MCP1633 datasheet(18/31 Pages) MICROCHIP

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MCP1633

DS20006289A-page 18

 2020 Microchip Technology Inc.

FIGURE 4-6:

Current Sense Amplifier Gain Set.

4.8

PWM Dimming

MCP1633 incorporates a high-performance dimming

mechanism. External PWM signal is used to modulate

the output current. Internally this signal in low state dis-

able the main driver (VEXT), disconnects the output of

error amplifier and disconnects the load (SDRV set low)

to maintain the steady state condition at the next

transition. When DIMM pin is high state the driver is

enabled, output of error amplifier is reconnected and

SDRV pin is set high. When dimming is not required,

connect the DIMM pin to the VCC pin. An internal pull-

down resistor sets the input to logic-low and disables

the device when the pin is floating. The SDRV pin is the

output of a secondary driver which controls a NMOS

transistor for dimming and is capable of sinking and

sourcing up to 50 mA of peak current. To ensure that

the applied dimming-pulse duration matches the

effective dimming-pulse duration, it is recommended to

synchronize the dimming pulses with the switching

clock of the controller.

4.9

Undervoltage Lockout (UVLO)

When the input voltage (VIN) is less than the UVLO

threshold, the VEXT is held in low state. This will ensure

that, if the voltage is not adequate to power the

MCP1633 device, the main power supply switch will be

held in off state. In order to prevent oscillations when

the input voltage is near the UVLO threshold, the UVLO

circuit offers 100 mV (typical) hysteresis. Typically, the

MCP1633 device will not start until the input voltage at

VIN is between 2.8V and 2.9V (typical).

4.10

Overtemperature Protection

To protect the VEXT output if shorted to VIN or GND, the

VEXT output of the MCP1632 device will be high-imped-

ance if the junction temperature is above the thermal

shutdown threshold. An internal 10 kΩ pull-down

resistor is connected from VEXT to ground to provide

some pull-down during overtemperature conditions.

The protection is set to +150°C (typical), with a

hysteresis of +20°C.

4.11

Overvoltage Protection

The OVP pin is a comparator used to prevent the power

system from being damaged when the load is discon-

nected. By comparing the divided down power train

output voltage with a 1.23V internal reference voltage,

the MCP1633 VEXT output switching is interrupted and

load disconnected when the output voltage is above a

pre-set value. This limits the output voltage of the

power train and the low comparator's hysteresis will

operate as a ripple regulator.

ISN

ISP

IOUT

GAIN

2R1



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