Datasheet
UCC28050, UCC28051
UCC38050, UCC38051
SLUS515F−SEPTEMBER 2002 − REVISED MARCH 2009
6
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BLOCK DIAGRAM
UDG−02008
1
2
5
6
7
8
3
4
40 k
W
5 pF
+
+
+
x
x
MULT
2.5 V
2.3 V
+
+
OVP
ENABLE
2.7/2.5 V
gm VOL.
ERROR AMP
0.67/0.57 V
0.23/0.15 V
PWM
SQ
Q
R
+
TIMER
+
V
REF
AND
BIAS REG
V
REF
INT. BIAS
1.7/1.4 V
UVLO
V
REF
GOOD
OVP
V0_SNS
COMP
MULTIN
CS ZCD
GND
DRV
VCCREF
ZERO
POWER
DETECT
PIN DESCRIPTIONS
VO_SNS (Pin 1): This pin senses the boost regulator output voltage through a voltage divider. Internally, this
pin is the inverting input to the transconductance amplifier (with a nominal value of 2.5 V) and also is input to
the OVP comparator. Additionally, pulling this pin below the ENABLE threshold turns off the output switching,
ensuring that the gate drive is held off while the boost output is pre-charging and also ensuring no runaway if
feedback path is open.
COMP (Pin 2): Output of the transconductance error amplifier. Loop compensation components are connected
between this pin and ground. The output current capability of this pin is 10-μA under normal conditions, but
increases to about 1-mA when the differential input is greater than the specified values in the specifications
table. This voltage is one of the inputs to the multiplier, with a dynamic input range of 2.5 V to 3.8 V. During zero
power or overvoltage conditions, this pin goes below 2.5 V nominal. When it goes below 2.3 V, the zero power
comparator is activated which prevents the gate drive from switching.
MULTIN (Pin 3): This pin senses the instantaneous boost regulator input voltage through a voltage divider. The
voltage acts as one of the inputs to the internal multiplier. Recommended operating range is 0 V to 2.5 V at high
line.
PIN DESCRIPTIONS (continued)
CS (Pin 4): This pin senses the instantaneous switch current in the boost switch and uses it as the internal ramp
for PWM comparator. The internal circuitry filters out switching noise spikes without requiring external
components. In addition, an external R-C filter may be required to suppress the noise spikes. An internal clamp
on the multiplier output terminates the switching cycle if this pin voltage exceeds 1.7 V. Additional external
filtering may be required. CS threshold is approximately equal to: