AP6501

Document number: DS36059 Rev. 1 - 2

9 of 15

www.diodes.com

September 2012

© Diodes Incorporated

AP6501

Applications Information (cont.)

Under Voltage Lockout (UVLO)

Under Voltage Lockout is implemented to prevent the IC from insufficient input voltages. The AP6501 has a UVLO comparator that monitors

the input voltage and the internal bandgap reference. If the input voltage falls below 4.0V, the AP6501 will latch an under voltage fault. In this

event the output will be pulled low and power has to be re-cycled to reset the UVLO fault.

Over Voltage Protection

When the AP6501 FB pin exceeds 20% of the nominal regulation voltage of 0.925V, the over voltage comparator is tripped and the COMP

pin and the SS pin are discharged to GND, forcing the high-side switch off.

Thermal Shutdown

The AP6501 has on-chip thermal protection that prevents damage to the IC when the die temperature exceeds safe margins. It implements a

thermal sensing to monitor the operating junction temperature of the IC. Once the die temperature rises to approximately +160°C, the thermal

protection feature gets activated. The internal thermal sense circuitry turns the IC off thus preventing the power switch from damage.

A hysteresis in the thermal sense circuit allows the device to cool down to approximately +120°C before the IC is enabled again through soft

start. This thermal hysteresis feature prevents undesirable oscillations of the thermal protection circuit.

Setting the Output Voltage

The output voltage can be adjusted from 0.925V to 20V using an external resistor divider. Table 1 shows a list of resistor selection for

common output voltages. Resistor R1 is selected based on a design tradeoff between efficiency and output voltage accuracy. For high

values of R1 there is less current consumption in the feedback network. However the trade off is output voltage accuracy due to the bias

current in the error amplifier. R1 can be determined by the following equation:

⎟⎟

⎠

⎞

⎜⎜

⎝

⎛

−

⋅

=

1

0.925

OUT

V

2

R

1

R

Figure 4. Feedback Divider Network

When output voltage is low, network as shown in Figure 4 is recommended.

Table 1 – Resistor Selection for Common Output Voltages

VOUT (V)

R1 (k

Ω)

R2 (k

Ω)

5

45.3

10

3.3

26.1

10

2.5

16.9

10

1.8

9.53

10

1.2

3

10

Compensation Components

The AP6501 has an external COMP pin through which system stability and transient response can be controlled. COMP pin is the output of

the internal trans-conductance error amplifier. A series capacitor-resistor combination sets a pole-zero combination to control the

characteristics of the control system. The DC gain of the voltage feedback loop is given by:

OUT

V

FB

V

VEA

A

CS

G

LOAD

R

VDC

A

×

×

×

=

Where VFB is the feedback voltage (0.925V), RLOAD is the load resistor value, GCS is the current sense trans-conductance and AVEA is the

error amplifier voltage gain.