Datasheet

DEVICE INFORMATION
ZCDA
VREF
GDA
PGND
VCC
GDB
CS
PWMCNTL
ZCDB
VSENSE
TSET
PHB
COMP
AGND
VINAC
HVSEN
1
2
3
4
5
6
7
8
16
15
14
13
12
11
10
9
UCC28061
www.ti.com .............................................................................................................................................................. SLUS837A – JUNE 2008 – REVISED JULY 2009
UCC28061D
SOIC 16-Pin (D)
Top View
TERMINAL FUNCTIONS
TERMINAL
DESCRIPTION
NAME NO. I/O
Analog ground: Connect analog signal bypass capacitors, compensation components, and analog
AGND 6 — signal returns to this pin. Connect the analog and power grounds at a single point to isolate high-current
noise signals of the power components from interference with the low-current analog circuits.
Error amplifier output: The error amplifier is a transconductance amplifier, so this output is a
high-impedance current source. Connect voltage regulation loop compensation components from this
pin to AGND. The on-time seen at the gate drive outputs is proportional to the voltage at this pin minus
an offset of approximately 125 mV. During soft-start events (undervoltage, brownout, disable or output
COMP 5 O
over voltage), COMP is pulled low. Normal operation only resumes after the soft-start event clears and
COMP has been discharged below 0.5 V, making sure that the circuit restarts with a low COMP voltage
and a short on-time. Do not connect COMP to a low-impedance source that would interfere with COMP
falling below 0.5 V.
Current sense input: Connect the current sense resistor and the negative terminal of the diode bridge
to this pin. Connect the return of the current sense resistor to the AGND pin with a separate trace. As
input current increases, the voltage on CS goes more negative. This cycle-by-cycle over-current
protection limits input current by turning off both gate driver (GDx) outputs when CS is more negative
than the CS rising threshold (approximately – 200 mV). The GD outputs remain low until CS falls to the
CS 10 I CS falling threshold (approximately – 15 mV). Current sense is blanked for approximately 100 ns
following the falling edge of either GD output. This blanking filters noise that occurs when current
switches from a power FET to a boost diode. In most cases, no additional current sense filtering is
required. If filtering is required, the filter series resistance must be under 100 Ω to maintain accuracy. To
prevent excessive negative voltage on the CS pin during inrush conditions, connect the current sensing
resistor to the CS pin through a low value external resistor.
GDA 14 O Channel A and channel B gate drive output: Connect these pins to the gate of the power FET for
each phase through the shortest connection practical. If it is necessary to use a trace longer than 0.5
inch (12.6 mm) for this connection, some ringing may occur due to trace series inductance. This ringing
GDB 11 O
can be reduced by adding a 5- Ω to 10- Ω resistor in series with GDA and GDB.
High voltage output sense: The UCC28061 incorporates FailSafe OVP so that any single failure does
not allow the output to boost above safe levels. Output over-voltage is monitored by both VSENSE and
HVSEN and shuts down the PWM if either pin exceeds the appropriate over-voltage threshold. Using
two pins to monitor for over-voltage provides redundant protection and fault tolerance. HVSEN can also
be used to enable a downstream power converter when the voltage on HVSEN is within the operating
HVSEN 8 I
region. Select the HVSEN divider ratio for the desired over-voltage and power-good thresholds. Select
the HVSEN divider impedance for the desired power-good hysteresis. During operation, HVSEN must
never fall below 0.8 V. Dropping HVSEN below 0.8 V puts the UCC28061 into a special test mode, used
only for factory testing. A bypass capacitor from HVSEN to AGND is recommended to filter noise and
prevent false over-voltage shutdown.
Power ground for the integrated circuit: Connect this pin to AGND through a separate short trace to
PGND 13 —
isolate gate driver noise from analog signals.
Phase B enable: This pin turns on/off channel B of the boost converter. The commanded on-time for
channel A is immediately doubled when channel B is disabled, which helps to keep COMP voltage
PHB 4 I constant during the phase management transient. The PHB pin allows the user to add external phase
management circuitry if they desire. To disable phase management, connect the PHB pin to the VREF
pin.
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Product Folder Link(s): UCC28061