Converting SC4524C/D to SC4524E/F Application Note

SC4524E/F Application Note
POWER MANAGEMENT
Converting SC4524C/D to SC4524E/F
AN-PM-1301
This application note is intended to assist designers in the transition from Semtech’s SC4524C and SC4524D step-down
switching regulators to the SC4524E and SC4524F devices. The SC4524E and SC4524F regulators have identical footprint
as the “C” and “D” versions so existing customers will not need to make any PCB changes. No external component change
is necessary to ensure that the SC4524E and SC4524F perform identically to the SC4524C and SC4524D.
Figure 1 — SC4524C/E Typical Application
Circuit Schematic
Figure 2 — SC4524D/F Typical Application
Circuit Schematic
Rev. 2.0
© 2013 Semtech Corporation
SC4524E/F Application Note
Bootstraping the power transistor
For VOUT > 8V SC4524C/D applications, a Schottky diode, D4 as shown in Figure 3, is required in parallel with the bootstrap
capacitor, C1. This extra schottky diode is not necessary in the SC4524E/F for VOUT > 8V applications. This is shown in
Figure 4. Figure 4 can be used for any output voltage including VOUT > 8V. Refer to the SC4524E/F datasheets for additional
information.
D1
BST
V IN
D4
C1
V O U T >8V
SW
IN
SC4524C/D
GND
D2
Figure 3 — SC4524C/D VOUT > 8V Application Circuit
Figure 4 — SC4524E/F VOUT > 8V Application Circuit
Electrical Characteristics
Almost all the specifications of SC4524C/D have been adopted for the SC4524E/F except the two below. In order to
better assist with creating designs using the SC4524E/F, the specification for maximum switch on-time has been added
to the electrical characteristics table, as shown in Tables 4 and 5 below.
Table 4 — SC4524C and SC4524E Electrical Characteristic Comparison
SC4524C
Parameter
Minimum
Typical
SC4524E
Maximum
Minimum
Typical
Maximum
Minimum Switch On-time (ns)
135
70
120
230
Minimum Switch Off-time (ns)
100
30
75
130
Table 5 — SC4524D and SC4524F Electrical Characteristic Comparison
SC4524D
Parameter
Minimum
Typical
SC4524F
Maximum
Minimum
Typical
Maximum
Minimum Switch On-time (ns)
135
70
120
230
Minimum Switch Off-time (ns)
100
30
75
130
AN-PM-1301
SC4524E/F Application Note
Frequently Asked Questions
Q1. Does my oscillator resistor value need to change?
A. No.
The switching frequency of the SC4524E/F is set with an external resistor from the ROSC pin to ground. When converting from the SC4524C/D to SC4524E/F, there is no need to change the frequency-setting resitor.
Q2. Do I need to change my compensation network component values?
A. No.
The switching regulators in the SC4524C/D and SC4524E/F require a simple Type-2 compensation network for stable
operation. The correct calculation of these component values (R7, C5 and C8) is very important to maintain the stability
of the circuit. It is essential to verify loop compensation by checking regulator load transient response. With the largest
load step pertinent to the application applied, the regulator output voltage and the load current were observed. These
transient waveforms should not show any ringing or excessive overshoot. It is required to adjust the component values
until we get a stable operation. While verifying the load transient response of SC4524E/F, no excessive ringing or overshoot was noticed. So no component change is needed while converting SC4524C/D to SC4524E/F.
Q3. If I replace SC4524C/D with SC4524E/F, will it impact the efficiency?
A. Efficiency is similar with both parts.
Q4. Do I need to change feedback resistor?
A. No, same feedback resistor can be used for both the parts.
AN-PM-1301
SC4524E/F Application Note
© Semtech 2013
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Contact Information
Semtech Corporation
Power Management Products Division
200 Flynn Road, Camarillo, CA 93012
Phone: (805) 498-2111 Fax: (805) 498-3804
www.semtech.com
AN-PM-1301
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