TPS2320, TPS2321
DUAL HOT SWAP POWER CONTROLLER
WITH INDEPENDENT CIRCUIT BREAKER
SLVS276A – MARCH 200 – REVISED APRIL 2000
17
POST OFFICE BOX 655303 • DALLAS, TEXAS 75265
APPLICATION INFORMATION
gate-drive circuitry
The TPS2320/TPS2321 includes four separate features associated with each gate-drive terminal:
D
A charging current of approximately 15 µA is applied to enable the external MOSFET transistor. This current
is generated by an internal charge pump that can develop a gate-to-source potential (referenced to DISCH1
or DISCH2) of 9 V–12 V. DISCH1 and DISCH2 must be connected to the respective external MOSFET
source terminals to ensure proper operation of this circuitry.
D
A discharge current of approximately 75 µA is applied to disable the external MOSFET transistor. Once the
transistor gate voltage has dropped below approximately 1.5 V, this current is disabled and the UVLO
discharge driver is enabled instead. This feature allows the part to enter a low-current shutdown mode while
ensuring that the gates of the external MOSFET transistors remain at a low voltage.
D
During a UVLO condition, the gates of both MOSFET transistors are pulled down by internal PMOS
transistors. These transistors continue to operate even if IN1 and IN2 are both at 0 V . This circuitry also helps
hold the external MOSFET transistors off when power is suddenly applied to the system.
D
During an overcurrent fault condition, the external MOSFET transistor that exhibited an overcurrent
condition will be rapidly turned off by an internal pulldown circuit capable of pulling in excess of 400 mA (at
4 V) from the 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 will be turned off rapidly . The other channel
will continue 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:
I
LMT1
+
R
ISET1
50
10
–6
R
ISENSE1
Typically R
ISENSE1
is very small (0.001 Ω to 0.1 Ω). 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 2 shows some of the current sense
resistors available in the market.
T able 2. Some Current Sense Resistors
CURRENT RANGE
(A)
PART NUMBER DESCRIPTION MANUFACTURER
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
4 to 6 WSL-2010, 0.010 1% 0.010 Ω, 0.5 W, 1% resistor