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| 120 mA, Current Sinking, 10-Bit, I2C DAC AD5398A FEATURES Current sink: 120 mA 2-wire, (I2C-compatible) 1.8 V serial interface 10-bit resolution Integrated current sense resistor Power supply: 2.7 V to 5.5 V Guaranteed monotonic over all codes Power down to: 0.5 A typical Internal reference Ultralow noise preamplifier Power-down function Power-on reset Available in 3 x 3 array WLCSP package Industrial Heater control Fan control Cooler (Peltier) control Solenoid control Valve control Linear actuator control Light control Current loop control GENERAL DESCRIPTION The AD5398A is a single, 10-bit digital-to-analog converter (DAC) with a current sink output capability of 120 mA. This device features an internal reference and operates from a single 2.7 V to 5.5 V supply. The DAC is controlled via a 2-wire (1.8 V, I2C(R)-compatible) serial interface that operates at clock rates up to 400 kHz. The AD5398A incorporates a power-on reset circuit, which ensures the DAC output powers up to 0 V and remains there until a valid write takes place. It has a power-down feature that reduces the current consumption of the device to 0.5 A typically. The AD5398A is designed for autofocus, image stabilization, and optical zoom applications in camera phones, digital still cameras, and camcorders. The AD5398A is also suitable for many industrial applications, such as controlling temperature, light, and movement without derating, over temperatures ranging from -30C to +85C. The I2C address range for the AD5398A is 0x18 to 0x1F inclusive. APPLICATIONS Consumer Lens autofocus Image stabilization Optical zoom Shutters Iris/exposure Neutral density (ND) filters Lens covers Camera phones Digital still cameras Camera modules Digital video cameras/camcorders Camera-enabled devices Security cameras Web/PC cameras FUNCTIONAL BLOCK DIAGRAM VDD POWER-ON RESET VDD SDA SCL I2C SERIAL INTERFACE 10-BIT CURRENT OUTPUT DAC D1 ISINK AD5398A REFERENCE R PD DGND DGND AGND Figure 1. Rev. 0 Information furnished by Analog Devices is believed to be accurate and reliable. However, no responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or other rights of third parties that may result from its use. Specifications subject to change without notice. No license is granted by implication or otherwise under any patent or patent rights of Analog Devices. Trademarks and registered trademarks are the property of their respective owners. One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A. Tel: 781.329.4700 www.analog.com Fax: 781.461.3113 (c)2008 Analog Devices, Inc. All rights reserved. 07795-001 RSENSE 3.3 AD5398A TABLE OF CONTENTS Features .............................................................................................. 1 Consumer Applications ................................................................... 1 Industrial Applications .................................................................... 1 General Description ......................................................................... 1 Functional Block Diagram .............................................................. 1 Revision History ............................................................................... 2 Specifications..................................................................................... 3 AC Specifications.......................................................................... 4 Timing Specifications .................................................................. 4 Absolute Maximum Ratings............................................................ 5 ESD Caution .................................................................................. 5 Pin Configuration and Function Descriptions..............................6 Typical Performance Characteristics ..............................................7 Terminology .......................................................................................9 Theory of Operation ...................................................................... 10 Serial Interface ............................................................................ 10 I2C Bus Operation ...................................................................... 10 Data Format ................................................................................ 11 Power Supply Bypassing and Grounding ................................ 12 Applications Information .............................................................. 13 Outline Dimensions ....................................................................... 14 Ordering Guide .......................................................................... 14 REVISION HISTORY 10/08--Revision 0: Initial Version Rev. 0 | Page 2 of 16 AD5398A SPECIFICATIONS VDD = 2.7 V to 5.5 V, AGND = DGND = 0 V, load resistance (RL) = 25 connected to VDD; all specifications TMIN to TMAX, unless otherwise noted. Table 1. Parameter DC PERFORMANCE Resolution Relative Accuracy 2 Differential Nonlinearity2, 3 Zero Code Error2, 4 Offset Error @ Code 162 Gain Error2 Offset Error Drift2, 4, 5 Gain Error Drift2, 5 OUTPUT CHARACTERISTICS Minimum Sink Current4 Maximum Sink Current Output Current During PD 5 Output Compliance5 Output Compliance5 Power-Up Time5 LOGIC INPUT (PD)5 Input Current Input Low Voltage, VINL Input High Voltage, VINH Pin Capacitance LOGIC INPUTS (SCL, SDA)5 Input Low Voltage, VINL Input High Voltage, VINH Input Low Voltage, VINL Input High Voltage, VINH Input Leakage Current, IIN Input Hysteresis, VHYST Digital Input Capacitance, CIN Glitch Rejection 6 POWER REQUIREMENTS VDD IDD (Normal Mode) IDD (Power-Down Mode) 7 1 2 Min B Version 1 Typ Max Unit 10 1.5 0 0.5 0.5 10 0.2 3 120 80 0.6 0.48 20 4 1 1 0.6 0.5 Bits LSB LSB mA mA % of FSR A/C LSB/C mA mA nA V V s Test Conditions/Comments VDD = 3.6 V to 4.5 V; device operates over 2.7 V to 5.5 V with reduced performance 117 A/LSB Guaranteed monotonic over all codes All 0s loaded to DAC at 25C VDD VDD VDD = 3.6 V to 4.5 V; device operates over 2.7 V to 5.5 V; specified maximum sink current may not be achieved PD = 1 Output voltage range over which maximum 120 mA sink current is available Output voltage range over which 90 mA sink current is available To 10% of FS, coming out of power-down mode; VDD = 5 V 1 0.54 1.26 3 -0.3 1.26 -0.3 1.4 0.05 VDD 6 50 2.7 0.5 0.5 5.5 1 +0.54 VDD + 0.3 +0.54 VDD + 0.3 1 A V V pF V V V V A V pF ns V mA A VDD = 2.7 V to 5.5 V VDD = 2.7 V to 5.5 V VDD = 2.7 V to 3.6 V VDD = 2.7 V to 3.6 V VDD = 3.6 V to 5.5 V VDD = 3.6 V to 5.5 V VIN = 0 V to VDD Pulse width of spike suppressed IDD specification is valid for all DAC codes; VIH = VDD, VIL = GND, VDD = 5.5 V VIH = VDD, VIL = GND, VDD = 3 V Temperature range for the B version is -30C to +85C. See the Terminology section. 3 Linearity is tested using a reduced code range: Code 32 to Code 1023. 4 To achieve near zero output current, use the power-down feature. 5 Guaranteed by design and characterization; not production tested. PD is active high. SDA and SCL pull-up resistors are tied to 1.8 V. 6 Input filtering on both the SCL and SDA inputs suppresses noise spikes that are less than 50 ns. 7 PD is active high. When PD is taken high, the AD5389A enters power-down mode. Rev. 0 | Page 3 of 16 AD5398A AC SPECIFICATIONS VDD = 2.7 V to 5.5 V, AGND = DGND = 0 V, RL = 25 connected to VDD, unless otherwise noted. Table 2. Parameter Output Current Settling Time Slew Rate Major Code Change Glitch Impulse Digital Feedthrough 3 1 2 Min B Version 1, 2 Typ Max 250 0.3 0.15 0.06 Unit s mA/s nA-sec nA-sec Test Conditions/Comments VDD = 5 V, RL = 25 , LL = 680 H 1/4 scale to 3/4 scale change (0x100 to 0x300) 1 LSB change around major carry Temperature range for the B version is -30C to +85C. Guaranteed by design and characterization; not production tested. 3 See the Terminology section. TIMING SPECIFICATIONS VDD = 2.7 V to 5.5 V. All specifications TMIN to TMAX, unless otherwise noted. Table 3. Parameter 1 fSCL t1 t2 t3 t4 t5 t6 2 t7 t8 t9 t10 t11 B Version Limit at TMIN, TMAX 400 2.5 0.6 1.3 0.6 100 0.9 0 0.6 0.6 1.3 300 0 250 300 20 + 0.1 Cb 3 400 Unit kHz max s min s min s min s min ns min s max s min s min s min s min ns max ns min ns max ns max ns min pF max Description SCL clock frequency SCL cycle time tHIGH, SCL high time tLOW, SCL low time tHD, STA, start/repeated start condition hold time tSU, DAT, data setup time tHD, DAT, data hold time tSU, STA, setup time for repeated start tSU, STO, stop condition setup time tBUF, bus free time between a stop condition and a start condition tR, rise time of both SCL and SDA when receiving Can be CMOS driven tF, fall time of SDA when receiving tF, fall time of both SCL and SDA when transmitting Capacitive load for each bus line Cb 1 2 Guaranteed by design and characterization; not production tested. A master device must provide a hold time of at least 300 ns for the SDA signal (referred to the VIH MIN of the SCL signal) to bridge the undefined region of the SCL falling edge. 3 Cb is the total capacitance of one bus line in pF. tR and tF are measured between 0.3 VDD and 0.7 VDD. Timing Diagram SDA t9 t3 t10 t11 t4 SCL START CONDITION REPEATED START CONDITION STOP CONDITION Figure 2. 2-Wire Serial Interface Timing Diagram Rev. 0 | Page 4 of 16 07795-002 t4 t6 t2 t5 t7 t1 t8 AD5398A ABSOLUTE MAXIMUM RATINGS TA = 25C, unless otherwise noted.1 Table 4. Parameter VDD to AGND VDD to DGND AGND to DGND SCL, SDA to DGND PD to DGND ISINK to AGND Operating Temperature Range Industrial (B Version) Storage Temperature Range Junction Temperature (TJ max) JA Thermal Impedance2 Mounted on 2-Layer Board Mounted on 4-Layer Board Lead Temperature, Soldering Maximum Peak Reflow Temperature3 1 2 Rating -0.3 V to +7 V -0.3 V to VDD + 0.3 V -0.3 V to +0.3 V -0.3 V to VDD + 0.3 V -0.3 V to VDD + 0.3 V -0.3 V to VDD + 0.3 V -40C to +85C -65C to +150C 150C 84C/W 48C/W 260C (5C) Stresses above those listed under Absolute Maximum Ratings may cause permanent damage to the device. This is a stress rating only; functional operation of the device at these or any other conditions above those listed in the operational sections of this specification is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability. Only one absolute maximum rating may be applied at any one time. ESD CAUTION Transient currents of up to 100 mA do not cause SCR latch-up. To achieve the optimum JA, it is recommended that the AD5398A be soldered onto a 4-layer board. 3 As per Jedec J-STD-020C. Rev. 0 | Page 5 of 16 AD5398A PIN CONFIGURATION AND FUNCTION DESCRIPTIONS 3 2 1 A B VIEW FROM BALL SIDE Figure 3. 9-Ball WLCSP Pin Configuration Table 5. 9-Ball WLCSP Pin Function Description Pin Number A1 A2 A3 B1 B2 B3 C1 C2 C3 Mnemonic ISINK NC PD AGND DGND SDA DGND VDD SCL Description Output Current Sink. No Connection. Power-Down. Asynchronous power-down signal. Analog Ground Pin. Digital Ground Pin. I2C Interface Signal. Digital Ground Pin. Digital Supply Voltage. I2C Interface Signal. 1400m PD 1 07795-021 C ISINK 8 DGND 2 1690m SDA 3 AGND 7 VDD 6 Figure 4. Metallization Photograph Dimensions shown in m Contact Factory for Latest Dimensions Rev. 0 | Page 6 of 16 07795-023 SCL 4 DGND 5 AD5398A TYPICAL PERFORMANCE CHARACTERISTICS 2.0 INL VDD = 3.8V TEMP = 25C 1.5 VERT = 50s/DIV INL (LSB) 1.0 0.5 3 0 07795-004 HORIZ = 468A/DIV CH3 M50.0ms 0 56 112 168 224 280 336 392 448 504 560 616 672 728 784 840 896 952 CODE Figure 5. Typical INL vs. Code Plot 0.6 0.5 0.4 0.3 DNL (LSB) 1008 1023 -0.5 Figure 8. Settling Time for a 4-LSB Step (VDD = 3.6 V) VERT = 2A/DIV 4.8A p-p DNL VDD = 3.8V TEMP = 25C 0.2 0.1 0 -0.1 07795-005 1 -0.2 -0.3 HORIZ = 2s/DIV CH1 M2.0s 0 56 112 168 224 280 336 392 448 504 560 616 672 728 784 840 896 952 CODE 1008 1023 Figure 6. Typical DNL vs. Code Plot 92.0 91.5 91.0 90.5 90.0 89.5 89.0 07795-006 Figure 9. 0.1 Hz to 10 Hz Noise Plot (VDD = 3.6 V) 0.14 IOUT @ +25C 0.12 IOUT @ -40C 0.10 0.08 0.06 0.04 0.02 0 IOUT @ +85C OUTPUT CURRENT (mA) 168 224 280 336 392 448 504 560 616 672 728 784 840 896 952 TIME CODE Figure 7. 1/4 to 3/4 Scale Settling Time (VDD = 3.6 V) Figure 10. Sink Current vs. Code vs. Temperature (VDD = 3.6 V) Rev. 0 | Page 7 of 16 1008 1023 100.0 -6 150.0-6 200.0-6 250.0 -6 300.0 -6 333.1-6 112 88.0 53.5-6 0 56 07795-009 88.5 IOUT (A) 07795-008 07795-007 AD5398A 2000 1800 1600 1400 0.45 VDD = 3.6V 0.40 0.35 ZERO CODE ERROR (mA) 0.30 0.25 0.20 0.15 0.10 07795-013 ACPSRR (A/V) 1200 1000 800 600 400 200 0 10 100 1k FREQUENCY (Hz) 10k 07795-010 VDD = 4.5V VDD = 3.8V 0.05 0 -40 -30 -20 -10 0 15 25 35 45 55 65 75 85 100k TEMPERATURE (C) Figure 11. AC Power Supply Rejection Ratio (VDD = 3.6 V) 3.5 3.0 POSITIVE INL (VDD = 3.8V) 2.5 2.0 POSITIVE INL (VDD = 4.5V) Figure 14. Zero Code Error vs. Temperature vs. Supply Voltage 1.5 VDD = 4.5V 1.0 0.5 FS ERROR (mA) VDD = 3.8V 0 -0.5 -1.0 -1.5 -2.0 INL (LSB) 1.5 1.0 0.5 0 -0.5 -1.0 NEGATIVE INL (VDD = 4.5V) -40 -30 -20 -10 0 15 25 35 45 55 65 75 85 TEMPERATURE (C) POSITIVE INL (VDD = 3.6V) NEGATIVE INL (VDD = 3.6V) NEGATIVE INL (VDD = 3.8V) 07795-011 VDD = 3.6V -40 -30 -20 -10 0 15 25 35 45 55 65 75 85 TEMPERATURE (C) Figure 12. INL vs. Temperature vs. Supply Voltage 1.0 0.8 0.6 0.4 POSITIVE DNL (VDD = 3.6V) POSITIVE DNL (VDD = 4.5V) Figure 15. Full-Scale Error vs. Temperature vs. Supply Voltage DNL (LSB) 0.2 0 -0.2 -0.4 -0.6 -0.8 -1.0 NEGATIVE DNL (VDD = 4.5V) NEGATIVE DNL (VDD = 3.6V) NEGATIVE DNL (VDD = 3.8V) POSITIVE DNL (VDD = 3.8V) -40 -30 -20 -10 0 15 25 35 45 55 65 75 85 TEMPERATURE (C) Figure 13. DNL vs. Temperature vs. Supply Voltage 07795-012 Rev. 0 | Page 8 of 16 07795-096 AD5398A TERMINOLOGY Relative Accuracy For the DAC, relative accuracy or integral nonlinearity is a measurement of the maximum deviation, in LSB, from a straight line passing through the endpoints of the DAC transfer function. A typical INL vs. code plot is shown in Figure 5. Differential Nonlinearity (DNL) Differential nonlinearity is the difference between the measured change and the ideal 1 LSB change between any two adjacent codes. A specified differential nonlinearity of 1 LSB maximum ensures monotonicity. This DAC is guaranteed monotonic by design. A typical DNL vs. code plot is shown in Figure 6. Zero-Code Error Zero-code error is a measurement of the output error when zero code (0x0000) is loaded to the DAC register. Ideally, the output is 0 mA. The zero-code error is always positive in the AD5398A because the output of the DAC cannot go below 0 mA. This is due to a combination of the offset errors in the DAC and output amplifier. Zero-code error is expressed in mA. Gain Error This is a measurement of the span error of the DAC. It is the deviation in slope of the DAC transfer characteristic from the ideal, expressed as a percent of the full-scale range. Gain Error Drift This is a measurement of the change in gain error with changes in temperature. It is expressed in LSB/C. Digital-to-Analog Glitch Impulse Digital-to-analog glitch impulse is the impulse injected into the analog output when the input code in the DAC register changes state. It is normally specified as the area of the glitch in nA-sec and is measured when the digital input code is changed by 1 LSB at the major carry transition. Digital Feedthrough Digital feedthrough is a measurement of the impulse injected into the analog output of the DAC from the digital inputs of the DAC, however is measured when the DAC output is not updated. It is specified in nA-sec and measured with a fullscale code change on the data bus, that is, from all 0s to all 1s and vice versa. Offset Error Offset error is a measurement of the difference between ISINK (actual) and IOUT (ideal) in the linear region of the transfer function, expressed in mA. Offset error is measured on the AD5398A with Code 16 loaded into the DAC register. Offset Error Drift This is a measurement of the change in offset error with a change in temperature. It is expressed in V/C. Rev. 0 | Page 9 of 16 AD5398A THEORY OF OPERATION The AD5398A is a fully integrated 10-bit DAC with 120 mA output current sink capability and is intended for driving voice coil actuators in applications such as lens autofocus, image stabilization, and optical zoom. The circuit diagram is shown in Figure 16. A 10-bit current output DAC coupled with Resistor R generates the voltage that drives the noninverting input of the operational amplifier. This voltage also appears across the RSENSE resistor and generates the sink current required to drive the voice coil. The R and RSENSE resistors are interleaved and matched. Therefore, the temperature coefficient and any nonlinearities over temperature are matched and the output drift over temperature is minimized. Diode D1 is an output protection diode. VBAT VOICE COIL ACTUATOR VDD RP RP SDA SCL I2C MASTER DEVICE AD5398A I2C SLAVE DEVICE I2C SLAVE DEVICE Figure 17. Typical I2C Bus VDD AD5398A REFERENCE POWER-ON RESET VDD SDA SCL I2C SERIAL INTERFACE 10-BIT CURRENT OUTPUT DAC D1 ISINK R PD RSENSE 3.3 07795-015 When the bus is idle, SCL and SDA are both high. The master device initiates a serial bus operation by generating a start condition, which is defined as a high-to-low transition on the SDA line while SCL is high. The slave device connected to the bus responds to the start condition and shifts in the next eight data bits under the control of the serial clock. These eight data bits consist of a 7-bit address, plus a read/write bit, which is 0 if data is to be written to a device, and 1 if data is to be read from a device. Each slave device on an I2C bus must have a unique address. The address of the AD5398A is 0001100; however, 0001101, 0001110, and 0001111 address the part because the last two bits are unused/don't care (see Figure 18 and Figure 19). Because the address plus R/W bit always equals eight bits of data, another way of looking at it is that the write address of the AD5398A is 0001 1000 (0x18) and the read address is 0001 1001 (0x19). Again, Bit 6 and Bit 7 of the address are unused, and, therefore, the write addresses can also be 0x1A, 0x1C, and 0x1E, and the read address can be 0x1B, 0x1D, and 0x1F (see Figure 18 and Figure 19). At the end of the address data, after the R/W bit, the slave device that recognizes its own address responds by generating an acknowledge (ACK) condition. This is defined as the slave device pulling SDA low while SCL is low before the ninth clock pulse, and keeping it low during the ninth clock pulse. Upon receiving an ACK, the master device can clock data into the AD5398A in a write operation, or it can clock it out in a read operation. Data must change either during the low period of the clock, because SDA transitions during the high period define a start condition as described previously, or during a stop condition as described in the Data Format section. I2C data is divided into blocks of eight bits, and the slave generates an ACK at the end of each block. The AD5398A requires 10 bits of data; two data-words must be written to it when a write operation occurs, or read from it when a read operation occurs. At the end of a read or write operation, the AD5398A acknowledges the second data byte. The master generates a stop condition, defined as a low-to-high transition on SDA while SCL is high, to end the transaction. DGND DGND AGND Figure 16. Circuit Diagram Showing Connection to Voice Coil SERIAL INTERFACE The AD5398A is controlled using the industry-standard I2C 2-wire serial protocol. Data can be written to or read from the DAC at data rates up to 400 kHz. After a read operation, the contents of the input register are reset to all zeros. I2C BUS OPERATION An I2C bus operates with one or more master devices that generate the serial clock (SCL), and read/write data on the serial data line (SDA) to/from slave devices such as the AD5398A. On all devices on an I2C bus, the SCL pin is connected to the SCL line and the SDA pin is connected to the SDA line. I2C devices can only pull the bus lines low; pulling high is achieved by the pull-up resistors, RP. The value of RP depends on the data rate, bus capacitance, and the maximum load current that the I2C device can sink (3 mA for a standard device). Rev. 0 | Page 10 of 16 07795-016 AD5398A DATA FORMAT Data is written to the AD5398A high byte first, MSB first, and is shifted into the 16-bit input register. After all data is shifted in, data from the input register is transferred to the DAC register. Because the DAC requires only 10 bits of data, not all bits of the input register data are used. The MSB is reserved for an activehigh, software-controlled, power-down function. 1 SCL 9 1 The data format is shown in Table 6. When referring to this table, note that Bit 14 is unused; Bit 13 to Bit 4 correspond to the DAC data bits, D9 to D0; and Bit 3 to Bit 0 are unused. During a read operation, data is read in the same bit order. 1 9 SDA START BY MASTER 0 0 0 1 1 X X R/W PD X D9 D8 D7 D6 D5 D4 ACK BY AD5398A D3 D2 D1 D0 X X X X ACK BY STOP BY AD5398A MASTER 07795-017 ACK BY AD5398A FRAME 1 SERIAL BUS ADDRESS BYTE FRAME 2 MOST SIGNIFICANT DATA BYTE FRAME 3 LEAST SIGNIFICANT DATA BYTE Figure 18. Write Operation 1 SCL 9 1 1 9 SDA START BY MASTER 0 0 0 1 1 X X R/W ACK BY AD5398A PD X D9 D8 D7 D6 D5 D4 ACK BY AD5398A D3 D2 D1 D0 X X X X ACK BY STOP BY AD5398A MASTER 07795-018 FRAME 1 SERIAL BUS ADDRESS BYTE FRAME 2 MOST SIGNIFICANT DATA BYTE FRAME 3 LEAST SIGNIFICANT DATA BYTE Figure 19. Read Operation Table 6. Data Format Serial DataWords Serial Data Bits Input Register Function1 1 Bit 15 SD7 R15 PD Bit 14 SD6 R14 X Bit 13 SD5 R13 D9 High Byte Bit Bit 12 11 SD4 SD3 R12 R11 D8 D7 Bit 10 SD2 R10 D6 Bit 9 SD1 R9 D5 Bit 8 SD0 R8 D4 Bit 7 SD7 R7 D3 Bit 6 SD6 R6 D2 Bit 5 SD5 R5 D1 Low Byte Bit Bit 4 3 SD4 SD3 R4 R3 D0 X Bit 2 SD2 R2 X Bit 1 SD1 R1 X Bit 0 SD0 R0 X PD = soft power-down; X = unused/don't care; and D7 to D0 = DAC data. Rev. 0 | Page 11 of 16 AD5398A POWER SUPPLY BYPASSING AND GROUNDING When accuracy is important in an application, it is beneficial to consider power supply and ground return layout on the PCB. The PCB for the AD5398A should have separate analog and digital power supply sections. Where shared AGND and DGND is necessary, the connection of grounds should be made at only one point, as close as possible to the AD5398A. Pay special attention to the layout of the AGND return path and track it between the voice coil motor and ISINK to minimize any series resistance. Figure 20 shows the output current sink of the AD5398A and illustrates the importance of reducing the effective series impedance of AGND, and the track resistance between the motor and ISINK. The voice coil is modelled as Inductor LC and Resistor RC. The current through the voice coil is effectively a dc current that results in a voltage drop, VC, when the AD5398A is sinking current; the effect of any series inductance is minimal. The maximum voltage drop allowed across RSENSE is 400 mV, and the minimum drain to source voltage of Q1 is 200 mV. This means that the AD5398A output has a compliance voltage of 600 mV. If VDROP falls below 600 mV, the output transistor, Q1, can no longer operate properly and ISINK might not be maintained as a constant. VBAT VOICE COIL ACTUATOR When the maximum sink current is flowing through the motor, the resistive elements, RT and RG, may have an impact on the voltage headroom of Q1 and may, in turn, limit the maximum value of RC because of voltage compliance. For example, if VBAT = 3.6 V RG = 0.5 RT = 0.5 ISINK = 120 mA VDROP = 600 mV (the compliance voltage) then the largest value of resistance of the voice coil, RC, is RC = V BAT - [V DROP + ( I SINK x RT ) + (I SINK x R G )] = I SINK 120 mA = 24 3.6 V - [600 mV + 2 x (120 mA x 0.5 )] For this reason, it is important to minimize any series impedance on both the ground return path and interconnect between the AD5398A and the motor. The power supply of the AD5398A should be decoupled with 0.1 F and 10 F capacitors. These capacitors should be kept as physically close as possible, with the 0.1 F capacitor serving as a local bypass capacitor, and therefore should be located as close as possible to the VDD pin. The 10 F capacitor should be a tantalum bead-type; the 0.1 F capacitor should be a ceramic type with a low effective series resistance and effective series inductance. The 0.1 F capacitor provides a low impedance path to ground for high transient currents. The power supply line should have as large a trace as possible to provide a low impedance path and reduce glitch effects on the supply line. Clocks and other fast switching digital signals should be shielded from other parts of the board by digital ground. Avoid crossover of digital and analog signals if possible. When traces cross on opposite sides of the board, ensure that they run at right angles to each other to reduce feedthrough effects through the board. The best board layout technique is to use a multilayer board with ground and power planes, where the component side of the board is dedicated to the ground plane only and the signal traces are placed on the solder side. However, this is not always possible with a 2-layer board. LC RC RT ISINK VC TRACE RESISTANCE VDD D1 Q1 VT RSENSE 3.3 VDROP AGND GROUND RG RESISTANCE GROUND LG INDUCTANCE VG 07795-019 Figure 20. Effect of PCB Trace Resistance and Inductance As the current increases through the voice coil, VC increases and VDROP decreases and eventually approaches the minimum specified compliance voltage of 600 mV. The ground return path is modelled by the RG and LG components. The track resistance between the voice coil and the AD5398A is modelled as RT. The inductive effects of LG influence RSENSE and RC equally, and because the current is maintained as a constant, it is not as critical as the purely resistive component of the ground return path. Rev. 0 | Page 12 of 16 AD5398 APPLICATIONS INFORMATION The AD5398A is designed to drive both spring preloaded and nonspring linear motors used in applications such as lens autofocus, image stabilization, or optical zoom. The operating principle of the spring-preloaded motor is that the lens position is controlled by the balancing of a voice coil and a spring. Figure 21 shows the transfer curve of a typical spring preloaded linear motor for autofocus. The key points of this transfer function are displacement or stroke, which is the actual distance the lens moves in millimeters (mm), and the current through the motor in milliamps (mA). A start current is associated with spring-preloaded linear motors, which is effectively a threshold current that must be exceeded for any displacement in the lens to occur. The start current is usually 20 mA or greater; the rated stroke or displacement is usually 0.25 mm to 0.4 mm; and the slope of the transfer curve is approximately 10 m/mA or less. The AD5398A is designed to sink up to 120 mA, which is more than adequate for available commercial linear motors or voice coils. Another factor that makes the AD5398A the ideal solution for these applications is the monotonicity of the device, which ensures that lens positioning is repeatable for the application of a given digital word. Figure 22 shows a typical application circuit for the AD5398A. 0.5 0.4 STROKE (mm) 0.3 0.2 START CURRENT 0.1 0 0 10 20 30 40 50 60 70 80 90 100 110 120 SINK CURRENT (mA) Figure 21. Spring Preloaded Voice Coil Stroke vs. Sink Current 0.1F VDD POWER-DOWN RESET VDD RP RP SDA SCL PD SDA SCL I2C SERIAL INTERFACE + VDD 10F VCC + 10F 0.1F AD5398A REFERENCE POWER-ON RESET VDD VOICE COIL ACTUATOR D1 ISINK 10-BIT CURRENT OUTPUT DAC I2C MASTER DEVICE I2C SLAVE DEVICE I2C SLAVE DEVICE R RSENSE 3.3 DGND DGND AGND Figure 22. Typical Application Circuit Rev. 0 | Page 13 of 16 07795-022 07795-020 AD5398A OUTLINE DIMENSIONS 1.575 1.515 1.455 0.65 0.59 0.53 SEATING PLANE 0.35 0.32 0.29 3 2 1 A BALL 1 IDENTIFIER 1.750 1.690 1.630 B 0.50 BSC BALL PITCH TOP VIEW (BALL SIDE DOWN) C Figure 23. 9-Ball Wafer Level Chip Scale Package [WLCSP] (CB-9-1) Dimensions shown in millimeters ORDERING GUIDE Model AD5398ABCBZ-REEL7 1 AD5398ABCBZ-REEL1 AD5398A-WAFER EVAL-AD5398AEBZ1 1 Temperature Range -30C to +85C -30C to +85C -40C to +85C Package Description 9-Ball Wafer Level Chip Scale (WLCSP) 9-Ball Wafer Level Chip Scale (WLCSP) Bare Die Wafer Evaluation Board Package Option CB-9-1 CB-9-1 091306-B 0.28 0.24 0.20 BOTTOM VIEW (BALL SIDE UP) Branding 1Z 1Z Z = RoHS Compliant Part. Rev. 0 | Page 14 of 16 AD5398A NOTES Rev. 0 | Page 15 of 16 AD5398A NOTES Purchase of licensed I2C components of Analog Devices or one of its sublicensed Associated Companies conveys a license for the purchaser under the Philips I2C Patent Rights to use these components in an I2C system, provided that the system conforms to the I2C Standard Specification as defined by Philips. (c)2008 Analog Devices, Inc. All rights reserved. Trademarks and registered trademarks are the property of their respective owners. D07795-0-10/08(0) Rev. 0 | Page 16 of 16 |
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