TPS5120

DUAL OUTPUT, TWOPHASE SYNCHRONOUS BUCK DC/DC CONTROLLER

SLVS278E – AUGUST 2000 – REVISED MARCH 2003

6

POST OFFICE BOX 655303

detailed description (continued)

current protection

Overcurrent protection is achieved by comparing the drain-to-source voltage of the high-side and low-side

TRIP1 or TRIP2 terminals. If the drain-to-source voltage up exceeds the set-point voltage during high-side

conduction, the current limit circuit terminates the high-side driver pulse. If the set-point voltage is exceeded

during low-side conduction, the low-side pulse is extended through the next cycle. Together this action has the

effect of decreasing the output voltage until the undervoltage protection circuit is activated and the fault latch

is set and both the high and low-side MOSFET drivers are shut off.

overvoltage protection

For overvoltage protection (OVP), the TPS5120 monitors INV pin voltage. When the INV voltage is higher than

0.95 V (+12%), the OVP comparator output goes high and the FLT timer starts to charge an external capacitor

connected to FLT. After a set time, the FLT circuit latches the MOSFET drivers off.

undervoltage protection

For undervoltage protection (UVP), the TPS5120 monitors INV pin voltage. When the INV voltage is lower than

0.68 V (–19.4%), the OVP comparator output goes high, and the FLT timer starts to charge an external capacitor

connected to FLT. Also, when the current comparator triggers the OCP, the UVP comparator detects the under

voltage output and starts the FLT capacitor charge. After a set time, the FLT circuit latches off all of the MOSFET

drivers.

FLT

When an OVP or UVP comparator output goes high, the FLT circuit starts to charge the FLT capacitor. If the

FLT pin voltage goes beyond a constant level, the TPS5120 latches the MOSFET drivers. At this time, the state

of MOSFET is different depending on the OVP alert and the UVP alert. Also, the enable time used to latch the

MOSFET driver is decided by the capacity of the FLT capacitor. The charging constant current value is also

different depending on whether it is an OVP alert or a UVP alert. The difference is shown in the following

equation:

FLT source current (OVP) = FLT source current (UVP)

× 5

shutdown

The TPS5120 can be shut down by grounding STBY1, STBY2, and 5V_STBY. The shutdown current is as low

as 1

µA.

UVLO

When the input voltage goes up to about 4 V, the TPS5120 is operational. When the input voltage is lower than

the turnon value, the device is turned off. The typical hysteresis voltage is 40 mV.

phase Inverter

Phase inverter controls the phase of SMPS1 and SMPS 2. SMPS1 operates in phase with the OSC. SMPS2

operates 180

° out of phase from SMPS1. This allows smaller input capacitors to be used.

oscillator

TPS5120 has a triangle oscillator generator internal to the IC. The oscillation frequency is set by the size of the

capacitor connected to the CT pin. The voltage amplitude is 0.43 V ~ 1.17 V.