Datasheet

+
-
-+
V
IN
I
UVLO
R13
R26
R25
8
23 PA
i
X
R25 =
R13 x 1.24V
V
INUV_UP
- 1.24V
©
§
¹
·
R13 =
V
HYST
23 PA
Evaluation Board Test Procedure www.ti.com
Step 1: Choose V
IN
voltage where converter starts to operate (V
UV_UP
) and choose VIN voltage where
converter shuts down (V
UV_DN
). V
HYST
= (V
UVLO_UP
- V
UV_DN
)
Step 2: Solve for resistor value R13 with the following equation.
(17)
Solve for resistor value R25 wit the following equation:
(18)
Example Calculation of UVLO with Hysterisis:
• V
IN
start-up = V
UV_UP
= 8.45V
• V
IN
shut down = V
UV_DN
= 8.2V
• I
UVLO
= 23 µA
• V
HYST
= 8.45V – 8.2 = 0.25V
• R13 ≊ 10 kΩ
• R25 ≊ 1.74 kΩ
If a small amount of hysteresis is desired and V
IN
is large, resistor R26 may need to be populated.
Figure 11. UVLO Circuit with R26 Populated for Small Hysteresis and Large Input Voltage
6 Evaluation Board Test Procedure
Proper Board Connections
Be sure to choose the correct wire size when connecting the source supply and load. Monitor the current
into and out of the unit under test (UUT). Monitor the voltages directly at the board terminals, as resistive
voltage drops along the wires may decrease measurement accuracy. The LM3423 evaluation board has
two pairs of positive and negative inputs connectors which allows for Kelvin connections to be made from
the power supplies to the evaluation board. These precautions are especially important during
measurement of conversion efficiency.
12
AN-1907 LM3423 Buck-Boost Configuration Evaluation Board SNVA376A–December 2008–Revised May 2013
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