Datasheet AMS1117 (Advanced Monolithic Systems) - 5
| Manufacturer | Advanced Monolithic Systems |
| Description | 1A Low Dropout Voltage Regulator |
| Pages / Page | 8 / 5 — AMS1117. APPLICATION HINTS. Figure 3. Connections for Best Load … |
| File Format / Size | PDF / 95 Kb |
| Document Language | English |
AMS1117. APPLICATION HINTS. Figure 3. Connections for Best Load Regulation. Ripple Rejection. Thermal Considerations. Table 1
Text Version of Document
AMS1117 APPLICATION HINTS
Connected as shown , RP is not multiplied by the divider ratio The total thermal resistance from junction to ambient can be as low as 45°C/W. This requires a reasonable sized PC board with at RP least on layer of copper to spread the heat across the board and PARASITIC couple it into the surrounding air. LINE RESISTANCE AMS1117 Experiments have shown that the heat spreading copper layer does VIN IN OUT not need to be electrically connected to the tab of the device. The ADJ PC material can be very effective at transmitting heat between the pad area, attached to the pad of the device, and a ground plane layer either inside or on the opposite side of the board. Although R1* RL the actual thermal resistance of the PC material is high, the Length/Area ratio of the thermal resistance between layers is small. The data in Table 1, was taken using 1/16” FR-4 board with 1 oz. copper foil, and it can be used as a rough guideline for R2* estimating thermal resistance. For each application the thermal resistance will be affected by thermal interactions with other components on the board. To determine the actual value some experimentation will be necessary. The power dissipation of the AMS1117 is equal to: *CONNECT R1 TO CASE PD = ( VIN - VOUT )( IOUT ) CONNECT R2 TO LOAD Maximum junction temperature will be equal to:
Figure 3. Connections for Best Load Regulation
TJ = TA(MAX) + PD(Thermal Resistance (junction-to-ambient)) Maximum junction temperature must not exceed 125°C. In the case of fixed voltage devices the top of R1 is connected Kelvin internally, and the ground pin can be used for negative side sensing.
Ripple Rejection
The ripple rejection values are measured with the adjustment pin
Thermal Considerations
bypassed. The impedance of the adjust pin capacitor at the ripple frequency should be less than the value of R1 (normally 100 The AMS1117 series have internal power and thermal limiting Ω to circuitry designed to protect the device under overload conditions. 200Ω) for a proper bypassing and ripple rejection approaching the values shown. The size of the required adjust pin capacitor is a However maximum junction temperature ratings of 125°C should function of the input ripple frequency. If R1=100Ω at 120Hz the not be exceeded under continuous normal load conditions. adjust pin capacitor should be Careful consideration must be given to all sources of thermal >13µF. At 10kHz only 0.16µF is needed. resistance from junction to ambient. For the surface mount package SOT-223 additional heat sources mounted near the device must be considered. The heat dissipation capability of the PC The ripple rejection will be a function of output voltage, in circuits board and its copper traces is used as a heat sink for the device. without an adjust pin bypass capacitor. The output ripple will The thermal resistance from the junction to the tab for the increase directly as a ratio of the output voltage to the reference voltage (V AMS1117 is 15°C/W. Thermal resistance from tab to ambient can OUT / VREF ). be as low as 30°C/W.
Table 1.
COPPER AREA THERMAL RESISTANCE TOP SIDE* BACK SIDE BOARD AREA (JUNCTION-TO-AMBIENT) 2500 Sq. mm 2500 Sq. mm 2500 Sq. mm 55°C/W 1000 Sq. mm 2500 Sq. mm 2500 Sq. mm 55°C/W 225 Sq. mm 2500 Sq. mm 2500 Sq. mm 65°C/W 100 Sq. mm 2500 Sq. mm 2500 Sq. mm 80°C/W 1000 Sq. mm 1000 Sq. mm 1000 Sq. mm 60°C/W 1000 Sq. mm 0 1000 Sq. mm 65°C/W * Tab of device attached to topside copper.
Advanced Monolithic Systems, Inc.
www.advanced-monolithic.com Phone (925) 443-0722 Fax (925) 443-0723
Connected as shown , RP is not multiplied by the divider ratio The total thermal resistance from junction to ambient can be as low as 45°C/W. This requires a reasonable sized PC board with at RP least on layer of copper to spread the heat across the board and PARASITIC couple it into the surrounding air. LINE RESISTANCE AMS1117 Experiments have shown that the heat spreading copper layer does VIN IN OUT not need to be electrically connected to the tab of the device. The ADJ PC material can be very effective at transmitting heat between the pad area, attached to the pad of the device, and a ground plane layer either inside or on the opposite side of the board. Although R1* RL the actual thermal resistance of the PC material is high, the Length/Area ratio of the thermal resistance between layers is small. The data in Table 1, was taken using 1/16” FR-4 board with 1 oz. copper foil, and it can be used as a rough guideline for R2* estimating thermal resistance. For each application the thermal resistance will be affected by thermal interactions with other components on the board. To determine the actual value some experimentation will be necessary. The power dissipation of the AMS1117 is equal to: *CONNECT R1 TO CASE PD = ( VIN - VOUT )( IOUT ) CONNECT R2 TO LOAD Maximum junction temperature will be equal to:
Figure 3. Connections for Best Load Regulation
TJ = TA(MAX) + PD(Thermal Resistance (junction-to-ambient)) Maximum junction temperature must not exceed 125°C. In the case of fixed voltage devices the top of R1 is connected Kelvin internally, and the ground pin can be used for negative side sensing.
Ripple Rejection
The ripple rejection values are measured with the adjustment pin
Thermal Considerations
bypassed. The impedance of the adjust pin capacitor at the ripple frequency should be less than the value of R1 (normally 100 The AMS1117 series have internal power and thermal limiting Ω to circuitry designed to protect the device under overload conditions. 200Ω) for a proper bypassing and ripple rejection approaching the values shown. The size of the required adjust pin capacitor is a However maximum junction temperature ratings of 125°C should function of the input ripple frequency. If R1=100Ω at 120Hz the not be exceeded under continuous normal load conditions. adjust pin capacitor should be Careful consideration must be given to all sources of thermal >13µF. At 10kHz only 0.16µF is needed. resistance from junction to ambient. For the surface mount package SOT-223 additional heat sources mounted near the device must be considered. The heat dissipation capability of the PC The ripple rejection will be a function of output voltage, in circuits board and its copper traces is used as a heat sink for the device. without an adjust pin bypass capacitor. The output ripple will The thermal resistance from the junction to the tab for the increase directly as a ratio of the output voltage to the reference voltage (V AMS1117 is 15°C/W. Thermal resistance from tab to ambient can OUT / VREF ). be as low as 30°C/W.
Table 1.
COPPER AREA THERMAL RESISTANCE TOP SIDE* BACK SIDE BOARD AREA (JUNCTION-TO-AMBIENT) 2500 Sq. mm 2500 Sq. mm 2500 Sq. mm 55°C/W 1000 Sq. mm 2500 Sq. mm 2500 Sq. mm 55°C/W 225 Sq. mm 2500 Sq. mm 2500 Sq. mm 65°C/W 100 Sq. mm 2500 Sq. mm 2500 Sq. mm 80°C/W 1000 Sq. mm 1000 Sq. mm 1000 Sq. mm 60°C/W 1000 Sq. mm 0 1000 Sq. mm 65°C/W * Tab of device attached to topside copper.
Advanced Monolithic Systems, Inc.
www.advanced-monolithic.com Phone (925) 443-0722 Fax (925) 443-0723
