Datasheet

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 +V
SEN
and -V
SEN
pins directly at the load
for better load regulation. The +V
SEN
and -V
SEN
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 F
SW
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 of slope added is controlled by 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.
V
REF
+V
SEN
-V
SEN
To Load
-I
SEN
+I
SEN
HDRV
LDRV
PHASE
LR
L
C
S
R
S
V
IN