Datasheet

LM4125
SNVS238A –MAY 2004–REVISED APRIL 2013 www.ti.com
PIN FUNCTIONS
Output (Pin 5): Reference Output.
Input (Pin 4): Positive Supply.
Ground (Pin 2): Negative Supply or Ground Connection.
APPLICATION HINTS
The standard application circuit for the LM4125 is shown in Figure 19. It is designed to be stable with ceramic
output capacitors in the range of 0.022µF to 0.1µF. Note that 0.022µF is the minimum required output capacitor.
These capacitors typically have an ESR of about 0.1 to 0.5Ω. Smaller ESR can be tolerated, however larger ESR
can not. The output capacitor can be increased to improve load transient response, up to about 1µF. However,
values above 0.047µF must be tantalum. With tantalum capacitors, in the 1µF range, a small capacitor between
the output and the reference pin is required. This capacitor will typically be in the 50pF range. Care must be
taken when using output capacitors of 1µF or larger. These application must be thoroughly tested over
temperature, line and load.
An input capacitor is typically not required. However, a 0.1µF ceramic can be used to help prevent line transients
from entering the LM4125. Larger input capacitors should be tantalum or aluminum.
The typical thermal hysteresis specification is defined as the change in +25°C voltage measured after thermal
cycling. The device is thermal cycled to temperature -40°C and then measured at 25°C. Next the device is
thermal cycled to temperature +125°C and again measured at 25°C. The resulting V
OUT
delta shift between the
25°C measurements is thermal hysteresis. Thermal hysteresis is common in precision references and is induced
by thermal-mechanical package stress. Changes in environmental storage temperature, operating temperature
and board mounting temperature are all factors that can contribute to thermal hysteresis.
Figure 19. Standard Application Circuit
INPUT CAPACITOR
Noise on the power-supply input can effect the output noise, but can be reduced by using an optional bypass
capacitor between the input pin and the ground.
PRINTED CIRCUIT BOARD LAYOUT CONSIDERATION
The mechanical stress due to PC board mounting can cause the output voltage to shift from its initial value.
References in SOT packages are generally less prone to assembly stress than devices in Small Outline (SOIC)
package.
To reduce the stress-related output voltage shifts, mount the reference on the low flex areas of the PC board
such as near to the edge or the corner of the PC board.
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