Datasheet

 2010-2013 Microchip Technology Inc. DS22260C-page 9
MTS62C19A
3.2 PWM Current Control
The current level in each motor winding is controlled by
a PWM circuit with a fixed T
OFF
time. The load current
flowing in the winding is sensed through an external
sensing resistor R
S
, connected between the power
bridge's source pin SENSE (sources of transistors Na
and Nb) and GND.
FIGURE 3-2: PWM Current Control Circuit Principle (Channel 1 Shown).
The voltage across R
S
is compared to a fraction of the
reference voltage V
REF
, chosen with the logic input bits
I0 and I1 (Table 3-3). The power bridge, and thus the
load current, can also be switched off completely when
both logic inputs are high. Note that any logic input left
unconnected will be treated as a high level (pull-up
resistor).
The maximum trip current for regulation, given for
I0 I1 = 00 is calculated in Equation 3-1.
EQUATION 3-1:
V
LOAD
SENSE
V
REF
I0
I1
COMPIN
C
C
R
C
C
t
R
t
R
S
RC
÷10
One-Shot
Source
Disable
Power
Bridge
Pa
Pb
Na
Nb
OUTA
OUTB
I
MAX
V
REF
10 R
S

------------------=
TABLE 3-3: CURRENT LEVEL CONTROL TRUTH TABLE
I0 I1 Comp. Trip Voltage Output Current
00V
TRIP
= 1/10 x V
REF
I
MAX
= V
REF
/10R
S
10V
TRIP
= 1/15 x V
REF
2/3 x I
MAX
= V
REF
/15R
S
01V
TRIP
= 1/30 x V
REF
1/3 x I
MAX
= V
REF
/30R
S
1 1 x 0 (no current)