AMS1117
1A Adjustable / Fixed Low Dropout Linear Regulator
WPMTEK
Description
1A Adjustable / Fixed Low Dropout Linear Regulator
1A Adjustable / Fixed Low Dropout Linear Regulator
AMS1117
The AMS1117 is a series of low dropout
voltage regulators which can provide up to 1A of
output current. The AMS1117 is available in six
fixed voltage, 1.2, 1.8, 2.5, 3.3 and 5.0V.
Additionally it is also available in adjustable
version. On chip precision trimming adjusts the
reference/ output voltage to within ± 2%. On-chip
thermal limiting provides protection against any
combination of overload and ambient
temperatures that would create excessive
junction temperatures.
The AMS1117 series is available in SOT-223,
TO-252 ,SOT89 packages. A minimum of 10uF
tantalum capacitor is required at the output to
improve the transient response and stability
Features
Low Dropout Voltage
Load regulation:0.5% Max.
Optimized for Low Voltage
On-chip thermal limiting.
Maximum Input Voltage : 20V
Adjustable Output Voltage or Fixed 1.2V,
1.8V, 2.5V, 3.3V, 5V
Standard SOT-223,TO-252 ,SOT89
Packages
Applications
Post Regulator for switching DC/DC
Converter
High Efficiency Linear Regulator
Battery Chargers
PC Add on Card
Motherboard clock supplies
LCD Monitor r
Set-top Box
A
Output voltage adjustment
The AMS1117 regulates the output by comparing the output voltage to an internally generated
reference voltage. On the adjustable version as shown in Fig.1, the VREF is available externally as
1.25V between VOUT and ADJ. The voltage ratio formed by R1 and R2 should be set to conduct 10mA
(minimum output load).
The output voltage is given by the following equation:
VOUT = VREF(1 + R2/R1) + IADJ X R2
On fixed versions of AMS1117, the voltage divider is provided internally.
Figure 1. Basic Adjustable Regulator
An input capacitor is recommended. A 10μF tantalum on the input is a suitable input bypassing for
almost all applications.
Adjust Terminal Bypass Capacitor
The adjust terminal can be bypassed to ground with a bypass capacitor (CADJ) to improve ripple
rejection. This bypass capacitor prevents ripple from being amplified as the output voltage is increased.
At any ripple frequency, the impedance of the CADJ should be less than R1 to prevent the ripple from
being amplified: (2π * fRIPPLE * CADJ)
The R1 is the resistor between the output and the adjust pin. Its value is normally in the range of 100-
200Ω. For example, with R1 = 124Ω and fRIPPLE = 120Hz, the CADJ should be > 11μF.
1A Adjustable / Fixed Low Dropout Linear Regulator
Integrated in
OVP&OCP products
provider
ev.A_Aug,2016 - - www.wpmtek.com
Output Capacitor
AMS1117 requires a capacitor from VOUT to GND to provide compensation feedback to the internal
gain stage. This is to ensure stability at the output terminal. Typically, a 10μF tantalum or 50μF aluminum
electrolytic is sufficient.
Note: It is important that the ESR for this capacitor does not exceed 0.5 Ω.
The output capacitor does not have a theoretical upper limit and increasing its value will increase
stability. COUT = 100μF or more is typical for high current regulator design.
6
Load Regulation
When the adjustable regulator is used (Fig.2), the best load regulation is accomplished when the top
of the resistor divider (R1) is connected directly to the output pin of the AMS1117. When so connected,
RP is not multiplied by the divider ratio. For Fixed output version, the top of R1 is internally connected to
the output and ground pins can be connected to low side of the load.
Figure 2. Best Load Regulation Using Adjustable Output Regulator
AMS1117 has thermal protection which limits junction temperature to 150°C. However, device
functionality is only guaranteed to a maximum junction temperature of +125°C. The power dissipation
and junction temperature for AMS1117 in DPAK package are given by
PD = (VIN – VOUT) * Iout
TJUNCTION = TAMBIENT + (PD * θ JA)
Note: TJUNCTION must not exceed 125°C
1A Adjustable / Fixed Low Dropout Linear Regulator
Integrated in
OVP&OCP products
provider
ev.A_Aug,2016 - - www.wpmtek.com
Thermal Consideration
The AMS1117 series contain thermal limiting circuitry designed to protect itself from over-temperature
conditions. Even for normal load conditions, maximum junction temperature ratings must not be
exceeded. As mention in thermal protection section, we need to consider all sources of thermal
resistance between junction and ambient. It includes junction-to case, case-to-heat-sink interface, and
heat sink thermal resistance itself.
Junction-to-case thermal resistance is specified from the IC junction to the bottom of the case directly
below the die. Proper mounting is required to ensure the best possible thermal flow from this area of the
package to the heat sink. The case of all devices in this series is electrically connected to the output.
Therefore, if the case of the device must be electrically isolated, a thermally conductive spacer is
recommended.
