Datasheet

INH/UVLO
VIN
R
UVLO1
R
UVLO2
A_VOUT
V
IN
( )
( )
-
= W
æ ö
-
+ ´
ç ÷
ç ÷
è ø
UVLO2
ON
3
UVLO1
1.25
R k
V 1.25
0.9 10
R
( )
UVLO1
3
0.5
R k
2.9 10
-
= W
´
LMZ34002
SNVS989A –JULY 2013–REVISED SEPT 2013 www.ti.com
Input Voltage
The LMZ34002 operates over the input voltage range of 4.5 V to 40 V. The maximum input voltage is 40 V,
however, the sum of V
IN
+ |V
OUT
| must not exceed 50 V.
See the Undervoltage Lockout (UVLO) Threshold section of this datasheet for more information.
Undervoltage Lockout (UVLO) Threshold
At turn-on, the V
ON
UVLO threshold determines the input voltage level where the device begins power
conversion. R
UVLO1
and R
UVLO2
set the turn-on threshold as shown in Figure 36. The UVLO threshold is not
present during the power-down sequence. Applications requiring a turn-off threshold must monitor the input
voltage with external circuitry and shut-down using the INH control (see Output On/Off Inhibit (INH)).
The V
ON
UVLO threshold must be set to at least 4.5 V to insure proper start-up and reduce current surges on the
host input supply as the voltage rises. If possible, it is recommended to set the UVLO threshold to
appproximantely 80 to 85% of the minimum expected input voltage.
Use Equation 2 and Equation 3 to calculate the values of R
UVLO1
and R
UVLO2
. V
ON
is the voltage threshold during
power-up when the input voltage is rising. Table 4 lists standard resistor values for R
UVLO1
and R
UVLO2
for
adjusting the V
ON
UVLO threshold for several input voltages.
(2)
(3)
Figure 36. Adjustable VIN UVLO
Table 4. Standard Resistor Values to set V
ON
UVLO Threshold
V
ON
THRESHOLD (V) 4.5 5.0 6.5 8.0 9.0 10.0 15.0 20.0 30.0
R
UVLO1
(kΩ) 174 174 174 174 174 174 174 174 174
R
UVLO2
(kΩ) 63.4 56.2 40.2 31.6 27.4 24.3 15.8 11.5 7.50
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