TPS54262-EP Datasheet, PDF (29/48 Pages) Texas Instruments – 2-A 60-V Step-Down DC-DC Converter With Low I(q) and Voltage Supervisor

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TPS54262-EP
SLVSDP3 – DECEMBER 2016
Typical Application (continued)
8.2.2.1.10 Resistors to Select Output Voltage (R4, R5)
To minimize the effect of leakage current on the VSENSE terminal, the current flowing through the feedback
network should be greater than 5 mA to maintain output accuracy. Higher resistor values help improve the
converter efficiency at low-output currents, but may introduce noise immunity problems. See Equation 1. TI
recommends fixing R4 to a standard value (for example, 187 kΩ) and calculate R5.
8.2.2.1.11 Resistors to Set Undervoltage, Overvoltage, and Reset Thresholds (R1, R2, R3)
8.2.2.1.11.1 Overvoltage Resistor Selection
Using Equation 9, the value of R3 can be determined to set the overvoltage threshold at up to 106% to 110% of
V_Reg. The sum of R1, R2, and R3 resistor network to ground should be approximately 100 kΩ .
8.2.2.1.11.2 Reset Threshold Resistor Selection
Using Equation 8 the value of R2 + R3 can be calculated, and knowing R3 from the OV_TH setting, R2 can be
determined. Suggested value of reset threshold is 92% of V_Reg.
8.2.2.1.11.3 Undervoltage Threshold for Low-Power Mode and Load Transient Operation
This threshold is set above the reset threshold to ensure the regulator operates within the specified tolerances
during output load transient of low load to high load and during discontinuous conduction mode. The typical
voltage threshold can be determined using Equation 7. Suggested value of undervoltage threshold is 95% of
V_Reg.
8.2.2.1.12 Low-Power Mode (LPM) Threshold
An approximation of the output load current at which the converter is operating in discontinuous mode can be
obtained from Equation 23 with ± 30% hysteresis. The values used in Equation 3 for minimum and maximum
input voltage will affect the duty cycle and the overall discontinuous mode load current. These are the nominal
values, and other factors are not taken into consideration like external component variations with temperature
and aging.
8.2.2.1.13 Enable Pin Pull-Up Resistor (R11) and Voltage Divider Resistor (R10)
An external pull-up resistor, R11= 30.1 kΩ, is recommended to enable the device for operation and R10 can be
left open.
Based on the application needs, if the device needs to be turned on at certain input voltage using EN pin
threshold, R10 can be used as a voltage divider resistor along with pull-up resistor (R11=30.1 kΩ) and R10 can
be calculated accordingly.
8.2.2.1.14 Pull-Up Resistor (R12) at RST Pin
A standard pull-up resistor, R12 = 2 K Ω can be used at this pin
8.2.2.1.15 Type 3 Compensation Components (R5, R6, R9, C5, C7, C8)
First, make the ZEROs close to double pole frequency, using Equation 12, Equation 13, and Equation 11.
fz1 = (50% to 70%) f_LC
fz2 = f_LC
Second, make the POLEs above the crossover frequency, using Equation 18 and Equation 19.
fp1 = f_ESR
fp2 = ½f_sw
8.2.2.1.15.1 Resistors
From Equation 1, knowing V_Reg and R4 (fix to a standard value), R5 can be calculated as shown in Equation 37:
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