TMC249 / TMC249A DATA SHEET (V2.10 / 2011-Aug-10)
10
Using additional Power Drivers
For higher voltage and higher output current it is possible to add external MOSFET gate drivers. Both,
dedicated transistor drivers are suitable, as well as a circuit based on standard HCMOS drivers. It is
important to understand the function of dedicated gate drivers for N-channel transistors: Since the
chopping also can be stopped in open load conditions, the gate drive circuit for the upper transistors
should allow for continuous ON conditions. In the schematic below this is satisfied by attaching a weak
additional charge pump oscillator and pumping the VS up to the high voltage supply. Do not enable the
TMC249, before the gate driver capacitors are charged to an appropriate voltage. A current sensing
comparator in the VM line pulling down the VT pin by some 100mV on overcurrent can be added, if
required. Since the TMC249 in this application can not sense switch-off of the transistor gates to
ensure break-before-make operation, the break before-make-delays have to be set by capacitive
loading of its transistor drive outputs. The capacitors CdHS and CdLS are charged / discharged with
the nominal gate current. The opposite output is not enabled, before the switching-off output has been
discharged to 0.5V. To calculate the timing, refer to the required logic levels of the attached power
driver, resp. the attached PMOS. For CdHS and CdLS 470pF give about 100ns. Both circuits do not
show decoupling capacitors and further details.
+12V
VS
to other
bridges
VT
+VM e.g. 50V
C-Pump
20kHz
ICM7555
CDHS
470p
High current, high
voltage MOS, e.g.
SI4450
1µF
22K
HA1
2n2
12V
small signal P-
MOS, e.g. BSS84
HS-Driver
N
N
N
N
390R
TMC249/
TMC239
Coil
LA1
LS-
Driver
390R
CDLS
470p
IR2101
SRA
RS
100R
4.7nF
opt.
SLP
10K
Set HS and LS
current to 10mA
+VS 7..15V
+VM 20..60V
VS
VT
VCC
High voltage logic
level MOS bridge
1K
120R
ADJ
1/2 74HC244
on high side
P
P
1K
100R
CDHS
390R
HA1
/OE
LM337
HV
GND
VCC
55V low current
N-MOS
OUT
VM-5.2V
+5V
Coil
IN
TMC249/
TMC239
1/2 74HC244
on low side
LA1
N
N
1K
100R
CDLS
/OE
GND
SRA
SLP
RS
set to 7 mA high-
side drive current
15K
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TRINAMIC [ TRINAMIC MOTION CONTROL GMBH & CO. KG. ]
