Step-up DC/DC Controller

EC9215

Page 13 of 15

5J15N-Rev.F001

Output Circuit

The output circuit is a typical push‐ pull configuration to drive an external NMOS transistor directly.

It can provide a 200mA source/sink to/from OUT (pin 5).

Soft-Start and Short Circuit Detection

Soft-start operation is set by connecting capacitor CSCP to the SCP pin (pin 2).Soft-start prevents

a current spike on start-up. On completion of the soft‐ start operation, the SCP pin (pin 2)

stays low and enters the short circuit detection wait state. When an output short circuit

occurs, the error amplifier output is fixed at 1.8V and capacitor CSCP starts charging.

After charging to approximately 0.8 V, the output pin (pin5) is set low and the SCP pin stays low.

Once the protection circuit operates, the circuit can be restored by resetting the power supply.

Short circuit detection time can be calculate as below:

Under-Voltage Lock Out (UVLO)

Transients during powering on or instantaneous glitches in the supply voltage can cause

system damage or failure. The circuit prevents malfunction at low input voltage detects a low

input voltage by comparing the supply voltage with the internal reference voltage. On detection,

the circuit fixes the output pin to low. The system recovers when the supply voltage rises back

above the threshold voltage of thermal function prevention circuit.

Layout Consideration

Switching Noise Decoupling Capacitor

A 0.1uF ceramic capacitor should be placed close to the VOUT pin and the GND pin of the chip to

filter the switching spikes in the output voltage monitored by the VOUT pin.

Feedback Network

The feedback networks should be connected directly to a dedicated analog ground plane and

this ground plane must connect to the GND pin. If no analog ground plane is available,

and then this ground must tie directly to the GND pin. The feedback network, resistors R2

and R3, should be kept close to the FB pin, and away from the inductor.

Input Capacitor

The input capacitor CIN in VIN must be placed close to the IC. This will reduce copper trace

resistance which effects input voltage ripple of the IC. For additional input voltage filtering, a 1uF

to the ground.