SiGe AATIAN92 Power path with input current limit and capacitor charger Datasheet

EVALUATION BOARD DATASHEET
EV-175
AAT4712 EVAL: Power Path with Input Current Limit and Capacitor Charger
Introduction
The AAT4712 is an integrated P-channel MOSFET load switch with adjustable current limits, integrated discharge path,
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; Figures 2 and 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.
EV-175.2010.07.1.0
www.analogictech.com
1
EVALUATION BOARD DATASHEET
EV-175
AAT4712 EVAL: Power Path with Input Current Limit and Capacitor Charger
Schematic
VCC
VCC
D1
LED
R1
100K
RDY
RSET
D2
LED
2
1.24M
3
4
5
SYS
6
7
8
C2
10μF
R2
100k
U1
AAT4712
1
RDY
POK
ISET
GND
NC
ADJ
SYS
VCC
SYS
VCC
SYS
OUT
SYS
OUT
SYS
OUT
16
POK
15
GND
RADJ
14
18.2k
13
12
VCC
C1
10μF
11
10
9
OUT
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 RSET = 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 VCC. 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 VCC with system load added. The AAT4712 integrates discharge path for SYS (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
VUVLO_OUT and SYS voltage by turning on the OUT to SYS switch discharge path and turning off the path of VCC to
SYS. The OUT to SYS switch remains continuously on until the OUT pin voltage falls below VUVLO_OUT.
2
www.analogictech.com
EV-175.2010.07.1.0
EVALUATION BOARD DATASHEET
EV-175
AAT4712 EVAL: Power Path with Input Current Limit and Capacitor Charger
Electronic LOAD
0 to 2A
I SYS
0.5F 75mΩ (TDK
EDLC272020 -501-2F-50) is
adopted as SuperCap for the
measurement of the file . The
balance resistors are 11kΩ.
Power Supply
2.5V to 5.5V
IOUT
ICC
Figure 3: AAT4712 Evaluation Board Demonstration Connection.
(a) Zoom in
(b) Zoom out
Figure 4: AAT4712 Start-up without System Load.
EV-175.2010.07.1.0
www.analogictech.com
3
EVALUATION BOARD DATASHEET
EV-175
AAT4712 EVAL: Power Path with Input Current Limit and Capacitor Charger
Figure 5 shows the dynamic process of the power path switching with VPOK_TH = 4.5V, 0.5F super capacitor with 75mΩ
ESR, VCC drops from 5V to 4V with 1A system load. D2 will be lighted when the OUT to SYS path is turned on and VCC
to the SYS path is turned off.
Figure 6 shows the waveform of the super capacitor supporting the system load as backup power when VCC is removed.
The supporting time can be calculated using the following formula:
TSUPPORT = (VDROP · IOUT · ESRSUPERCAP) ·
CSUPERCAP
IOUT
VDROP is the delta voltage when the super capacitor is active to support the system load and is equal to VCC minus
VUVLO_OUT.
For the condition as shown in Figure 6, the VDROP is 3V by VCC 5V minus VUVLO_OUT 2V. The supporting time can be calculated using the following equation. The calculation result is same as the measurement result.
TSUPPORT = (3V - 1A · 75mΩ) ·
0.5F
= 1.46 sec.
1A
Discharge path management by the AAT4712 can also be observed by observing the input current ICC, system load ISYS,
and super capacitor charge current IOUT. The input current is equal to the SYS current plus the OUT charging current as
shown in the formula below and if the SYS load current increases/decreases, the OUT charging current will automatically decrease/increase accordingly via the device control loop.
ICC = ISYS + IOUT
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
VCC Drops from 5V to 4V with 1A System Load.
4
Figure 6: AAT4712 Backup Time when 5V VCC is
Removed with 1A System Load and 0.5F SuperCap.
www.analogictech.com
EV-175.2010.07.1.0
EVALUATION BOARD DATASHEET
EV-175
AAT4712 EVAL: Power Path with Input Current Limit and Capacitor Charger
Figure 7: AAT4712 Startup with 1A System Load.
Current Limit and POK Setting
The input current limit is programmed by by the RSET resistor from the ISET pin to ground in the range from 150mA to
2.4A. RSET can be calculated by:
RSET =
ILIM
1.6
Table 1 lists some 1% standard metal film resistor values for current limit settings.
RSET (kΩ)
Current Limit (A)
1500
1240
1000
931
750
620
560
499
432
374
316
249
187
93.1
2.4
2
1.6
1.5
1.2
1
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.15
Table 1: Recommended Current Limit RSET Values.
EV-175.2010.07.1.0
www.analogictech.com
5
EVALUATION BOARD DATASHEET
EV-175
AAT4712 EVAL: Power Path with Input Current Limit and Capacitor Charger
The POK detect threshold can be programmed by the external resistor RADJ connected from the ADJ pin to GND. The
RADJ value can be calculated by:
60
RADJ = V
POK_TH - 1.2
Table 2 lists some 1% standard metal film resistor values for various VPOK_TH settings.
RADJ (kΩ)
VPOK_TH (V)
15.8
18.2
20.5
26.1
33.2
47
5.0
4.5
4.0
3.5
3.0
2.5
Table 2: Recommended Resistor Values for VPOK_TH Setting.
Printed Circuit Board
(a) Top Layer (not to scale)
(b) Bottom Layer (not to scale)
Figure 8: AAT4712 Evaluation Board.
6
www.analogictech.com
EV-175.2010.07.1.0
EVALUATION BOARD DATASHEET
EV-175
AAT4712 EVAL: Power Path with Input Current Limit and Capacitor Charger
AAT4712 EVAL Component Listing
Component
Part Number
Description
Manufacturer
U1
R1,R2
RSET
RADJ
C1,C2
C3
D1, D2
SUPERCAP, RB1, RB2
AAT4712
RC0603FR-071K74L
RC0603FR-071M24L
RC0603FR-0718K2L
GRM21BR61C106K
GRM21BR60J226M
0805KRCT
Not populated
Current Limited Switch with Capcitor Charger
RES 1.74KΩ 1/10W 1% 0603 SMD
RES 1.24MΩ 1/10W 1% 0603 SMD
RES 18.2KΩ 1/10W 1% 0603 SMD
Cap Ceramic 10μF 0805 X5R 16V 10%
Cap Ceramic 22μF 0805 X5R 6.3V 20%
Red LED 0805
AnalogicTech
Yageo
HB
Table 3: AAT4712 Evaluation Board Bill of Materials.
Advanced Analogic Technologies, Inc.
3230 Scott Boulevard, Santa Clara, CA 95054
Phone (408) 737-4600
Fax (408) 737-4611
© Advanced Analogic Technologies, Inc.
AnalogicTech cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in an AnalogicTech product. No circuit patent licenses, copyrights, mask work rights, or other intellectual
property rights are implied. AnalogicTech reserves the right to make changes to their products or specifications or to discontinue any product or service without notice. Except as provided in AnalogicTech’s terms and
conditions of sale, AnalogicTech assumes no liability whatsoever, and AnalogicTech disclaims any express or implied warranty relating to the sale and/or use of AnalogicTech products including liability or warranties
relating to fitness for a particular purpose, merchantability, or infringement of any patent, copyright or other intellectual property right. In order to minimize risks associated with the customer’s applications, adequate
design and operating safeguards must be provided by the customer to minimize inherent or procedural hazards. Testing and other quality control techniques are utilized to the extent AnalogicTech deems necessary to
support this warranty. Specific testing of all parameters of each device is not necessarily performed. AnalogicTech and the AnalogicTech logo are trademarks of Advanced Analogic Technologies Incorporated. All other
brand and product names appearing in this document are registered trademarks or trademarks of their respective holders.
EV-175.2010.07.1.0
www.analogictech.com
7
Similar pages