Datasheet

R
VSENSE1_TOP
+
V
O1_min
* 1.225
1.225
R
VSENSE1_BOT
I
LMT1
+
R
ISET1
50 10
–6
R
ISENSE1
TPS2300
TPS2301
www.ti.com SLVS265H –FEBRUARY 2000–REVISED JULY 2013
pin. Once the gate has been pulled below approximately 1.5 V, this driver is disengaged and the UVLO driver
is enabled instead. If one channel experiences an overcurrent condition and the other does not, then only the
channel that is conducting excessive current is turned off rapidly. The other channel continues to operate
normally.
SETTING THE CURRENT-LIMIT CIRCUIT-BREAKER THRESHOLD
Using channel 1 as an example, the current sensing resistor R
ISENSE1
and the current limit setting resistor R
ISET1
determine the current limit of the channel, and can be calculated by the following equation:
(2)
Typically R
ISENSE1
is usually very small (0.001Ω to 0.1Ω). If the trace and solder-junction resistances between the
junction of R
ISENSE1
and ISENSE1 and the junction of R
ISENSE1
and R
ISET1
are greater than 10% of the R
ISENSE1
value, then these resistance values should be added to the R
ISENSE1
value used in the calculation above.
The above information and calculation also apply to channel 2. Table 4 shows some of the current sense
resistors available in the market.
Table 4. Some Current Sense Resistors
CURRENT RANGE
PART NUMBER DESCRIPTION MANUFACTURER
(A)
0 to 1 WSL-1206, 0.05 1% 0.05 Ω, 0.25 W, 1% resistor
1 to 2 WSL-1206, 0.025 1% 0.025 Ω, 0.25 W, 1% resistor
2 to 4 WSL-1206, 0.015 1% 0.015 Ω, 0.25 W, 1% resistor
Vishay Dale
4 to 6 WSL-2010, 0.010 1% 0.010 Ω, 0.5 W, 1% resistor
6 to 8 WSL-2010, 0.007 1% 0.007 Ω, 0.5 W, 1% resistor
8 to 10 WSR-2, 0.005 1% 0.005 Ω, 0.5 W, 1% resistor
SETTING THE POWER-GOOD THRESHOLD VOLTAGE
The two feedback resistors R
VSENSEx_TOP
and R
VSENSEx_BOT
connected between V
Ox
and ground form a resistor
divider setting the voltage at the VSENSEx pins. VSENSE1 voltage equals:
V
I(SENSE1)
= V
O
× R
VSENSE1_BOT
/(R
VSENSE1_TOP
+ R
VSENSE1_BOT
)
This voltage is compared to an internal voltage reference (1.225 V ±2%) to determine whether the output voltage
level is within a specified tolerance. For example, given a nominal output voltage at V
O1
, and defining V
O1_min
as
the minimum required output voltage, then the feedback resistors are defined by:
(3)
Start the process by selecting a large standard resistor value for R
VSENSE1_BOT
to reduce power loss. Then
R
VSENSE1_TOP
can be calculated by inserting all of the known values into the equation above. When V
O1
is lower
than V
O1_min
, PWRGD1 is low as long as the controller is enabled.
UNDERVOLTAGE LOCKOUT (UVLO)
The TPS2300/01 includes an undervoltage lockout (UVLO) feature that monitors the voltage present on the
VREG pin. This feature disables both external MOSFETs if the voltage on VREG drops below 2.78 V (nominal)
and re-enables normal operation when it rises above 2.85 V (nominal). Since VREG is fed from IN1 through a
low-dropout voltage regulator, the voltage on VREG tracks the voltage on IN1 within 50 mV. While the
undervoltage lockout is engaged, both GATE1 and GATE2 are held low by internal PMOS pulldown transistors,
ensuring that the external MOSFET transistors remain off at all times, even if all power supplies have fallen to
0V.
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