Introduction EVALUATION BOARD DATA SHEET The AAT4712 is an integrated P-channel MOSFET load switch with adjustable current limits, integrated discharge paths, over-temperature protection, a power loop and a super capacitor charger. The input current limit control is combined with an over-temperature thermal limit and power loop circuit to provide a comprehensive system to protect the load switch and its supply from load conditions exceeding the supply specifications. A brief Getting Started section is included to help the user to begin operating the evaluation board. The AAT4712 evaluation board is shown in Figure 1; Figure 2 and Figure 8 depict the board schematic and layout. For additional information, please consult the AAT4712 product datasheet. Board Picture (a) Top Side (b) Bottom Side Figure 1: AAT4712 Evaluation Board Picture. 1
Schematic EVALUATION BOARD DATA SHEET VCC VCC RDY R SET 1.24M D1 LED R1 1.74k 1 2 3 4 5 6 7 U1 AAT4712 RDY ISET N/C POK 16 GND 15 ADJ 14 VCC 13 VCC 12 OUT 11 OUT 10 D2 LED R2 1.74k C1 10µF R ADJ 18.2k POK GND VCC 8 OUT 9 OUT C2 10µF C3 22µF RB1 Super Cap RB2 Figure 2: AAT4712 Evaluation Board Schematic. Getting Started 1. Connect a DC power supply and a super capacitor or ultra capacitor to the AAT4712 evaluation board as shown in Figure 3. Set the DC power supply to 5V and the load to 0A. After power on, a current up to the current limit (2A set by R SET = 1.24M) charging the super capacitor can be observed by either current meter in the power supply or current probe of an oscilloscope. Figure 4 shows the start-up waveform of charging the super capacitor with softstart at 5V V CC. The operating voltage may vary from 2.5V to 5.5V. 2. After the power is on and the super capacitor is fully charged, the integrated discharge path management can be observed by decreasing the V CC with system load added. The AAT4712 integrates discharge path for (to system load) from the VCC input and OUT input (connect to super capacitor). After the power is on and the super capacitor is fully charged, the super capacitor is used as a backup power to support the system load for a short time when the input voltage drops below the power good detect (POK) threshold and the OUT pin voltage is greater than the V UVLO_OUT and voltage by turning on the OUT to switch discharge path and turning off the path of V CC to. The OUT to switch remains continuously on until the OUT pin voltage falls below V UVLO_OUT. 2
Figure 3: AAT4712 Evaluation Board Demonstration Connection. (a) Zoom in (b) Zoom out Figure 4: AAT4712 Start-up without System Load. 3
Figure 5 shows the dynamic process of the power path switching with V POK_TH = 4.5V, 0.5F super capacitor with 75mΩ ESR when V CC drops from 5V to 4V with 1A system load. D2 will be lighted when the OUT to path is turned on and the VCC to path is turned off. Figure 6 shows the waveform of the super capacitor supporting the system load as backup power when V CC is removed. The supporting time can be calculated using the following formula: T SUPPORT = (V DROP I OUT ESR SUPERCAP ) C SUPERCAP I OUT V DROP is the delta voltage when the super capacitor is active to support the system load and is equal to V CC minus V UVLO_OUT. For the condition as shown in Figure 6, the V DROP is 3V by V CC 5V minus V UVLO_OUT 2V. The supporting time can be calculated using the following equation. The calculation result is same as the measurement result. T SUPPORT = (3V - 1A 75mΩ) 0.5F 1A = 1.46 sec. Discharge path management by the AAT4712 can also be observed by observing the input current I CC, system load I, and super capacitor charge current I OUT. The input current is equal to the current plus the OUT charging current as shown in the formula below and if the load current increases/decreases, the OUT charging current will automatically decrease/increase accordingly via the device control loop. I CC = I + I OUT Figure 7 shows the measurement waveform when powering on the AAT4712 with 1A system load. Make sure the super capacitor is fully discharged before doing the measurement. Figure 5: AAT4712 Operating Waveform When V CC Drops from 5V to 4V with 1A System Load. Figure 6: AAT4712 Backup Time when 5V V CC is Removed with 1A System Load and 0.5F SuperCap. 4
Figure 7: AAT4712 Startup with 1A System Load. Current Limit and POK Setting The input current limit is programmed by by the R SET resistor from the I SET pin to ground in the range from 150mA to 2.4A. R SET can be calculated by: R SET = I LIM 1.6 Table 1 lists some 1% standard metal film resistor values for current limit settings. R SET (kω) Current Limit (A) 1500 2.4 1240 2 1000 1.6 931 1.5 750 1.2 620 1 560 0.9 499 0.8 432 0.7 374 0.6 316 0.5 249 0.4 187 0.3 93.1 0.15 Table 1: Recommended Current Limit R SET Values. 5
The POK detect threshold can be programmed by the external resistor R ADJ connected from the ADJ pin to GND. The R ADJ value can be calculated by: R ADJ = 60 V POK_TH - 1.2 Table 2 lists some 1% standard metal film resistor values for various V POK_TH settings. R ADJ (kω) V POK_TH (V) 15.8 5.0 18.2 4.5 20.5 4.0 26.1 3.5 33.2 3.0 47 2.5 Table 2: Recommended Resistor Values for V POK_TH Setting. Printed Circuit Board (a) Top Layer (not to scale) (b) Bottom Layer (not to scale) Figure 8: AAT4712 Evaluation Board. 6
AAT4712 EVAL Component Listing EVALUATION BOARD DATA SHEET Component Part Number Description Manufacturer U1 AAT4712 Current Limited Switch with Capcitor Charger Skyworks R1,R2 RC0603FR-071K74L Res 1.74KΩ 1/10W 1% 0603 SMD R SET RC0603FR-071M24L Res 1.24MΩ 1/10W 1% 0603 SMD R ADJ RC0603FR-0718K2L Res 18.2KΩ 1/10W 1% 0603 SMD Yageo C1,C2 GRM21BR61C106K Cap Ceramic 10µF 0805 X5R 16V 10% C3 GRM21BR60J226M Cap Ceramic 22µF 0805 X5R 6.3V 20% D1, D2 0805KRCT Red LED 0805 HB SUPERCAP, RB1, RB2 Not populated Table 3: AAT4712 Evaluation Board Bill of Materials. Copyright 2012 Skyworks Solutions, Inc. All Rights Reserved. Information in this document is provided in connection with Skyworks Solutions, Inc. ( Skyworks ) products or services. These materials, including the information contained herein, are provided by Skyworks as a service to its customers and may be used for informational purposes only by the customer. Skyworks assumes no responsibility for errors or omissions in these materials or the information contained herein. Skyworks may change its documentation, products, services, specifications or product descriptions at any time, without notice. Skyworks makes no commitment to update the materials or information and shall have no responsibility whatsoever for conflicts, incompatibilities, or other difficulties arising from any future changes. No license, whether express, implied, by estoppel or otherwise, is granted to any intellectual property rights by this document. Skyworks assumes no liability for any materials, products or information provided hereunder, including the sale, distribution, reproduction or use of Skyworks products, information or materials, except as may be provided in Skyworks Terms and Conditions of Sale. THE MATERIALS, PRODUCTS AND INFORMATION ARE PROVIDED AS IS WITHOUT WARRANTY OF ANY KIND, WHETHER EXPRESS, IMPLIED, STATUTORY, OR OTHERWISE, INCLUDING FITNESS FOR A PARTICULAR PURPOSE OR USE, MERCHANTABILITY, PERFORMANCE, QUALITY OR NON-INFRINGEMENT OF ANY INTELLECTUAL PROPERTY RIGHT; ALL SUCH WARRANTIES ARE HEREBY EXPRESSLY DISCLAIMED. SKYWORKS DOES NOT WARRANT THE ACCURACY OR COMPLETENESS OF THE INFORMATION, TEXT, GRAPHICS OR OTHER ITEMS CONTAINED WITHIN THESE MATERIALS. SKYWORKS SHALL NOT BE LIABLE FOR ANY DAMAGES, IN- CLUDING BUT NOT LIMITED TO ANY SPECIAL, INDIRECT, INCIDENTAL, STATUTORY, OR CONSEQUENTIAL DAMAGES, INCLUDING WITHOUT LIMITATION, LOST REVENUES OR LOST PROFITS THAT MAY RESULT FROM THE USE OF THE MATERIALS OR INFORMATION, WHETHER OR NOT THE RECIPIENT OF MATERIALS HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. Skyworks products are not intended for use in medical, lifesaving or life-sustaining applications, or other equipment in which the failure of the Skyworks products could lead to personal injury, death, physical or environmental damage. Skyworks customers using or selling Skyworks products for use in such applications do so at their own risk and agree to fully indemnify Skyworks for any damages resulting from such improper use or sale. Customers are responsible for their products and applications using Skyworks products, which may deviate from published specifications as a result of design defects, errors, or operation of products outside of published parameters or design specifications. Customers should include design and operating safeguards to minimize these and other risks. Skyworks assumes no liability for applications assistance, customer product design, or damage to any equipment resulting from the use of Skyworks products outside of stated published specifications or parameters. Skyworks, the Skyworks symbol, and Breakthrough Simplicity are trademarks or registered trademarks of Skyworks Solutions, Inc., in the United States and other countries. Third-party brands and names are for identification purposes only, and are the property of their respective owners. Additional information, including relevant terms and conditions, posted at www.skyworksinc.com, are incorporated by reference. 7