TLE7274_05 Datasheet, PDF (8/19 Pages) Infineon Technologies AG – 5-V Low Drop Voltage Regulator

TLE 7274
Additionally a buffer capacitor C_B of > 10µF should be used for the output to suppress
influences from load surges to the voltage levels. This one can either be an aluminum
electrolytic capacitor or a tantalum capacitor following the application requirements.
A general recommendation is to keep the drop over the equivalent serial resistor (ESR)
together with the discharge of the blocking capacitor below the allowed Headroom of
the Application to be supplied (e.g. typ. dV_Q = 350mV).
Since the regulator output current roughly rises linearly with time the discharge of the
capacitor can be calculated as follows:
dVC_B = dI_Q*dt/C_B
The drop across the ESR calculates as:
dV_ESR = dI*ESR
To prevent a reset the following relationship must be fullfilled:
dV_C + dV_ESR < V_RH = 350mV
Example: Assuming a load current change of C_B = 100mA, a blocking capacitor of dI_Q =
22µF and a typical regulator reaction time under normal operating conditions of dt ~
25µs and for special dynamic load conditions, such as load step from very low base
load, a reaction time of dt ~ 75µs..
dV_C = dI_Q*dt/C_B = 100mA * 25µs/22µF = 113mV
So for the ESR we can allow
dV_ESR = V_RH2 - dV_C = 350mV - 113mV = 236mV
The permissible ESR becomes:
ESR = dV_ESR / dI_Q = 236mV/100mA = 2.36Ohm
During design-in of the TLE7469 product family, special care needs to be taken with
regards to the regulators reaction time to sudden load current changes starting from very
low pre-load as well as cyclic load changes. The application note “TLE7x Voltage
Regulators - Application Note about Transient Response at ultra low quiescent current
Voltage Regulators” (see 3_cip05405.pdf) gives important hints for successful design-in
of the Voltage Regulators of the TLE7x family.
Data Sheet
8
Rev. 1.1, 2005-07-30