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RC5036
PRODUCT SPECIFICATION
10
Figure 2. RC5036 Block Diagram
LINEAR
ENABLE
SWITCHER
SELECT
I
O
I
ON
CONSTANT ON-TIME
OSCILLATOR
RC5036
gm
gm
V
H
V
L
ANALOG
SWITCH
–
+
VOSW
VOL
+5V
VREF
gm
SWCTRL
LIN_EN
+12V
+12V
REF
High Current Output Drivers
The RC5036 switching high current output driver (SDRV)
contains high speed bipolar power transistors configured in a
push-pull configuration. The output driver is capable of sup-
plying 0.5A of current in less than 100ns. The driver’s power
and ground are separated from the overall chip power and
ground for added switching noise immunity.
Internal Reference
The reference in the RC5036 is a precision band-gap type ref-
erence. Its temperature coefficient is trimmed to provide a near
zero TC. For guaranteed stable operation under all conditions,
a 0.1μF capacitor is recommended on the VREF output pin. No
load may be attached to this pin.
Constant-On-Time Oscillator
The RC5036 switch-mode oscillator is designed as a fixed
on-time, variable off-time oscillator. The constant-on-time
oscillator consists of a comparator, an external capacitor, a
fixed current source, a variable current source, and an analog
switch that selects between two threshold voltages for the
comparator. The external timing capacitor is alternately
charged and discharged through the enabling and disabling of
the fixed current source. The variable current source is con-
trolled from the error inputs that are received from the current
and voltage feedback signals. The oscillator off-time is con-
trolled by the amount of current that is available from the
variable current source to charge the external capacitor up to
the high threshold level of the comparator. The on-time is set
be the constant current source that discharges the external
capacitor voltage down to the lower comparator threshold.
Using SWCTRL and LIM_EN
When the SWCTRL pin is HIGH, the switching regulator
will set its output at 3.5V using two internal precision resis-
tors. When this pin is LOW, the switching regulator output
can be set to any voltage between 1.5V and 3.6V using exter-
nal precision resistors. The LIN_EN pin is used to enable or
disable the linear regulator. When the LIN_EN pin is HIGH,
the linear regulator will be disabled. If this pin is LOW, the
linear regulator output can be set from 1.5V to 3.5V using
external precision resistors. The linear regulator output can
be left on to provide power to other 3.3V components.