LMZ21701_15 Datasheet, PDF (13/37 Pages) Texas Instruments – LMZ21701 1 A SIMPLE SWITCHER® Nano Module with 17 V Maximum Input Voltage

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LMZ21701
SNVS853D – AUGUST 2012 – REVISED NOVEMBER 2014
9.2.2.2 Output Capacitor (C_OUT)
Similarly to the input capacitor, it is recommended to use low ESR multi-layer ceramic capacitors for C_OUT.
Ceramic capacitors with X5R and X7R temperature characteristics are recommended. Use 10 µF or larger value
and consider the DC voltage bias characteristics of the capacitor when choosing the case size and voltage
rating. For stability, the output capacitor should be in the 10 µF – 200 µF effective capacitance range.
9.2.2.3 Softstart Capacitor (C_SS)
The softstart capacitor is chosen according to the desired softstart time. As described in the Softstart and
Tracking Function section the softstart time T_SS = C_SS x 1.25 V / 2.9 μA.
A minimum C_SS value of 1000 pF is required for monotonic V_OUT ramp up.
9.2.2.4 Power Good Resistor (R_PG)
If the Power Good function is used, a pull up resistor R_PG is necessary from the PG pin to an external pull-up
voltage.
The minimum R_PG value is restricted by the pull down current capability of the internal pull down device.
R_PG-MIN= V_PULL-UP / 2 mA
(5)
The maximum R_PG value is based on the maximum PG leakage current and the minimum “logic high” level
system requirements:
R_PG-MAX= (V_PULL-UP – V_LOGIC-HIGH) / I_{LKG_PG}
(6)
9.2.2.5 Feedback Resistors (R_FBB and R_FBT)
The feedback resistors R_FBB and R_FBT set the desired output voltage. Choose R_FBB less than 400 kΩ and
calculate the value for R_FBT using the following formula:
R_FBT = R_FBB x (V_OUT/ 0.8 – 1)
(7)
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