CS1630/31
A current proportional to the AC input voltage is supplied to the
IC on pin IAC and is used by the boost control algorithm.
5.6.1 Maximum Peak Current
The maximum boost inductor peak current is configured by
adjusting the peak switching current with IPK(code). The
PEAK_CUR register (see "Peak Current (PEAK_CUR) –
Address 51" on page 39) is used to store IPK(code). Maximum
power output is proportional to IPK(code), as shown in
Equation 3:
Vrect
R3
IAC
RIA C
R4
CS1630 /31
IPK VRMStyp
Iref
[Eq.3]
-----------------------------------------------
=
PINmax
15k
2
IAC
2
ADC
where,
12
= correction term = 0.55
VRMS(typ) = nominal operating input RMS voltage
Figure 13. IAC Input Pin Model
IPK = IPK(code) 4.1mA
Resistor RIAC sets the IAC current and is derived from
Equation 5:
5.6.2 Output BSTOUT Sense & Input IAC
Sense
RIAC = RBST
[Eq.5]
A current proportional to boost output voltage VBST is supplied
to the IC on pin BSTOUT and is used as a feedback control
signal. The ADC is used to measure the magnitude of the
IBSTOUT current through resistor RBST. The magnitude of the
IBSTOUT current is then compared to an internal reference
current (Iref) of 133A.
For optimal performance, resistors RIAC and RBST should use
1% tolerance or better resistors for best VBST voltage
accuracy.
5.6.3 Boost Auxiliary Winding
The boost auxiliary winding is used for zero-current detection
(ZCD). The voltage on the auxiliary winding is sensed through
the BSTAUX pin of the IC. It is also used to deliver startup
current during startup time (see "Startup Circuit" on page 12).
VBST
R8
IBSTOUT
RBST
5.6.4 Boost Overvoltage Protection
R9
CS1630 /31
The CS1630/31 supports boost overvoltage protection (BOP)
to protect the bulk capacitor C8 (see Figure 14). If the boost
output voltage exceeds the overvoltage protection thresholds
programmed in the OTP registers a BOP fault signal is
generated. The voltage level, VBOP(th), can be set within 227V
to 257V for a CS1630 and 432V to 462V for a CS1631 (see
"Configuration 53 (Config53) – Address 85" on page 45). The
control logic continuously averages the BOP fault signal using
a leaky integrator. When the output of the leaky integrator
exceeds a certain threshold, which can be set using bits
BOP_INTEG[3:0] in register Config53 (see "Configuration 53
(Config53) – Address 85" on page 45), a boost overvoltage
fault is declared and the system stops boosting. More
information on the leaky integrator size and sample rate is
provided in section 6.23 "Configuration 18 (Config18) –
Address 50" on page 38.
Iref
15k
BSTOUT
16
ADC
Figure 12. BSTOUT Input Pin Model
Resistor RBST sets the feedback current at the nominal boost
output voltage. For 230VAC line voltage applications, RBST is
calculated as shown in Equation 4:
VBST
400V
-------------
-----------------
3M
RBST
=
=
[Eq.4]
Iref
133A
where,
VBST = Nominal boost output voltage
Iref = Internal reference current
During a boost overvoltage protection event, the second stage
is kept enabled only if the MAX_CUR bit in register Config45
(see "Configuration 45 (Config45) – Address 77" on page 40)
is set to ‘1’ (enabled), and its dim input is railed to full scale.
This allows the second stage to quickly dissipate the stored
energy on the bulk capacitor C8, bringing down the boost
output voltage to a safe value. A visible flash on the LED might
appear, indicating that an overvoltage event has occurred.
When the boost output voltage drops to 195V (for a 120V
application), or 392V (for a 230V application), the boost stage
is enabled if bit BOP_RSTART in register Config54 (see
For 120VAC line voltage applications (CS1630), nominal
boost output voltage VBST is 200V, and resistor RBST is
1.5M. By using digital loop compensation, the voltage
feedback signal does not require an external compensation
network.
DS954F2
15
APEX [ CIRRUS LOGIC ]
