics VIN = VCC = 3.3 V ± 5%, TJ = 0 °C to 125 °C, typical values at TJ = 25 °C, unless otherwise specified. Table 6. Electrical characteristics Symbol Parameter Test conditions Min. Typ. Max.
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Electrical specifications Table 6. Symbol PM8903A Electrical characteristics (continued) Parameter Test conditions Min. Typ. Max. Unit 0.69 0.72 0.75 V Over and undervoltage protection FB rising OVP OVP threshold LS turns off, FB falling UVP IFB UVP threshold FB falling FB disconnection bias current Sourced from FB 0.30 0.45 0.48 V 0.
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PM8903A 4.4 Electrical specifications Typical operating characteristics In the demonstration board, as described in Section 7.1, RPM = 0 Ω, VIN = VCC = 3.3 V, VOUT=1V5, TJ = 25 °C, unless otherwise specified. Figure 4. Efficiency vs. output current VIN = 3.3 V, RPM = 240 kΩ Figure 5. Efficiency vs. output current VIN = 5 V, RPM = 240 kΩ Figure 6. Load regulation - VIN = 3.3 V Figure 7. Load regulation - VIN = 5 V Figure 8.
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Device description 5 PM8903A Device description The PM8903A is a high efficiency synchronous step-down monolithic switching regulator capable of delivering up to 3 A continuous output current. The power input voltage (VIN) can range from 2.8 V to 6 V, the signal input voltage (VCC) can range from 2.9 V to 5.5 V. Thanks to the 0.6 V internal reference and 0-100% duty cycle capability, the PM8903A can precisely regulate output voltages ranging from 0.6 V to almost VIN (limited only by minimum TOFF time).
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PM8903A Device description To properly supply the power section the following is advised: Caution: ● Bypass VIN pins to PGND pins as close as possible to the IC package with high quality MLCC capacitors (at least 10 µF). ● Connect the bootstrap capacitor (typically a 100 nF ceramic capacitor rated to stand VIN voltage) from the BOOT pin to the PHASE pin to supply the HS driver. Do not connect an external bootstrap diode.
PAGE 14
Device description PM8903A The PM8903A implements the soft-start by gradually increasing the internal reference from 0 V to 0.6 V in a 1024 switching clock (0.79 ms typ.), linearly charging the output capacitors to the final regulation voltage in closed loop regulation. The soft-start prevents high inrush current from power supply rail. 5.2.
PAGE 15
PM8903A Device description The protection is triggered when the voltage sensed on the FB pin rises over the OVP threshold (0.72 V typ.) and the device acts as follows: ● HS MOSFET is suddenly forced OFF ● LS MOSFET is turned on (to discharge the output and protect the load) until VFB drops to 0.3 V, it is then turned off (to avoid negative spikes on the output voltage). If VFB recrosses OVP rising threshold, LS is turned on again. This protection state is latched, cycle EN or VCC to recover. 5.3.
PAGE 16
Device description 5.4 PM8903A Overcurrent protection Overcurrent protection is active as soon as the device is enabled and both VCC and VIN voltages are above the respective UVLO levels.
PAGE 17
PM8903A Caution: Device description Do not connect together the synchronization pin of two master devices in order to avoid any damage to the ICs. When two PM8903As are synchronized together they act as follows: ● Master mode The SYNCH pin is configured as clock output. The device provides, on the SYNCH pin, its internal switching clock information with a 180 ° time shifting. ● Slave mode The SYNCH pin is configured as clock input.
PAGE 18
Application information PM8903A 6 Application information 6.1 Compensation network The PM8903A implements a voltage mode control loop (see Figure 11). The output voltage is regulated to the internal reference (offset resistor between FB node and GND can be neglected in control loop calculation). Error amplifier output is compared with the oscillator sawtooth waveform to provide the PWM signal to the driver section. The PWM signal is then transferred to the switching node with VIN amplitude.
PAGE 19
PM8903A Application information stability, it should not exceed FSW/2π. To achieve a good phase margin, the control loop gain must cross the 0 dB axis with -20 dB/decade slope. For example, Figure 12 shows an asymptotic bode plot of a type III compensation. Figure 12.
PAGE 20
Application information PM8903A The following suggestions may be followed in order to place the poles and zeroes of the compensation network. ● Select a value for RFB in the range of some kΩ ● Select RF in order to obtain the desired closed loop regulator bandwidth according to the approximate formula: F0dB ΔV OSC R F = ------------ ⋅ ---------------------- ⋅ R FB F LC V IN_MAX ● Select CF in order to place FZ1 below FLC (typically 0.
PAGE 21
PM8903A 6.3 Application information Inductor design The inductance value is defined by a compromise between the dynamic response time, the efficiency, the cost, and the size. The inductor must be calculated to maintain the ripple current (ΔIL) between 20% and 30% of the maximum output current (typ.).
PAGE 22
Application information PM8903A Electrolytic capacitors have a large capacitance to minimize voltage deviation during load transients while they do not show the same ESR values as the MLCC, resulting then in higher ripple voltages. A mix between an electrolytic and MLCC capacitor can be used to minimize ripple as well as reducing voltage deviation in dynamic mode.
PAGE 23
PM8903A 7 PM8903A demonstration board PM8903A demonstration board The PM8903A demonstration board realizes, in a four-layer PCB, a high efficiency synchronous step-down monolithic switching converter capable of delivering up to 3 A continuous output current. The demonstration board shows the operation of the device in a general purpose application.
PAGE 24
PM8903A demonstration board 7.1 PM8903A Detailed demonstration board description This section describes: ● Demonstration board schematics, see Figure 14 ● Demonstration board layout, see Figure 15 ● Demonstration board BOM (bill of materials), see Table 8. Furthermore, the following sub-sections detail how to configure and use the standard demonstration board.
PAGE 25
PM8903A PM8903A demonstration board Figure 14.
PAGE 26
PM8903A demonstration board PM8903A Figure 15. PM8903A demonstration board layout Table 8. TOP LAYER INNER-1 LAYER INNER-2 LAYER BOTTOM LAYER PM8903A demonstration board - bill of material Reference Alias Value Manufacturer P.N.
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PM8903A Table 8. PM8903A demonstration board PM8903A demonstration board - bill of material (continued) Reference Alias Value Manufacturer P.N. Package Supplier R15, R33 RFB2(1,2) 3.3 kΩ 0603 R16, R34 ROS(1,2) 2.2 kΩ 0603 R28 RPM(2) 0Ω 0603 C1, C17 CVCC(1,2) 1 µF, X7R 0603 C2, C3, C18, C19 CVIN(1,2) 22 µF, X5R, 6.3 V, 10% MLCC C4, C20 CVIN(1,2) 100 nF, X7R 0603 C5, C21 CBOOT(1,2) 100 nF, X7R 0603 C6, C8, C9, C22, C23, C24 COUT(1,2) 10 µF X7R 6.
PAGE 28
PM8903A demonstration board 7.1.1 PM8903A Power input (VIN) Connect a power supply to connectors J4(VIN) and J5(GND) on the demonstration board to provide voltage on the power input pins of both devices. Input voltage can range from 2.8 V to 6 V bus. If the voltage is between 2.9 V and 5.5 V, it can also supply the signal input pins of both devices (through the VCC pin). In this case, make sure that resistors R2/R20 are NM (not mounted) and mount 0 Ω resistors on R1/R19 locations. 7.1.
PAGE 29
PM8903A 7.1.4 PM8903A demonstration board Test points and jumper connection Use the following test points in order to measure the most important signals of the PM8903A.
PAGE 30
Package mechanical data 8 PM8903A 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 10. VFQFPN16 3 x 3 x 1.0 mm mechanical data mm Dim. Min. Typ. Max. 0.80 0.90 1.00 A1 0.02 0.05 A2 0.65 1.00 A3 0.20 A b 0.18 0.25 0.30 D 2.
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PM8903A Package mechanical data Figure 16.
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Revision history 9 PM8903A Revision history Table 11.
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PM8903A 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.