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RC5037
PRODUCT SPECIFICATION
2
P
Functional Description
The RC5037 contains a precision trimmed zero TC voltage
reference, a constant-on-time architecture controller, a high
current output driver, and a low offset op-amp. The detailed
block diagram in Figure 1 shows how the RC5037 works
together with external components to achieve a high-perfor-
mance switching power supply.
Switch-Mode Control Loop
The main control loop for the switch-mode converter
consists of a current conditioning amplifier and a voltage
conditioning amplifier. The voltage amplifier compares the
voltage from the internal reference with the converter’s out-
put voltage divided by an internal resistor divider. The cur-
rent amplifier senses the current by comparing the voltages
at the IFBH and IFBL pins, which are attached to either side
of the current sense resistor. The signals from the voltage and
current amplifiers are summed together, the result being use
to control the off-time of the oscillator. The current feedback
signal is also used as part of the RC5037 short-circuit
protection.
High Current Output Drivers
The RC5037 high current output driver (SDRV) contains
high speed bipolar power transistors configured in a
push-pull configuration. The output driver is capable of
supplying 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 RC5037 is a precision band-gap type
reference. Its temperature coefficient is trimmed to provide a
near zero TC.
Constant-On-Time Oscillator
The RC5037 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
controlled from the error inputs that are received from the
current and voltage feedback signals. The oscillator off-time
is controlled 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 by the constant current source that discharges the exter-
nal capacitor voltage down to the lower comparator
threshold.
Figure 1. RC5037 Detailed Block Diagram
I
O
I
ON
Constant On-Time Oscillator
gm
gm
V/I
V
H
V
L
V/I
VOUT
+5V
VCCA
IFBL
IFBH
VCCP
FBSW
SDRV
GNDP
CEXT
65-5037-07
+12V
REF
6
5
1
2
4
3
8
7