lt3692a Linear Technology Corporation, lt3692a Datasheet - Page 28

• Manufacturer Part Number: lt3692a
• Description: Monolithic Dual Tracking 3.5a Step-down Switching Regulator
• Manufacturer: Linear Technology Corporation

LT3692A
Die Temperature and Thermal Shutdown
The LT3692A T
internal junction temperature. The T
250mV for 25°C and has a slope of 10mV/°C. Without the
aid of external circuitry, the T
to 150°C (200mV to 1.5V) with a maximum load of 100μA.
Full Temperature Range Measurement
To extend the operating temperature range of the T
put below 20°C, connect a resistor from the T
negative supply as shown in Figure 20. The negative rail
voltage and T
following equations:
where:
For example:
APPLICATIONS INFORMATION
28
TEMP(MIN)°C is the minimum temperature where a
valid T
V
TEMP(MIN)°C = –40°C
V
V
R1≤
V
NEG
NEG
NEG
NEG
Figure 20. Circuit to Extend the T
= Regulated negative voltage supply.
≤ –0.8V
= –1, R1 ≤ |V
33μA
≤
V
J
NEG
pin output is required.
2 • TEMP(MIN)°C
J
J
pin resistor may be calculated using the
pin outputs a voltage proportional to the
100
LT3692A
NEG
GND
|/33μA = 30.2kΩ
T
J
J
pin output is valid from 20°C
R1
3692 F20
J
Pin Operating Range
J
+
V
pin typically outputs
NEG
J
pin to a
J
out-
Generating a Negative Regulated Voltage
The simple charge pump circuit in Figure 21 uses the
CLKOUT pin output to generate a negative voltage, elimi-
nating the need for an external regulated supply. Surface
mount capacitors and dual-package Schottky diodes
minimize the board area needed to implement the nega-
tive voltage supply.
As a safeguard, the LT3692A has an additional thermal
shutdown threshold set at a typical value of 163°C for each
channel. Each time the threshold is exceeded, a power on
sequence for that channel will be initiated. The sequence
will then repeat until the thermal overload is removed.
It should be noted that the T
a steady-state temperature and should not be used to
guarantee that maximum junction temperatures are
not exceeded. Instantaneous power along with thermal
gradients and time constants may cause portions of the
die to exceed maximum ratings and thermal shutdown
thresholds. Be sure to calculate die temperature rise for
steady state (>1Min) as well as impulse conditions.
Figure 21. Circuit to Generate the Negative Voltage Rail to
Extend the T
D3, D4: ZETEX BAT54S
J
Pin Operating Range
LT3692A
GND
CLKOUT
T
J
330pF
30k
J
D3
pin voltage represents
D4
3692 F21
0.1μF
3692af