NCP4371
www.onsemi.com
9
APPLICATION INFORMATION
The NCP4371 is designed to operate as an output voltage
and current controller for USB chargers, which resides on
the secondary side of the off−line adapter. It enables to
accommodate the output voltage based on the request from
the portable device in order to optimize the battery charge
time. The NCP4371 is compatible with Qualcomm Quick
Charge 3.0 HVDCP specification. The output voltage can be
increased or decreased in discrete steps. The output current
is limited not to exceed the maximum power limit for given
output voltage level. The internal discharge switch
discharges the output capacitors to a safe voltage level in a
case of the cable unplug.
Voltage Regulation
The Voltage Regulation Path eliminates a need for a voltage
shunt regulator at the secondary side of the off−line supply.
The voltage on VCC pin is divided by internal resistor divider
(R
VSNS_UP
, R
VSNS_DWN
) and compared with the internal
precise voltage reference V
REFV
. The voltage difference is
amplified by g
mV
of the transconductance amplifier. The
amplifier output current is connected to the DRIVE pin. This
DRIVE pin drives regulation optocoupler that provides
regulation of primary side. The internal voltage reference
V
REFV
is adjustable based on the command from the Portable
Device compatible with Qualcomm Quick Charge
specification. The voltage control loop compensation
network shall be connected between DRIVE and COMP pins.
Current Regulation
The output current is sensed by the shunt resistor
R_SENSE in series with the load. Voltage drop on
R_SENSE is compared with internal precise voltage
reference V
REFC
at ISNS transconductance amplifier input.
Voltage difference is amplified by g
mC
to output current of
amplifier, connected to the DRIVE pin.
HVDCP Mode
After power−up pins D+ and D− of NCP4371 are shorted
with impedance
R
DCP_DAT
and internal reference voltage
V
REFV
is set to V
BUS
voltage 5 V. The device is in a BC1.2
compatible mode. If a portable device compatible with the
Qualcomm Quick Charge specification is connected a
negotiation between HVDCP and PD is executed. Once the
negotiation is successful the NCP4371 opens D+ and D−
short connection and D− is pulled down with a
R
DM_DWN.
The
NCP4371 enters HVDCP mode. It monitors D+ and D−
inputs. Based on the specified control patterns the internal
voltage reference value V
REFV
is adjusted in order to
increase or decrease output voltage to the required value.
The NCP4371 is available in Class A and Class B version.
Class A allows to change the output voltage up to
V
BUS
= 12 V. Class B allows output voltage up to 20 V. If
the unplug event is detected the decoder circuitry turns−on
an internal current sink, which discharges the output
capacitors to a safe voltage level. If the NCP4371 is set to a
Continuous mode it responds to the PD requests in a Single
request mode. It does not support Group request mode.
Table 4. D+ AND D− OUTPUT VOLTAGE CODING
Portable Device HVDCP Class A HVDCP Class B
D+ D− Adapter Voltage Adapter Voltage
0.6 V 0.6 V 12 V 12 V
3.3 V 0.6 V 9 V 9 V
0.6 V 3.3 V Continuous mode Continuous mode
3.3 V 3.3 V Previous voltage 20 V
0.6 V GND 5 V 5V
D+
D−
DP_SEL_REF
DM_SEL_REF
DP_DAT_REF
DM_DAT_REF
Figure 16. HVDCP D+ and D− Comparators
R
DAT_LKG
R
DM_DWN
V
SEL_REF
V
DAT_REF
V
DAT_REF
V
SEL_REF
HVDCP Mode – Continuous Mode
The continuous mode of operation leverages the
previously unused state in QC2.0. If the portable devices try
and utilize this mode, it applies voltages on D+ and D− per
Table 4. Assuming the HVDCP supports this mode of
operation, it will glitch filter the request as it currently does,
using T
GLITCH_V_CHANGE
. Before the portable device can
begin to increment or decrement the voltage, it must wait
T
V_NEW_REQUEST_CONT
before pulling D+ and D− high or
low. Once this time has finished, the portable device now
attempts to increment or decrement the voltage. To
increment, the portable device sends a pulse of width
T
ACTIVE
by pulling D+ to V
DP_UP
and then must return D+
to V
DP_SRC
for T
INACTIVE
.
The NCP4371 responds to the increment/decrement
request in a single request mode, i.e. the output voltage is
changed immediately with each request. For the single
request, and HVDCP recognizes a rising edge on D+ for an
increment, and falling edge on D− for a decrement, and
glitch filters this with T
GLITCH_CONT_CHANGE
. After this
period, it begins changing its output voltage by incrementing
or decrementing in a 200 mV step. The output voltage is at
its final value within T
V_CONT_CHANGE_SINGLE
.
