10
P
F
FB
FB
PGND
SGND
EN
10
P
F
R
T
R
B
C
VC
V
CON
V
IN
V
REF
V
OUT
C
IN
C
OUT
LMZ10500
SNVS723C – OCTOBER 2011 – REVISED MARCH 2013
www.ti.com
THERMAL OVERLOAD PROTECTION
The junction temperature of the LMZ10500 should not be allowed to exceed its maximum operating rating of
125°C. Thermal protection is implemented by an internal thermal shutdown circuit which activates at 150°C (typ).
When this temperature is reached, the device enters a low power standby state. In this state switching remains
off causing the output voltage to fall. Also, the V
CON
capacitor is discharged to SGND. When the junction
temperature falls back below 130 °C (typ) normal startup occurs and V
OUT
rises smoothly from 0V. Applications
requiring maximum output current may require derating at elevated ambient temperature. See the
Typical
Performance Characteristics
section for thermal derating plots for various output voltages.
Application Information
Figure 38. Typical Application Circuit
SETTING THE OUTPUT VOLTAGE
The LMZ10500 provides a fixed 2.35V V
REF
voltage output. As shown in
Figure 38
above, a resistive divider
formed by R
T
and R
B
sets the V
CON
pin voltage level. The V
OUT
voltage tracks V
CON
and is governed by the
following relationship:
V
OUT
= GAIN x V
CON
where
•
GAIN is 2.5V/V from V
CON
to V
FB
.
(1)
This equation is valid for output voltages between 0.6V and 3.6V and corresponds to V
CON
voltage between
0.24V and 1.44V, respectively.
R
T
and R
B
Selection for Fixed V
OUT
The parameters affecting the output voltage setting are the R
T
, R
B
, and the product of the V
REF
voltage x GAIN.
The V
REF
voltage is typically 2.35V. Since V
CON
is derived from V
REF
via R
T
and R
B
,
V
CON
= V
REF
x R
B
/ (R
B
+ R
T
)
(2)
After substitution,
V
OUT
= V
REF
x GAIN x R
B
/ (R
B
+ R
T
)
(3)
R
T
= ( GAIN x V
REF
/ V
OUT
– 1 ) x R
B
(4)
The ideal product of GAIN x V
REF
= 5.875V.
Choose R
T
to be between 80k
Ω
and 300k
Ω
. Then, R
B
can be calculated using
Equation 5
below.
R
B
= ( V
OUT
/ (5.875V – V
OUT
) ) x R
T
(5)
Note that the resistance of R
T
should be
≥
80k
Ω
. This ensures that the V
REF
output current loading is not
exceeded and the reference voltage is maintained. The current loading on V
REF
should not be greater than 30
µA.
16
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