MCP19111 datasheet(16/222 Pages) MICROCHIP

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MCP19111

DS22331A-page 16

 2013 Microchip Technology Inc.

Individual control of the HDRV or LDRV signal is

accomplished by setting or clearing the HIDIS or

LODIS bits in the ATSTCON register. When either

driver is disabled, the output signal is set low.

3.3

Output Voltage

The output voltage is configured by the settings

contained in the OVCCON and OVFCON registers. No

external resistor divider is needed to set the output

voltage. Refer to Section 6.10 “Output Voltage

Configuration”.

The MCP19111 contains a unity gain differential

amplifier used for remote sensing of the output voltage.

Connect the +VSEN and -VSEN pins directly at the load

for better load regulation. The +VSEN and -VSEN are the

positive and negative inputs, respectively, of the

differential amplifier.

3.4

Switching Frequency

The switching frequency is configurable over the range

of 100 kHz to 1.6 MHz. The Timer2 module is used to

generate the HDRV/LDRV switching frequency. Refer

to Section 26.0 “PWM Module” for more information.

Example 3-1 shows how to configure the MCP19111

for a switching frequency of 300 kHz.

EXAMPLE 3-1:

CONFIGURING FSW

3.5

Compensation

The MCP19111 is an analog peak current mode

controller with integrated adjustable compensation.

The CMPZCON register is used to adjust the

compensation zero frequency and gain. Figure 3-1

shows the internal compensation network with the

output differential amplifier.

FIGURE 3-1:

SIMPLIFIED INTERNAL

COMPENSATION

3.6

Slope Compensation

In current mode control systems, slope compensation

needs to be added to the control path to help prevent

subharmonic oscillation when operating with greater

than 50% duty cycle. In the MCP19111, a negative

slope is added to the error amplifier output signal

before it is compared to the current sense signal. The

amount

slope

added

controlled

the

SLPCRCON register, Register 6-7.

The amount of slope compensation added should be

equal to the inductor current down slope during the

high-side off time.

3.7

Current Sense

The output current is differentially sensed by the

MCP19111. The sense element can be either a resistor

placed in series with the output, or the series resistance

of the inductor. If the inductor series resistance is used,

a filter is needed to remove the large AC component of

the voltage that appears across the inductor and leave

only the small AC voltage that appears across the

inductor resistance, as shown in Figure 3-2. This small

AC voltage is representative of the output current.

FIGURE 3-2:

INDUCTOR CURRENT

SENSE FILTER

BANKSEL

T2CON

CLRF

T2CON

;Turn off Timer2

CLRF

TMR2

;Initialize module

MOVLW

0x19

;Fsw=300 kHz

MOVWF

PR2

MOVLW

0x0A

;Max duty cycle=40%

MOVWF

PWMRL

MOVLW

0x00

;No phase shift

MOVWF

PWMPHL

MOVLW

0x04

;Turn on Timer2

MOVWF

T2CON

Note 1: To

enable

the

slope

compensation

circuitry, the ABECON<SLCPBY> bit

must be cleared.

VREF

+VSEN

-VSEN

To Load

-ISEN

+ISEN

HDRV

LDRV

PHASE

LRL

VIN

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